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Redroach
04-21-2011, 10:29 PM
Introduction: Yes, I know about engine torque and propwash and the like. But in the Hurricane (Rotol), engine torque seems to be quite excessive. I'm no expert on that but early-war engines shouldn't have the power to drag the whole plane into a steep spin if you leave it alone for a short while (depends on engine mounting, too, I think).

Basically, I've not yet been able to find a combination of throttle/prop angle/mixture etc. to get the hurricane flying straight and level. So you have the options of either grab the stick and apply aileron, probably for hours on end, or apply such excessive rudder trim that your plane basically flies sideways.

Planes without aileron trim in Il-2 1946 always (or mostly :rolleyes:) had some point where the plane was trimmed - i.e. the Bf-109 was trimmed in cruise flight - 50-55% throttle. And if going combat power, the engine torque was probably thrice as light than in the current CoD hurricane (late- war 109s included (!) )

As said, I'm no engine buff and I AM a realism fan, but still, guts tell me that the engine torque of the hurricane is just too much.

And I can't remember strong engine torque in 1946's Hurricane either.

DC338
04-21-2011, 11:57 PM
Torque in the game is far too little not far too much.

Approach to stall in landing config and rapidly apply full power should produce a torque roll that it almost impossible to counter act yet in game is easy.

jdbecks
04-22-2011, 12:12 AM
I think you should back your statement up with technical support/proof instead of theorys..Not that I think your right or wrong, but when it comes to flight models only authentic data should be used/supplied then the changes made to the flight model can follow. Otherwise the simulation starts to become to in accurate.

Redroach
04-22-2011, 01:07 AM
With my OP, I didn't just mean: "reduce engine torque by some arbitrary value". Instead, I am of the opinion that the Hurricane FM should be looked into. If it's really correct the way it is now (contrary to the FM in 1946), then so be it. However, I still think engine torque IS excessive in the Hurricane ^-^

Peril
04-22-2011, 01:18 PM
I think what the man wants is the ability to manually change the trim on the ground, bending trim tabs etc. So the plane whilst in 'cruise' speed is trimmed neutral in roll. On most early war planes this 'is' the historic way to do it Only here it seems planes are set with no counter trim at all, which is 'not' historic. Fixed trim counters the 'average' of the torque effect. Therefore with engine off you roll right slightly, engine on you roll left slightly, rather than all left, all the time.

However, I can find no evidence of trim tabs on Hurri ailerons, I also found the below document confirms the stick was needing to be held to the right a lot of the time.

I am concerned about adverse Yaw, and below I have the document to reference it @ 12 deg. Feels like we are seeing more in game just not sure how we measure that?

------------------------------------------

Memorandum report Army Airforces Material Command.

Measurement of the flying qualities of a Hawker Hurricane airplane.

Points of interest.

Ailerons we asymmetric in application as follows:

Right
21.5 down, 20.6 up
Left
19.2 down 22.4 up

Found this quantification of the adverse yaw:

The maximum angle of yaw due to full application of the ailerons was 12deg.

Effects of yaw on roll were minimal.


If anyone needs the document I have a copy.

Redroach
04-22-2011, 01:33 PM
hmm maybe you got a point. But I still find the un-countered engine torque itself is just too much right now.

Viper2000
04-22-2011, 01:45 PM
Most of the aeroplanes I've flown in the sim will actually sort themselves out in cruise. However, you have to be flying at the correct speed, boost, rpm and altitude, otherwise it's not going to work.

These aeroplanes weren't designed for low altitude cruising.

Equally, cruising wasn't really a very good idea because of the time taken to get the mixture rich, prop into fine pitch/high rpm and boost to combat levels and speed to something sensible for combat.

This was learned the hard way in 1941 by Spitfire V pilots over northern France when the first Fw190s arrived on the scene.

As for actual values of torque, if we get +12 then combat power would be 1310 bhp at 3000 engine rpm. The reduction gear of the Merlin III is 0.477:1, so the prop rpm is about 1431.

bhp = torque[lb-ft]*rpm/5252

bhp*5252 = torque[lb-ft]*rpm

bhp*5252/rpm = torque[lb-ft]

Filling in the numbers I get roughly 4808 lb-ft. The maximum weight of the aeroplane is rather less than 7000 lb. Go figure...

TomcatViP
04-24-2011, 12:26 PM
Hi Vip,

1310HP in combat setting during the BoB days ???!!! Seems awfully over estimated IMHO

~S

Sternjaeger II
04-24-2011, 12:32 PM
Hi Vip,

1310HP in combat setting during the BoB days ???!!! Seems awfully over estimated IMHO

~S

Viper uses a thing called "evidence" to support his statements, I'm sure he's about to give you a good demonstration ;)

As for torque, from what I've seen and heard so far it really looks like it's seriously undermodelled.

Aeroplanes with more than 600hp engines have an incredible torque tendency: the T-6 and Mustang will both tend to torque themselves out of the top of a looping, u need to keep em aligned with rudder and aileron work all the time even if you're all trimmed for aerobatics.

Redroach
04-24-2011, 01:30 PM
Most of the aeroplanes I've flown in the sim will actually sort themselves out in cruise. However, you have to be flying at the correct speed, boost, rpm and altitude, otherwise it's not going to work.

These aeroplanes weren't designed for low altitude cruising.

Equally, cruising wasn't really a very good idea because of the time taken to get the mixture rich, prop into fine pitch/high rpm and boost to combat levels and speed to something sensible for combat.

This was learned the hard way in 1941 by Spitfire V pilots over northern France when the first Fw190s arrived on the scene.

As for actual values of torque, if we get +12 then combat power would be 1310 bhp at 3000 engine rpm. The reduction gear of the Merlin III is 0.477:1, so the prop rpm is about 1431.

bhp = torque[lb-ft]*rpm/5252

bhp*5252 = torque[lb-ft]*rpm

bhp*5252/rpm = torque[lb-ft]

Filling in the numbers I get roughly 4808 lb-ft. The maximum weight of the aeroplane is rather less than 7000 lb. Go figure...

Hmm i can't figure... could you please explain what that means for me?

Viper2000
04-24-2011, 09:47 PM
1310 bhp at +12 psi, 3000 rpm at 9000'.

R.M.1.S. rating.

Alternatively, on 87 octane, you'd get 1000 bhp at +6¼ psi, 3000 rpm at 15500' (which is preserved in the R.M.2.S rating).

Harvey-Bailey, A. H. 1995 The Merlin in Perspective - the combat years 4th edition. Derby: Rolls-Royce Heritage Trust.

AFAIK these are static ratings (ie without intake ram effect; therefore the FTHs are somewhat lower than would be achieved during a level speed run).

///

4800 lb-ft of torque into rather less than 7000 lbm of aeroplane means that the torque at the prop shaft would be able to oppose the entire weight of the aeroplane with a moment arm a bit more than 6" long.

To put it another way, a hurricane has a wingspan of 40'; so the semi-span is 20'.

The torque is therefore equivalent to a 240 lb mass sat on one wing tip.

There is also propwash and p-factor to consider.

TomcatViP
04-24-2011, 10:10 PM
I am not sure those value can be applied to the Hurri or the Spitfire.

Does it include compressor neg torque (some said that it was pumping out 25% of available Pow) and the prop gear box losses ?

Modern turbin are quoted in Shaft HP, value that does not include gearbox etc...

The 240lb mass does not shock me. We can compare that to the force generated by the portion of the wing fitted with the aileron let says 1/3 of the wing area -> 7000lb/3 = 2300lb = 10 time more ;-)

~S!

Viper2000
04-24-2011, 10:42 PM
It's the rated bhp, i.e. the nett horsepower measured on the dyno.

If you go back through the original data, then you find that bhp is at the end of a long chain of subtractions. IIRC it goes like this:

IHP>SHP>BHP

However the details are in this book (http://www.amazon.com/Performance-Supercharged-Aero-Engine-Technical/dp/1872922112), my copy of which has vanished (presumably "borrowed") by somebody :evil:.

It's the definitive work on the Merlin engine, and was originally published in 1941. You can actually build a pretty accurate model of the Merlin with the equations provided (and indeed, since they are general, you can also input data for the Griffon and get good results too).

Note that bhp doesn't include the exhaust thrust, which is very roughly 1/10th of the bhp in lbf.

For this reason ehp was invented in the turboprop era, though often the conversions used were somewhat approximate and primarily used for brochure purposes rather than performance calculation.

Redroach
04-24-2011, 10:42 PM
and what I don't get, in this case, is that the devs (the real devs) shouldn't have been aware of this and tried to counter it. Maybe some asymmetrical dihedral in the wings, or trim tabs pre-set (mechanically) to some value.
I did fly model airplanes for some time and the standard solution for counteracting engine torque there was to mount the engine slightly off-center in an angle. I had an easymode-to-fly standard motorplane trainer and bought a very strong engine for it, waaaay overmotorizing the plane. Nevetheless, the building instructions recommended mounting the engine about 3° off-center and that worked quite well, actually.
And right now, I can't see why that shouldn't be possible for real airplanes.
That said, theory aside, there's got to be some way to counter that engine torque, inherently. And there's got to have been some dev at Hawker to realize this.
Therefore, I still consider current engine torque too strong :)

RAF74_Winger
04-24-2011, 11:16 PM
what I don't get, in this case, is that the devs (the real devs) shouldn't have been aware of this and tried to counter it

Probably because you can't counter it over the whole of the speed range for the aircraft - any 'fix' would have to be an aerodynamic one; so a compromise was reached such that the effects were minimised in the normal operating range.

BTW real 'devs' are called engineers.

W.

RAF74_Winger
04-24-2011, 11:21 PM
Oh, and thanks for the link Viper. Thanks to the wonders of Amazon, I should soon have a copy.

W.

b101uk
04-25-2011, 12:35 AM
[QUOTE=Viper2000;270501] The reduction gear of the Merlin III is 0.477:1, so the prop rpm is about 1431.QUOTE]

the reduction gear is ~2.0964:1 to give an output of ~1431rpm from an input of 3000rpm.

0.477:1 would give an output ~6289.3rpm from an input of 3000rpm

You seam to have a habit of fudging your figures I.e. showing the correct result but the wrong equation ware RPM’s is concerned. ;)

Also the torque at 3000rpm will be somewhat less than the torque available at peak torque rpm which will be at a lower rpm than rated power, hence why rpm’s fall lower than 3000rpm back towards peek torque rpm when a course pitch is selected.

Viper2000
04-25-2011, 01:41 AM
3000*0.477 = 1431

Rocket science it ain't...

The convention is that the gear ratio is output:input. The maintenance of this convention obviates the need to say "reduction" or "step-up"; but doing so provides an additional check. The same sort of logic applies to the Pressure Ratio of a gas turbine compressor (such that if you want a nice number >1 when considering turbine performance, you'd call it Expansion Ratio instead).

Now, since the above answer is exact, you may be wondering why I said "about" 1431 rpm. Well, there are several reasons. Firstly, I haven't counted the teeth so I don't know if 0.477 is exact or whether it's an approximation. Secondly this whole business is somewhat approximate anyway; I don't know how accurate the rpm measurement would be, and it doesn't make any difference to the argument, so why worry?

You also don't need a torque curve to explain the fact that rpm falls when pitch is coarsened.

Blade alpha increases, therefore blade CL and CD increase. The power required to drive the prop is larger than the power supplied (since input power hasn't changed, and the system was in equilibrium before).

However, the force on the blade is proportional to the square of the tip speed; thus the power required is proportional to the cube of the tip speed.

At constant engine torque (i.e. roughly constant BMEP) the engine power varies directly with rpm.

Therefore as the prop slows down its power demand falls much faster than the engine power output and so a new equilibrium rpm is reached.

No torque curve required.

Buzpilot
04-25-2011, 02:06 AM
3000*0.477 = 1431

Rocket science it ain't...

A engine running at 1431 rpm, making propel go 3000 rpm, seems quite odd to me.
More like 3000/0.477 = 6289 rpm in engine. Thats quite high exept for formula1 cars.

Redroach
04-25-2011, 02:12 AM
Probably because you can't counter it over the whole of the speed range for the aircraft - any 'fix' would have to be an aerodynamic one; so a compromise was reached such that the effects were minimised in the normal operating range.

yes, that's what I'm 'campaigning' for. Obviously, the aircraft development team (engineers are the lowly folks that actually calculate with numbers and stick prototypes together ;) ) of the Bf-109 took the problem into account and trimmed the plane level in a throttle range of 50-55% (constant prop rpm), as modelled in Il2-1946.
But, as already said, I just can't find a throttle/PP/maybe mixture - combination to go more or less straight ahead (while allowing rudder trim to cancel sideslip, of course) on the hurricane in CoD. It seems to get better at full open throttle and not too coarse PP, but I would project the 'crossover point' at about 140-150% throttle at least...
If I've been just too noobish and somebody *has* found a certain cruise setting, torque-wise, please enlighten me! After all, nobody wants to do a lengthy cruise and then engage the enemy with cramps in his right hand :rolleyes:

Viper2000
04-25-2011, 02:22 AM
A engine running at 1431 rpm, making propel go 3000 rpm, seems quite odd to me.
More like 3000/0.477 = 6289 rpm in engine. Thats quite high exept for formula1 cars.

3000 engine rpm * 0.477 = 1431 prop rpm

Come on, it really isn't that hard is it?

Sternjaeger II
04-25-2011, 11:22 AM
3000 engine rpm * 0.477 = 1431 prop rpm

Come on, it really isn't that hard is it?

Lol it isnt but what did I tell you about keeping it simple? ;-)

Peril
04-26-2011, 12:02 AM
What you may be looking for is evidence that the wing, engine mount or rudder has been shaped with this 'counter' torque rotation in mind.

I fly and build RC planes too ;)


I'll see what I can find in my data set on the Hurricane.

----------------------------------------------------------------------------------------

The Vstab of the Hurricane was offset 1.5 deg to the left. That offset should provide some point where the plane rolls to the right. Does it yaw right with throttle off in CoD? If not, why not??

Logical progression here, this offset was intended to counter some of the torque, most likely neutral for cruise speeds?

----------------------------------------------------------------------------------------

See below the tested speeds at which the plane was neutral in trim, under climb power (most torque effect) and at the glide (least effect).

It appears at around 130mph the plane was neutral in 'roll' but did still have a slight side slip. Note here the key is neutral in roll, ie. no aileron input needed to maintain bank angle. Side slip generated in the glide was undoubtedly due to the 1.5deg fixed vstab, thus evidence of this functioning as an intended counter to torque whilst under power. Furthermore at climb speeds above 130mph it was necessary to apply left aileron likely because of the 1.5deg vstab incidence influence was greater than that of the torque under power.

Hope this helps someone make a more accurate sim.

Order of graph:

Aileron Angle
Rudder Angle
Elevator Force
Elevator Angle

http://www.targetrabaul.org/peril/hurricane_trimtest.jpg

b101uk
04-26-2011, 12:47 PM
3000*0.477 = 1431

Rocket science it ain't...

The convention is that the gear ratio is output:input. The maintenance of this convention obviates the need to say "reduction" or "step-up"; but doing so provides an additional check. The same sort of logic applies to the Pressure Ratio of a gas turbine compressor (such that if you want a nice number >1 when considering turbine performance, you'd call it Expansion Ratio instead).

Now, since the above answer is exact, you may be wondering why I said "about" 1431 rpm. Well, there are several reasons. Firstly, I haven't counted the teeth so I don't know if 0.477 is exact or whether it's an approximation. Secondly this whole business is somewhat approximate anyway; I don't know how accurate the rpm measurement would be, and it doesn't make any difference to the argument, so why worry?

yes "output:input" is all well and good but if you look up automotive ratios for e.g. gearbox and rear axels or portal box they are almost exclusively done as per I have stated (input : output) and as most people will be familiar with, what next will we get fractions allowing the use of numbers less than <1 or numbers with decimal placing, in the world of describing things to “normal” people saying ~2.0964:1 instead of 0.477:1 works better because MOST people attribute that number for each ~2.0964 turns of the engine the propeller will turn once which is a reduction, if you give a figure of 0.477:1 it normally signifies to the masses a ratio higher than 1:1 e.g. each part turn of 0.477 of a crank revolution the propeller/prop shaft/wheel will turn once given that last part of a ratio is normally “:1”

Do you not see any perversity of logic in describing a physical system mathematically (reduction gearbox) that acts as a devisor (as dose #:#) by using a multiplier number (* 0.477) rather than a devisor number (/ ~2.0964) that mimics the systems function given most gearbox in this world around us are reduction gearbox that make something turning faster into something that turns slower and has more torque as a logical consequence. ;)

As for “I don't know how accurate the rpm measurement would be, and it doesn't make any difference to the argument, so why worry” lol, because RPM is of every relevance, differential of RPM denotes ratio, HP dose not exist without a quotient of speed which RPM is and the engine speed being reduced via reduction box on a Merlin is not because they need more torque its because as you know you would have to use a smaller diameter propeller to stop the tips going to fast and would need more blades to have sufficient surface area which would yield a heavier more expensive prop with more moving parts which takes proportionally longer to make and blows more air backwards onto the aircraft nose (rather than past it) which is in all less efficient, however obvious torque increase from reducing RPM’s with a reduction box dose enable a big propeller diameter to be used wile keeping tip speed lower.

You also don't need a torque curve to explain the fact that rpm falls when pitch is coarsened.

Blade alpha increases, therefore blade CL and CD increase. The power required to drive the prop is larger than the power supplied (since input power hasn't changed, and the system was in equilibrium before).

However, the force on the blade is proportional to the square of the tip speed; thus the power required is proportional to the cube of the tip speed.

At constant engine torque (i.e. roughly constant BMEP) the engine power varies directly with rpm.

Therefore as the prop slows down its power demand falls much faster than the engine power output and so a new equilibrium rpm is reached.

No torque curve required.

Err yes you do need to account for torque fully in every way, the first rule of any mechanical system is there MUST be sufficient force to induce movement, in this case torque is that force and coupled with RPM denote power BUT if torque is insufficient something will not turn regardless of computed notional power (HP), you can forget you fancy pants “CL and CD increase and your force on the blade is proportional to the square of the tip speed …………..etc” guff above and get back to basics to understand torque, you could have 200000000HP but if you lack torque by even 0.0001lbft you are not going to educe movement, if you have a constant torque engine and a fixed gear reduction then err torque will remain constant across the RPM range and HP will be the figure that changes the most HOWEVER if you lack torque at one RPM you will lack it at ALL RPM’s! thus as most engines DON’T have constant engine torque but instead have a curve of torque so there are natural shifts in torque along the rpm range and that peak torque is almost exclusively at a lower RPM than rated power so that means rated power speed has less torque than the peak torque value!

So in the case of the Merlin if you are at 3000rpm and you apply load via increasing prop pitch which exceeds available torque at 3000rpm then rpm’s will fall to the point on the torque curve ware there is sufficient torque, as a natural consequence of something turning slower than it was it consumes less notional power but ALWAYS MUST HAVE SUFFICIENT TORQUE, therefore torque and torque curve is of every relevance so my statement of

Also the torque at 3000rpm will be somewhat less than the torque available at peak torque rpm which will be at a lower rpm than rated power, hence why rpm’s fall lower than 3000rpm back towards peek torque rpm when a course pitch is selected.
is correct with reference to being a larger value than your approximation of ~4808 lb-ft assuming that was near correct @ 3000rpm and a course pitch was applied which dragged the engine down lower than 3000rpm to ware there is more torque available on the torque curve.

You should get it into your head that HP doesn’t really exist its purely notional and in the case of HP is any force that equals 550lb/ft/sec or 33000lb/ft/min equals 1HP, so 1lb @ 550ft/sec or 550lb @ 1ft/sec or 275lb @ 2ft/sec or 33000lb @ 1ft/min or 1lb @ 33000ft/min and so on ALL equal 1HP.

Revelation
04-26-2011, 04:12 PM
Everything in this thread makes my brain cry in confusion.

But as far as my 2 cents go, torque feels a little gimped, as someone stated earlier, applying full throttle when near stall speed should send your hurri into one hell of a spin afaik.

Viper2000
04-26-2011, 06:58 PM
yes "output:input" is all well and good but if you look up automotive ratios for e.g. gearbox and rear axels or portal box they are almost exclusively done as per I have stated (input : output) and as most people will be familiar with, what next will we get fractions allowing the use of numbers less than <1 or numbers with decimal placing, in the world of describing things to “normal” people saying ~2.0964:1 instead of 0.477:1 works better because MOST people attribute that number for each ~2.0964 turns of the engine the propeller will turn once which is a reduction, if you give a figure of 0.477:1 it normally signifies to the masses a ratio higher than 1:1 e.g. each part turn of 0.477 of a crank revolution the propeller/prop shaft/wheel will turn once given that last part of a ratio is normally “:1”

Welcome to aerospace engineering. Enjoy your stay. You can complain about the conventions we use all you like, but they won't change.

Do you not see any perversity of logic in describing a physical system mathematically (reduction gearbox) that acts as a devisor (as dose #:#) by using a multiplier number (* 0.477) rather than a devisor number (/ ~2.0964) that mimics the systems function given most gearbox in this world around us are reduction gearbox that make something turning faster into something that turns slower and has more torque as a logical consequence. ;) Not really. As I have said, you've got a nice sanity check from the combination of the convention output:input and the use of the word "reduction". If the number and the convention don't line up then this a good cue that you need to check further. Safety is paramount because once you're past V1 you can't just pull over onto the hard shoulder in the event of mechanical failure.

As for “I don't know how accurate the rpm measurement would be, and it doesn't make any difference to the argument, so why worry” lol, because RPM is of every relevance, differential of RPM denotes ratio,
drpm/d? = ? : ?
Answers on a postcard...
HP dose not exist without a quotient of speedAre you Charlie Sheen?

which RPM is and the engine speed being reduced via reduction box on a Merlin is not because they need more torque its because as you know you would have to use a smaller diameter propeller to stop the tips going to fast Ah yes, Fast, that well-known holiday destination for propeller blades...

and would need more blades to have sufficient surface area which would yield a heavier more expensive prop with more moving parts Why must a bigger propeller have more moving parts rather than simply the same number of larger parts?

which takes proportionally longer to make and blows more air backwards onto the aircraft nose (rather than past it) which is in all less efficient, however obvious torque increase from reducing RPM’s with a reduction box dose enable a big propeller diameter to be used wile keeping tip speed lower. So in addition to groceries you also sell reduction gear boxes with which to dose those suffering from some kind of peculiar ailment or other.

No tiger blood? But of course that wouldn't be in the grocery department! Silly me!

Actually the main argument for increasing propeller disk area is that it allows you to move more air and thus approach a higher limiting Froude efficiency at any given operating point (TAS, altitude, input power).

Err yes you do need to account for torque fully in every way, the first rule of any mechanical system is there MUST be sufficient force to induce movement, in this case torque is that force Torque is not a force...
and coupled with RPM denote power BUT if torque is insufficient something will not turn This really doesn't make any sense. Torque is a special case of a moment, i.e. force*distance. Force is a vector. If there is zero nett torque then "something" will keep on turning at the same rate as before. If nett torque is negative then "something" will experience an angular acceleration in the opposite direction to that which you first thought of when setting up your coordinate system.
regardless of computed notional power (HP), There's nothing "notional" about brake horsepower. Hence the need for a whacking great water or electrical dynomometer to measure it.
you can forget you fancy pants “CL and CD increase and your force on the blade is proportional to the square of the tip speed …………..etc” guff above
I'm sorry, but this isn't the school playground. However, I suppose your misapprehension that it is would go some way towards explaining your obvious difficulties with basic spelling and punctuation, let alone engineering science. In the adult world, you will find that attempts to disguise your intellectual inadequacy by disparaging that which you fail to understand is not an effective strategy for winning friends or influencing people.
and get back to basics to understand torque, you could have 200000000HP but if you lack torque by even 0.0001lbft you are not going to educe movement, if you have a constant torque engine and a fixed gear reduction then err torque will remain constant across the RPM range and HP will be the figure that changes the most HOWEVER if you lack torque at one RPM you will lack it at ALL RPM’s!
No, as I explained, the torque required to drive a propeller through the air will vary as the square of its rpm; the power required varying as the cube of rpm. I don't need any groceries either.
thus as most engines DON’T have constant engine torque but instead have a curve of torque No, most engines don't have constant torque simply because that doesn't happen to be how the physics generally works out. In the case of piston engines, torque variation as a function of rpm is caused by changes in induction, scavenging, frictional and heat transfer losses, as well as changes in charge temperature in the case of a supercharged engine.
so there are natural shifts in torque along the rpm range and that peak torque is almost exclusively at a lower RPM than rated power so that means rated power speed has less torque than the peak torque value!This is a circular argument.

It is not immediately obvious that an engine must achieve its rated power at a higher rpm then its maximum torque. It is certainly true that this is often the case, but in the end it depends upon the design of the engine and especially upon its physical size.

Generally speaking, the maximum rpm that a piston engine can attain is set by the acceleration loads imposed upon its reciprocating components.

To a first order, torque is independent of rpm because if you think about it, it's just the product of the BMEP and the piston area. The piston area is fixed, and the BMEP is set by the thermodynamics of the cycle.

So you know from the start of the design process that you're most likely to get more power at higher rpm.

Therefore you tend to set up the valve timing with that in mind, and so it's pretty unsurprising that peak power tends to end up close to peak rpm.

However, the engine will generally tend to breathe better at lower rpm because more time is available to fill and empty the cylinders. This means that you'll get a slightly higher MEP at lower rpm.

In the automotive world, people generally install large amounts of excess power in order to achieve rapid acceleration. Since gearboxes are expensive, you'll get better performance per unit cost if the engine's power curve is flat with respect to rpm, even if this costs you peak power.

Therefore you'll tend to tweak the exhaust and induction systems to improve low rpm performance, probably using something like Ricardo Wave if your design organisation doesn't have the necessary technical resources or motivation to produce its own code.

If the engine is intended to be anything like domestic then you'll probably also put quite a bit of effort into giving it a reasonable idle; this can mitigate quite strongly against the use of aggressive valve timing, because the sort of "characterful" refusal to idle smoothly at low rpm which sounds good for a few minutes at a drag strip gets very old very quickly in the real world, especially if you're the one paying for the fuel.

This enforced emphasis upon nice behaviour at low rpm will tend to reduce torque at high rpm because there just won't be enough valve overlap to let the engine breathe properly.

Of course, variable valve timing can solve that problem if you're prepared to suffer the increased cost and complexity...

But in any case, it is the nature of car engines that in the absence of a constant speed drivetrain of some sort they must have excess torque available across their operating range to provide acceleration.

Peak power is an entirely academic quantity in this context, because you can't use it anyway; inevitably it's a transient to be accelerated through shortly before the next gear change.

Aircraft engines are fundamentally different machines. You can quite confidently optimise them for a far smaller rpm range, and with a constant speed propeller you can quite easily maintain constant rpm from takeoff to landing if you so desire.

This means that the design drivers are totally different from the automotive world.

The same sort of argument applies to stationary power or marine engines. A really big industrial diesel engine can easily produce 10^5 bhp. Obviously, such an engine is extremely large, and turns at a relatively low (constant) rpm despite having a perfectly respectable piston speed.

It is quite easy to see how the peak torque and maximum rpm of such a machine might coincide.

So really it's not reasonable to assume that peak torque is naturally and inevitably at some "low" rpm for any given engine.

Thankfully, such an assumption is unnecessary for the reasons which I have already explained.

So in the case of the Merlin if you are at 3000rpm and you apply load via increasing prop pitch which exceeds available torque at 3000rpm then rpm’sNo, I still don't want any groceries to go with your "interesting" views on engineering. But do go on...

will fall to the point on the torque curve ware there is sufficient torque, as a natural consequence of something turning slower than it was it consumes less notional power but ALWAYS MUST HAVE SUFFICIENT TORQUE Writing in capital letters is not an especially effective rhetorical device.

, therefore torque and torque curve is of every relevance so my statement of

Also the torque at 3000rpm will be somewhat less than the torque available at peak torque rpm which will be at a lower rpm than rated power, hence why rpm’s fall lower than 3000rpm back towards peek torque rpm when a course pitch is selected.

is correct with reference to being a larger value than your approximation of ~4808 lb-ft assuming that was near correct @ 3000rpm and a course pitch was applied which dragged the engine down lower than 3000rpm to ware there is more torque available on the torque curve.

You should get it into your head that HP doesn’t really exist its purely notional and in the case of HP is any force that equals 550lb/ft/sec or 33000lb/ft/min equals 1HP, so 1lb @ 550ft/sec or 550lb @ 1ft/sec or 275lb @ 2ft/sec or 33000lb @ 1ft/min or 1lb @ 33000ft/min and so on ALL equal 1HP.

Firstly, power has just as much existence as force, distance or time.

Secondly, check your units. :-P

Thirdly, you'll find it much easier to get ahead in life if you learn to spell and punctuate.

Buzpilot
04-26-2011, 07:12 PM
3000 engine rpm * 0.477 = 1431 prop rpm

Come on, it really isn't that hard is it?

I didn't know it was the engine that is locked at 3000rpm, always seemed logic to me that it was the prop that used constant speed.:confused:

Viper2000
04-26-2011, 07:29 PM
They are connected together with a fixed ratio gear box so it amounts to the same thing...

Buzpilot
04-26-2011, 08:00 PM
They are connected together with a fixed ratio gear box so it amounts to the same thing...

Yes, I see now, a 3000rpm propella ,de Havilland 9 ft 8 in (2.97 m) diameter would run at about 466m/s, a bit faster than sound :)
And at 1431, it's only about 222m/s.

Viper2000
04-26-2011, 09:33 PM
However, once the aeroplane is flying, the tip speed is

((static tip speed)^2+TAS^2)^0.5

So at say 150 m/s TAS your static 222 m/s tip speed becomes more like 268 m/s.

At 20,000 feet this is a Mach number of about 0.85.

kimosabi
04-26-2011, 09:51 PM
This thread is what happens when engineers and theorists sober up.

Viper2000
04-26-2011, 10:04 PM
This thread is what happens when engineers and theorists sober up.

So you're saying that this thread is a massive coffee binge, followed by feverish attempts to catch up on all the work that should have been done during the party? :-P

kimosabi
04-26-2011, 10:24 PM
Ya.

Peril
04-26-2011, 10:52 PM
Must be 109 pilots throwing in a red herring ;) Hehehehehe.

'Peril looks at the Hurricane tested data posted above and scratches his head'. You guys interested in what 'actually' happened in the case of the Hurricane or what mathematically should have happened but didn't?

Basically, I've not yet been able to find a combination of throttle/prop angle/mixture etc. to get the hurricane flying straight and level. So you have the options of either grab the stick and apply aileron, probably for hours on end, or apply such excessive rudder trim that your plane basically flies sideways.

So, to round that up for you, the plane should trim neutral in roll @ ~130mph, seems you missed the answer or at least the point to the question? (not 42 in this case)

ElAurens
04-26-2011, 11:18 PM
Interesting discussion Viper, thank you.

I am a mechanic, not an engineer, and I work on vintage/veteran automobiles.

I have always wondered why you never see Brake Mean Effective Pressure used in modern automobile engine specifications. All the old English cars I work on usually have this listed in their manuals, and it is indeed indicative of their maximum development potential. We race a Triumph TR3, and after all the years of development and money spent on this old design, the maximum BHP that they produce now is still just about what tuners got out of them in the 1960s. Just no way to get around that BMEP thing in any meaningful way. The only thing that has changed over the years is the ability to have much flatter torque and BHP curves, so the engines are more flexible and lap times decrease, even if maximum power is about the same.

Sorry to go off topic, but I rarely get to talk about these things outside of our small vintage racing community.

Viper2000
04-26-2011, 11:32 PM
Must be 109 pilots throwing in a red herring ;) Hehehehehe.

'Peril looks at the Hurricane tested data posted above and scratches his head'. You guys interested in what 'actually' happened in the case of the Hurricane or what mathematically should have happened but didn't?

So, to round that up for you, the plane should trim neutral in roll @ ~130mph, seems you missed the answer or at least the point to the question? (not 42 in this case)

It's really not that simple, since we don't know very much about the test aeroplane, the power setting (i.e. manifold pressure & rpm) used or the altitude at which the test was carried out.

In fact, for all we know at this point, it could have been a Hurricane II with a Merlin XX, metal wings & ailerons at one extreme, or an early Hurricane I with a Merlin II or III, wooden wings and fabric covered ailerons at the other, and climb power could mean anything from 2600 rpm, +6¼ psi (Merlin II or III) to 2850 rpm +9 psi (Merlin XX; which also has a 0.42 reduction gear instead of 0.477 for the Merlin II & III).

Viper2000
04-27-2011, 12:08 AM
Interesting discussion Viper, thank you.

I am a mechanic, not an engineer, and I work on vintage/veteran automobiles.

I have always wondered why you never see Brake Mean Effective Pressure used in modern automobile engine specifications. All the old English cars I work on usually have this listed in their manuals, and it is indeed indicative of their maximum development potential. We race a Triumph TR3, and after all the years of development and money spent on this old design, the maximum BHP that they produce now is still just about what tuners got out of them in the 1960s. Just no way to get around that BMEP thing in any meaningful way. The only thing that has changed over the years is the ability to have much flatter torque and BHP curves, so the engines are more flexible and lap times decrease, even if maximum power is about the same.

Sorry to go off topic, but I rarely get to talk about these things outside of our small vintage racing community.

I think that the people who produce the brochures these days are afraid that BMEP is too technical for their market.

I think that they emphasise peak bhp because it's a nice big number that's relatively easy to massage in order to sell next year's model.

Really of course you get a better indication of car engine performance around a track by looking at the area under the power curve. This is much harder to massage because generally when you start tuning you end up adding to one part of the curve and subtracting from another unless you either supercharge (and thus increase BMEP) or increase cubic capacity; both of these options are obviously expensive.

Of course, if you improve the gearbox then you can win by tuning the induction & exhaust systems and accepting a peakier power curve. But new gearboxes are also expensive.

If you're stuck with the stock gearbox and don't want to supercharge then really all that you can do is blueprint the engine, perhaps clean up the induction & exhaust systems if possible, and obviously take great care with balancing it. All of this was obviously perfectly possible to do by hand and eye back in the 1960s.

This sort of work might allow you to increase the rev limit a little, but unless you start tweaking the valve and ignition timing this probably won't gain you an awful lot; and of course you'll then find that the gear ratios don't necessarily play nicely with the new power curve.

So in the end you're stuck with the fact that the vehicle is a system of systems, and they all have to work together to produce a fast lap; meanwhile the engineers who originally designed the car (and the tuners who first tried to make it go a bit faster) weren't stupid, and so beating their performance isn't going to be easy.

I think that it's probably easier to improve cars of this vintage by making aerodynamic tweaks; I'd be inclined to pay particular attention to the undertray if there are no rules preventing you from doing so, as quite often old cars are quite poor in this area.

If the track is fast you can probably also reduce drag by cutting down on engine cooling intakes, since they tend to be oversized for road use, based upon the worst case hot-weather uphill traffic jam scenario.

Indeed, if the race is short you could potentially win by going to a total loss cooling system.

Likewise, getting rid of engine accessories that you don't need will save both power & weight. You might also replace the original lead-acid battery with a lithium one, get rid of the alternator entirely and run the coolant & fuel pumps from the battery. And of course you can also down-size your spare tyre (or delete it completely if you don't need to remain road legal).

You can also potentially start playing with the weight distribution by moving the battery around.

New wheels can help to reduce the unsprung mass, and this will open up additional options for tuning the suspension.

But once you start down this path, either you'll run into regulations* if you're racing in some kind of vintage formula, or else you'll be in the slightly unsatisfying position of driving a very fast, very new and extremely expensive car with a vintage numberplate...

PS - glad you enjoyed the discursive part of my little rant. I fear I was being somewhat harsh, but from time to time hecklers get the better of me and I bite...

*Of course, regulations in any serious competition are an exhortation to find innovative ways of violating the spirit of the law without transgressing its letter; if the other teams aren't periodically complaining about aspects of your design then you're doing it wrong. :twisted:

ElAurens
04-27-2011, 12:25 AM
As Kas Kastner, one of America's legendary road racing team managers says, "The rule book is grist for the thinking man".

;)

Actually the biggest gains over the last 7 odd years have been in camshaft technology, at least in the old crocks we race. It's all in the ramps. A true black art. All I know is the valve acceleration with these new grinds has forced everyone that uses them to dramatically increase the strength of the rocker shaft assembly.

Oddly, much of what has been done is a result of studying modern variable valve timing set ups, and a very close look at modern motorcycle practice, as far as cam profiles go.

Cheers.

Viper2000
04-27-2011, 12:35 AM
If you go down that path then the next thing to do is to start looking very closely at what the valves are actually doing when the engine is running; you may find that they aren't quite behaving as you expect.

You may also find that the valve springs become unhappy.

There may be some performance advantage to be had from new valves made out of superior materials, especially if you can save weight.

Of course, all of this stuff gets expensive rapidly, and so it's worthwhile to decide what price you're prepared to pay for say 0.01 s/lap. Then you can start analysing your options and rationally allocating budget.

Of course, for this to work really well you need a simulator so that you can investigate the way in which your driver will respond to car performance changes; you may find that changes in power or grip have surprising unintended consequences for the racing line that your driver elects to take around the track, which can either positively or negatively affect the overall lap time.

As with so many things in life, the job is never finished; eventually you just have to decide when to stop.

Peril
04-27-2011, 10:28 AM
Your a funny man Viper, you think like an opposing team not wanting improvements.

For info it was a Hurricane II with a Merlin XX, Rotol constant Speed prop, document is 'Measurements of the Flying Qualities of a Hawker Hurricane, by Neilsen and phillips. You could have this test data on your HD already I suppose?? But if you don't and want to improve the sim, 'please supply more data' would be a good start. I tested the Hurricane in game marked as a Rotol prop Hurricane, not sure if that is a definitive match, it's hard to tell based on that description.

So you are aware, I spent the last 6 years building and researching FM for another sim focused on realism, so I have some experience and data to call upon and know what is required. I too didn't modify my FMs without good data but I'm not one to ignore what is logical either. If it is of interest we had to apply on average 0.2 deg of wing twist to obtain an outcome that match reality re roll trims. Sims are great representations but unfortunately they are rarely perfect in result because of using the simplified code they have to use due to the limits of home computing. Before you go off all negative, think about what we have proved here and work backwards from there, I always found the answer could be somewhere in the middle.

Feel free to use any alt, power and the glide test data to confirm, I think you'll find it likely has a problem ;)

That would confirm some changes are needed, some of us are here to 'help' where we can...the only agenda I have is FM realism.

TomcatViP
04-27-2011, 11:23 AM
Home computating power is not the real limiter for flight Sim.
Think that your FM does not hve to compute how your plane will behave to any kind of solicitation. Most of the Maths are done once for all B4 you release your FM.

For example if I want to simulate flight buffeting on low level flight at high speed I won't hve to actually calculate for each image projected on the screen how my ctrl surface will behave and than what wld be the amplitude of the plane then pilot head shaking !! An average non harmonic solicitation will do the trick ;)

Good Phy and Math are essential to hve a nice FM. But an overall comprehension of what you hev to look too or generally speaking a comprehension of the flight phenomenas (and I didn't say "sciences") is of utmost importance.

Years ago Engineers where computing real FM with computers that had the power of a today pocket calculator. Nowadays a millions more power is used at every steps of the process by any one in the dev chain (thx to CAO requirements)... And we don't do better planes (F35/Typhoon/A400M etc...)

Sternjaeger II
04-27-2011, 11:41 AM
Home computating power is not the real limiter for flight Sim.

erm... it is actually. There is virtually no limit to the intricateness of a flight model, but it will need more and more computing power. You could build a CAD model of a Spitfire and simulate fatigue on each single screw if you wanted to, but it will need a lot of computing power.


Think that your FM does not hve to compute how your plane will behave to any kind of solicitation. Most of the Maths are done once for all B4 you release your FM.

For example if I want to simulate flight buffeting on low level flight at high speed I won't hve to actually calculate for each image projected on the screen how my ctrl surface will behave and than what wld be the amplitude of the plane then pilot head shaking !! An average non harmonic solicitation will do the trick ;)

Good Phy and Math are essential to hve a nice FM. But an overall comprehension of what you hev to look too or generally speaking a comprehension of the flight phenomenas (and I didn't say "sciences") is of utmost importance.

Years ago Engineers where computing real FM with computers that had the power of a today pocket calculator. Nowadays a millions more power is used at every steps of the process by any one in the dev chain (thx to CAO requirements)... And we don't do better planes (F35/Typhoon/A400M etc...)

I'm sorry but I don't think you have a full understanding of the topic man, or if you do, your explanation is ridden with generalisations.

Engineers don't calculate flight models, a flight model, even when accurate, is an approximation used for simulators. To design a plane you can render in CAD the surface and structure and calculate loads or aerodynamic coefficients, but you will still need to build and test prototypes.

jf1981
04-27-2011, 12:44 PM
Most of the aeroplanes I've flown in the sim will actually sort themselves out in cruise. However, you have to be flying at the correct speed, boost, rpm and altitude, otherwise it's not going to work.

Filling in the numbers I get roughly 4808 lb-ft. The maximum weight of the aeroplane is rather less than 7000 lb. Go figure...

Hi,

I double checked and found roughly your figures. I further estimate the plane would fall (roll) on the side by 10 to 15 degree in a second if you would'nt compensate.

How comes the counter torque effect is lowered with hight speed (when not compensated, it would roll fast at low sped, but roll less at high speed) ?

Regards
JF

Viper2000
04-27-2011, 01:07 PM
Your a funny man Viper, you think like an opposing team not wanting improvements.
Only if your definition of "improvement" is "change for the sake of change".

For info it was a Hurricane II with a Merlin XX, Rotol constant Speed prop, document is 'Measurements of the Flying Qualities of a Hawker Hurricane, by Neilsen and phillips. You could have this test data on your HD already I suppose?? Nope. If I had the data I wouldn't have been asking about it.

But if you don't and want to improve the sim, 'please supply more data' would be a good start. I tested the Hurricane in game marked as a Rotol prop Hurricane, not sure if that is a definitive match, it's hard to tell based on that description. They are different aeroplanes with very different engines (Merlin XX is single stage 2 speed with a redesigned supercharger), a different wings (Hurricane II has a 12 gun/4 cannon metal wing vs the 8 gun metal or wooden wing of the Hurricane I) and a different fuselage length (Merlin XX is longer so the Hurricane II has a longer fuselage).

Obviously these are quite substantial design changes, and for this reason it isn't obvious that the Hurricane II would have the same trim behaviour as the Hurricane I.

I'm all in favour of making the sim as good as it can be, but I don't think that there's much to be said for deliberately asking for trim behaviour to be based upon that of a substantially different, albeit related, aeroplane.

Given a comprehensive "changelog" between the Mark I and Mark II aeroplanes (which I don't have, before you ask; I know the broad brush strokes, but I can't immediately bring to mind the sort of specific details required to get trim behaviour right) we could potentially try to reverse engineer Mark I data from the Mark II data that you've found.

So you are aware, I spent the last 6 years building and researching FM for another sim focused on realism, so I have some experience and data to call upon and know what is required. I too didn't modify my FMs without good data but I'm not one to ignore what is logical either. If it is of interest we had to apply on average 0.2 deg of wing twist to obtain an outcome that match reality re roll trims. Sims are great representations but unfortunately they are rarely perfect in result because of using the simplified code they have to use due to the limits of home computing. Before you go off all negative, think about what we have proved here and work backwards from there, I always found the answer could be somewhere in the middle.

Feel free to use any alt, power and the glide test data to confirm, I think you'll find it likely has a problem ;)

That would confirm some changes are needed, some of us are here to 'help' where we can...the only agenda I have is FM realism.

Building sim models is all about matching.

The problem is that there are lots of variables to consider, and depending upon the underlying flight model of the simulator itself it may or may not be possible to accurately match all of the available test data.

For example, you can't make an accurate WWII fighter in X-Plane without recourse to plugins because X-Plane just can't model a WWII engine properly; you can't get realistic supercharger behaviour because it only allows for turbonormalising, and you can't get a satisfactory model of exhaust thrust either. Which means that most people end up with inaccurate airframe drag and/or an inaccurate propeller model in an attempt to match the headline top speed of the aircraft. This then results in incorrect cruise and glide behaviour. Essentially, the tighter you squeeze any one parameter, the more likely the others are to slip through your fingers.

The most dramatic instance of this I ever encountered was a Corsair which flew nicely and looked pretty but was almost impossible to land. What happened was that the guy who'd made the model didn't realise that the R-2800 has a 0.5:1 reduction gear. So he had a very supersonic prop with awful performance, and this had forced him to dramatically reduce the airframe drag in order to match the stated top speed; it was therefore basically impossible to get the thing to descend for landing!

Until such time as the SDK is released and documented, and the major engine bugs are squashed, it's pretty difficult to work out the specifics of the model used in CoD, and therefore it's hard to form a sensible opinion as to how good the models are given whatever the limitations of the overall FM are.

Sternjaeger II
04-27-2011, 01:11 PM
Hi,

I double checked and found roughly your figures. I further estimate the plane would fall (roll) on the side by 10 to 15 degree in a second if you would'nt compensate.

How comes the counter torque effect is lowered with hight speed (when not compensated, it would roll fast at low sped, but roll less at high speed) ?

Regards
JF

because at higher speeds, when the wing lift is more pronounced (efficient), torque is partially compensated by your wing lift.

Sternjaeger II
04-27-2011, 01:14 PM
The most dramatic instance of this I ever encountered was a Corsair which flew nicely and looked pretty but was almost impossible to land. What happened was that the guy who'd made the model didn't realise that the R-2800 has a 0.5:1 reduction gear. So he had a very supersonic prop with awful performance, and this had forced him to dramatically reduce the airframe drag in order to match the stated top speed; it was therefore basically impossible to get the thing to descend for landing!

wow, I'm surprised the thing gets airborne in the first stance! Does X-Plane model propeller cavitation too?

TomcatViP
04-27-2011, 01:42 PM
erm... it is actually. There is virtually no limit to the intricateness of a flight model, but it will need more and more computing power. You could build a CAD model of a Spitfire and simulate fatigue on each single screw if you wanted to, but it will need a lot of computing power.



I'm sorry but I don't think you have a full understanding of the topic man, or if you do, your explanation is ridden with generalisations.

Engineers don't calculate flight models, a flight model, even when accurate, is an approximation used for simulators. To design a plane you can render in CAD the surface and structure and calculate loads or aerodynamic coefficients, but you will still need to build and test prototypes.

Dear SternJ,

I am sry but you didn't took the train on time. See bellow post of Vip to understand that I was talking abt tweaking to simulate complicated probs.

Moreover it's over insupportable to hve to read on each of your post basically the "You don"t know as your are not this or that and blablabla"

Firsty I have reasonable confidence of my knowledge and I am always pls to learn/re-learn new things
Secondly I am debating here with all the people that are enjoying on this forum a new sim that is a step further toward our expectation regarding realism. I am not talking to you abt myself, you or my own lovely stern.

Pls open up and be alert and positive

Viper2000
04-27-2011, 01:46 PM
wow, I'm surprised the thing gets airborne in the first stance! Does X-Plane model propeller cavitation too?

You can't get cavitation in air; cavitation is a phase-change phenomenon.

You can certainly stall the propeller in X-Plane, and it will suffer shock losses. Actually the propeller model is one of its nicer features.

However, in general the underlying assumptions are undocumented and subject to change without notice. So you build a nice model, and then find that Austin has decided to tweak something in the next version and suddenly the predicted performance changes dramatically.

For this reason, it can't be used for serious work where fidelity is important.

Austin is a law unto himself and his system does not necessarily follow the conventions one would expect (eg although the underlying model seems to use SI, airframe dimensions are input in decimals of feet. Meanwhile, propeller root and tip chords are input in decimals of inches...). The engine model is a bit crazy, kinetic heating data is very questionable for M>>2, transonic behaviour is obviously lacking in fidelity, etc etc.

It's very good at replicating Austin's personal flying experience, but that's basically limited to GA piston singles. So although the simulator will allow you to build a rocketship and fly into LEO, the results have problems.

Of course, the average user doesn't understand the limitations of the code, not least because the underlying assumptions are undocumented, and therefore tends to believe that because the computer told them that their design would do this then it must be true.

So I fear that it's probably only a matter of time before some fool conducts virtual spin testing of their homebuilt masterpiece in X-Plane and then wins a Darwin award by assuming that X-Plane has validity in this regime simply because it produces output...

Sternjaeger II
04-27-2011, 01:59 PM
You can't get cavitation in air; cavitation is a phase-change phenomenon.

You can certainly stall the propeller in X-Plane, and it will suffer shock losses. Actually the propeller model is one of its nicer features.

However, in general the underlying assumptions are undocumented and subject to change without notice. So you build a nice model, and then find that Austin has decided to tweak something in the next version and suddenly the predicted performance changes dramatically.

For this reason, it can't be used for serious work where fidelity is important.

Austin is a law unto himself and his system does not necessarily follow the conventions one would expect (eg although the underlying model seems to use SI, airframe dimensions are input in decimals of feet. Meanwhile, propeller root and tip chords are input in decimals of inches...). The engine model is a bit crazy, kinetic heating data is very questionable for M>>2, transonic behaviour is obviously lacking in fidelity, etc etc.

It's very good at replicating Austin's personal flying experience, but that's basically limited to GA piston singles. So although the simulator will allow you to build a rocketship and fly into LEO, the results have problems.

Of course, the average user doesn't understand the limitations of the code, not least because the underlying assumptions are undocumented, and therefore tends to believe that because the computer told them that their design would do this then it must be true.

So I fear that it's probably only a matter of time before some fool conducts virtual spin testing of their homebuilt masterpiece in X-Plane and then wins a Darwin award by assuming that X-Plane has validity in this regime simply because it produces output...

yeah sorry, we erroneously refer to stalling as cavitation, but in fact it's propeller stall. Sounds interesting, does it also make the typical noise?

As for your last statement, there's nothing better than natural selection man ;)

Sternjaeger II
04-27-2011, 02:03 PM
Dear SternJ,

I am sry but you didn't took the train on time. See bellow post of Vip to understand that I was talking abt tweaking to simulate complicated probs.

Moreover it's over insupportable to hve to read on each of your post basically the "You don"t know as your are not this or that and blablabla"

Firsty I have reasonable confidence of my knowledge and I am always pls to learn/re-learn new things
Secondly I am debating here with all the people that are enjoying on this forum a new sim that is a step further toward our expectation regarding realism. I am not talking to you abt myself, you or my own lovely stern.

Pls open up and be alert and positive

no man, I'm really trying to be nice, but you were talking baloney.. and fair enough, it's not like we can know everything about everything, but if there's a topic you don't have a complete understanding of, just don't give statements like that, because people like me, who are driven by a particularly pedantic nature, won't like it.. it's for the sake of science really..

Peril
04-27-2011, 02:15 PM
Thanks Viper, you are resistant to change, having just re tested the Rotol version I do detect a roll to the right at low power. So it seem I was mistaken in that some left fin offset has been implemented already, so happy with that as logical in implementation of some offset..

As to the accuracy of the result, well, if CoD get a MkII I'll have the data to confirm that plane, which in turn can be used to reverse engineer the MK1.

So what officially is the Rotol Hurricane mk in game? A Mk1A? Correct labels will help define data here.

As you can tell I'm not that familiar with the European aircraft, for info US and Japanese are my forte'. However; I do have many gigs on German and RAF stuff I have acquired in my travels as well, BTW I didn't work on X-plane.

Sternjaeger II
04-27-2011, 02:20 PM
Think out of the presumptions you make for no trim change and the obvious is the following, plane designers don't build planes with disregard to torque. The outcome being there will be 'always' some consideration of this factor in the designs.


ha, maybe today, but back in the days there was a lot of pioneering in design.. the early Macchi fighters and designs suffered from the torque snap rolls for design flaws, and it's not until the Macchi 202 that they introduced a wing longer than the other to compensate for it (and still wasn't enough..).

TomcatViP
04-27-2011, 02:37 PM
So if it's for the sake of sciences :rolleyes:

But btw and I'msry If I blow all this lovely wall of smokes but 1300+ Hp for early merlin is still awfully overestimated. Did all the historians hve lied to us for such years ?

Before reading your reply I am packing all my books in the backyard with my diploma on top ready to set a holly fire :grin:

By the way : tail offsetting/twisting was a really draggy choice but used widely. Oh and don't forget were the torque act on the airframe to see it's a 3D prob tht need to be discussed with such a geo in mind (tip : early PushPull or Cessna 337 - Me 109)

jf1981
04-27-2011, 05:04 PM
You can't get cavitation in air; cavitation is a phase-change phenomenon.[...]
So I fear that it's probably only a matter of time before some fool conducts virtual spin testing of their homebuilt masterpiece in X-Plane and then wins a Darwin award by assuming that X-Plane has validity in this regime simply because it produces output...

Quite an interesting post. Thanks.

TomcatViP
04-27-2011, 05:38 PM
Quite an interesting post. Thanks.

Well you can alrdy see on YoutuBe designer projects being "Flight-Tested" with X-Plane :grin:

Viper2000
04-27-2011, 07:50 PM
So what officially is the Rotol Hurricane mk in game? A Mk1A? Correct labels will help define data here. Interesting question. I think it's a Mark Ia or Mark I revised, depending upon what nomenclature you prefer.

http://en.wikipedia.org/wiki/Hawker_Hurricane

Note that the stuff about water cooled engines running 70ºC cooler is not correct. It's probably meant to be 70ºF, since this would be about 39ºC, rather closer to the 30ºC reduction in metal temperature quoted by the RRHT.

As you can tell I'm not that familiar with the European aircraft, for info US and Japanese are my forte'. However; I do have many gigs on German and RAF stuff I have acquired in my travels as well, BTW I didn't work on X-plane.

As for X-Plane, I simply mentioned it because it is a sim I am extremely familiar with, as I have used it for over a decade, starting back in the V.5 days...

Peril
04-27-2011, 10:33 PM
You can't get cavitation in air; cavitation is a phase-change phenomenon.[...]

Mm, that phenomenon would be better referred to as a stalled prop or portion of the prop blade.

If it helps.

OH and don't trust wiki data, to unreliable, I see enough typos in core data as is ;)

I have cooling tests here if they help? AVIA_681_Report_689c_Part_01_Page_19. The full document is missing, a bugga as I can't confirm which Hurricane.

Viper2000
04-28-2011, 12:00 AM
There's nothing wrong with Wikipedia; it's pretty much as (un)reliable as any other secondary/tertiary source.

The world would be a much better place if people treated all sources with the same level of scepticism that they treat Wikipedia.

Peril
04-28-2011, 05:18 AM
Yep, which is why I use primary data mostly and why I started gathering primary data 10 years back, to help improve accuracy of sims and educate myself in the process ;)

Peril
04-28-2011, 08:31 AM
Try the new patched Hurricane for trim, I think they fiddled with the Hurricane FM?? Some others have noticed changes as well, perhaps a bug fix somewhere?

Can someone else verify this, perhaps I'm dreaming or it's the bottle of Red wine??

Redroach
04-29-2011, 11:29 AM
Thanks for the graph, Peril; I've been away for a few days and I've yet to catch up reading this thread, but I'll use that as a starting point.
Maybe the FM changes you mentioned fixed things a bit, too :)

Peril
04-29-2011, 01:36 PM
Please check it again, I did have a bottle of Red but it seemed lots better.

jimbop
04-29-2011, 01:41 PM
Haven't noticed any difference.

Redroach
04-29-2011, 02:35 PM
yeah, after a quick check with the new beta patch, it seems that the torque effect seems to have been toned down somewhat. Going full throttle, torque is feasibly counter-able by rudder trim.

Got more engine misfires, though and "high"-alt flying seems to be even more broken than before :rolleyes:

Peril
04-30-2011, 03:22 AM
Red roach, I don't use CEM, it's defiantly 'broken' IMHO too.

Try testing with CEM off because I think this gives the 'intended' best performance of the current engine. Doesn't make it correct but at least you can fly the damn thing to what feels like it's potential. This is of course just a gut feeling I have as being best potential but you can get it to perform smooth with CEM off. I got the Hurricane to 30000ft OK with no buffets at all, just ran out of climb rate.

The 110 now flies smooth until 490 IAS, I think that is better as well, but after here it gets a bit, uummm right words fail me, overly cautious with the onset speed of destabilisation FX?

TomcatViP
04-30-2011, 02:53 PM
I don't catch you there.

Just went in my first series of flight in Hurris and didn't hve any prob with torque, rpm and what ever.

The Hurri (Rotol prop) is one of the easiest plane to accelerate, climb and fight (nearly didn't touch the throttle during close knife dogfight with 6Cr42 that went back to base missing two of them).

Oh yes there is torques but ... wait ... I 've got a pair feet too ! :rolleyes:

To quote one of the great flyer here and around, Better learn to fly guys, after years of IL2 ninja's plane it's time !

PS: IMHO dear devs, with the hurri regarding the Rudder effectiveness : too much induced rolls with too weak sliding effect. When I add aileron to keep her level that's were she start to slide (due to 'ron drag ?).