Hurricane engine torque

[Viper2000]

Originally Posted by Peril

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".

Originally Posted by Peril

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.

Originally Posted by Peril

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.

Originally Posted by Peril

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]

Originally Posted by Viper2000

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?

[Viper2000]

Originally Posted by Sternjaeger II

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]

Originally Posted by Viper2000

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

[Peril]

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]

Originally Posted by Peril

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]

So if it's for the sake of sciences

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

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)

[Viper2000]

Originally Posted by Peril

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.

Originally Posted by Peril

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]

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]

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.