Spit/109 sea level speed comparisons in 1.08 beta patch

[Glider]

Originally Posted by Kurfürst

Actually drag is the factor where the 109 may win out at high speeds. Parasitic drag is much lower on the 109 than on the Spitfire, and parasitic drag is what dominates total drag at higher speeds. The Spitfire turns better at low speeds because it has lower induced drag, and induced drag is what dominates total drag at low speeds.

Sustained turn is just the maximum g-load at which drag = thrust. Maximum sustained turn (i.e. the number usually quoted for turn times) is always achieved at lower speeds, but that doesn't mean the trends continue to high speeds and may be reversed. I am not sure if there is much to it - it can be well true that both aircraft can only turn so slowly in a sustained fashion that there is no tactical point in it.

Bottom line, a faster aircraft will always outturn a slower aircraft at high speeds, the question is not really wheter this happens or not, but: by how much?

I don't know the numbers for the parasitic drag for these aircraft but would expect the difference to be marginal. The Spitfire is a larger aircraft and this would count against it but the 109E has less curves and is less aerodynamic which would balance it out. Indeed the 109F was more streamlined and this contributed to its improved performance. Which has the advantage I don't know but I would expect it to be close.

I believe your bottom line re a faster aircraft always outturning a slower one to be wrong. If it were right the 262 would out turn everything

[Glider]

Originally Posted by Crumpp

Not sure you understand much of the science at all. I certainly don't like the attitude or implication I have something to prove or a vested interest in the outcome.

The math is what it is.....

I don't know if your trying to prove that the 109 had a better sustained turn or straight line speed and don't see how the diagram helps either case.

In short I don't see how it proves anything.

[MusseMus]

Inspired by another post here about possible speed gauge error I made a little test.

I created a mission in FMB, where I let 2 AI planes fly next to each other for some miles. One was a 109E-4 and the other a Spit 1 and they were programmed to go at 300 kph at 500 meters.
I measured the time it took for them to travel 20 km and I checked their speed gaugets (AI on).

Observation 1: The 109E-4 outran the Spit on every try No idea why they did not match speed since I used exactly the same settings on them.

Observation 2:
The airspeed gauge on the 109 red 310 kph, but the calculation gave me 325 kph=a difference of about 5%

The spits gauge showd 170 mph=273 kph, but the calculations gave me 316 kph=a difference of about 15%

I'm aware that I'm comparing IAS and ground speed here, but the difference at 500 meters should not be this big, right?

Compare theese results with Cambers table
Coincidence?

/m

Originally Posted by camber

[Crumpp]

In short I don't see how it proves anything.

Well, that is because you don't understand aircraft performance.

That is ok and you are not alone.

It proves exactly what I said and the math does not lie nor is it bias.

I will see if I can help you. If I can't, oh well, it does not change the physics or the math.

Angle of bank and load factor have a fixed relationship in a steady state turn.

For example, 60 degree of bank will always produce a 2g load factor no matter what the aircraft under consideration.

Turn rate and radius is a function of angle of bank and velocity.

All aircraft at the same angle of bank and velocity will make exactly the same turn. So if a Cessna Corvalis and a Boeing 747 are going 200 knots and banks 60 degrees, they will both make the same rate and radius of turn.

Radius is very velocity dependant.

From an FAA question when getting your commercial certificate.....

An aircraft holds a constant angle of bank and velocity increases. What is the effect on radius?

The correct answer is load factor remains constant and radius increases.

At the same velocity, the aircraft which can sustain the highest angle of bank is achieving the higher load factor and will make a smaller radius as well as higher rate of turn.


So that diagram shows the Spitfire cannot realize a sustained turn performance advantage until it reaches the portion of the envelope the Bf-109 cannot fly in anyway. Then the Bf-109 must reduce its angle of bank in order to match speed and the Spitfire can sustain a higher angle of bank in that portion of the envelope.

If a Spitfire enters a turn fight with a Bf-109, the Bf-109 can force the Spitfire into this low speed realm. The Bf-109 will simply outturn or match any Spitfire that tries to remain at the same speed or maintain velocity.

So both pilots have to make a choice. The Spitfire pilot can choose to hold onto his airspeed and be shot down. The Bf-109 pilot can choose to follow the Spitfire into the low speed realm and be shot down.

Factor in stability and control, these aircraft are even more equal dogfighters. The Bf-109 pilot can precisely attain and hold a target load factor to achive maximum performance.

The Spitfire requires a skilled pilot to precisely achieve and maintain a target load factor in order to achieve maximum performance.

Understand?

[ACE-OF-ACES]

Originally Posted by MusseMus

Coincidence?

There is some debate on this issue.. But one thing that I am sure of (99%) is the guage values are.. well.. not great! I have seen that they lag other values (see below), I think to simulate guage reaction times.. Also they have some strange offsets associated with them.. For example, the ROC reads around 65+ fpm while sitting still on the runway! So for those reason and more I have been leaning towards using the 3D world relative values (Z) over the cockpit guage aka indicated (I) values. They are not without issues either.. I say issue but it just maybe something we are not told about them yet, maybe the soon to be released read me will clear some of that up? Anyway the Z values seem to be the way to go for now IMHO.

[Crumpp]

I believe your bottom line re a faster aircraft always outturning a slower one to be wrong.

An aircraft at Vmax has zero excess power.

So, the slower airplane has zeo excess power at its top level speed while the faster still has excess power to maneuver.

Understand?

[Crumpp]

For example, the ROC reads around 65+ fpm while sitting still on the runway!

Have you sat in the cockpit of many real airplanes?

[IvanK]

Emm we have this chart from RAE



It clearly shows that the Spitfire MK I has better sustained turn performance throughout the speed range than the Bf109E3. It also shows Max sustained G of the Spit as 3G whilst the max sustained G of the BF109E3 is about 2.3G. With the Spit I weighing 6000lbs and the 109E3 weighing 5600lb.

We then have this chart



Which shows the BF109E3 having a better sustained turn performance than the Spifire MKI throughout the speed range. This chart shows (at Take off weight nonetheless) the Spitfire max sustained G of 3.2 g and the BF109E3 max sustained G of 3.25g

Whose chart do you believe RAE or this other thing ?

[Al Schlageter]

Well Ivan I would believe the chart made by a practicing aeronautical engineer over a theoretical aeronautical engineer.

[camber]

Originally Posted by Crumpp

Not sure you understand much of the science at all. I certainly don't like the attitude or implication I have something to prove or a vested interest in the outcome.

The math is what it is.....

math is math, and physics is physics.

But coding useful models is a different animal. Part of my job is coding physical process simulations. Providing you have implemented the correct maths, your output depends on the physical constants you choose as appropriate.

Perhaps if you listed the constant values you used for the Spit and 109 we could evaluate your graph a little better. The math equations would be good too.

camber