Throwing some light on rates of turn

[IvanK]

the conclusion if you can really call it that is covered in the intro summary and the endpapers:





Crumpp I presume you are referring to these NACA documents:





If so I have them. The RAE report is quoted as a source or reference in these NACA reports. In addition the first one also references the other RAE report "Notes on the dogfight"

All three documents are imo in general agreement. The Devs should study these ! "Combat" flap usage in the classic IL2 imo was totally out of whack with reality ... sadly I am not so sure much has changed in CLOD.

[Crumpp]

All three documents are imo in general agreement. The Devs should study these ! "Combat" flap usage in the classic IL2 imo was totally out of whack with reality ... sadly I am not so sure much has changed in CLOD.

Right, for some reason people tend to think of flaps as a magical aid to turn performance and a crutch for poor ADM.

They are of very limited use in maneuvering to the average pilot.

I think the NACA conclusion in ACR #222 sum it up the best. In general flaps can offer some turn performance improvements beyond the clean configuration stall point but not above it.

In order to realize that improvement, a pilot must be able to precisely deploy the exact amount of flap required at the optimum speed to achieve that benefit.

IIRC, the example they use is 130 mph and 127mph....

That small speed difference with the right amount of flaps realizes a turn performance increase but the same amount of flaps at just 3 mph slower speed results in worse turn performance.

[Holtzauge]

Originally Posted by Crumpp

We are not going to do another 100 pager because you lack formal education in aerodynamics.

EAS is the most common expression for velocity in all aircraft performance calculation. It is the preferred expression because it is so simple to use.

It is too easy to convert to TAS any performance derived with EAS and you don't have worry about density effects in the mechanics of the calculation. Just convert at the end.

It also a great approximation of Indicated Airspeed and very easy to convert to that with a PEC chart and a universal compressibility.






http://www.google.com/url?sa=t&rct=j...o9yenlVuG8g5Zw







If you are trying to quickly gauge relative performance you don't have to convert back to TAS. The specific numbers for rate and radius will change in proportion to density ratio which is a universal application.

The problem is that your turn time of 21 s at 20,000ft is physically impossible. No amount of posturing and posting irrelevant book quotes underlined in red will change that fact:

You have claimed R=900 ft turn radius and turn time T=21 s at 20,000 ft:

Since I'm a metrics guy I will convert R to SI units, i.e. 274.3 m

This gives a turn speed of 82.08 m/s (2*pi*R/T)

So from this we calculate the turn acceleration: a=v**2/R=24.56 m/s**2

So load factor is n= sqrt(a**2+g**2)/g=2.696

Let's calculate the Cl this would require:

n*m*g=0.5*ra*v**2*Cl*S

Spitfire data:

W=6000lb=2724 Kg
S=242 sqft=22.36 m**2
ra=0.65 (Approx at 6.1 Km alt)

Solving for Cl:

CL=(2.696*2724*9.81)/(0.5*0.65*82.08**2*22.36)=1.47

Now NACA claims Clmax for the Spitfire at 1.2 which is a bit low but according to RAE it is 1.36 tops. Your claim leads to a Cl of 1.47 which is clearly unrealistic and like you fails the sanity check.

BTW: I found a RAE report, R&M 2349, Notes on the turning performance of the Spitfire as affected by altitude and flaps.

On page 4 there is a figure 4 which gives the following results for the Spitfire at 20,000 ft: R=1045 ft and T=31.5 s

With my C++ simulations I get R=337 m (1106 ft) and T=31.65 s.

You claim 21 s turn time and 900 ft radius of turn. I get 31.65 s and 1106 ft while Morgan & Morris in R&M get 1045 ft and 31.5 s.

So on the one hand we have C++ simulation data and the data from the RAE report R&M 2349 which seems to tally and on the other hand we have your overbearing attitude and simplistic calculations leading to an off the chart Clmax. What could be the right number I wonder , 21 or 31 s?

Finally, I think the only thing we actually agree on is the other parties lack of formal aerodynamic training. We have been down this road before and as I've told you before I have an Mcs in aeronautical engineering from the Royal Institute of Technology in Stockholm from 1986 and more than 10 years in the business working in the defense industry for Ericsson and SAAB on the Viggen and Gripen fighter systems.

Tell me, What aeronautical companies have you worked with and the Msc in aeronautics from Embry-Riddle you claim to have, which year did you graduate and was that before or after your stint in US Special Forces?

[ATAG_Colander]

Math is good. Me likes math.

[ATAG_Snapper]

Originally Posted by ATAG_Colander

Math is good. Me likes math.

Me too. In fact, my favourite snakes are adders!

[nakedsquirrel]

Originally Posted by ATAG_Colander

Math is good. Me likes math.

It's not fair. I see all of the math but I still can't shoot anybody down =(

I don't like math.

[MiG-3U]

Originally Posted by Crumpp

It is not hard to do at all. We can use the first entry for flaps up turn performance at 12000 feet.

V = TAS/SMOE = EAS

Standard Means of Evaluation at 12,000 feet = 1.2011

Flaps up TAS at 12,000 feet = 160 mph TAS

160/1.2011 = 133 mph EAS

133 mph EAS * .869 = 115.6 KEAS

Oh check it out....They give you EAS on the report. Gee, wasn't that another 100 page discussion on these forums?

Anyway, once you have EAS you can easily convert the performance to any atmospheric condition you want.

I like working with BGS but the units do not matter. Just don't put the correction factors like "1091" and "11.26" if you are using metric and keep your units straight.

Our formula becomes:

Radius = (VKeas * SMOE)^2 / 11.26tan <theta>

<theta> = angle of bank which is a fixed relationship with load factor irregardless of altitude

If you use the above formula and knots, our radius calculates out to be 693 feet and the RAE measurement is 695 feet. Pretty good agreement.


Radius is not the primary turn characteristic in a fighter. It not so important how small the circle but how fast we can bring the nose around to put guns on target.

So lets check our rate of turn based on the document:

Flaps up = 160 TAS * .869 = 139 KTAS

1091(tan 68 ) / 139 KTAS = 19.42 degrees a second

360/19.42 = 18.56 seconds to complete a 360 degree turn

18.6 and 18.56 are a match....

Now let's see what it does at 20000 feet:

160 TAS at 12000 feet = 133 mph EAS


133 mph EAS * .869 = 115.6 KTAS

SMOE @ 20000 feet from our Standard Atmospheric Data = 1.3700

Radius = (VKeas * SMOE)^2 / 11.26tan <theta>

Radius = {115.6*1.3700}^2 / 11.26tan <68>

= 899.97 or just 900 feet @ 20,000 feet

Rate = 1091(tan 68 ) / (115.6KEAS*1.3700)

= 17.05 degrees a second

= 360/17.05 = 21 seconds to complete a 360 degree turn at 20,000 feet

All you calculate here is the turn times at constant KEAS and constant g load (2.68 g which corresponds angle of bank 68 deg) at two altitudes, 12k and 20k. Then you claim that an airplane which can do this kind of sustained turn at 12k, can do sustained turn at same g load at 20k at same given KEAS. Note that your calculation does not account the engine power and the power might be different at 12k than at 20k.

Now, think this for a minute instead insult the other members of the board.