Throwing some light on rates of turn

[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!

[Crumpp]

21 or 31 s?

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




115.6*1.3700 = 158.4 KTAS

Looks like 21s when we ask the US Navy or use any universal turn performance chart!!

Ha ha ha

[Crumpp]

we have C++ simulation data

The output is only as good as the input...

[Crumpp]

Yes Holtzauge, I am employed full time in aviation as a pilot.

Yes, I retired from the US Army before I went into aviation as a second career.

How about you? You do C+++++ simulations for a living?

[Crumpp]

Your claim leads to a Cl of 1.47 which is clearly unrealistic and like you fails the sanity check.

Anyhow, CL, CD or Cwhatever values mean absolutely NOTHING if reference surface (and reference length for couple of forces) is unknown. Anybody with basic notions in aerodynamics should know this. I can announce CL values of 1700 for a brick if I just select a reference surface small enough if I wish to do so and nobody could claim me wrong.

The CL values in this report are only interesting in relative terms with respect to different flap angles.

[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.

[Crumpp]

IIRC CL does depend on Mach number even at subsonic speeds

Yes it does but the RAE was using subsonic incompressible flow theory in that report.

In subsonic incompressible theory, Coefficient of Lift is independent of altitude and mach number.

A compressibility correction to velocity is used to account for it.

In the formulation, compressibility is factored in when converting from CAS to EAS.

How does the lift coefficient for maximum range vary with altitude? (No compressibility effects.)

A: The lift coefficient decreases with increasing altitude.
B: The lift coefficient is independent of altitude.
C: The lift coefficient increases with increasing altitude.
D: Only at low speeds the lift coefficient decreases with increasing altitude.

Answer: B

http://www.thedailyatpl.com/atpl/per/how-does-the-lift-coefficient-for-maximum-range-vary-with-altitude-no-compressibility-effects/

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.

That certainly depends on which merlin and which variant we are discussing. I don't know as only snippets of the report have been posted and would only be guessing.

If you read the thread, the question was how to convert that performance to other altitudes.

The answer to that is to use the EAS scale provided in the RAE chart and convert to what ever density altitude you wish.

[Al Schlageter]

Originally Posted by Crumpp

That certainly depends on which merlin and which variant we are discussing. I don't know as only snippets of the report have been posted and would only be guessing.

On the first page it says 'Merlin II Spitfire'.