Throwing some light on rates of turn

[Kurfürst]

Ahw. :/ I wonder if its possible to convert the figures to different altitudes..?

[Robo.]

Good stuff IvanK, only thing that confuses me is the 'Merlin XX', i guess that's a typo of some sort, or was that some Mk.III testing?

Good information regarding Spitfire flaps down behaviour at page 11 of this document:

http://ntrs.nasa.gov/archive/nasa/ca...1993092582.pdf

[IvanK]

There is a Pencil Note on the first page next to the title "MKIII". This I presume is an annotation to indicate that the document is based on the spitfire MKIII which would also match the XX Merlin. A weird choice of variant to do tests with !

Got the NACA report.

[Crumpp]

An excerpt from AVIA 6/2422 "Notes on the turning performance of the Spitfire as affected by Altitude and Flaps"

You have the entire report?

I am sure it does not say lower 85 degrees of flap and fly around in small circles.

[IvanK]

Yes

[Crumpp]

I wonder if its possible to convert the figures to different altitudes..?

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

[IvanK]

Here are 3 Relevant Fan plots from the report posted without comment

Clean:


Flap 30


Flap 60 and Full at 85.

[Crumpp]

Here are 3 Relevant Fan plots

Do you have the conclusions stated in the report and the conditions?

It appears the RAE contradicts the NACA's findings on the effect of flaps on turn performance as well as what is taught in modern curriculum's.

I really don't think that is the case and I bet that agreement is in the details of the report you posted.

I understand your reluctance to share those details in this report. I would be happy to provide you the NACA findings on this subject.

[Holtzauge]

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

As you yourself said there have been many 100 page discussions about your use of EAS to estimate turn performance in the forums you post in and it seems that you still have not mastered the art.

The way you simply use EAS above to derive results for 20,000 ft gives erroneous results that bear no relation to actual performance of the Spitfire at this altitude and a more realistic turn time under these conditions would be about 30 to 31 s.

[Crumpp]

As you yourself said there have been many 100 page discussions about your use of EAS to estimate turn performance in the forums you post in and it seems that you still have not mastered the art.

The way you simply use EAS above to derive results for 20,000 ft gives erroneous results that bear no relation to actual performance of the Spitfire at this altitude and a more realistic turn time under these conditions would be about 30 to 31 s.

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.

The flight speed corresponding to maximum climb angle, θmax, is the optimum flight speed, usually measured in EAS,

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.