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Old 10-08-2015, 12:30 AM   #11
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The landing speed of the Fw190D9 was ~170 km/h at full weight, and 165 km/h with 50% fuel IIRC.
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Old 10-08-2015, 12:35 AM   #12
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http://www.wwiiaircraftperformance.o...-47-1658-D.pdf

118 mph is mentioned for the clean stall =190 kph. It gives CLmax =1.26 for 4100 kg. THat is very close (regarding Re changes) to the wind tunnel tests.

And 168 kph for landing configuration.
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Old 10-08-2015, 02:12 AM   #13
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Quote:
THis lift off speed does not seem very good to calculate CL because of two factors - ground effect and TO power. The more accurate result would give stall speed in clean configuration (power-off for sure) or touchdown speed (stilll with ground effect though).
I agree it is not good for specifically nailing down the CL max but that is not the intention.

It is good for a ballpark figure and the 1.58 is unlikely to be the landing flaps CLmax. The coefficient of lift returned by using Vmu certainly agrees well with a split flap equipped wing.

Unfortunately, Focke Wulf did not care to test the stall speed AFAIK.

Here is the landing reference chart used by FW-190A8 pilots. By convention, Vref approximates 1.3 the 1G stall speed for landing configuration.



Using that convention, the CL max returned throughout the curve is ~2.67 with 40 degrees of flap.

That ballpark seems to give agreement with the findings of the NACA investigation into trailing edge high lift devices.

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Old 10-08-2015, 02:20 AM   #14
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Quote:
Originally Posted by Yo-Yo View Post
http://www.wwiiaircraftperformance.o...-47-1658-D.pdf

118 mph is mentioned for the clean stall =190 kph. It gives CLmax =1.26 for 4100 kg. THat is very close (regarding Re changes) to the wind tunnel tests.

And 168 kph for landing configuration.


It is a small world, LOL.

That is the report I was going to post to show the 1.58 as 1G stall speed.

Basically, the report is uncorrected and without weight and balance information.

He uses an approach speed of 130 IAS which is fast by Focke Wulf data but not out of the realm of possibility in practical piloting.

The IAS data for stall, clean and in landing configuration is without any altitude data. The 94.4KEAS is equivalent airspeed.

It is very doubtful that pilot tested the stall speed at an altitude below 10,000 nor is that data corrected to standard. Most likely, it is just we he read on the airspeed indicator in the winter of 1943. If he climbed to 20,000 feet, account for colder than standard day effects on IAS and you convert the IAS to EAS.....the 1.58 becomes very plausible for the 1G clean configuration CLmax.

Like I said, the most damning evidence is the combination of wing airfoils and split flaps would have to been extremely poorly designed to only achieve a 1.58 CLmax with 40 degrees of flap.

Last edited by Crumpp; 10-08-2015 at 02:41 AM.
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Old 10-08-2015, 02:23 AM   #15
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Oh yeah, I used an FW-190A4 ladeplan minus the ammo and then determined if he climbed what fuel he would burn and if he had the time to do the test.

It was tight, but it worked out.
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Old 10-08-2015, 03:19 AM   #16
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BTW,

Yo-Yo this thread is not at all a call for you to change anything. Our methods might be different but the general result is the same and gives good agreement.

http://forums.eagle.ru/showpost.php?...&postcount=105

http://forums.eagle.ru/showpost.php?...0&postcount=83
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Old 10-08-2015, 12:11 PM   #17
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Quote:
Yo-Yo says:
118 mph is mentioned for the clean stall =190 kph.
94.4KEAS * 1.15 = 108.56 mph EAS

108.56 mph EAS - (+1) = 109.56mph CAS

109.56mph CAS + 7 mph PEC = 116.56mph IAS = 117 mph IAS

That is not even an 1% error.


Now if we look just above the CLmax on Weiderstandaten Von Flugzuegen we can see Focke Wulf lists the Coefficients of Lift for:

CaR = cruise flight

CaA = Approach

CaSt = Climb

CaA (Approach) Clmax exactly fits this curve of approach speeds.

An 8800 lbs Aircraft in Landing configuration at a Vref of 170kph needs:

170kph = 106mph IAS +3mph PEC = 109 mph CAS = 109mph EAS * 1.15 = 94.7KEAS

q = 94.7KEAS^2/295 = 30.4p/ft^2

CL = Weight/(q*S) = 9800lbs/(30.4p/ft^2*197ft^2) = 1.47

Well that agrees with Focke Wulf's approach Coefficient of lift.

If our CL max in landing condition is 1.58 then we only need to reduce velocity to 91.4KEAS.

That is 3.3 knots between approach speed and the stall. A 7 knot gust and you are stalling on approach.

That seems like some very tight landing margins and not very likely.


http://i61.tinypic.com/15ekdvo.png

Of course you know changing Vref is typical of aircraft that have a large weight variance. In the Airlines, we "get the numbers" every take off and landing.

I thought it was interesting that the FW-190 pilots also "got the numbers"!
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Old 10-08-2015, 12:52 PM   #18
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Quote:
Crumpp says:
94.4KEAS * 1.15 = 108.56 mph EAS

108.56 mph EAS - (+1) = 109.56mph CAS

109.56mph CAS + 7 mph PEC = 116.56mph IAS = 117 mph IAS

That is not even an 1% error.
If you work the Vs2 back to EAS from 105 mph IAS...

105mph IAS - 7 PEC = 98mph CAS - 1CeC = 97mph EAS = 84 KEAS

I chalked up his fast approach speed to performing an in-flight stall at altitude on a winter's day. He is doing the same thing I do when when I fly a new airplane. Take it up to up to altitude and stall it in landing configuration to get your approach speed.

105 IAS * 1.3 = 136 mph IAS which is why he used the 130mph IAS ballpark for Vref.

His Indicated Airspeed will read fast in the winter at altitude. It takes a 3% error to put us right back in the CL range of a split flap system.

Last edited by Crumpp; 10-08-2015 at 01:10 PM.
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Old 10-08-2015, 02:57 PM   #19
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Quote:
Originally Posted by Hummingbird View Post
Good post Crumpp

Unfortunately I don't believe our ingame Fw190 features this CLmax figure. Either that or the P-51 features a windtunnel derived CLmax, i.e. assuming a completely smooth surface for laminar flow, something which was NOT possible in production aircraft, let alone in the field.

A factory fresh condition NACA 6 digit airfoil (i.e. std. roughness) produced a CLmax around 1.3.

By comparison the NACA 23xxx series didn't suffer any negative effects to its Cd or CLmax characteristics under operational surface conditions, as one can observe in NACA tests concerning this specific subject = surface roughness effects on various airfoils.
That is really Ok, Hummingbird. Just as there are different ways to skin a cat, there is different theory in aerodynamics. Mixing them can bring trouble. Even switching between the BGS and SI can deliver slightly different results.

What is important is not the specifics but the performance trend. There is margin of error in everything. The math shows us what is possible and simply a description of the physical world. What matters in the result in the physical world.

Outside of a small Rate of Turn difference, the analysis are almost the same.

You know, I have seen several folks post their math and theory pushing it off as some kind of holy grail of absolute truth.....that is not really true or correct. Yo-Yo models reflect reality "in the realm of significant digits" as one of my college professors was so found of saying. That is all you can ask of him.

As for the P-51...

I used the stall speed chart presented in the POH and interpolated for the max TO weight of 9611lbs for a stall speed of 102.8 mph IAS WITH wing racks.

I then corrected that IAS to CAS at sea level using a P-51 PEC curve.

102.8mph + 5.8mph = 108.6 mph CAS; CAS = EAS at sea level = 108.6 mph EAS*.869 = 94.3KEAS

An 9611lbs Aircraft traveling at 94.3KEAS needs:

q = 94.3KEAS^2/295 = 30.14p/ft^2

CL = Weight/(q*S) = 9611lbs/(30.14p/ft^2*235.75ft^2) = 1.35
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Old 10-08-2015, 03:38 PM   #20
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The next nail from my side :

You operate wind tunnel data. As well as German-French WT test. But the point is that the flight tests always shows lower CLmax because of trim losses - I mean stabiliser negative lift that is very sufficient at high trimmed CL's.

And the second point, I guess, you must take in account: the wing area taken for the plane generally includes the area of the fuselage that has very different lift/drag properties. The actual lift for the whole plane is produced by the wings (of less area that is specified for the plane) and the fuselage. So, the airfoil section numbers must be used very carefully.
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Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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