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Dora stall speed


Crumpp

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the laminar flow airfoil performs noticably worse in CLmax than the NACA 23xxx series,

 

I did not do the Re calculations for a 36 inch chord.

 

I can do it later but I am sure they will be close just as the Lift formula predicts.

1395673601_P-51NACA45-100.jpg.4afc85f2edbd2eddc7101778ebad63ae.jpg

Wind-Tunnel_Investigation_of_Profile_Drag_and_Lift..._Abbot,_Underwood,_1943.pdf

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Yes, the windtunnel section mock ups pretty much all show very high CLmax figures, but the real aircraft didn't achieve anywhere near such results.

 

The typical operational aircraft featured small bumps and dimples along its entire wing surface, all of which had an impact on the aerodynamics. The laminar flow type designs were especially sensitive in this regard, as also explained by Lednicer.

 

Hence the NACA 23xxx series was prefered for aircraft where high lift was a necessity under all operational conditions, such as with carrier aircraft.

 

Under identical windtunnel conditions the NACA 23012 performed only sligthly better:

Pages%20from%20naca-report-824.jpg


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Yes, the windtunnel section mock ups pretty much all show very high CLmax figures, but the real aircraft didn't achieve anywhere near such results.

 

The typical operational aircraft featured small bumps and dimples along its entire wing surface, all of which had an impact on the aerodynamics. The laminar flow type designs were especially sensitive in this regard, as also explained by Lednicer.

 

Hence the NACA 23xxx series was prefered for aircraft where high lift was a necessity under all operational conditions, such as with carrier aircraft.

 

Under identical windtunnel conditions the NACA 23012 performed only sligthly better:

Pages%20from%20naca-report-824.jpg

 

Correct but lets make sure we do not misapply it to one aircraft and not the other.

 

On the surface without a Reynolds number conversion for the P-51's NACA 44-100.

 

We can take a small risk that Re number will not change the significance and say:

 

Focke Wulf figure for a CLmax of 1.58 for the airplane gives good agreement with all the 2D data and the fact our full sized airplane will not attain the CLmax of 1.8.

 

The North American CLmax of 1.6 of the NACA 44-100 also gives good agreement with the 1.41 CLmax calculated by the lift formula for the full sized P-51.

 

A CLmax of 1.41 is not a "low CLmax" for a World War II fighter, it is just typical.

 

Interestingly enough, the NACA concludes the change is ~.2 on the CLmax.

 

1.8-1.58 = .22 change coefficient of lift for the Focke Wulf

 

1.6-1.41 = .19 change in coefficient of lift for the P-51.

 

That agrees with the NACA results.

 

I agree with you on the laminar flow but that really has no effect on anything important to a DCS player.

Answers to most important questions ATC can ask that every pilot should memorize:

 

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I did not do the Re calculations for a 36 inch chord.

 

I can do it later but I am sure they will be close just as the Lift formula predicts.

 

(13110000*.000157926)/3 = 685.77fps = 467mph for the wing section = CLmax 1.75

 

(13110000*.000157926)/8.8 = 233fps = 159mph for the XP-51

 

(9030000*.000157926)/3 = 472fps = 322mph for the wing section = CLmax 1.7

 

(9030000*.000157926)/8.8 = 161fps = 109mph for the XP-51

 

(6100000*.000157926)/3 = 319fps = 217mph for the wing section = CLmax 1.65

 

(6100000*.000157926)/8.8 = 109fps = 75mph for the XP-51

 

Interestingly enough, the NACA concludes the change is ~.2 on the CLmax.

 

1.8-1.58 = .22 change coefficient of lift for the Focke Wulf

 

1.7-1.41 = .29 change in coefficient of lift for the P-51.

 

The CLmax of 1.41 comes from the lift formula and represents the clean stall speed for a TO weight P-51D with wing racks installed.

 

Using the 1944 Mustang POH which does not have a good PEC curve in the vicinity of Vs for the Mustang and interpolating the stall speed....

 

I get a clean configuration CL max of 1.53 for the Mustang and puts the analysis spot on with Yo-Yo's work.

 

1.7-1.53 = .17 change in coefficient of lift for the P-51 so the PEC curve maybe throwing us off somewhat and shows the analysis could be a hair optimistic.

 

The ROT advantage for the Dora is only a one hundreth of a degree per second and the Dora cannot match the P-51's speed nor can the P51 Match the Dora's turn speeds.

 

If either aircraft tries to fly to the others speeds, they will be outturned.

 

There is some "wiggle room" because of the lack of good clean configuration stall speed data on the Mustang. I do not think the Mustang could ever outturn a Dora at the Dora's turn speeds. The best the Mustang can do is match the turn rate.

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1. No, I do not have a pen. 2. Indicating 250

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I would like to see better stall speed data on the P-51. That is why I use the CLmax of 1.41 because it represents a more solid data point than the 1944 P-51 Operating Instructions give me.

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That's the way of saying. I use it because it fits my way of thinking better. Stick to the data.

 

Also stall speeds are listed in the manual with and without flaps, what more do you want?

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That's the way of saying. I use it because it fits my way of thinking better. Stick to the data.

 

Also stall speeds are listed in the manual with and without flaps, what more do you want?

 

It is a way of saying EXACTLY what I said:

 

Crumpp says:

I would like to see better stall speed data on the P-51. That is why I use the CLmax of 1.41 because it represents a more solid data point than the 1944 P-51 Operating Instructions give me.

 

 

The Stall Speeds are listed in Indicated Airspeed not True Airspeed.

 

It must be converted to True Airspeed at sea level on a standard day. The position error data in the 1944 manual ends almost 100 miles per hour above the stall speed. There is no PEC curve in the 1944 manual, just data points. That leaves much to interpolated and opens up for a very large margin of error. That leaves no curve to use in picking the Stall Speed. It simply not an accurate data point for converting indicated airspeed to calibrated airspeed in the 1944 manual. It was not intended for engineers and pilots do not care about calibrated airspeed in a stall.

 

Here is a typical Position Error Curve:

 

59zll.jpg

 

Here is a good Position Error Curve on the P-51. Because of the nature of installation error, it is dependent upon angular velocity of the air impacting the pitot tube. That can induce large error in the individual data points. Notice the two oulier data points at 210 mph and 218 mph.

 

2cdjwhv.jpg

 

 

The other data is much better and leaves nothing to interpolation therefore has a much smaller margin of error.

 

That is why I use it.

Answers to most important questions ATC can ask that every pilot should memorize:

 

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First we need to understand the concept of Reynolds number (RN). Simply put, RN is a measurement of the "stickiness" of the air. It is the viscosity.

 

Someone has probably already mentioned it, but, this is incorrect, the Reynolds number is not a measurement of the stickiness, it is an indicator of whether you have laminar or turbulent flow, and can be used to determine where the flow changes from laminar to turbulent.

 

One of the variables used to determine it is the viscosity, or more accurately the kinematic viscosity, but the RN itself certainly is NOT the viscosity.

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Cap'n kamikaze says:

Someone has probably already mentioned it, but, this is incorrect, the Reynolds number is not a measurement of the stickiness, it is an indicator of whether you have laminar or turbulent flow, and can be used to determine where the flow changes from laminar to turbulent.

 

Everything I have said is correct.

 

I think what seems confusing is one has to understand that the amount of laminar flow to turbulent flow is a result of the "stickiness of the air"! :thumbup:

 

 

The Reynolds Number, the non-dimensional velocity, can be defined as the ratio of

 

the inertia force (ρ u L), and

the viscous or friction force (μ)

 

http://www.engineeringtoolbox.com/reynolds-number-d_237.html

 

Like air, water also has viscosity or stickiness. While you are moving your rowboat through the water, the flow of the water creates skin-friction on the wetted hull-surfaces. Thus while rowing you have to overcome two different kinds of forces. There's the inertia, caused by the water's density, and the friction, caused by its stickiness.

 

He found that laminar flow or turbulent flow depends only on the ratio of the inertial forces over the friction forces.

 

http://www.aerodrag.com/Articles/ReynoldsNumber.htm

 

It is most commonly used in aerodynamics as a scaling factor to relate our tiny wind tunnel models to the big airplanes we fly! :smilewink:

 

To properly model these effects, aerodynamicists use similarity parameters, which are ratios of these effects to other forces present in the problem. If two experiments have the same values for the similarity parameters, then the relative importance of the forces are being correctly modeled.

 

The important similarity parameter for viscosity is the Reynolds number. The Reynolds number expresses the ratio of inertial (resistant to change or motion) forces to viscous (heavy and gluey) forces.

 

 

o5swgm.jpg

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Crumpp says:

It is the viscosity.

 

No, this is not correct and is just a consequence of trying to "simplify" a complex explanation.

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Reynolds number is not a measurement of the stickiness' date='[/quote']

 

It is actually the main idea behind Reynolds number and what I focused on in my first reply to you.

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  • 2 years later...

Weight was 4100 kg

 

Tested it on the far eastern valley on the NTTR map, altitude was between 50-100 m.

 

The aircraft toppled over at 200 km/h TAS (Ctrl Y), but it had already started plummiting downward before that.

 

By comparison the 109 & P-51 both stalled at ~160 km/h TAS with 50% fuel ingame.

 

 

Real life figures for clean idle stalls are:

K-4 = ~160 km/h at 3,200 kg

P-51D = ~170 km/h at 4300 kg

190D = ~180 km/h at 4100 kg

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Weight was 4100 kg

 

Tested it on the far eastern valley on the NTTR map, altitude was between 50-100 m.

 

The aircraft toppled over at 200 km/h TAS (Ctrl Y), but it had already started plummiting downward before that.

Don't have NTTR installed. Confirm 50-100m MSL?

 

Stall speed is usually measured in IAS and/or CAS, not TAS.

 

Don't understand the sentence about the stall speed. What you you mean with it 'toppled over at 200 km/h TAS, but it had already started plummiting downward before that'

 

A stall is clearly defined and has to be performed at with a speed reduction of approx 1kts/sec.

 

I assume you didn't try to test the stallspeed during level flight with a high rate of speed reduction...

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Stall speed is usually measured in IAS and/or CAS, not TAS.

 

Don't understand the sentence about the stall speed. What you you mean with it 'toppled over at 200 km/h TAS, but it had already started plummiting downward before that'

 

A stall is clearly defined and has to be performed at with a speed reduction of approx 1kts/sec.

 

I assume you didn't try to test the stallspeed during level flight with a high rate of speed reduction...

 

In fact, I agree with your considerations.

 

:thumbup:

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Don't have NTTR installed. Confirm 50-100m MSL?

 

Stall speed is usually measured in IAS and/or CAS, not TAS.

 

Don't understand the sentence about the stall speed. What you you mean with it 'toppled over at 200 km/h TAS, but it had already started plummiting downward before that'

 

A stall is clearly defined and has to be performed at with a speed reduction of approx 1kts/sec.

 

I assume you didn't try to test the stallspeed during level flight with a high rate of speed reduction...

 

I tried to maintain altitude at ~100 m MSL, but around 210-220 km/h TAS I couldn't maintain altitude anymore and the aircraft began to sink whilst speed kept dropping. At around 200 km/h & 50 m MSL the left or right wing dropped and I crashed.

 

Tried the same procedure with the 109 & P-51 which both started to sink at around 180 km/h TAS and stall (wing drop) at around 160 km/h TAS & 50 m MSL.

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I tried to maintain altitude at ~100 m MSL, but around 210-220 km/h TAS I couldn't maintain altitude anymore and the aircraft began to sink whilst speed kept dropping. At around 200 km/h & 50 m MSL the left or right wing dropped and I crashed.

 

If you are trying to maintain level fligtht at idle, speed will drop rather quick and to maintain altitude you have to increase backpressure on the stick rather fast, hence g-load will be higher than 1.0 and the stall speed will increase!

 

Furthermore most ASIs will read low at low speed and/or high AoA, so the IAS stall speed is usually way lower than a TAS stall speed would be.

 

Don't know if DCS simulates the installation error for the ASI, but in any case, you should only use the ASI value to establish the indicated stall speed (and a low rate of speed reduction and a higher altitude!!!)

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