Author Topic: Questions on Max CL  (Read 356 times)

Offline M.C.202

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Questions on Max CL
« on: December 12, 2000, 11:59:00 PM »
F4UDOA posted this:

> If you know the level stall speed of an A/C you can determine the Max Cl very quickly.

>Cl = Lift * 391 / (V^2 * WingArea) = 12000 *391 / (100^2 * 314) = 1.49

For the Macchi M.C.200 I get 1.80, and for the M.C.202 I get 1.7.

Does the performance in AH match this? And how does thrust from the prop (blown air) add to this?

No axe to grind, just trying to learn.

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M.C.202
Dino in Reno

Offline wells

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Questions on Max CL
« Reply #1 on: December 13, 2000, 12:15:00 AM »
Where did you find stall speeds for those planes?

Thrust will increase the V^2 term, increasing the lift and reducing stall speed, it doesn't affect CLmax.  Well, I should elaborate a little bit...if one is to calculate the CLmax from the indicated speed on the gauge, it would appear to increase with thrust as the stall speed decreases, but really, there is a higher velocity of airflow over the wing than what the gauge reads.  I would guess that the CLmax you got were with flaps down.  It's too high for a ww2 fighter in the clean configuration.

[This message has been edited by wells (edited 12-13-2000).]

Offline M.C.202

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Questions on Max CL
« Reply #2 on: December 13, 2000, 12:22:00 AM »
202 was from factory prototype data "mimimum speed 88.8 at sea level"

200 was from from a book that gave "TM C.A.444, issue October 1940" as it's source. "mimimum speed 79.5 M.P.H." is what I used. Might not be stall, but it looks like it to me. Take off distance was 805 feet.

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M.C.202
Dino in Reno

[This message has been edited by M.C.202 (edited 12-13-2000).]

Offline juzz

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Questions on Max CL
« Reply #3 on: December 13, 2000, 12:42:00 AM »
F4U-4 and F6F-5 both have wings with NACA 23000 series airfoils - and funnily enough using the power-off stall figures in the US Navy History .pdf files and the above formula I calculate CLmax as being about 1.95 for both a/c. This must be flapped?

What is the (2d)Clmax of a NACA 23000 series airfoil anyway?

Offline Zigrat

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« Reply #4 on: December 13, 2000, 02:07:00 AM »
1.7 for a clear infite 23000 (varies slightly on exactly which 23000 (%thcknesses commonly range 12-15%)

Offline F4UDOA

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Questions on Max CL
« Reply #5 on: December 13, 2000, 10:39:00 AM »
M.C.202,

The best place to get the stall speeds is from the pilots manuals. I have the F4U manual which list the range of stall speeds from 10,000lbs to 15,000lbs as well as climb in those weighted conditions. I also have the P-38 manual that list the same although not quite as detailed unfortunately. As you calculate the max Cl  at different weights it will vary slightly but you will get the idea within a couple of tenths.

Here is another fun calc.

For instance if you know that the F4U stalls at 96mph at 11,300lbs the you can find out the 3G stall speed very quickly also. Just take the square of the of the G factor(3) which is 1.732 and multiply it with the stall speed of 96mph.

3G stall =166.27MPH

How do you know it's right? Compare it to the flight test data and it is so close it's scary. This number obviously changes with weight but the max Cl will stay the same unless flaps are deployed then the Cl goes up and stall speed goes down.

Also try Zigrats spreadsheet

 http://www.iit.edu/~buonmic/aircraft-test.xls

It is very close and easy to read. But again you need to know the 1G stall at what weight. Very important that the stall is at the correct weight or else it porks everything.

BTW, Those calcs I listed came from Wells. So if I'm wrong blame him, just kidding.

Niklas also knows this stuff but he likes to use max Cl numbers from just the wing with no prop or prop wash so they always come out to low. But he is a Luftwabble so he might have some stuff on the C200, C202 and C205.

Later
F4UDOA


Offline F4UDOA

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Questions on Max CL
« Reply #6 on: December 13, 2000, 10:54:00 AM »
Juzz,

From the F4U-1 manual

Landing condition 50 degrees Flap(Full flap)
At 11,300LBS
Power off stall=75knots
Power on stall =66Knots

Clean no flap
Power off stall = 87knots
Power on stall  = 84Knots

P-38 from the manual

Note power on not given but on the 38 power off stall is the lower of the two conditions. Don't know why, ask Wells.
15,000lbs power off
Clean no Flaps stall=94mph
Full flaps          =69MPH

17,000lbs
clean no flaps stall = 100mph
Full flaps stall     =  74mph

19,000lbs  
clean no flaps stall = 105mph
Full flaps stall     =  78mph

If I was a P-38 pilot in AH I might be asking Pyro if these numbers match.

Offline M.C.202

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Questions on Max CL
« Reply #7 on: December 13, 2000, 11:58:00 AM »
Thanks to all, does anyone have clean (non-flap) stall speeds for the following:

M.C.200
M.C.202
M.C.205
Any of the Re2000/1/2/5
Paggio P119
S.I.A.107/207/403
Ambrosini S.S.4

Thanks again


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M.C.202
Dino in Reno