Forum: F-16 Design & Construction

Hello,

My name is Yogev frome isreall i am learning mecanical engeniring

I am trying to calculate the forces on the F-15/F-16 air brake , (the draft )

But I am having some problems with it, is there anyone that could help me ?

Could it be that the draft force is 3 tons? (at leanding)

Thank you !!

Yogev .k

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Yogev,

Welcome to F-16.net!

In 1975, I was the engineer who calculated the design forces on the F-16 speedbrake, based on flight test of the YF-16. Because landing is such a low speed, I did not bother to calculate those forces. But to estimate the force on the speedbrake at landing, you can use the dynamic pressure at landing speed x speedbrake area x cos 60 deg x Cd

dynamic pressure q ~ 125 lb/sq ft (from q/M^2 = 1480 lb/sq ft)
area ~ 4 sq ft x 4
cos 60 deg = .866
Cd ~ .7

total drag force ~ 1212 lb

That is the total force (parallel to the fuselage centerline) on all four panels at landing speed. It is much less than 3 tons.

I hope this helps you.

If anyone knows a better source to answer this question than the engineer who did the original calculations, please step up!!

Best Regards,

Cosine of 60 degrees is 1/2, sine of 60 degrees is .866.

JoeSambor wrote:

If anyone knows a better source to answer this question than the engineer who did the original calculations, please step up!!

Eh...er...ah...I've got nothing. Laughing

Excellent post John! I'm not an Aerospace Engineer, but I play one on tv, and it would be interesting to apply your formula to several other planes...including mine.

Aub,
Thanks for the correction, should have said sin 60 or cos 30. Anyway the .866 is correct.

TC,
The equations I showed are F-16 geometry specific and would not work on any other airplane. But if you tell me the geometry I can make an estimate of the load.

Hi johnwill,

First of all tank you.

I was examined my calculations and got different results.

Please your opinion :

D=0.5X(density of air at sea level) x (V^2) x (A )x sin(60) x (Cd)

A=1.45 X 3 = 4.35 [M^2] (47 sq ft)

Density=1.226 [kg/M^3] (sea level)

V=93 [m/sec] (180 knots) at lending

Cd=0.7

D=13881.19 [N] == 1.424 tons ==3144 lbf

(The plane Weights 12 to 20 tons)

Hoped that it is clear enough and waiting for your professional Opinion.

Thank you,
y.k

Yogev,
The first thing I see is your area is not correct. I estimated the area as 1 ft x 4 ft for each of the four panels = 16 sqft. Your 47 sqft is much too large. Another difference is the speed. I estimated 150 kt, you used 180 kt, so there is a large difference due to velocity squared. I am not familiar with the the density in kg/m^3, so I have to assume that is correct. Density x v^2 /2 is called dynamic pressure (q). I used another equation to calculate q, q/mach^2 = 1480 lbf/sqft at sea level.

My numbers were just quick estimates to show the method I used, not intended to be a perfect answer. There is nothing wrong with your method, just double check the variables you used (especially area).

Edit:
I used the area for an F-16. Perhaps you used the F-15 area, as it is larger.

johnwill, F-16.net's best asset!

Cheers

JpoLqr,
Thanks for the kind words, but they are not deserved, and I'll have a beer with you anytime!

Come on JpoLgr.... There's Gums, Roscoe, JoeSambor, Outlaw162, That Engine Guy, LMAggie, Raptor_Claw, Raptor_One, Henrik, Asif, AfterburnerDecalsScott, J.J., Sixerviper, TC, JakeMelampy, parrothead, JR007, Varkvet, MKopak, Steve Davies, Jon...just to name a few. Admit it this is a great site period.

By the way Johnwill, it am truly glad your here to share. It is awesome to be able to correspond with a guy that built the jet when I was dreaming of flying it. My dad was a F-16 pilot in the first F-16 wing after 20 + years of flying all sorts of jets and a couple of tours in Vietnam in the Phabulous Phantom. I did a junior high project that discussed the multi-role multi country purchase of the F-16 back in 79. Ironic that I'm where I'm at now.

Anyway, lets face it this is an awesome forum. I probably need to find more like it to discuss all the topics that interest me (my wife will kill me, if she reads this).

This has unfortunately replaced the O'club and squadron bar as a place to discuss flying for me. Can't take the chance and actually imbibe and talk about flying in the bar because even a suggestion of alcohol will get you grounded.

This is the place now where the 'old heads' get to relate how it was...and how hard it was.... Where the FNG's get to ask dumbass questions (not that any question is dumb) about what to flying is like. The Air Force has gotten away from a very important part of its heritage which was the young ask the old and learn. It will cost you your career if you attempt to learn the old fashioned way, so guys won't even try anymore.

Sorry for the diatribe......but the scotch is good, surprised I can even type....

Wow, blacked out again..What were we talkin' about???? Air Brakes? Seriously??? Never would have thought to ask that question in the bar. I just assume that if the engineer put it on the jet it works......
Mr. Green

Hi johnwill, thank you for your willingness to share this expert info with an Israeli student, who was just a newbie on the forum after all.

F16guy, thanks for the positive comments about the forum. It's nice to hear it is being appreciated. From our side I must admit that we have to moderate it only very little nowadays as most posters really seem to have a positive attitude.

Love of aviation can bring out the best in people, and the worst, but less frequently.

F16guy wrote:

Come on JpoLgr.... There's Gums, Roscoe, JoeSambor, Outlaw162, That Engine Guy, LMAggie, Raptor_Claw, Raptor_One, Henrik, Asif, AfterburnerDecalsScott, J.J., Sixerviper, TC, JakeMelampy, parrothead, JR007, Varkvet, MKopak, Steve Davies, Jon...just to name a few. Admit it this is a great site period.

Nobody said otherwise Wink

Those are the reasons for me waisting my time on this forum!! Very Happy

F-16.net FTW!!!

F16guy wrote:

By the way Johnwill, it am truly glad your here to share. It is awesome to be able to correspond with a guy that built the jet when I was dreaming of flying it.

Now you're setting the record straight-That's what I was saying, cheers to one of the guys that designed my ride!

Last edited by F16guy on Nov 27, 2008 - 12:22 PM; edited 1 time in total

Jpolgr,

Now you're just bragging. Nice pic.
I don't think anyone is wasting time here on this forum. (Except for those that are told by multiple people that they are wrong but they still persist.)

I was merely commenting on the fact that we have a team of 'Best Assets' here.

Almost got me to post one of my pics..... Wink

Forum: F-16 Design & Construction

The F-16/F-15 air brake