F-4 flapa behaviour of different versions

[Anatol Pigwa]

Hi,

 

I read somewhere, sometime, that the flaps behaved differently for different versions of the F-4 on the ground.

 

Of course I cannot find the source now!

 

Can someone please shed some light into this? I am particularly interested in the behaviour if the F-4F flaps.

[Ben Brown]

F-4 leading edge and trailing edge devices are so much fun!   Almost as much fun as Spitfire wings. 😀 
 

Trailing edge flaps were either up, half (can’t recall how many degrees), or down (again, can’t recall the degrees).
 

On the leading edge slat-equipped F-4E, F, G, and S, any time the flaps were half or down, the leading edge slats were out (extended). Leading edge slats were either in or out; they didn’t have any intermediate positions. In the air, when the flaps were up, the slats operated automatically based on angle of attack. On the F-4C/D/E/F/G, ailerons (outboard of the trailing edge flaps) did not droop when the flaps were down, unlike the F-4B/J/S.

On the F-4B, C, D, early E, and J, these versions had leading edge flaps (not slats) that dropped any time the flaps were lowered. Many F-4 fans call these “hard wing” jets to distinguish them from the slat-equipped jets.

 

If you’re building your F-4 as parked and sitting on the ramp, the ailerons could both be lowered a little. They did this on all versions as the hydraulic pressure bled off after engine shutdown.

 

HTH.

 

Ben

Edited November 16, 2021 by Ben Brown

[Anatol Pigwa]

Thanks for the insight Ben. What confuses the hell out of me, that on pictures of the F-4F I either see the flaps and ailerons in the "up" position or the inner flaps up and the alierons "down". As I said I think I read somewhere about there being a locking mechanism in the F-4F for flaps, slats it alierons (don't remember which) and that they operated differently from any other Version of the F-4.

[Ben Brown]

Glad to be of help! Yes, the flaps/slats were mechanically held in place, while the ailerons were hydraulically actuated. The USAF, USN, and USMC usually parked their F-4s with flaps up, unless they needed maintenance. I’ve read that the Germans often parked their F-4Fs flaps down/slats out for maintenance.

As hydraulic pressure bled off after shutdown, the ailerons could be anywhere from up to fully down and everywhere in between. You’ll often see one side drooping more than the other until they’ve both bled all the way down. They’ll be all the way down if the jet has been parked for a while. I’ve been told that crew chiefs would sometimes push down on an aileron (probably by pushing directly on the NO PUSH stencil! 😃) to pop the opposite spoiler up for maintenance.

 

Ben

[Anatol Pigwa]

Thanks Ben,

 

I am still slightly confused, but after finding this picture on the net I will stop worrying and build the flaps and ailerons, so that they just look cool

 

 

[Anthony in NZ]

This is really interesting information you guys thanks. 
 

Im thinking of raising the spoilers on one upper surface (left or right, I haven’t decided yet). Is this something that is possible with both ailerons down? I’m sure I have seen this before 

 

Sorry to go off track a little 

 

cheers

Anthony

[Adrian W65]

2 hours ago, Anatol Pigwa said:

Thanks Ben,

 

I am still slightly confused, but after finding this picture on the net I will stop worrying and build the flaps and ailerons, so that they just look cool

 

 

I`ll try a bit more explaining.

This pic shows the trailing edge flaps at 1/2 flap. The ailerons look strange merely because the control stick most likely was pushed to the

left as the hyd. pressure bled off on shut down; that would have trended the rh aileron down and the left up. [F4 Ailerons didn't really go up much more than a couple

of degrees, relying on extending the spoilers that side to take the wing down]

 

Mostly flaps were kept up on parked F4s because when they were down they allowed BLC air to be bled off off the engines if they were running. Also not good form to

start an engine with flaps down as this would bleed air as it tried to start. If wings were folded and flaps selected down then hot hazardous gasses would come out

of the BLC bellows at the wing fold.

Mechanical connections physically opened the 4 BLC valves as the LE/TE flaps moved. A microswitch allowed hotter/higher pressure bleed air to enter the

manifold as the TE flaps went from 1/2 full position.

 

Part of the procedure for rigging TE flaps is adjusting the length of its Jack eye-end to create a stretching tension on the jacks internal mechanism so that

when the flap meets the upstop a certain hyd pressure is required to seat an internal lock in the jack. This keeps the flap mechanically locked up even when hyd

pressure is removed. A jack eye-end incorrectly rigged would allow the jack to `lock-in` too easily and thus not really be locked-in when hyd pressure is removed.

A flap rigged that way can be pulled down and droop, but you would never see this on an operational F4.

The 1/2 flap position of the T/E flap is also an internal detent in the jack [I don't remember any adjustment for this]

L/E flaps were either up or down. Both positions maintained by an over-centering of a pivoting mechanism that stopped movement when Hyd pressure removed.

This is how I remember what we did, but it was a very long time ago.

[Anthony in NZ]

That's really interesting, thank you!

[Ben Brown]

Note that the slats on that F-4F are out, too.

 

There used to be a great USAF training video on YouTube that compared the slatted F-4E wings to the earlier, non-slatted wings. It showed the operation of the slats and flaps. It apparently disappeared when Periscope went under, so now there is only this short version showing the slats operating:  Slats video 

 

Ben

[Tailspin Turtle]

Navy vs Air Force slats: https://tailspintopics.blogspot.com/2012/12/f-4s-wing.html