Mustang P51 Combat Flaps

[Milt]

The Mustang had combat flaps the could be used at any speed. Flew them in the Korean War with 77 Sqdn RAAF and never had a need to use the flaps in combat except when executing a hard break to avoid attacks by USAF F80s.

Not too many of us left who flew Mustangs in combat.

Does anyone know if those combat flaps were actually used in combat and to what advantage?

Perhaps the rarety of use made them to be unnecessary and only added extra weight and complexity to the Mustangs.

In any case they were a good idea by the aircraft designer or a smart inclusion in the specifications.

I recall that the Harrier could achieve a rapid change in manoeuver using vectored thrust. Is this called Swishing?

[Darwinism]

Hello Milt, I've had the pleasure to meet you on a couple of occasions. I don't know about the Mustang combat flaps but do remember that the Harrier direction change manoeuvre was called 'viffing' or 'vectoring in flight'.
Regards.

[Buster Hyman]

Sorry, but I'm just in awe of the fact that you flew the Mustang in combat! Aaaand that's about all that I can contribute to this thread...sorry. ;)

[Courtney Mil]

Wow. Great respect, Milt. :ok: Sorry I can't help with your question, but we'd all love to hear more about your experiences in the P-51. Please.

[thunderbird7]

What a casual way to start a thread!! My equivalent would be " When I was cutting the grass the other day, I noticed the mower was a Briggs & Stratton..."

Yes please! Lets hear some more!!!

[beardy]

The Hunter also had combat flaps which above a certain speed stalled the tailplane and caused an increasing nose down pitch with back stick!

[LOMCEVAK]

I cannot comment on how the Mustang was flown in combat but I can give you a few numbers on P-51D and Hunter flap limiting speeds.

The P-51D flaps can be selected in 10 degree increments from 0 to 50 degrees. The limiting speed for 10 degrees is 400 mph (Vne is 505 mph below 9000 ft). There is no additional g limit with the flaps extended and thus 10 degrees of flap can be considered as combat flaps which can give an increase in instantaneous turn performance. Note that 400 mph is well above corner speed and thus effectively there is no practical speed limit for 10 degrees of flap. The 20 degree flap speed limit is 275 mph so even that can be useful for low speed manoeuvring.

The Hunter also has no g limit on the flaps and at angles of 38 degrees (approx 1/2 deflection) or less the speed limit is 300 KIAS/0.9 M. Above 300 KIAS the airflow will blow the flaps back in and you will see some pilots using 23 degrees of flap in displays at speeds that are probably above this. Any flap extension results in a nose down pitching moment and thus requires an increase of aft stick to counter the trim change. The problem comes at above 0.9 M (ie at high altitude) when stalling of the elevator hydro-booster jack occurs because the aerodynamic loads on the elevator are greater than the hydro-booster can overcome. Therefore, although the pilot may pull full back stick the elevator does not deflect to oppose the nose down pitch and thus the aircraft will continue in an ever steepening dive. The only recovery is to raise the flaps, close the throttle and extend the airbrake. Even in the Hunter's latter days at TWU a couple were lost due to this. This is certainly one characteristic that I have never demoed!

[BEagle]

LOMCEVAK - indeed. During the late summer of 1976, a student on one of the courses disappeared during a GH trip over the Oggin and was never seen again. It was a hot, hazy day with a poor horizon; I was one of a pair doing canned ACM training, towing for the other which was a T7. As we transited out to sea, I called a single Hunter manoeuvring which might have been him, but as it wasn't a threat or part of our formation we continued - treating it as just a normal sighting exercise.

The haze was so bad that we were obliged to fly radar to visual on recovery, but of the solo student there was sadly no sign, we later learned.

If I recall correctly, his aircraft had been flying, unusually, with 2 x full 230 gall tanks and it was thought that the poor horizon and heavyweight aircraft might have been factors - he was due to do some aeros, which would probably have included some 23° flap work and the consensus was that he might have left it down, become disorientated and met the M0.9 jackstall problem.

Others on his course alleged that no-one had ever briefed them about the 23° flap / M0.9 limit, which I find hard to believe. As someone commented "That's about as likely as someone not knowing that a Chipmunk can groundloop!". So they were all rebriefed and 'the system' also limited us to 8 hr days...

RIP Bloggs - and XG191.

[Wensleydale]

What a casual way to start a thread!! My equivalent would be " When I was cutting the grass the other day, I noticed the mower was a Briggs & Stratton..."

Yes please! Lets hear some more!!!


I always wanted to contribute positively to a thread about my rotary experience, and now I can! My Mountfield 18" had a 3.5hp Briggs and Stratton engine. Bought it in Elgin in 1983 because the Moss in my quarter in Kinloss had already burned out two electric mower motors. Lasted me until 2011! I hope that my new Honda 15" rotary will be as reliable.

[RequestPidgeons]

Without wishing to get too technical, I presume the combat flap was designed to give a large Centre of Pressure change, resulting in high pitch rates?

Therefore, greater manoevrability in the pitch axis...

I dont think I would want to be fighting at the top end of the drag curve with no Potential Energy for the sake of a bit of lift.

[Trim Stab]

I always wanted to contribute positively to a thread about my rotary experience, and now I can! My Mountfield 18" had a 3.5hp Briggs and Stratton engine. Bought it in Elgin in 1983 because the Moss in my quarter in Kinloss had already burned out two electric mower motors. Lasted me until 2011! I hope that my new Honda 15" rotary will be as reliable.

To really be up to speed on this thread you should buy a Mustang Zero-Turn mower

http://www.troybilt.com/equipment/troybilt/mustang-46-zero-turn-riding-lawn-mower-mustang-46.

[orca]

In the Harrier 1 we had manual flaps that we dropped from inter (default setting - flap up felt horrible) to 'down' whenever we went below 300 kts. VIFF was good fun but of use only in two or three occasions in my view as it was a great way of getting the nose moving but an even better way of losing energy.

As always there was a trade off, and in a fair amount of cases you'd be just as well to use the combat modes of the radar than get too bunched about a throttle-nozzle-flap juggle.

[LOMCEVAK]

RequestPidgeons,

The use of flap in combat is to give a higher maximum lift coefficient. In other words, for a given speed and altitude you can pull more g. Inevitably there is a drag penalty so its use is not a 'put it down and leave it down' option but something to use as the fight dictates, basically when you want a better instantaneous turn rate and/or lower corner speed.

L

[Rigga]

The Buccaneer had an "Aileron Gear Change", increasing control surface movement for the same input, making it quite agile too (to be fair I only rigged it, not used it)

[Stitchbitch]

Rigga, LOMCEVAK might be able to give you a steer on the Buc (if he's who I think he is.:E ).

[LOMCEVAK]

Milt,

Apologies for the thread creep but if people have an interest in flight control systems and I can answer their questions ....

Stitchbitch,

I am obviously too transparent!

Rigga,

The aileron gear change was used to give increased roll performance during landing although it could be used for take-offs in strong crosswinds also. The roll rate that is generated when deflecting the ailerons is a function of, essentially, indicated airspeed. The faster you fly, the higher the roll rate for a given aileron deflection. At high speeds the maximum aileron angle has to be limited for several reasons. The twisting moment on the wings may result in excessive structural loads, the sideslip caused whilst rolling could exceed the fin strength limits and the aircraft could depart. Also, the gearing between the stick and the ailerons is dictated by the available stick movement whilst ensuring that the aircraft is not too sensitive in roll such that low roll rates can be generated when needed. However, once this gearing has been set for the high speed case there may be insuffucient roll control on the approach, especially for a crosswind landing. Therefore, some aircraft have an incease in stick to aileron gearing at low speeds. In the Buccaneer this was manually selected by the pilot. In the Tornado, it is selected automatically when the flaps are greater than 15 deg (in the 'full CSAS' normal control law).

Back to the P-51, it had 3 different aileron gearing settings which were changeable only by maintenance action. The high gearing did put large loads on the wings and I am not sure how much it was used for combat sorties. The middle gearing was the normal position and the low gearing was, I believe, used when carrying heavy underwing stores because of the excessive roll inertia that would be generated at high roll which made it difficult to stop a rolling manoeuvre.

[clicker]

LOMCEVAK,

Was that a difficult thing to change or was it done on a mission by mission basis?

[LOMCEVAK]

Clicker,

I have asked a few questions and it is about 1/2 day to change it as there are significant rigging checks to be done. I have discussed this with a very experienced current P-51 engineer who says that he thinks that now most operators use the high gearing (15 deg aileron deflection) so I was wrong about the structural loads being a problem (that came from another engineer many moons ago). He thinks that the only reason now why someone might use the medium gearing (12 deg aileron angle) would be if it proved difficult to rig the ailerons so as to maintain cleaarance between the ailerons and the wing skins when set at 15 deg.

[Rigga]

Thanks LOMCEVAK, Very comprehensive answers - even I understood 'em.

[Stitchbitch]

The Mustang has always been a favourite aircraft of mine. Please excuse my ignorance, but would lowering combat flap make any diffrence to the high speed stall characteristics of the wing by altering the angle of attack?

[Onceapilot]

LOMCEVAK quote:
"Back to the P-51, it had 3 different aileron gearing settings which were changeable only by maintenance action. The high gearing did put large loads on the wings and I am not sure how much it was used for combat sorties. The middle gearing was the normal position and the low gearing was, I believe, used when carrying heavy underwing stores because of the excessive roll inertia that would be generated at high roll which made it difficult to stop a rolling manoeuvre."

This is interesting because two weaknesses of pure manual ailerons are, the lack of aileron deflection (and roll rate) at high speed due to pilot strength and the lack of authority at low speed due to limited range of movement. The former requires a low gearing for high speed and the later requires a high gearing for low speed. Obviously, the lack of power assistance made the overall quality of the ailerons performance a major factor in the handling of the aircraft at high and low speeds. Some compromise was required (middle setting?) but, I suspect that the satisfactory low speed control requirement was the overiding aim. I would presume that a low geared P51D would therefore be optimised for very high speed manoevre.
I can understand that the present day airshow P51D would have the high geared setting as they need all the slow speed authority they can get and, most aerobatic displays are well below 505mph IAS.

As an aside, 505 mph Vne might be a post WW2 limitation? I have a combat report from November 1944 that states a speed of 550mph indicated at low altitude during fighting over Germany:ooh:.

OAP










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[clicker]

Thanks LOMCEVAK, clearly not something a squadron would do on a regular basis.

[Onceapilot]

LOMCEVAK quote:
"Therefore, some aircraft have an incease in stick to aileron gearing at low speeds. In the Buccaneer this was manually selected by the pilot. In the Tornado, it is selected automatically when the flaps are greater than 15 deg (in the 'full CSAS' normal control law)."

Just to note, the Panavia Tornado does not have ailerons;).

OAP

[LOMCEVAK]

OAP,

With respect to the Tornado, good spot and thanks for the correction- I was just being a little too colloquial. I should have said that the roll command path gain increases when flaps are lowered through 15 deg; I have no idea whether the increased roll comes from the spoilers, differential tailerons or both.

With respect to roll control at high speeds with manual ailerons, the force required to achieve large aileron deflections is a function of the aerodynamic balancing characteristics, affected by various types of tabs, and it may or may not be possible easily to achieve full aileron at high speeds. I have certainly flown an aircraft where it is possible to apply full lateral stick at 450 KIAS (Meteor). However, some aircraft suffer from a reduction in roll performance at high speed due to adverse wing twisting at large aileron deflections.

The 505 mph Vne does come from a post war -1 Manual and I do not know if that was also promulgated as the limit during WWII. Even if it was, would I be surprised in someone went to 550 mph in combat? Certainly not (although I would like to know if they came back with the rudder trim tab still attached as they have a propensity to 'buzz' and detach at high speed).

[Onceapilot]

LOMCEVAK:

You might be surprised. Depends if you believe a genuine copy of a combat report dated 8th November 1944?

OAP

[Marbles]

This practice goes back further than 1944. From a combat report by F/Lt J.A. Coghlan, 56 Sqn, for July 10th, 1940:

"I found that I could better out-manoeuvre the Me 109’s and 110’s with 5 to 10 degrees of flap lowered. The loss of speed to my Hurricane was not appreciable. Engine revs were 28.00 on my rotol airscrew.”