Elevator trim during Combat

[Soren]

Improper aileron adjustment plus a faulty engine is what caused the poor turn performance at wright field buzzard. The high elevator forces are suspect as-well as the 190 featured perhaps some the lightest control forces of any a/c of WW2.

A good example of when the ailerons were properly adjusted are the British tests with a heavy Jabo version, this a/c despite being heavier less aerodynamically clean and running at low power was able to turn just as well the P-51 Mustang Mk.III. This a/c did also, unlike the others with improper aileron adjustment, give the pilot warning of the approaching stall with a slight buffet. (Just like vet Fw-190 pilots note it did)

 

[drgondog]

drgondog,

I was simply quoting verbatim from the book. And I was wondering if the use of the variable incidence tailplane (VIT) in such a manner was SOP or not. As for the abrupt stall of the 190, the report I posted from in the 'Germany'44' thread mentioned that in a tight turn to the left near stall speed, the a/c exhibited a tendency to reverse aileron control and then stall without warning. No mention was made of utilizing the VIT in the turning test. The use of the VIT probably just exacerbated the problem.

Here's something that is probably not relevant, but it is interesting...

This is from an interview with Kurt Tank concerning the effects of modifying the 190 prototype to accept the BMW 801.

"Although the extra 50 hp was useful, we found that the extra 160 kg of engine weight plus the additional structure to carry it, and the weight of the armor and the additional equipment the Luftwaffe now wanted, had increased [the fighter's] all-up weight by about a quarter. The wing loading rose from 1.6 kg/m2 [38lb/sq,ft.] of the first prototype to 1.9 kg/m2 [46 lb/sq.ft.], and the turning performance deteriorated accordingly. To restore the aircraft's previously pleasant handling characteristics, we enlarged the wing by extending each tip by just over 50 cm [20"] and reducing the amount of taper so that the outer sections were somewhat wider. In this way, we increased the wing area by just over 3.5 m2 [35 sq.ft.] and lowered the wing loading to a more reasonable 1.5 kg/m2 [35.8 lb/sq.ft.]"

It is EXTREMELY relevant - you found a jewel. This explains why the Fw 190 did not undergo an entire wing re-design. What they did was increase the span (and aspect ratio) and increase the tip/chord ratio to improve induced drag characteristics... what they didn't do is maintain the same twist ratio on the extension - resulting in the unanticipated bending problems combined with torsion at the tip - thereby losing tip control in a High G turn -

causing all the trauma Soren and I have been duking it out on.. Great Catch!

He goes on to say that the wing remained unchanged in all the low-medium alt. models of the 190. (The metric wing loading numbers look to me like a mis-transcription... )I don't have anything else on the VIT 'problem' (I think the 'problem' was pilot-induced...)

KK89,

Lockheed's attempt to solve the compressibility problem by modifying the tail-plane only made it worse...In the compressibility zone, the lift generated by the tail-plane overcame that of the wing, and pulling back on the stick (if you had the strength) only increased the uploading on the tail...and steepened the dive. The compressibility-induced turbulence generated by the wing often tore off the tail. It was by installing small dive-flaps under the wing to increase lift (without increasing the AoA), that the problem was solved.


JL

If I could restate their problem (P-38). The transonic issues created a lot of turbulent flow between the engines/fuse wing body -----> leading to masking of the horizontal tail. That alone would tend to an 'pitch down' problem.

From my perspective the wing dive brakes created enough drag that the P-38 that it kept the airspeed in a controllable flight regime ~ .65-70 Mach in a dive and below the compressibility effect - in effect a 'governor' .

That's my story and I'm sticking to it - I have been wrong before.

 

[kool kitty89]

I think the dive flaps did both, obviously adding a lot of drag (35 degree deployment), but they also caused a pitch up (with the elevator neutral or inoperable). (the shock wave dispersion thing was totally wrong though)

Hence the reason the P-80 was fitted with BOTH a belly mounted air brake and wing root mounted dive recovery flaps.

 

[kool kitty89]

Wikipedia seems to have gotten it right:

After months of pushing NACA to provide Mach 0.75 wind tunnel speeds (and finally succeeding), the compressibility problem was revealed to be the center of lift moving back toward the tail when in high-speed airflow. The compressibility problem was solved by changing the geometry of the wing's underside when diving so as to keep lift within bounds of the top of the wing. In February 1943, quick-acting dive flaps were tried and proven by Lockheed test pilots. The dive flaps were installed outboard of the engine nacelles and in action they extended downward 35° in 1½ seconds. The flaps did not act as a speed brake, they affected the center of pressure distribution so that the wing would not lose its lift.

Also buffetting was entirely separate problem which, unlike the compressibility problems, was completely solved:

Buffeting was another early aerodynamic problem, difficult to sort out from compressibility as both were reported by test pilots as "tail shake". Buffeting came about from airflow disturbances ahead of the tail; the airplane would shake at high speed. Leading edge wing slots were tried as were combinations of filleting between the wing, cockpit and engine nacelles. Air tunnel test number 15 solved the buffeting completely and its fillet solution was fitted to every subsequent P-38 airframe. Fillet kits were sent out to every squadron flying Lightnings. The problem was traced to a 40% increase in air speed at the wing-fuselage junction where the chord/thickness ratio was highest. An airspeed of 500 mph (800 km/h) at 25,000 ft (7,600 m) could push airflow at the wing-fuselage junction close to the speed of sound. Filleting forever solved the buffeting problem for the P-38E and later models.

 

[buzzard]

drgondog,

I'm glad you like the 'jewel' It did seem that it might have some possible relevance to the point of contention, altho' with my rudimentary knowledge of aerodynamics, I wasn't sure. I should also mention that Tank said that the tail surfaces were also increased in proportion to the enlarged wing.

Tank's goal was to build a 'Dienstpferd'; a cavalry horse, not a racehorse, and he over-designed the '190 for future weight gain. Perhaps the basic wing design was considered strong enough to handle the extra area without subtantial modification of the basic structure, and this contributed to higher than expected deformation under the increased tip load. Understand that this is pure conjecture on my part. I know little beyond the basics of aero theory.

As to the P-38...As a big fan of the P-38, I've read numerous accounts of the compressibility problems, its causes, and the rationale behind the solution. They consistantly mirror what I and KK89 have posted.

JL

 

[FLYBOYJ]

Hence the reason the P-80 was fitted with BOTH a belly mounted air brake and wing root mounted dive recovery flaps.

Wing root dive recovery flap? You sure about that? It's been about 8 years since I last flew in a T-33 and I could tell you there were flaps and speed brakes, don't recall no wing root mounted dive recovery flaps....
I think early P-80s and leading edge brakes on the bottom of the wings that were subsequently removed in later models (and on the T-33) as the dive brake was all that was needed "to stay out of trouble."

 

[kool kitty89]

That info was from a NASA article on WWII jets, referring to the P-80A.

ch11-2

the P-80 had a small dive-recovery flap near the leading edge of the lower surface of the wing. Again like later versions of the P-38, the P-80 had power-operated ailerons.

 

[FLYBOYJ]

Yep - saw that. It mentions the "leading edge of the lower surface of the wing," not "wing root mounted dive recovery flaps" as mentioned in your earlier post. In either case I think it's wrong, at least on production aircraft. In our tech library there is an F-80 flight manual - it makes reference to the wing flaps and dive flaps only. There is no other reference of a "fence type" dive brake on the aircraft as used on the P-38.

On page 23 of the -1 it gives instructions when a dive in excess of .75 - .8 Mach is encountered. On page 25 it gives part of the landing checklist and it states "wing Flaps down under 200MPH, dive flaps down if required." In the after landing check list on page 26 it says to bring the flaps and dive flaps up prior to taxi. Through out the entire -1 there is no other speed control device mentioned. On page 10B there is a picture of the actual switch.

I also have part of a CAF T-33 maintenance manual volume. The electrical system doesn't seem to show any other electrical augmentation of any other type of dive brake (now called speed brakes) within the system.

http://www.ww2aircraft.net/forum/other-mechanical-systems-tech/lockheed-p-80-shooting-star-9666.html

....

 

[kool kitty89]

Ok I don't know why, for some reason when I read that it made me think the 'dive flaps' were located just outboard of the wing root.

But continuing that, do you know where on the LE of the wings the dive flaps were located?

 

[FLYBOYJ]

Ok I don't know why, for some reason when I read that it made me think the 'dive flaps' were located just outboard of the wing root.

But continuing that, do you know where on the LE of the wings the dive flaps were located?

I would guess they'd be on the lower inboard wing close to a main spar similar to a p-38.

 

[kool kitty89]

They have a side-view cut-away diagram that shows the dive flaps on that manual you linked to.


What did you mean by "fence type" airbrakes on the P-38? I thought it was only fitted with dive flaps.


I don't see any disagreement with that NASA article and the P-80 manual.

 

[drgondog]

I would guess they'd be on the lower inboard wing close to a main spar similar to a p-38.

I would suspect you are dead on - maybe just aft of wheel well - maybe at 25% chord

 

[FLYBOYJ]

They have a side-view cut-away diagram that shows the dive flaps on that manual you linked to.


What did you mean by "fence type" airbrakes on the P-38? I thought it was only fitted with dive flaps.


I don't see any disagreement with that NASA article and the P-80 manual.

There are "Dive Brakes" AKA Speed Brakes and wing flaps, no wing root mounted dive recovery flaps.

Here's the P-38 dive recovery flaps I'm talking about...

 

[FLYBOYJ]

I would suspect you are dead on - maybe just aft of wheel well - maybe at 25% chord

Agree Bill.

 

[FLYBOYJ]

Another View - this type of flap is also known as a "fence." Some General Aviation aircraft have similar...

 

[FLYBOYJ]

And just to further clarify, the speed brakes, dive brake are under the fuselage...

 

[FLYBOYJ]

Here's the warning placard inside the brake

 

[kool kitty89]

When I said wing root "dive flaps", I was referring to the P-80. (only on early models and different from the belly mounted speed brake)

I know the P-38's "dive flaps" were located just outboard of the engine nacelles.

look at the discussion with buzzard and me on pg #3 of the thread:

KK89,

Lockheed's attempt to solve the compressibility problem by modifying the tail-plane only made it worse...In the compressibility zone, the lift generated by the tail-plane overcame that of the wing, and pulling back on the stick (if you had the strength) only increased the uploading on the tail...and steepened the dive. The compressibility-induced turbulence generated by the wing often tore off the tail. It was by installing small dive-flaps under the wing to increase lift (without increasing the AoA), that the problem was solved.

JL

I think the dive flaps did both, obviously adding a lot of drag (35 degree deployment), but they also caused a pitch up (with the elevator neutral or inoperable). (the shock wave dispersion thing was totally wrong though)

Hence the reason the P-80 was fitted with BOTH a belly mounted air brake and wing root mounted dive recovery flaps.

Wikipedia seems to have gotten it right:

After months of pushing NACA to provide Mach 0.75 wind tunnel speeds (and finally succeeding), the compressibility problem was revealed to be the center of lift moving back toward the tail when in high-speed airflow. The compressibility problem was solved by changing the geometry of the wing's underside when diving so as to keep lift within bounds of the top of the wing. In February 1943, quick-acting dive flaps were tried and proven by Lockheed test pilots. The dive flaps were installed outboard of the engine nacelles and in action they extended downward 35° in 1½ seconds. The flaps did not act as a speed brake, they affected the center of pressure distribution so that the wing would not lose its lift.

Also buffetting was entirely separate problem which, unlike the compressibility problems, was completely solved:

Buffeting was another early aerodynamic problem, difficult to sort out from compressibility as both were reported by test pilots as "tail shake". Buffeting came about from airflow disturbances ahead of the tail; the airplane would shake at high speed. Leading edge wing slots were tried as were combinations of filleting between the wing, cockpit and engine nacelles. Air tunnel test number 15 solved the buffeting completely and its fillet solution was fitted to every subsequent P-38 airframe. Fillet kits were sent out to every squadron flying Lightnings. The problem was traced to a 40% increase in air speed at the wing-fuselage junction where the chord/thickness ratio was highest. An airspeed of 500 mph (800 km/h) at 25,000 ft (7,600 m) could push airflow at the wing-fuselage junction close to the speed of sound. Filleting forever solved the buffeting problem for the P-38E and later models.

As to the P-38...As a big fan of the P-38, I've read numerous accounts of the compressibility problems, its causes, and the rationale behind the solution. They consistantly mirror what I and KK89 have posted.

JL

 

[FLYBOYJ]

When I said wing root "dive flaps", I was referring to the P-80. (only on early models and different from the belly mounted speed brake).

And again I'm saying the P-80 never had "wing root dive flaps." They have always been on the belly, from the P-80A to the C and those A's and B's modified to C's as well, and as far as I could see in photos it was that way on the XP-80 as well.

"Hence the reason the P-80 was fitted with BOTH a belly mounted air brake and wing root mounted dive recovery flaps."

Bottom line, there were wing flaps (on the wings, used during landings) and speed brakes (dive brakes, dive flaps) on the belly - nothing else...

 

[kool kitty89]

Then what were you talking about here?

I think early P-80s and leading edge brakes on the bottom of the wings that were subsequently removed in later models (and on the T-33) as the dive brake was all that was needed "to stay out of trouble."

Which agrees with the NASA site I linked to:

Evident in the photograph is the deployed speed brake located on the bottom of the fuselage.

--------------------------------------------------------------------------------

Figure 11. 4 - Lockheed P-80B Shooting Star single-engine jet fighter. [mfr via Martin Copp]

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Like the P-38 described in chapter 5, the P-80 had a small dive-recovery flap near the leading edge of the lower surface of the wing.

One interesting note is that the Meteor was fitted with "fence type" air brakes (opening to ~90 degrees, and slotted, opening above and below the wing) brakes were provided on the upper and lower surfaces of the wing between the nacelles and the sides of the fuselage.