Elevator trim during Combat (1 Viewer)

Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

None had the slab tail (except maybe for experimental testing), they had normal elevators, but (like the Me 262) they featured a variable incidence tailplane which was used for trim instead of tabs. (and iirc the metal fairing at the stabilizer junction was the the location of the trimming axis)

And using that would facilitate recovery from high compressibility dives, but obviously not with the same response as slab elevators.
 
The '109 had a variable incidence tailplane that could be adjusted in flight. You can see it in cutaway drawings, and Eric Brown mentions it in his books:

"The flaps were raised manually by means of the outer of two concentrically mounted wheels to the pilot's left; the inner wheel adjusted tailplane incidence"

I don't have anything as to the degree of movement.

PS: Hmmm...I see that cur was first...
 
On the Emil it was +3 degrees to -8 degrees, I am not sure of the F-K models, looking at a drawing of the K`s control movements its not entirely clear to me what it means, but it seems to repeat the same values as the G-2 Handbuch, ie. +2 to - 6 degrees. Presumably the F series Flossenstellung limits were similiar.
 
On the Emil it was +3 degrees to -8 degrees, I am not sure of the F-K models, looking at a drawing of the K`s control movements its not entirely clear to me what it means, but it seems to repeat the same values as the G-2 Handbuch, ie. +2 to - 6 degrees. Presumably the F series Flossenstellung limits were similiar.

Norwarra did mention the change to the F tail design because of structural failures due to resonance but didn't mention installation of a 'slab tail'.

Interesting - how did they do it with the E and the strut? and why would they leave a movable, hinged elevator of that size instead of simply put trim tabs back there?

That would imply huge potential changes to pitch forces, which in a high speed dive would be 'interesting' structurally.

In many cases from one mod to another the elevator incidence was (permanently) changed for a gross weight change or to solve a high speed pitch problem - the 51 made several changes like that going from B to D to H.. but little changes

Kurfurst - what design problem were they trying to solve?
 
does this help
 

Attachments

  • IMG_2390 1.jpg
    IMG_2390 1.jpg
    42.2 KB · Views: 146
does this help

It does Pb - thx for clearing it up for me - the screw thread definitely indicates adjustment.. wonder how is it boosted from cockpit to take into account flight loads - and lock when you don't want it to move under vibration?

Second question - is that the leading edge of the horizontal stabilizer shown in photo. It looks too far aft of the front of the vertical stabilzer leading edge (if that is what it is?) but probably OK.

Is the hole above the leading edge and attach point for a small fairing to cover the top vert stabilizer/horizontal interface? I keep seein what looks like a contoured "L" shaped piece of metal there.
 
That's the 109E you have access to right pbfoot?


Bill, yes thats the LE of the tail, I have a book with a good drawing right here and the conection point is quite clear in that shape, it just looks weird becouse of the close-up shot.

You can see it if yo look really closely at this one:
profile_romanian_03.jpg



And they seemed to have changed it a bit on the later models, at least externaly, apearing much like the Me 262's tailplane at the intercetion with the fin. (with kind of a bordering edge around the tailplane root)

it can somewhat be seen here:
Drago_Profile_1.jpg
 
In our tech section we have an "E" parts breakdown - I bet there is a simple bolt at where the strut attaches to the horizontal stabilizer that allows movement.
 
I ran across this while looking thru Putnam's "German Aircraft of the Second World War", JR Smith and AL Kay, '72...

"During dogfights between Fw 190s and RAF fighters it was not uncommon for the Luftwaffe aircraft to flick on their backs from a very tight turn and crash at full throttle. The cause of this disastrous behaviour was the pilot making excessive use of the electric tail-trimmer, an ingenious invention of Focke-Wulf, in an attempt to tighten an already very high 'g' turn, the aircraft eventually entering a high speed stall from which there was no recovery".

JL
 
I ran across this while looking thru Putnam's "German Aircraft of the Second World War", JR Smith and AL Kay, '72...

"During dogfights between Fw 190s and RAF fighters it was not uncommon for the Luftwaffe aircraft to flick on their backs from a very tight turn and crash at full throttle. The cause of this disastrous behaviour was the pilot making excessive use of the electric tail-trimmer, an ingenious invention of Focke-Wulf, in an attempt to tighten an already very high 'g' turn, the aircraft eventually entering a high speed stall from which there was no recovery".

JL

Buzzard - there is a possible alternate cause. The Germans recognized the problem of high speed stall and eventually figured out one cause (could have been more) for the violent High G Stall.

They figured out that outer wing span area stalled about the same time the as the inboard 80%. The Fw 190 had a fairly unusual application of chord twist, starting at positive 2 degrees at root and ending at 0 at 81.5% of the span - then zero to tip. Most wings will twist all the way to the tip to ensure that the tip will stall last at high angles of attack.

I haven't read the report itself but familiar with the conclusions which state the outboard tip are stalled as a result of elastic deformation under load.

The mode is something I am not sure of just yet.

The aileron on the down wing is 'up' which would make the mean chord, locally in the aileron area, 'negative' in that it would be negative angle from the inboard wing.

The load due to the aileron in that outer region could be torsional (likely) or pure bending if the center of that load was on the main spar.

I suspect torsion, and further suspect that it was to twist the tip area 'up' meaning that the local Angle of Attack reached CLmax faster or at the same time as the inboard region.

The net is that I don't know for sure, but this is more plausible to me than changing horizontal stabilizer incidence to cause the subsequent stall. Changing the tail incidence to me could dangerously increase loads on the fuselage as well as create potential stability issues.

Do you have another source that I could find on the Fw 190 elevator incidence problem?
 
Though it does seem, by that quote, that the stall was worsened by excessive use of trim, hence the irrecoverable part. (I'd imagine recovery would be possible if it was re-trimmed though, as long as they weren't on the deck)
 
Soren briefly mentioned the use of the 109 adjustable stabilizer as a means of accelerating a dive pull out.

Does anybody know one way or the other?

It would be interesting to compare that approach to the opposite approach for the Mustang, P-38 and P-47 in which the use of just the trim tab to assist the pullout was specifically 'discouraged' (I mean if you're gonna do it - what does 'prohibited' mean if you survive it.)

Relatively speaking the trim tabs on all those ships are much smaller in area and should be far less effective at transmitting tail loads to their respective fuselages than an entire 'moving horizontal slab' from an area stanpoint.
 
Wasn't there some problems with parts of the elevator or the tab gatting ripped off when used at high speeds? (the full span servo tab tested in attempt to improve control in compressibility on the P-38 ripped the whole elevator off when used, or possibly overused)

IIRC most of the structural failures were of the tail itsself due to excessive aerodynamic forces on a relatively small area (also experienced if too much elevator was applied once the a/c reached denser air), not excessive G forces, and not structural failure elsewhere on the a/c. So the use of a large area (the entire tailplane) moved in small increments could have been a safer procedure in that light.

I'd immagine such a feature on the P-38 would have helped greatly in dive recovery. (and iirc the trim tabs weren't very effective in helping recovery either) Another thought would have been boosted elevator controls.
 
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.]"

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
 
Bill,

The problem 109 pilots faced at over 750 km/h was that elevator authority reached almost nil, the stick was near solid. The same happened to the P-51 when it redlined.

However the Bf-109 has the advantage of a variable incidence horizontal stabilizer, which was easy to operate. This meant that if entering a high speed dive, wether it was above or below the redline speed the recovery could be significantly speeded up by adjusting the incidence of the tailplane.

This feature was also used to cancel out the 109's habbit of experiencing downwards trim in high speed level flight.

Here is one account of a Bf-109 getting away from a US P-51 pilot by pulling up much quicker than the -51 pilot was able to:

Thomas L. Hayes, Jr., American P-51 ace, 357th Fighter Group, 8 1/2 victories:
"Thomas L. Hayes, Jr. recalled diving after a fleeing Me-109G until both aircraft neared the sound barrier and their controls locked. Both pilots took measures to slow down, but to Hayes' astonishment, the Me-109 was the first to pull out of its dive. As he belatedly regained control of his Mustang, Hayes was grateful that the German pilot chose to quit while he was ahead and fly home instead of taking advantage of Hayes' momentary helplessness. Hayes also stated that while he saw several Fw-190s stall and even crash during dogfights, he never saw an Me-109 go out of control."-


Btw, as mentioned the Fw-190 featured a variable incidence tail plane as-well, which was esp. useful at high speed for trimming. However when entering a dogfight the pilot had to remember to trim back to normal or turn performance seriously suffered. And infact during the US post war flights with a captured Fw-190 Dora the ill turn performance experienced was it seems in big part because of the tail plane being improperly set, making it very difficult for the US test pilot to stall the a/c in turns as he himself explained there not enough force supplied by the elevators. The other reason was ofcourse the low power setting at which the test was performed.
 
Yep (on the P-38 ) and there seems to be some misinformation about the dive flaps, the biggest (which I had assumed as correct) claiming that the flaps reduced the shockwave and allowd elevaor operation. Others state them as simple airbreaks, but as mentioned they act to quickly increase lift w/out changing AoA and thus pitching up.

Similar flaps were installed on late model P-47's and on P-80's (in addition to the airbrake) and in all cases facilitated recoveries from dives exceeding limiting Mach. (a totaly different problem was found on the P-84 with the violent pitch-up stall when ~.8 mach was exceeded at low level)


The variable incedence tail also helped the Me 262 maintain control at limiting mach, and facilitated recovery from dives exceeding this. (and kept the a/c from pitching down and failing under high -G loads)
(similar to the advantages on the 109, albeit at a considerably higher Mach number)
 
This is from a test report of the Fw-190 at Wright Field, spring '44.

" The outstanding maneuverability feature of this airplane is it extremely high rate of roll. The radius of turn, however, is poor and it is only slightly improved by using the maneuvering flap position of 15 degrees. If pulled fast, the airplane tends to stall out abruptly with little warning. Elevator control forces are very heavy in a tight turn, requiring constant use of the elevator trim control."

It looks like the use of the VIT trim was likely commonly used in turning fights.

The VIT in WWII fighter design seems to be an exclusively German phenomena. Did any Allied fighters have this feature?

JL
 

Users who are viewing this thread

Back