IAR-80/81 trims

The trims on IAR-80/81 were only adjustable on the ground or could one adjust the trim while airborn ?

The only trim control that could be operated from the cockpit was the taiplane incidence (the entire taiplane moved like on the PZL11/24). This was controlled by a wheel on the left side of the seat. Its purpose was to trim the plane as the weitght shifted when the fuel and ammunition was expended. The ailerons and rudder were fitted with fixed trim tabs (strips of metal) adjustable only on the ground. The elevators had compensation trims, but these were not controlled by the pilot - they adjusted themselves according to the movement of the elevators.
HTH
Radu

Thank you Radub !

Radub, could you please elaborate on how IAR 80’s tailplane was mobile?

<<the entire taiplane moved like on the PZL11/24>>.
From the few available images, the tailplane appears to be quite rigidly riveted to the fuselage. Also, a moving tailplane could not work with the tail struts found on dive bomber models.


(image courtesy of cartula.net)

BDan,

Let us get one thing clear here: if a plane is fitted with a tailplane support strut, it does not mean that the tailplane cannot be moved. There are plenty of examples of planes fitted with both support struts and trimming tailplanes: PZL11, PZL24, Bf109 B/C/D/E. The explanation is obviously simple: the strengthening strut is attached to the tailpane along the pivot line (which is usually a spar).

The pilot needs to have some sort of means to adjust the pitch of the plane. While the center of gravity shifts as the fuel and ammunition is expended, trimming is necessary to keep the airplane level. BTW, same applies to modern planes.

Now, let is return to the IAR80. Yours is actually a good observation.
First of all, there is a trim wheel on the left side of the cockpit, right next to the seat. See the Modelism drawings - that wheel is labelled #138. Modelism describes it as "roata comanda compensatoare profundor" [aileron compensation control wheel]. It is a pitch trim allright, but the text implis that it actually controls the aileron (maybe via trim tabs?) only. You may be on to something here.

So, here is my revised conclusion:
The IAR80 had a pitch trim, there is no doubt about that.
It is likely that pitch trimming was done by moving trim tabs on ailerons.
Maybe someone else knows more?

HTH
Radu

This post has been edited by Radub on September 13, 2006 09:47 am

"roata comanda compensatoare profundor" means "ELEVATOR compensators control wheel". It has nothing to do with the ailerons.
The pitch trimming can be achieved either by moving the entire horisontal stabilizers (like on the Bf-109) or by moving only the elevators themselves, so they stay in a "up" (or down) position during flight, or by moving some smaller parts placed on the elevators (wich work in a similar fashion to the actual elevators.I think they are called Flettner tabs).

This post has been edited by D13-th_Toppy on September 13, 2006 12:09 pm

Thank you for clarifying the fine issue of moving tailplanes and struts. Actually I was not aware that BF109’s stabilizer was mobile, or that such a design was common on WWII fighters.
Now, it would be quite interesting the actual solution used on IAR 80. A more accurate translation of "roata comanda compensatoare profundor" would be "Elevator compensator control wheel”.
In the image you can see the trim tab (1), and its control rod (2). I don’t know how to explain the plate (3), whether it belongs to a fixed or a moving stabilizer.


(picture: Ion Dobran, "Junalul locotenentului Dobran", MODELISM, 1998)

--BDan

Touche D-13Toppy!
Yes, that was my mistake - I meant to say elevators not ailerons. You know very well what I meant, we were talking about the tail controls after all!

BDan,
I cannot find any technical drawing that proves whether the entire tailplane moved or was fixed. Maybe others know more.

BTW, all Bf109 models had a moving tailplane, but only the B/C/D/E/ types had the support strut.

HTH
Radu

This post has been edited by Radub on September 13, 2006 01:26 pm

Several drawing sets can be found here: http://www.airwar.ru/other/draw_fw.html

The horizontal stabilizer was definitely fixed. This is quite obvious for the folowing reasons:
1. The horizontal stabilizer structure:


As it can be seen, it is made in one piece, in a very strong and "homogenous" manner. The shape and construction, would not allow it to move without some big (and obviously visible) gaps on the vertical stabilizer. For a comparision here is the bf-109E stabilizer:

The gaps are visible there. For the IAR they should not only be at the ends of the stabilizer, but over it's entire width, to allow a free movement. Such gaps are not visible in any drawings or pictures, neither is any kind of "mask" over them.

2. The piece seen on the forward joint of the horizontal and vertical stabilizers:

it is made out of 3 different plates ovelaped and along their contour they are visibly riveted to the stabilizers and fuselage. Therefore, cound not posibly allow the movement of the horizontal stabilizer.

3. Finally, the most obvious thing: the tabs and control rods on the elevators:


I think the conclusion is overwhelmingly (does this word even exists? ) obvious.

Hi D13-th_Toppy,
Those are the Modelism drawings I was referring to above. (BTW, when those Russians pirated them, they made a mess of them ) I have those 1/25 scale drawings printed on heliograph paper (blueprints), the 1/32 scale drawings printed in the Modelism magazine in 89 (which these guys pirated) and the scans messed up a lot of detail.

HOWEVER,
they do not prove conclusively that the IAR80 tailpanes were fixed.

Then, the Bf109 is not related in any way to the 109, so it is irrelevant.

The closest relative of the IAR80, the PZL11 had a one-piece moving tailplane as well as trim tabs. Have a look here: http://aircraftwalkaround.hobbyvista.com/pzl11/pzl11.htm
especially here: http://aircraftwalkaround.hobbyvista.com/pzl11/pzl11_14.jpg
http://aircraftwalkaround.hobbyvista.com/pzl11/pzl11_03.jpg

then have a look here: http://img110.imageshack.us/img110/9199/pzl11lp7.jpg (Scan from the instructions of the Halinski/Kartonowy Arsenal P.11c)
and here:
http://img110.imageshack.us/img110/4416/pzl111in1.jpg
http://img110.imageshack.us/img110/3808/pzl112fh7.jpg
http://img110.imageshack.us/img110/7031/pzl113vi5.jpg (all three are scans from "PZL11c by Bartoloej Belcarz and Tomasz J. Kopanski)

Anyway, all of the above proves that it is possible to have a one-piece movable tailplane and elevators with trims. Trims do not negate a movable tailplane.

However, in the case of IAR80 it is very possible that it was a fixed tailplane, and as a matter of fact, now I am almost sure that it was so (I still have a little shadow of a doubt , but just a little one...)
I scoured the book "Vanatorul IAR80 Istoria unui erou necunoscut" by Dan Antoniu and George Cicos for info on the tailplanes but found precious little. On page 27 there is only one line that says "Suprafetele de comanda ale ampenajului orizontal au primit compensatoare dinamice" [The tailplane control surfaces were fitted with trims], but we know that already . That is it!
I am still looking.

HTH
Radu

Well, you just made my point. The 109 reference in my post had the same purpose as the P.11 in yours. In both the 109 and the P.11 there are visible spaces for the tailplane to move.
These 2 pictures you posted:
http://img110.imageshack.us/img110/7031/pzl113vi5.jpg
http://img110.imageshack.us/img110/9199/pzl11lp7.jpg
show the spaces left and the joint piece, that is riveted on the fusselage only on the upper side, leaving the rest clear for the stabilizer movement.
On the IAR, that part is solid with the fusselage and the stabilizer, like seen in this photo:
http://www.d13-th.com/user/toppy/iar.jpg (source Romanian Aeronautics in the second world war, ed. Modelism, 2003, page 192. the quality is bad, i took it with my camera, but it shows that place pretty well. There is also a good picture of the right side of the stabilizers on page 117).

Beside, i personally don't see the use of having both trimming sistems. IMO, a stronger tail structure, with only (in flight adjustale) trim tabs would be preferrable over a weaker structure with both sistems and more moving parts.

Hi D13-th_Toppy,
The fact of the matter is that, as I said before (a few times actually), I also largely agree that the tailplane of the IAR 80 was fixed. I agree with you.

A movable tailplane is not a weak structure. It is still attached to the fuselage in the same way as a fixed one, the only difference is that one of the attachment points is movable. The movement is nothing dramatic, just a couple of degrees either way which does not always requite a gaping hole for clearance - see the Bf109G, Me262, ju87, Macchi 202, etc. (but then again, those are different planes and not relevant here ).

HTH
Radu

Just looking at the original factory drawings published in Modelism No.3(4) 1984,
it is plainly obvious that the tailplane was fixed.
(source quoted above)
Sorted!
HTH
Radu

A movable horizontal stabilazer is not weaker, in fact most of the new generation multirol fighter have them.

The stabilazer was fixed,the elevator had an "flettner" comanded fron the cockpit.
George