[CLOSED]Bf-109 Trim controls

[Pilum]

I bit a of a side question, but why was fabric used/preferred so long for control surfaces?

 

Even though many planes switched to light metal cover on some control surfaces when problems arose with balooning at high speed for example, but the industry standard remained fabric for a curiously long time... was there any inherent advantage to it, besides lightness?

 

I guess it gives advantages of composites. Fabric and a kind of resin gives very light and strong surface.

 

The problem with metal covering on control surfaces compared to fabric is that the control surface needs to be balanced around the hinge to avoid flutter problems. Given that most of the control surface is behind the hinge line this means that a large amount of weight (e.g. lead) needs to be added forward of the hinge line to balance which leads to the complete control surface being much, much heavier than just the difference in weight between the metal and fabric coverings.

[Pilum]

Concerning the trim problem this is IMHO a no-brainer: No pilot IRL would fly around in a plane that was not in trim if you could avoid it: The first thing you would do on landing your 109 as currently implemented in DCS would be to adjust the tab slightly up to move the adjustable elevator trim range to a suitable range.

 

So if we don’t get a game controlled tab, just introduce a constant to the elevator hinge moment coefficient. This would be the equivalent of setting the tab at a slight angle. This would not only eliminate all the discussion in the forum but also be more realistic since no pilot will fly around holding a constant forward pressure on the stick if he can avoid it by adjusting a tab. Period.

 

This type of adjustment was done all the time on these types of aircraft because no two elevators, ailerons or rudders were the same due to production issues. Usually the actual structure underneath the fabric was wood or sheet metal and an ever so small cusp or angle on the trailing edge translates to a significant hinge moment which the tab can and was used to compensate for.

 

If there is no tab there are other methods: For example on the Spitfire the same effect was achieved on the ailerons by doping a piece of string on the trailing edge to balance the plane in roll. Legend has it that some test pilots after a while became so adept at judging needed trim that they would on landing not only be able to tell the riggers where to apply the string but also how long the piece of string should be :)

 

On the issue if something is wrong or not I think I’ll pass on that one because based on experience this always seems to be such a sore point. But to sum up: No pilot will willingly fly around in a plane that cannot be trimmed if it can be avoided and since the IRL 109 had the tab it makes sense to use it also ingame in DCS. Sorry to be so blunt but should this discussion really require more than 30 pages and that some people who have a valid point are belittled because they may perhaps be a bit off on the technical description of the problem?

[NineLine]

No pilot IRL would fly around in a plane that was not in trim if you could avoid it: The first thing you would do on landing your 109 as currently implemented in DCS would be to adjust the tab slightly up to move the adjustable elevator trim range to a suitable range.

 

 

Yet here we are still getting posts that seemingly ignore the fact that Yo-Yo has talked, and still talks to a Luftwaffe pilot that spent a great deal of time in numerous variants of the 109, in actual combat situations...

 

In my mind a couple things could be at play.

 

1) the design of the 109 was such that the nose heaviness couldnt be trimmed out because it adversely effected performance. If I am a combat pilot and you asked me, do you want your plane to fly level and be a little slower, and maybe harder to pull out of a dive, or do you want to have a slight push on the stick, be faster (or perform better) and have a better chance at recovering from a high speed dive, what would I pick?

 

2) and/or the magical trim tabs everyone wants to "fix" the 109 are not enough to make the "problem" go away... after all, as I have said OVER and OVER... I can trim the 109 to not only fly level at cruise, I can have it nose down on its own if I go full trim...

 

So before someone else posts the same redundant stuff, please read the thread, understand the issue and provide valid proof that ED, its SME for the 109, and data are wrong... otherwise of course you arent going to change anyone minds on this... Santa is real if I am not required to prove otherwise...

 

PS some one with a flight stick the same length as a 109K-4 tell me they have the same issues as someone with a short stick sitting on their desktop...

Edited June 26, 2015 by NineLine

[Pilum]

You know what? You keep bringing up that some of the devs do this for a living and that they have access to former WW2 pilots. Well, I have seen former WW2 pilots on Discovery CH say some pretty weird stuff and the devs sometimes have some interesting ideas and explanations as well as witnessed in the exhaust thrust discussions we have had earlier. None of us are fault free.

 

In addition, some of us here in the forum have a pretty solid background in aerodynamics, both in terms of education and work experience and some of us have also worked in the aeronautical industry for a living.

 

So IMHO what is redundant is your implication that we don't understand the issue and should "read the thread". In addition, if you had a basic understanding of how a trim tab works you would not call it magical. It is in fact a pretty simple and powerful trim device one you understand how it works :)

[NineLine]

I am not in a position where I need to prove anything, its on you guys to prove that ED's research is wrong. You still haven't done that. It's not on ED to prove they are right, even though Yo-Yo spends a lot of time doing just that.

 

Oh wait... you saw something on Discovery channel?? Wait... I'll have the changes made right away... never mind, I just watched the Red Tails movie... now I am more experienced... ;)

 

Seriously though... provide something solid beyond personal opinion. Yo-Yo did as much already in this thread.

 

You know what? You keep bringing up that some of the devs do this for a living and that they have access to former WW2 pilots. Well, I have seen former WW2 pilots on Discovery CH say some pretty weird stuff and the devs sometimes have some interesting ideas and explanations as well as witnessed in the exhaust thrust discussions we have had earlier. None of us are fault free.

 

In addition, some of us here in the forum have a pretty solid background in aerodynamics, both in terms of education and work experience and some of us have also worked in the aeronautical industry for a living.

 

What is magical about the trim tabs is what everyone thinks they are capable of, even if its from a picture of some guy adjusting one with no real info about the picture or anything else. So again, come back with something firmer than you have shown, because at this point you need to prove this thread needs to stay open, let alone anything is wrong with the 109 FM.... also if you understand how a trim tab works, you might also understand how much or how little they can do, or how they might effect performance. But I am sure you have taken that into account.

 

So why can I trim my 109 just fine without them?

 

So IMHO what is redundant is your implication that we don't understand the issue and should "read the thread". In addition, if you had a basic understanding of how a trim tab works you would not call it magical. It is in fact a pretty simple and powerful trim device one you understand how it works :)

Edited June 26, 2015 by NineLine

[msalama]

...and yet, you DO need to prove it's wrong. Or things most likely won't change, regardless of whether it is indeed harder to prove a negative than a positive...

 

Me? Dunno. Am a groundpounder more than anything at any rate, but having skimmed through this thread still, have to say that no-one has really proved anything so far so it's all claims all around really - as seems to often be the case in these discussions anyway. But who knows? It certainly CAN still be wrong for all we know - but again, where's the proof?

 

See how it goes? To claim something is cheap. To _prove_ something, OTOH, can be anything but...

 

OK, getting me coat before Sith throws it out, now :D

[Yo-Yo]

You know what? You keep bringing up that some of the devs do this for a living and that they have access to former WW2 pilots. Well, I have seen former WW2 pilots on Discovery CH say some pretty weird stuff and the devs sometimes have some interesting ideas and explanations as well as witnessed in the exhaust thrust discussions we have had earlier. None of us are fault free.

 

In addition, some of us here in the forum have a pretty solid background in aerodynamics, both in terms of education and work experience and some of us have also worked in the aeronautical industry for a living.

 

So IMHO what is redundant is your implication that we don't understand the issue and should "read the thread". In addition, if you had a basic understanding of how a trim tab works you would not call it magical. It is in fact a pretty simple and powerful trim device one you understand how it works :)

 

Please take a look at the trim diagrams both from Germany and Russia and do not post the common sense speculation.

[msalama]

But still a PS. Anecdotes? All well and good, and they do have their value as evidence too, but how the hell do you QUANTIFY them?

[Ala13_ManOWar]

PS some one with a flight stick the same length as a 109K-4 tell me they have the same issues as someone with a short stick sitting on their desktop...

I think mine is more or less like Bf109 stick :lol:. Of course I have trim issues if I want to hold it using maximum power, but I can hold it easily. Anyway will tests a bit thoroughly tomorrow, using cruise setting, changing speeds, and so.

 

S!

[NineLine]

I think mine is more or less like Bf109 stick :lol:. Of course I have trim issues if I want to hold it using maximum power, but I can hold it easily. Anyway will tests a bit thoroughly tomorrow, using cruise setting, changing speeds, and so.

 

S!

 

Do you have a short stick as well? You would be best to compare directly... what might be a larger move for a shorter stick might be all but un-noticeable with a longer one... BUT AGAIN, I must add, I can trim the 109 level... so I still really dont know where the issue really is :)

[gavagai]

...and yet, you DO need to prove it's wrong. Or things most likely won't change, regardless of whether it is indeed harder to prove a negative than a positive...

 

In science and law the burden of proof is almost always on the positive. Proving a negative is so hard to do that requiring it has its own name: the burden of proof fallacy.

 

Yo yo has done a good job of backing up his work, but requiring everyone to be convinced unless they can prove him wrong is funny.:smilewink:

[NineLine]

but requiring everyone to be convinced unless they can prove him wrong is funny.:smilewink:

 

You arent required to be convinced, you are required to accept that ED is happy with how it works currently and plans no changes. You can think its wrong all you want, but the subject has been addressed by the developer.

[hegykc]

what might be a larger move for a shorter stick might be all but un-noticeable with a longer one

 

If you're going by my post, I used poor wording there and that particular statement was not correct. Obviously the shorter the stick, the less movement it requires for the same effect.But it's a very weird and limited wrist movement vs. a very natural and easy full arm forward. In other words, a wrist might engage 30% of it's uncomfortable range to level the plane, vs. the arm that has to engage 15% of a very natural range. Although the actual distance measured is greater for a long stick, the arm has several times more range of movement then the wrist. Plus the warthog spring is quite strong on the wrist, and with an extension it's barely noticeable.

 

To me it seems this is a question of what is "cruise", first. Otherwise we're comparing apples and oranges.

Edited June 27, 2015 by hegykc

[Sokol1_br]

WW2 pilots on Discovery CH

 

? :D

[AussieFX]

To me it seems this is a question of what is "cruise", first. Otherwise we're comparing apples and oranges.

 

Bingo! :smilewink:

 

 

Using a car analogy, do you go and get the milk in an F1 Ferrari when you've got an S class in the shed?

[ZaltysZ]

There is a way to have poor mans trim tabs. Try making a response curve similar to one in screenshot.

 

Be warned the more you "trim" (adjust the curve) this way the more of resolution you loose in negative pitch, so try finding a good balance, i.e. adjust just barely enough for your chosen cruise speed/power setting, and not for more.

[msalama]

requiring everyone to be convinced unless they can prove him wrong is funny.:smilewink:

And yet, an absolute precondition for getting anything changed is being able to prove the original implementation incorrect, no? Which then brings us back to square 1 again, i.e. there'll most likely be no changes unless something stronger than claims is presented for public and/or YoYo's scrutiny and perusal. Wouldn't you agree?

[gavagai]

We're not trying to prove anyone wrong or right. We're asking to adjust an elevator trim tab [sic]. And now the thread is 32 pages long.

 

I normally hate these, but we need something lighthearted:

 

 

:music_whistling:

[Anatoli-Kagari9]

The big problem here is that, most probably, it isn't even modeled in the K4 module. The fact that DCS's advanced flight dynamics model uses some sort of BeT for it's resultant calculations doesn't mean it can't make some cuts in some of the surfaces, to simplify.

 

Probably what we had in the Fw190 was experimental ?

[Pilum]

So now we need to prove that an adjustment of the elevator trim tab would have the effect that the 109 became more nose heavy? Maybe the 109 is special in this case? Any other plane would react as expected but we need to prove this specifically for the 109? Or is it the K4 that is special so we need data for that? Where is the goalpost? As explained before, the trim tab is a basic aerodynamic trim device. Either you believe a trim tab can change trim or you don’t.

 

Take the DCS 109 K4 and max it out and see how much you need to change the elevator angle to trim out. Go external. You can barely see the delta in elevator angle. So the change in elevator angle the trim tab has to generate is minimal.

 

Frankly, questioning that a trim tab could do this is like questioning that moving the elevator will have an effect on pitch or that turning a steering wheel on a car will make it change direction.

 

I have never driven a 1965 Mini Cooper but still I believe turning the steering wheel on a 1965 Mini Cooper will make it turn. Can I prove it? No. I don’t have the data. I don’t think I can find the data.

 

However, maybe I can find some data on another car. However, since I cannot find data on the 1965 Mini Cooper a valid standpoint would be that the 1965 Mini Cooper does not respond to steering wheel inputs? Give me a break…..:doh:

[NineLine]

So now we need to prove that an adjustment of the elevator trim tab would have the effect that the 109 became more nose heavy?

 

Nope, you are missing the point, but now my patience has run out on this thread.

[NineLine]

Re-opening this thread at Yo-Yo's request. He was able to talk with Klaus Plasa (he flies a Me 109G-6), one of the topics was trim. He stated that the plane trims to 400-450 kph, but not beyond, this pretty much mirrors what we currently see in the sim.

[Anatoli-Kagari9]

He stated that the plane trims to 400-450 kph, but not beyond

 

In Pitch ? Roll ? Yaw ?

 

I tested it yesterday with the 250kg bomb. At 1,4 ATA it still wants to nose up as soon as it leaves the rw, even at full nose heavy stabilizer trim and 20º flaps!

Edited July 10, 2015 by jcomm

[NineLine]

BTW: Did Yo-Yo take that chance to ask about:

 

- Climb rates;

- Control stiffness in Yaw at higher dynamic pressures ? Presently CTRL-ENTER reveals limitations only in Pitch and Roll, and even at very high speeds, where the

stick freezes almost completely in roll authority, it is still possible to use full rudder deflection to the point of being able to perform a tonneau!

 

This thread is about trim, if Yo-Yo has anything else to share I am sure he will. He was just confirming trim in the sim worked like the actual aircraft.

[Ala13_ManOWar]

Re-opening this thread at Yo-Yo's request. He was able to talk with Klaus Plasa (he flies a Me 109G-6), one of the topics was trim. He stated that the plane trims to 400-450 kph, but not beyond, this pretty much mirrors what we currently see in the sim.

Wow, FINALLY. After so much talking and lasts documents shown here I was quite sure about that, but good to know :beer: . Truly thanks for the info.

S!

Edited July 10, 2015 by Ala13_ManOWar