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-   -   Vertical tail size getting smaller?? (http://www.rcuniverse.com/forum/aerodynamics-76/2467518-vertical-tail-size-getting-smaller.html)

Ben Lanterman 12-25-2004 02:48 PM

Vertical tail size getting smaller??
 
I take quite a few model airplane magazines and have noticed over the last couple of years that the size of the vertical tails on the pattern airplanes designs seems to have gotten really small, even to point of looking funny. I have tried to take into account camera angles and lenses, etc. I assume it has something to do with doing maneuvers that need a lot of yaw looseness but don't have a clue.

Am I right or just hallucinating again?

Merry Christmas to all,

Ben

Mike James 12-25-2004 03:24 PM

RE: Vertical tail size getting smaller??
 
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Hi Ben,

I've got a huge folder of photos and drawings related to Pattern planes, as background material for the one I'm building. One of the best sites, where you can see Mr. Naruke's planes, in nearly isometric views, is http://oxai.us/ (image attached, too.)

I think three things have happened in the last 10 years...
Proportionate to the wing area, tail sizes do seem to have dropped into the 20% range, from say, 25% in the .60 and .91-powered days, and also lower aspect ratios. But I think the main thing is that the frontal area of these planes has increased a lot, from the slim, "steramlined" look of the 70's and 80's, to the ZN Line, or Oxai sort of look, which adds to the illusion. There's so much fuselage area up front, and the fuselages are also taller, back near the tail, that it definitely has changed the appearance.

True, there are more "snap"-type maneuvers in today's schedules, so maybe these planes have given up some of their yaw dampening, but I think most of it is just the new fuselage shapes.

rmh 12-26-2004 09:29 PM

RE: Vertical tail size getting smaller??
 
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Easy answer - and again we went to this setup years back -see our EMC2 design - 1997 and it was used very successfully -by both East and West coast flyers.
basically the model just has more vertical fuselage area around the CG .
you keep whacking down the rudder/fin -till yaw damping is poor and add a bit back -
Also you can reduce roll couple when doing this .
When we first did it it was not the "kool" setup - but -- there ya go --
The new (?) wide look is much the same - the models are quite low in wing loading and very neutral .
My latest foamie stuf even for 3D is much the same - my Cassut is a prime example .
Goerge Hicks' Tensor, is a study in this setup -and it is extremely effective - to the point of being a bit different in required control inputs.
The need for rudder inputs is very low for any maneuver.

Ben Lanterman 12-26-2004 10:46 PM

RE: Vertical tail size getting smaller??
 
You can reduce yaw damping by two approaches, cut down on the vertical tail size or move the CG aft, but the CG is set by longitudinal stability. That leaves tail size.

But what I really don't know is - why you would want to reduce yaw damping? A nicely damped airplane is one that, when the control surfaces are released, stops rotating dright there on the proverberal dime. Big movable surfaces such as the big rudder on George's Tensor give maneuverability and also have high yaw dampening.

rmh 12-28-2004 07:51 AM

RE: Vertical tail size getting smaller??
 
Lateral area at the CG is important- for highly maneuverable , slow speed flying.
No ballistic flying here!
Do a very slow roll -in horizontal flight
The model with the best lateral area placement will do this the most easily.
If the model had no side area except for the tail - it would be impossible to hold attitude -or altitude , using rudder deflection.
George's Tensor needs lots of rudder for fast tight turns but none for flying on it's side
Read his write up in 3Dflyer .
Well written.
Moving CG ft moves relative lateral area forward. Y/N?
I have two new Tensors over in the corner --one for my son -one for me .
Get one and see what George has done with this setup
interesting .

Ben Lanterman 12-28-2004 10:25 AM

RE: Vertical tail size getting smaller??
 
Totally agree Dick, the big side area is great for what you mention but I don't think that goes along with what I thought I noticed, but George's Tensor (and I would have one except I bought the little blue Edge first) has big vertical surfaces and lateral areas and is well damped in all axes. This is especially effective in dampening the oscillations in yaw because of the low inertias of the little beast. His responses are due to the really big controls overcoming the natural dampening due to the big surfaces.

I'm not too sure the little monsters are going to be representative of the trend that I thought I was noticing in the bigger pattern ships. But will work on it.

I don't remember your EMC2 design. You upped the forward fuse area and chopped down the vertical tail area. The side area could be seen in knife edge easily but what maneuver or maneuvers were you looking at when you did the vertical tail work?

Back to the little monsters, I don't think I have ever had as much fun flying a model as with them. Just for kicks I made like a UC flyer one day (well I was outside the circle). Full rudder and had a horizontal flat turn, great fun.

Oh one last thing. I read George's remarks on the effects of props and thought them well thought out and well written. But one thing I disagreed on was the effect of engine torque on the airplane. He mentioned that when the airplane was in a partial throttle hover and you increased the throttle that the airplane's rotation would slow down. He said it was due to the motor moving out of the maximum torque RPM range. I would expect rather that it was the increased amount of spiral propwash acting on the wings. It doesn't create a yawing or pitching moment on the wings such as on the tail but surely there would be a rolling moment due to it's impact on the wing which is closer and bigger and it's in the right direction to slow the torque roll.

Well one more last thing. Chip Heyde said he sets up his airplanes with 1/2 degree on the wing and 0 on the tail.

How do you set up your big airplanes? I can't see any benefit to Chip's setup. Why not just use some elevator trim to do the same thing?

Johng 12-28-2004 11:54 AM

RE: Vertical tail size getting smaller??
 
Holy Cow:

WE might get out of this more or less all agreeing on a point.

My own way of thinking about it is just like longitudinal stability, just without the contribution of the wing. That leaves the vertical tail, the fuse shape, the prop effect, and the CG as the big (or not so big) factors.

AS with longtdl. stability, more yaw stability means less maneuverability. I think in the past, the vertical was sized by TLAR and was generally overkill.

What Ben says about large tail size and damping is absolutely true as well, but I just think the whole sizing has been overkill in the past.

I think there is a combination of things here, the large fuselage side area visually makes the vertical look small, because the amount of fin above the turtledeck is shorter. AND, the vertical is a bit shorter, but not as bad as it looks. People have cut back to where the stability and damping just starts to fall off for maneuverability.

I have nothing but observation and a little flying experience, but it does seem that a smaller vertical with 80% rudder area (for example) is more responsive than a larger vertical with the same rudder area ratio. The only real explanation is the larger relative influence of the fuselage side area.

Here's a plane designed for fully neutral aerobatics with a cheap wacker conversion motor by a friend of mine. THe vertical looks too small, but is the size settled on after plenty of development flying. I've flown it myself and it's really perfect with much response and very little wagging on a hammerhead downline - no more than any sport or aerobatic plane I've flown anyway:
http://www.laserlizard.com/images/ToysforTots%20002.jpg

Ben Lanterman 12-28-2004 12:40 PM

RE: Vertical tail size getting smaller??
 
Thanks John, we tend to like what we were first imprinted with I guess.

rmh 12-28-2004 12:51 PM

RE: Vertical tail size getting smaller??
 
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TheEMC 2 (photo below is a version with the wing elevated ) was designed for slow flight
Most "pattern" guys were into going fast and playing follow the leader --
anyway the lateral area setup allowed for rolls which required little trim chage during rolls at slow speeds .
I learned this doing the Jungmanns for TOC in 1989 (flown in 91-)
Steve thought the rudder fin was way too small -I was adamant it was plenty as the fuselage setup (being between the wings ) afforded excellent lift(lots of uninterrupted area) and the rudder simply had to act as a trim tab - (sorta).
A larger rudder and fin INCREASES AOA on fuselage required for knife edged flight .
The lateral area distribution goes to pot.
Geo's comment on the torque also caught my eye - I thought the same thing but I suspected it had nothing to do with being out of the "torque band of the engine".
Props know nothing about torque bands
Also- I can shift the max torque band on any good gas engine -by retiming and pipe setup -
I must ask George exactly what it meant --
Chip's 1/2 degree thing is a carry over from when ever --
1/2 degree is 3/32 in one foot (aprox).
if one trims ailerons a hair - effective symmetrical airfoil -goes out enough to cancel that -
I see errors of 1/2 degree in models all the time . (not mine of course)
I setup my big planes as zero as possible - and some have high thrust lines - some ar zero.
The real fix of course is ----------- low wing loading which = low trim drag changes and lots of power which fixes all of my other screw ups .

Ben Lanterman 12-28-2004 01:24 PM

RE: Vertical tail size getting smaller??
 
Thanks Dick, That is the most number of really good words you have ever written and I find myself nodding in agreement. Thanks for the reply. Let me know what George says. The EMC2 certainly looks fine.

By the way, if that is your flying field, whow!

rmh 12-28-2004 03:11 PM

RE: Vertical tail size getting smaller??
 
that field is in Ca. The model is from my kit, sold to a flier who lives there.


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