RE: Airfoil shapes used as Horizontal/Vertical Stabilizers  
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RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/16/2008 2:22:01 AM   
da Rock



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Joined: 10/11/2005
From: western, NC, USA
Status: offline 		Yeah, I forgot that. Too far in the past...

But we got some good out of it as Dick's aluminum tubing idea was worth the side tracking.

(in reply to iron eagel)
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RE: Airfoil shapes used as Horizontal/Vertical Stabili... - 2/16/2008 2:34:43 AM   
iron eagel



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Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		You right Dick's idea works great!!!
I used that method for my GP Cessna, the stock struts kept failing at the part where they were joined by the CA hinges.

A lot of stress from those bank and yank moves I guess.... We won't even talk about the wings I have folded back over the years.

Hey you did not comment about these questions...
lol
While laying out the new components for this assembly I came up with yet more questions.
Manny others have modified this airplane by adding both area and larger throws to the elevator and rudder to male them more effective. A lot have used counterbalances to the control surfaces as well.

Doesn’t the increase in span from the addition of counterbalances reduce things like roll response?

By adding more rudder surface up higher from the central axis via the counterbalance method , cause reverse roll coupling?

Isn’t it far better to increase the cord of the control surface closer to the central axis of the plane and pay the price of the higher drag that will cause rather than cause control coupling issues?

When you increase the cord you shift the MAC reward also does that not make the surfaces more effective because you are extending the moment arm?

One final question if I can reduce the mass of the components used in the tail surface construction will that not in itself make the control response better?


< Message edited by iron eagel -- 2/16/2008 2:37:11 AM >

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/16/2008 3:50:58 AM   
BMatthews



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From: Burnaby, BC, CANADA
Status: offline 		For all those other than the counter balance ears the answers are "yes... but". The differences you'll see will be hidden by other factors. The changes you're talking about are just too small to make an overriding difference in terms of the unwanted side effects.

In the case of the counter balances it won't reduce the roll couple because they are moving portions that will aid the rolling. At least in terms of the ailerons. If you're worried about adding some span to the tails and having it reduce the roll there again it's just too small an effect to make enough difference to notice.


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Free Flighters go that extra mile........

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/16/2008 4:08:47 AM   
iron eagel



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Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		Thanks Bruce!

I was just curious as to what if any effect these type of design considerations had when weighed against overall performance. And if this was something that one should take a hard look at before just adding more surface without thinking about what other things it might do as well.

If I do do a modification I want to as much as possible do so in a manner that it will enhance performance, rather than just be ok, to try to gain something even of that gain is small. Hence that is why as far as the tail group I am looking at increasing the root cord the most in adding some additional area to the overall control surfaces, although a small increase in span might be needed at least for the elevator. You must be able to read minds, because I have not really focused that much on the ailerons as of yet, and had thought this might be somewhere where the counterbalance idea might be used effectively. Although I am a bit concerned that by doing so it might be an invitation to flutter as far as the ailerons go, although I am using a pull/pull setup on this planes ailerons (so I can move the servos inboard to keep more of the mass closer to the roll axis) and that should be less prone to flutter.

Regards,
Paul

< Message edited by iron eagel -- 2/16/2008 4:14:52 AM >

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The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/16/2008 3:39:45 PM   
cyclops2


 

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I stopped having flutter by going to pre-tensioned, pull - pull controls. Todays servos are so powerfull that there never is any reason not to use them.
Oh yes. I only use real, flat type, hinges with removable pins. They allow perfectly aligned surfaces.
Anything like DUBRO is fine.

Rich

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/16/2008 6:27:09 PM   
dick Hanson



Posts: 9930
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		When in doubt
build a flat foam model and try out the idea
you can do it quickly cheaply and in the process, DEBUNK a lot of ideas accepted as fact.
then build your "nice" model accordingly.
Did you know--- bracing struts at the rear of the plane INCREASE drag at the rear of the plane -where many models need it. also the braces add more stability for less weight
( look at an ME109)
or a Gee Bee Zeta.

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< Message edited by dick Hanson -- 2/16/2008 8:01:28 PM >

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 12:54:55 AM   
iron eagel



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From: Middleboro, MA, USA
Status: offline 		Thanks Dick,

I hear you about the foam test bed, I have done flat balsa gliders before (just freeflight toss it in the air) but never thought about foamie as a powered test bed...

So the drag of the braces make up for a lack of stability in some designs, interesting...

< Message edited by iron eagel -- 2/17/2008 12:57:53 AM >

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The Wrights never crashed, they only had hard landings. I 've had some hard landings myself. AMA EAA AOPA revver #185

(in reply to dick Hanson)
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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 1:15:52 PM   
dick Hanson



Posts: 9930
Joined: 12/12/2001
From: slc, UT, USA
Status: offline 		It is all a compromise--
With enough power -none of this is necessary
or if light enough, the power can be reduced to zero
etc..
That's what makes it interesting

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 1:25:07 PM   
da Rock



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quote:

ORIGINAL: iron eagel

Thanks Dick,

I hear you about the foam test bed, I have done flat balsa gliders before (just freeflight toss it in the air) but never thought about foamie as a powered test bed...

So the drag of the braces make up for a lack of stability in some designs, interesting...



Not really beyond "some designs".

But the airplanes with braces on the tails do fly more like arrows fly than they would without them. Stability? Not the kind we're looking for. If it was, then airfoiled tails would be just as beneficial. And you're heard again, and again, and again how flat plates are just perfect while airfoiling back there just adds profile drag and weight. Can't have it both ways.

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 3:43:05 PM   
dick Hanson



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From: slc, UT, USA
Status: offline 		Well you lost me there-
I guess you feel I advocate nothing but flat plates and old fashioned support struts.
If so- you completely misunderstand what I say.
To hopefully clarify - the struts add rigidity ( integrity) to the airframe- not stability.
I thot it obvious that when I said stability, I was referring to stabilizing the flex and bending in an airframe
Did not mean to confuse the two .
FWIW- why are you opposed to flat plates?
They are easy to do and properly braced - for most small light models are an excellent approach.
Streamlining I DO understand . also parasitic and induced and profile etc., drag.
The point I have always tried to make is that streamlining in it's self - adds very little to small aircraft which are flown at relatively slow speeds
To be pointy fingered-- if weight can be reduced by eliminating streamlining - overall performance is often improved.

< Message edited by dick Hanson -- 2/17/2008 3:44:52 PM >

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 5:44:40 PM   
da Rock



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quote:

ORIGINAL: dick Hanson

I guess you feel I advocate nothing but flat plates and old fashioned support struts.


Please don't assume what I might think. I'm not clear on what I think more than half the time. I think......

I've really only been trying to get across that braces of any type with out models are pretty much a bad fix for a problem that doesn't have to exist. And if you're going to brace instead of build adequate structures, then use simple and light ones that give less drag. And all I've ever seen from braces is negative aerodynamically.

As for what I think you advocate all the time???? You want a straight answer? Really? You ready for this?

Good building practices,
a really good test method,
sensible material selections,
and a lot of worthwhile experience mixed into your advice.

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 5:56:17 PM   
da Rock



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From: western, NC, USA
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quote:


So the drag of the braces make up for a lack of stability in some designs, interesting...


Not really.

If just adding some kind of drag to the rear of a bad design would give it more stability, you'd see some lousy designs with parachutes back there. OK.... that's more joke than truth..... hmmmm, or is it?

You've read where flat plates work well in our environment. They do. But it's not because they're more draggy. It's because we don't get the same differences in drag the full scales get between a flat faced plate and a true airfoil.

So we can use a flat plate with maybe more drag or maybe not, or a NACA0012 with it's rounded nose and the difference in drag isn't why the flat plate works as well.

(in reply to iron eagel)
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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 6:15:43 PM   
dick Hanson



Posts: 9930
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From: slc, UT, USA
Status: offline 		OK-
I am a firm advocate of the ez approach.
ya got me there.

The problem I see on our small sport models is in trying to reproduce shape criteria (hows that) which is the best COMPOMISE on a large airframe --and expect/hope to see relevant results on the model.
EXAMPLE, a typical question:
"my Top Flite .60 powered P 51 snaps on take off , so what changess to the airfoil will correct this problem?
The question presupposes that the airfoil can cause or correct this condition .
In all probability, the problem is due to excessive wing loading and an attenpt to take off before usuable maneuvering speed is reached.
This is a problem I have seen over and over -
On the new Parkflier models (RTF trainers ) they add clear plastic drooped chord extensions to helpthis situation -- it looks awful to me but the REAL problem with the old TP P51 has been (in my book) addressed - there simply iwas not enough wing to to make the design work well at typical model take off speeds .
A second problem was that the early scale tail group was no good at low speeds -- the wing COULD supply lift but the tail group was not yet able to CONTROL a high drag/lift on the wing panels - any slight change in lift symmetry induced a nice "flick".
Back to square one
The real fixin about --99.9% of the problems such as noted in the example -- is weight .
reducing weight will cure more problems than all the other efforts combined
For those flying slope gliders - bugger off - this is a whole different matter .

.

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RE: Airfoil shapes used as Horizontal/Vertical Stabil... - 2/17/2008 6:52:38 PM   
iron eagel