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Old Mar 01, 2007, 09:12 PM
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signflyer's Avatar
United States, MO, Springfield
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Question
Bipe vs Mono aileron hinge line

I've noticed that most mono wing designs have an aileron hinge line that is swept forward relative to the fuse, whereas most bipes have an aileron hinge line that is perpendicular to the fuse. Why is this? What effect does changing this hinge line have?

I've thunk and thunk, till there was nothing left to think...(can't remember the next line, but it has something to do with drinking )
-Scott
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Old Mar 05, 2007, 05:32 PM
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No one knows, or is there not an aerodynamic reason for the difference?

I thought this was an interesting variable in design, but maybe not...
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Old Mar 05, 2007, 05:53 PM
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Usually, the tapered hingeline on a monoplane is to put more surface area near the prop wash where its most effective. At least thats my understanding of it.

On a bipe, its usually not needed because of the four ailerons instead of two.

Also, some monowing designs have a tapered trailing edge...like the edge 540, where there is a constant chord aileron all the way out to the tips, but the hingeline is not perpendicular to the fuselage, because if it were, it would result in a tapered aileron.

As far as what effect a constant chord aileron would have vs a tapered aileron...who knows.
I just make the ailerons 1/3 the chord of the wing, and roll with it.
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Old Mar 05, 2007, 07:54 PM
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Usually the hinge line sweep is a product of the planform sweep and the desired distribution of aileron area rather than a concious decision about the hinge line. these 3 are inseparably linked and I think most people would consider the specific hingline angle the least critical, or possibly irrelevent altogether.
In the case of my Index design the hinge line was straight which allowed a simple trailing edge spar across the whole span but this would have been changed if it had not also provided the aileron sizing I wanted with the proposed planform.

The current style for monoplane designs seems to relflect full size planforms which have very little taper at the 1/4 chord position. This means that unless you're using massive 75% ailerons or you are using massive amounts of aileron taper with almost nothing near the tips, the aileron hinge line will be swept forward.
The style for biplanes on the other hand tends towards wings that are swept aft at the 1/4 chord line which makes it quite possible that the aileron hinge line will be nearly unswept or completely parallel to the span.

I don't think hinge line sweep is a particularly critical aspect of these designs. Feel free to correct me!

F3P design is heavily influenced by the current trends and styles in the areas that are not obviously important for performance. For example they nearly all still look like full size planes to some extent, with cockpits and asymetrical fuselages! lt's not all based on the flight dynamics.

Aidan
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Old Mar 05, 2007, 07:59 PM
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I talked with Greg Ward about this once asking about designing biplanes. He said that he kept the hinge lines on the reflection perpendicular because anything else would make it roll non axial. So there is some sort of relationship there but i don't know exactly what it is.

Of interest; the hinge line on the Vrolet is actually swept back. Its rather hard to make that happen just by accident when you draw a wing. So i think it was a deliberate thing that Jason did to cure a particular performance gremlin. Same with the elevator being below the thrust line. Deliberate changes to make the airplane fly in a more neutral way.

I get the feeling that some people know what this does and how to exploit it but I have never seen anyone publish a good explanation.
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Old Mar 05, 2007, 08:03 PM
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There may be a benefit to having the hinge line more perpendicular to the aileron pushrods. On monoplanes, the pushrods tend to angle outwards because the ailerons begin outside of the horizontal fuselage member.

Tom
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Old Mar 05, 2007, 08:07 PM
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Hmm... it could just have to do with keeping enough material at the tip of the wing to keep the tips strong...?

I like the black magic theory though : )

It matters immensely on Rudder hingelines. However with them, you create an asymmetric situation (as opposed to ailerons)
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Old Mar 06, 2007, 10:29 PM
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A few thoughts on the subject....

I have become interested in these airplanes since watching Jason Noll demo his airplane at the E- Fest. Pretty impressive performance.

There are design aids (if memory serves me right) that let you determine what the hinge line effects are but most of them are based on a configuration that would let you design a F-15 or Cub and are useless for the machines we are interested in with the monster aileron sizes. They simply aren't valid for our designs.

In general what happens now is that once an aspect ratio of the wing is set up (which will definitely effect a lot of things) most designers just eyeball a constant percent chord, or what might look OK, or maybe draw in something based on what everyone else is using (especially if they won something recently).

The problem with these small airplanes is the differences in a configuration change such as aileron hinge line angle should be determined by flight tests using one airplane with only that change being made (use removable interchangable wing panel sections) between flights.

But most of us want to change more than one thing at a time or we build two different airplanes and try to compare them. And of course, then the results must be analyzed by visual feedback only, from a disconnected human, that might have a gas pain between flights. The results of a single small change becomes a very hard thing to pin down.

Honestly - things like a little differential throw sneaking in, aspect ratio of the aileron relative to the wing, and angle of attack of the airplane due to extra weight are more important when it comes to getting a nice smooth roll rate. The lightest airplane (low wing loading) that is the most symmetrical is going to perform the best when rolling with the smallest deviations from the flight path.

One additional thing just occurred to me after watching a viedo - most of these airplanes are rolling at relatively high angles of attack. The non-linear response of yaw due to aileron reflection would far outweigh the effect of sweep of hinge line.

Good Flying,

Ben
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Old Mar 06, 2007, 10:45 PM
Huh?! well waddayouknow!?
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signflyer is always thinking somebody must be paying him for it.tee hee what up man
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Old Mar 06, 2007, 11:43 PM
Watts is where its at!
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Ben, welcome to the F3P forum.

Ben is right and I'm as guilty as anyone else. I change too many things on each airplane. Every time I fly I get a bit better and so my subjective experience is different. In my defense I don't have the time it would take to do that kind of single variable testing. I certainly don't have the cool hands needed to know when something has absolutely made a small difference.

I further submit that none of us here has that kind of time (unless its your job ). By posting our experiences here hopefully we can correlate our findings and determine things we could not have on our own. This too is part of the scientific method. In doing so we expand our knowledge and save each other time.

So maybe, signflyer, its up to you to answer this question by experiment for us.
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Old Mar 07, 2007, 10:28 AM
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Thanks

I am looking forward to some interesting reading and education here. I am a retired aero engineer (McDonnell Douglas aero group on F-15 and F-18) and life long R/C modeler and find these airplanes totally interesting.

I covered the E-Fest for Model Aviation and have kept up with the standard indoor stuff but this was my first exposure to this type of precision flying. I had just never ran across it before for some reason. It is terrific!

I spent a lot of time in wind tunnels and so come at airplane design from the one change at a time approach.

I can really appreciate flyers that can evaluate airplanes from the natural feel. It's a difficult thing to do. I personally can barely tell when I go from a Lite Stick to my big P-51.
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Old Mar 07, 2007, 11:12 AM
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Hi Ben,

I did wind tunnel work myself for my MSc but I haven't worked in the field. Engineering work in Ireland tends to revolve around the medical device, pharmaceutical and electronics industries. I did an MSc in Aerospace Dynamics then took a job working with cleanrooms! I do agree with you about making one change at a time in order to do proper analysis but being slow at building and having changable taste I tend to do total re-designs. I think the Index 2 is the only new plane I've designed that had much in common with one of my previous designs. I comfort myself with the fact that I'm probably not a good enough pilot for it to matter.

Aidan
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Old Mar 07, 2007, 11:33 AM
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A long time ago, there were two aircraft inventors that took very different approaches to how aircraft were designed. One was of course the Wright Brothers which utilized small modifications to their existing designs in an attempt to "perfect" it.

The other was Louis Bleriot which constantly tried completely new designs in an attempt to "find" the correct design.

Lately, Ive been using the Bleriot method and zipping back and forth between many designs. Im going to use the Wright method and stick with one design until its "perfected". It should be faster and as history would dictate....more successful.
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Old Mar 07, 2007, 03:18 PM
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Chuckle!!

I should mention that although I might mention that one thing at a time is good I don't think I have ever used it myself :-)

There are so many great ideas running around that it's almost impossible to not want to try them all at once - especially if practice and experience has indicated it would work OK.

The one thing at a time approach would work great on things like using a control surface aero balance. Since the primary need for aero balances doesn't really exist on these small airplanes it seems pretty useless except for a hook to hang up a model. See the Feeding Frenzy photos at the E-Fest. He was hung up by the aero balance on the rudder.

I would think that just enlarging the rudder/elevator to the same area without the aero balance would be just as effective. Certainly having the fixed portion of the vertical there makes construction easier and lighter.

The nice thing about foam is the ease and freedom of making changes. One thing that makes the whole thing hard to do is that the existing designs are very close to being optimized for their use. Maybe use a large full fuselage with a hydrogen filled balloon inside to lower the wing loading :-)
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Old Mar 07, 2007, 03:58 PM
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One thing weve found with counterbalances or "aerobalances" is that you can often use them to get other effects. Obviously we dont need counterbalances to offset airflow resistance straining the linkages....but....

Counterbalances on a rudder can be used to correct or reduce coupling in KE, and Counterbalances on ailerons can make them much more effective...including in tail first maneuvers like found with VPP or even simple tail slides.
Counterbalances on elevators....just more surface area, tends to work almost like a stabilators on a jet aircraft.
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