I tried posting this in Aerodynamics:

I'm new to the hobby. I've met a group at a local flying field that I'm convinced will help keep me on track. I have sooo many questions.

I've recently made 2 deals here on this site. The first one was for a realitively large glider- a Sailaire, which isn't going to be built until I can confidently fly the one currently being built on my bench- a 2 meter Easy Eagle. And the second was for a JR Tx/Rx: both of these I believe will keep me busy for a while......

The questions I have are with regard to flight characteristics of polyhedral wings. Stable as hell- that part I understand. Most of the glider models with polys (sans ailerons) I've seen sport some very large vertical stabs or vees. As I grow with this sport, I will want to "graduate" to an aileron model. If I constructed a wing with ailerons using the models original wingplan without the polyhedral (well, maybe I would be wise to include some dihedral), would I also have to consider a revised empennage?- with smaller vertical control surfaces? Or are there other factors I should be considering? What about the inclusion of flaps and/or spoilers? If I include these features, should I be considering a different airfoil...?

I read somewhere that putting ailerons on the polyhedral wing of a floater was a waste of time. Could someone explain why?

Comments welcomed.

Ted

Ted:

Some polys are offered with a multiple plan ideas for 'full house' use also. The Sagitta Brothers (600 and 900) or even the newer Spriit 100 can be built with either poly wings or full house ones with ailerons and/or flaps. The one set of Sagitta plans I have shows the wing as a poly with ailerons, so that has been done too. As far as the other parts go, the design of the plane still has to follow certain 'requirements' and follow the same general rules of design in order to be a 'good' flyer etc.

There has been recent articles during the last two months in the Sailplane sections of Model Aviation (AMA magazine) that discussed increased dihedral and the increased stability of an aileron equipped ship. Seems to me like this would work ok from what I have read.

As far as adding flaps go, I have a Gemini that was modified to have flaps almost the entire length of the wings and it did not impede it's flight any. Launching has been another problem but the flaps have no impact on the particular problems I am experiencing.

Also, the spoilers can be of assistance in getting out of a strong thermal (we need to be so lucky all the time) if you need them, especially a stock poly design. They work pretty good during the spot landing phase too. Ollie suggests that if you use the 'barn door' type spoilers they should be mounted approximately 60% back on the chord though, as they would not be as likely to cause aerodynamic problems with the wing when set back this far and yet would be effective for landing. With the small sized servos available today, it would be easiest to have a servo sitting right near each spoiler without a large weight penalty. This also makes it much easier to connect an electronic connection vice the strings or cables usually associated with spoiler operations.

Good Luck,

Gene

My view is that you should not try to do aerodynamic modifications to a model like the Sailaire that so many people like the way it is. Instead, you should build it stock and fly it long enough to apopreciate its virtues and its faults. It is really a variety of models depending on how you adjust the CG and control throws. Fly it enough with various combinations of control throws and CG locations to experience the full range of its adjustments to see where you like it setup. Fly it long enough that you know it well enough to get the most benefit from its virtues before moving on to the next model or modifying the Sailaire. There is no sense hitching a mule to your new Cadilac to save gas.

If you want to try an aileron ship after you know all there is to know about the Sailaire, then buy a ship that is designed for ailerons. You have to experience each type in depth before you can develop a mature flying style of your own and begin to fit model selection or design to your true desires instead of your imagined desires. Before you go ruining a good design with modifications, get a book like Model Aircraft Aerodynamics by Martin Simons. Read it and reread it until you begin to understand the many tade offs in aircraft design and their purpose. Then you will have equipped yourself to do some fruitful kit bashing or original design work.

Which group are you flying with Shredz?

There's a good chance we'll be bumping noses this coming year. After almost 10 years of flying Old Timer Free Flight I'm getting the itch to get back into my glider flying on a more than casual basis. I used to fly with the Okalla Hawks and I'll probably be going back to them.

Gene,
Thanks! The Easy Eagle (a discontinued Ace R/C bird) has flaps, but they aren't full length. I'm going to try a few things with this plane later on in it's life, but for now I'm going to get very familiar with it. The order of business is to complete the construction so I can enjoy what it has to offer, do some reading about aerodynamics (so I don't have to concoct analogies from such limited experience when trying to explain things ), and THEN start changing things....
I want to develop a "feel" for building- something that I know will come with more time.




Ollie,
I won't be changing the Sailaire. I'm going to leave it just the way it is..... I will, however, play with the Easy Eagle. It's part of my process. I don't own a mule, but with the price of gas the way it is, maybe I might tie one to my Trans Am.

Bruce,
I'll see you at Burnaby Lake- if it stops raining long enough (FYI There's going to be an AGM January 18 at Bonsor Rec.)

Thanks guys!

Ted

Ted,

Sure you can modify any plane you want, itīs impresive what someone can do to a model with a little imagination....however, this is a knoledge that comes with experience.... Plans have their reson to be, itīs all in the C.G you can play a little with it but not too much, cuz a sailplane with an incorrect C.G simply wont fly.......it becomes a wild horse in the air.....so take this very in mind when making changes.

Sailplanes With polyhedral wings dont like ailerons, because itīs the dyhedralīs work to bank the plane when turning on the rudder...... adding ailerons on this type planes, will result in veeeeery slow respond to them.....so in this cases itīs better to stick to the rudder....also the wing profile is very important, because a non simetrical wing = to a slow plane = to a slow aileron response......


Ohh and never change the basic design of the wing, or it wont fly right, if you want to make it go faster, add some aunces at the C.G you will be thrilled of the difference.....

Big birds donīt usualy like ailerons, specially if the the wing is non simetric......because the glider responds very slowly to ailerons......
sailplanes are critical , changes they are sometimes NOT welcome on gliders if done incorrectly, they simply dont fly if changes are barely drastic....you will figure this out after a while....

my advise is to stick to your plans, and after a little experience is achived get yourself an aileron desing.....they are very fun and you will find that the wing profile is different ( more symetric ) as they need a bit more speed to make the ailerons take effect...

safe flying!
Rod

P.S. I have some pic, of modified gliders, I could E mail them if interested....Flat wings and stuff like that.