SeditiousCanary

I recently acquired a new/in box Sterling Models Inc. Diamant Sailplane. After being away from model airplanes for well over fifteen years, I have a re-sparked interest in flying models. CA glues were a somewhat new and servos were huge. I find myself with more options in some areas like servo options and better batteries, while having far fewer when it comes to kits and designs. I really enjoy building wings instead of using foam or shell wings, and there just don't seem to be many options. I also have a strong fondness for dihedral wing over polyhedral wings, of which there also seem to be very few choices. After reading a few manufacture websites, I have a good knowledge of servos that are being made, but little understanding when it comes to applying it.
I am considering designing and building my own sailplane with AutoCAD 2004. I would be doing mostly thermaling with a few tricks thrown in. I have found Micheal Selig's website (http://www.aae.uiuc.edu/m-selig/) to be very helpful on the listing of airfoils, but I am still having difficulties selecting a airfoil to use that have minimal drag and good lift. I plan on the model having about a six to seven foot wingspan and target weight of about four pounds. (Or less. I bet much less, but I tend to overbuild things so I don't have to rebuild things.) Here are a few questions I have that I am hoping you can give me some advice on.

What torque servos should I be using for:
Rudder?
Elevators?
Flaps?
Ailerons?

What suggestions would you give me to make the wings removable (I have a small car)?

Do you think a T-style horo stab or conventional horo stab has better performance (I can't stand V-tails, call me a facist)?

Can you suggest any reading material to bolster my knowledge of aerodynamics or give me a few suggestions on well-suited airfoils?

Thanks for your time and help!

Chris

Soar Head

My Feedback: (5)

For your plane 72-100", as you specified.


rudder - most any mini/micro will do. HS-85BB is an example
elevator - same
ailerons - same
flaps - competition pilots land with flaps 90 degrees down for very slow controllable pinpoint landings. if this is your application, metal geared servos are the ticket. Mostly due to gears stripping if you forget to retract the flaps right before landing.

I would favor a fairly strong and well centering servo for the elevator.

If you are planning on building a 120" or larger span, stronger servos like HS-225MG for flaps, elevator would suffice.

Removable wings are common. Basically a steel wing joiner rod, which passes through the fuselage and into the root of each wing is one option. 3-pc wings have two joiners holding the center section and the tips together. Wings are often held together with 3m electrical tape.

Here are a few vendors selling kits similar to planes you describe.

http://www.isthmusmodels.com/pages/sailplanes.html
http://www.skybench.com

PizzaMan

My Feedback: (4)

I found Martin Simons "Model Aircraft Aerodynamics" to be a good place to start. If your a Mechanical Engineer, it will not be mathematical or advanced enough. There is a lot of discussion that directly applies to sailplanes.

The high performance sailplanes (full size) seem to all use the "T" tail. I believe that this is to get the elevator in "clean" air. For your design, it probably comes down to how much work you want to put into control linkages, and stiffening up the vertical stab vs the benefits.

BMatthews

How light do you want this model to be? What sort of winds will it be expected to fly in?

Airfoil section- If you're looking for something wooden and built up that will still penetrate but will slow down quite well then consider Mark Drela's AG34. It's intended for sheeted leading edge and open rear areas. It's a thin low camer section so it'll penetrate winds well and you can hinge the flaps and ailerons at the rear covering support spar to maintain the proper airfoil shape. Being thin though you'll need to go high tech on the spars if you'll be doing high power launches. If it'll be a basic high start then good spruce spars and common webbing will be fine.

Wing mounted servos are the way to go these days. For a thin wing like this the HS81MG's are the budget concious choice. There's other choices both of equivalent price and up.

The joiner will likely be at the center and it'll be a steel rod of probably 5/16 to 3/8 diameter and it'll fit into aluminium tubing receivers installed between the upper and lower spars and potted in place with a sawdust and epoxy mixture. A secondary anti twist rod or pin of about 3/32 or 1/8 will be back near the flap hinge. The hot setup for aligning all this during building is to do the whole wing in one piece with a 1/8 inch gap at the center. The tubing is bondo'd in place in one piece and a razor saw or fine tooth hacksaw used to cut it at the joint. This ensures a truly accuratley aligned center joint. Dihedral is limited by the angle achievable within the gap between the spars. Or you can use a bent rod or some other option of your own devising. Either way the rod MUST be spring tempered steel properley heat treated. Mild steel or raw unheattreated tool steel will both bend permanently under heavy launch loads. Yes even the 3/8 stuff. The spring temper does not make it bend any less but it ensures it'll return to it's rest shape when the loads are gone.

T tails are nice to look at but the elevator install can be a pain to engineer and the fin must be that much stronger to take the extra loading. If you do go T tail keep the stabilizer and elevator VERY light and use the weight you save in the fin for strength. A built up thicker airfoil with 1/64 ply sheeting on the fin portion is my suggestion. The rudder itself can be made open ribbed.

How about a double size Diamant but with uprated construction detailing?

BMatthews

I took the liberty of moving this over to here as it's more specific to sailplanes.