I am a scratch builder who has never built a R/C aircraftmy expierience has been in free flight up till now. I have a decent understanding of basic aerodynamics as they pertain to the type of aircraft I have designed and built so far, but have a couple of questions for you smart folks-1)What is the proper incidence angle for the tail(in general)? I use up to three deg.Positive in my freeflites but suspect that this won't do for radio control.2) What about thrust angles? 3 down and 3 right for freeflight but ???Thanks!!

Boatman,

We need more information.  There are too many variables depending on the wing and stabilizer airfoil, location on the fuselage, dihedral, c.g., etc.  Tell us what you've built and we can help.

pmw

Further to pmw's reply is this an Aerobatic, trainer or load carrier/photo hauler? Some of the factors change with each use. And just as you found with your free flights one choice affects the next since the trim is all tied together.

RC models are basically FF models with less auto-correcting capacity.
As a matter of fact, manny FF old timers are build as RC today.

A trainer is closer to a pure FF than an aerobatic model.

1) What is the proper incidence angle for the tail? As for FF models, the proper incidence angle for the tail depends mainly on the desirable pitch stability, and on the position of the main wing respect to the tail (which is more or less affected by the downstream produced by the wing).

2) What about thrust angles? Same as 1 above. I have seen from 5-2 to 0-0.

A good source of reference are the many published manuals for commercial RC kits.

Further questions could find specific responses from these folks:

http://www.rcuniverse.com/forum/forumid_196/tt.htm

  Thanks guys!! I have not started my RC project yet but it will be a sport/trainer-I have an OS 40 FP and have been flying a Greatplanes realflight simulator for several monthstime permiting I will be flying this summer. One more question-although I really enjoy building, I would consider an ARF for my first time out if you all think that would be a better route and have a specific recomendation or two. I don't want something with auto-correction electronics although I really enjoy flying the Nexstar on the sim-(with the gimmicks turned off) Thanks again for your kind and prompt responsesG.C.Arlt in sunny Eastern Washington 

Modeling has an excellent book that explains R/C design from A to Z.  It could be a textbook except it's so readable. 

R/C Model Aircraft Design by Andy Lennon.

It explains everything and does it simply.  There are some formulas, but after you've read it, you'll understand the few that're needed.  And they're simple ones.   Amazing book.   It's so good that Model Airplane News published it, undoubtedly because it is so understandable.

It's often sold in LHSs and is usually about $20.

As I recall, most free flight models are set up as essentially a tandem wing plane with both the main wing and the stab having upward force. The CG can be as far back as 70% of the MAC. This works for free flight, giving pitch up and climb under power and 2 lifting surfaces under glide.

This arrangement doesn't work well for RC. The plane will be extremely sensitive to elevator and very power sensitive. RC planes normally balance from 25%-30% of the CG, with some fun fly and 3D planes farther back. The force from the stab is downward to counteract the pitch forward rotation.

I have flown several old time free flights converted to RC with elevator, rudder and throttle. If they are balanced around the main spar, they fly very well. A buddy and I have a Quaker Flash on glo that we take out every once in a while and it's an excellent flying RC conversion. It has the CG around 30% of the MAC.

After instructing for about 30 years I gave it up four years ago, so my opinions may be somewhat out of date. I don't know if it is still available, but I thought the Midwest Aerostar 40 built  from a kit was a great trainer. I flew dozens of them and only one didn't fly well. Never did figure what was wrong with that model, but the student only showed up one time. At our field the current instructors seem to fly the ARF's with the "gimmicks turned off.' The Mustang and Raptor PTS have a bad reputation here; other than that they are all very simmilar. 

You're welcome, Boatman.

The simulator is great practice.

As you are an experienced builder, I would suggest to start off a commercially available kit of a proven trainer (Sig, Goldberg, etc.).

There is much information available, if you have the time to read through.

Right here in RCU, there are two excellent threads:

http://www.rcuniverse.com/forum/m_8503667/tm.htm

http://www.rcuniverse.com/forum/m_4537845/tm.htm

Also AMA E-publication:
http://www.masportaviator.com/index.asp (Pull down the main menu on the left)

For kit reviews: http://www.masportaviator.com/fh_otfl.asp

For trimming: http://www.masportaviator.com/ah.asp?CatID=8&ID=141 (Series of three articles)

Best regards!

One option that would produce a very nice trainer that is quick to build is to do a sheet fuselage version of one of the old timer classic free flight designs.  Along with the basic sheet box fuselage I'd also switch the wing airfoil over to a Clark Y shape if it isn't that option already.  Something like the Quaker shown above would work very well.


Ed, the sensitivity to pitch doesn't come from the CG being so far back on the wing but from the CG being too close to the aircraft neutral point.  I've flown RC conversions of more recent designs that have long tails with generous stabilizer areas and they are not sensitive to pitch in any sort of dangerous way despite having the CG back well behind normally accepted standards by RC rules.  Case in point is my own Henry Struck Record Hound.  The CG is currently at 50% and I'm looking to push it back even further since it has all the signs of far too much pitch stability at this point.  As it sits now it is as gentle as a trainer.  But although I have not checked out the Neutral Point location in the calculator I can assure you that it's well back there.  Perhaps even as far back as 80% which is extreme due to the planform.  But the airplane design needs to support this sort of CG positioning.  Something like the Quaker shown in you post would not tolerate that because it does not have the extreme tail volume coefficient.  But then the Quaker doesn't fly with the extreme back CG in free flight mode either.

I do quite a bit of scratch building from plans. USUALLY the incidence angle is stated on the plans. If there is no incidence angle stated, I use 0/0 (0 on the main wing and 0 on the horizontal stab).

A good example of what I am saying is: I built the Blue Flash (FlyRC plan). There was no thrust angle stated and no incidence angle stated so I used 0/0. A Miles M-28 Messenger I am working on calls for a zero thrust on the engine and a 3 degree positive incidence on the main wing.