Converting Control Line to RC

Charlie Fite explains how to turn a control line plane into an RC plane!

Splash

By Charlie Fite

Control Line to RC...

One of my favorite things to do is to take an old control line stunter and convert it to 4 or 5 channel RC. I’ve done it four times, once with the old Flite Streak, once with the original 1951 Ringmaster, and twice with the Altagerra. All of them flew great. However, it’s not as easy as it may seem. You can’t just stick a radio in a C/L airframe and think it will fly. Well it’ll fly, but probably not like you want it to.

Here’s what I’ve learned. Control line stunt aircraft usually have very large, thick wings; they are short coupled with an oversized stab and elevator, and almost no fin/rudder. The wings can be asymmetrical, and the fixed fin is usually set slightly to the right. The “ailerons” can even be slaved to the elevator to increase the aerobatic ability of the airframe.

Well, all that has to change..

Conversion

The first thing I look at is the airfoil. Almost all stunt aircraft have symmetrical airfoils (no camber) with a maximum thickness of around 15% at 25% to 30% of the MAC. Some may be thicker, some thinner, but not by much. A perfect example of this is the 15% Joukowski airfoil, one of the most popular. I like a little thinner, faster airfoil to reduce the drag and lower the Reynolds number. (The Reynolds number is an indication of how easy or difficult it is for a wing to penetrate the airstream.) Fat wings usually have large Reynolds numbers. One of my favorite airfoils is the Wortmann FX76-120, a 12% symmetrical, and of course, the 12% Joukowski. You can find both on AirfoilTools.com

The second thing I look at is both the wing shape and its symmetry. I like constant chord wings because I’m lazy and they’re easy to build. I can affect the taper and the sweep somewhat by the position and orientation of the leading edge and the shape of the ailerons, but for the most part I build straight rectangular wings with the appropriate wing tips and ailerons. Then I’ll set the wingspan, the spacing of the ribs, and the shape of the wing tips. And I make darn sure the port and starboard wings have the same span.

Now comes the hard part

Control line stunt aircraft are notoriously short coupled. They have to be so that they can execute those dizzying stunts in such a small aerobatic box. I’m not saying that you MUST increase the distance between the CG and the tail surfaces, but it makes the aircraft a lot easier to fly. It also helps to reduce the size of the stab and elevator a bit, and increase the size of the fin and rudder, sometimes significantly. The question is, “How much?”. Well, you need to determine the tail volumes for both the horizontal and vertical stabilizers. It can be tedious because it can take several iterations to get the right combination of areas and distances from the CG.

There is a wonderful article written by Stan Hall, a technical advisor for the EAA, called “How Big the Tail”. Here’s the link: https://www.eaa62.org/technotes/tail.htm. As I said, the calculations can be tedious because they involve the CG, MAC, tail areas, the aerodynamic centers of the surfaces, the wings area, and the wing span. But it’s worth the effort, because if the tail volumes are correct, you all but eliminate the possibility of Dutch roll and porpoising. Typical horizontal tail coefficients (Vh) range between 0.3 and 0.7 while the vertical tail coefficients (Vv) range between 0.02 and 0.04. I try to set Vh at 0.35 and Vv at 0.025. It works for me and the way I like to fly. But again, you have to play a lot of “What If”. As an example, I lengthened the fuselage of the Altagerra by 15%, decreased the size of the stab by 15%, and increased the fin by 25%. The airplane was still short coupled because I didn’t want to stray too far from the original design.

So now, we know what the wing looks like, how long the fuselage is between the wing and the tail, and how big the stab and fin are. Almost done !

I haven’t flown a liquid fueled aircraft since the early 1970’s, and when I returned to the hobby about 7 years ago, I decided to go all electric. That, in and of itself, can cause a few problems because a lot of the control line airplanes have a short nose, and it becomes a hassle to try to fit a battery and an ESC in not enough room. It can also cause balance problems. Piston engines of comparable size are much heavier than their electric counterparts, though the battery can offset the difference…..but then there’s not enough room. I had to lengthen the nose of the Altagerra by almost 2” to be able to stuff all that equipment under the hatch, and not have to skimp on the battery or add lead to the nose for balance.

Basically, the conversion of a control line stunter to RC is a trade-off in almost every aspect. You don’t want the airplane to fly like an epileptic monkey on meth, but you still want to try to maintain the looks of the original. It’s a challenge.

I hope this helps anyone that wants to tackle a conversion. To me, it’s worth it. Y’all keep your nose up in the turns.

Last edited by Jim T. Graham; Jul 01, 2021 at 04:47 PM..
Thread Tools
Jul 02, 2021, 12:12 AM
Registered User
Bob Reynolds's Avatar
You miss the whole point.

Control line flying is RC flying. No other type of flying model aircraft share the Real Control of flying a model.

Free flight has no direct control of the model.

Radio control has no direct control of the model.

Only control line flying has direct Real Control of the model.
Jul 02, 2021, 05:31 AM
Ad eos qui nesciunt crepitus
Old_Pilot's Avatar
Interesting comment....but if I remember my days of flying the circle, you can't roll a C/L, you can't spin it, you can't do a rudder turn, you can't do a knife edge, on a 2-wire system, you can't control the throttle, and you certainly can't hang it on its prop. It's either full throttle or nothing. And if the lines go slack, you have no control at all.

Personally, I got bored with it rather quickly because of its limitations. So when the first multi-channel radio's came out in the 70's, I was first in line. Besides, this article is about converting a C/L to RADIO CONTROL....
Last edited by Old_Pilot; Jul 02, 2021 at 05:38 AM.
Jul 02, 2021, 07:03 AM
jrb
jrb
Member
jrb's Avatar
Would have thought the other way around!

Not many UC/CL kits; but, a lot of RC that could become UC/CL.

IIRC, may have been a recent article as well.

Jim B.
Jul 02, 2021, 07:15 AM
Registered User
PaulB's Avatar
All good fun, from someone who has spent quite a bit of time over the last 2 - 3 years converting RC models to Control Line....

However, great article and I do remember back in the 70's and early 80's when lots of people tried to convert CL to RC unsuccessfully for the reasons that you have outlined, compounded by poor quality and heavy RC stuff available at the time.

Interesting project and I am sure that lots of good will come out of it.

Paul
Latest blog entry: Just To Say Hello.......
Jul 02, 2021, 07:58 AM
Ad eos qui nesciunt crepitus
Old_Pilot's Avatar

Conversion to radio control


Paul B, jrb,

Thank you for your kind comments....Conversions going either way have their challenges, and that's what attracts me.....I'm a scratch builder, from my own drawings...that too appeals to me too...I'm a retired engineer and I have to keep both my mind and my hands busy, not to mention staying out of the kitchen.. LOL.

I'm a full time RC pilot and a member of a club with almost 150 members. We had an area reserved for control line, but in the 7 years I've belonged to the club, it's never been used. We finally converted it to parking...

Y'all keep your nose up in the turns

O_P

P.S. there's over 1800 plans for C/l up on OuterZone....pretty much where I live when looking for suitable subjects
Latest blog entry: Playing chase again
Jul 02, 2021, 07:58 AM
AndyKunz's Avatar
I've done several C/L to RC conversions. My favorite was converting Walt Musciano's "Stunt Trainer" to a UMX-sized RC. I didn't change anything about the planform, only the construction (much lighter).

I also converted the http://www.rcgroups.com/forums/showt...il Satan to RC, but that required some changes to the planform - increasing side area and extending the tailplane a bit further back.

I had such a great time with the micro Stunt Trainer that I upscaled it to .25 size. Before doing that, I visited Walt in the nursing home and asked if he minded me making a few adjustments, such as a slightly longer nose and taller tail, all of which he blessed.

There are a lot of very good opportunities in converting. I suggest people try it! If you have questions, ask and I'll be happy to help.

Andy
Jul 02, 2021, 08:42 AM
Ad eos qui nesciunt crepitus
Old_Pilot's Avatar

Conversion to radio control


Andy,

I remember both your Lil' Satan and Stunt Trainer builds....that was BBCC 7. (Balsa Builders Conversion Contest)..I built the Altagerra I....
It's kinda sorta the reason I wrote this article.....

The BBCC's were a lot of fun, with loads of tips/info/friendly banter etc. Sadly, they morphed into something that I didn't want to compete in.

Keep your nose up in the turns

O_P
Latest blog entry: Playing chase again
Jul 02, 2021, 09:59 AM
AndyKunz's Avatar
Yes, your conversion was fun to watch as well.

People should join us in Vintage. The "contests" really aren't much "competition" but they are a lot of fun to watch build all sorts of things. Every six months a new theme.

The theme for this period (which just started yesterday) is ABAK - Anything But A Kit. Which is the perfect complement to the first half, which was VOK - Vintage Open Kit (vintage kit of any type of model).

Andy
Jul 02, 2021, 10:20 AM
Registered User
JimboPilotFL's Avatar
I have a Sig control-line Magnum kit on the shelf that I have had for more than 15 years. I have been thinking about making the Magnum into an R/C plane. I have the feeling it would take a lot of work and might not be worth it. I could always use the light foam wings on an R/C plane. ...or I could just sell the kit, engine, tank and hardware that I have for it.
Last edited by JimboPilotFL; Jul 02, 2021 at 10:30 AM.
Jul 02, 2021, 12:22 PM
AndyKunz's Avatar
As long as the wing panels are the same size (C/L often adds a smidgen to the inboard wing) then there's no reason not to give it a try.

With the stabilization capabilities of modern receivers, the pitch sensitivity can be largely programmed out. You might want to enlarge the fin and rudder some.

GO FOR IT!

Andy
Jul 02, 2021, 03:12 PM
Intermediate Multi
Trisquire's Avatar
Aren't flying wings essentially extremely short coupled planes? When properly set up, they don't appear to have any quirky flying characteristics.
Jul 02, 2021, 03:20 PM
Ad eos qui nesciunt crepitus
Old_Pilot's Avatar

Conversion to radio control


See below
Last edited by Old_Pilot; Jul 02, 2021 at 03:25 PM.
Jul 02, 2021, 03:22 PM
Ad eos qui nesciunt crepitus
Old_Pilot's Avatar

Conversion to radio control


Quote:
Originally Posted by Trisquire
Aren't flying wings essentially extremely short coupled planes? When properly set up, they don't appear to have any quirky flying characteristics.
I don't disagree......but you can control their quirky control characteristics with wash out and elevon throws..I have 2
Latest blog entry: Playing chase again
Jul 02, 2021, 03:24 PM
Ad eos qui nesciunt crepitus
Old_Pilot's Avatar

Conversion to radio control


Quote:
Originally Posted by JimboPilotFL
I have a Sig control-line Magnum kit on the shelf that I have had for more than 15 years. I have been thinking about making the Magnum into an R/C plane. I have the feeling it would take a lot of work and might not be worth it. I could always use the light foam wings on an R/C plane. ...or I could just sell the kit, engine, tank and hardware that I have for it.
No, no, no, no. that's a perfect candidate......a little smaller elevator and a little bigger fin, and you're in business. The nose is long enough and the moment couple isn't too short....go for it
Latest blog entry: Playing chase again


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Convert RC Plane to Control Line fix-n-fly Control Line 15 Mar 04, 2017 08:48 AM
Discussion Converting a Control line engine to an RC Engine MerlinV Engines 10 Mar 30, 2009 11:38 PM
Discussion Converting control line kit to RC donfl3344 Scale Kit/Scratch Built 10 Oct 20, 2007 05:10 PM
Convert control line motor to rc motor just be replacing carby? ontheweekend Engines 22 Oct 06, 2004 03:32 AM
converting old control line motors to RC RSCherry Engines 4 Dec 06, 2002 09:18 AM