Electric Orange: E-Combat P51D - Page 25 - RC Groups
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Jul 11, 2011, 08:27 PM
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vtdiy's Avatar
Don't use that 9 gram servo, way too heavy, and far more power than you need -- also its current draw is up to half an amp -- don't know what the AR6400 aileron output is rated at.

There are similar looking 4 gram servos. But if you keep this thing light I think the best choice will be the Parkzone servos. Seems like you may be able to produce a plane of similar weight and size as the original.

Paint will make it heavy really fast, so you're going to have to resist that, and the stick-on paper emblems and tapes like we have done on the larger combat versions.

I would say that any decoration ought to be applied with markers, and maybe maiden it with no decoration at all.

Then paint it if you want, and see what the difference is. Your airframe weighs 9 grams now, and it wouldn't be hard to double that with a full paint job. Or more.


Re. your brick (Rx):

If you mount it under the wing with the servos pushing aft, you could hook up a single aileron very simply with a short rod to the aileron control horn. I think you need only one aileron to fly this thing, and it will greatly simplify things and make the plane lighter.

Put a vee shaped kink in the pushrod so you can adjust its length. At the servo end make a Z shaped bend to lock it in the hole. At the other end, make an L shaped bend to fit it into the control horn. Put it into the hole in the horn. Take another 1 inch length of wire and lay it across the L so it locks the control horn in place. Wrap thread around the pushrod and keeper at the fwd end and saturate with glue. It is now a wire spring that allows you to remove the pushrod from the horn, but prevents it coming off in flight.

Glue the other aileron in place. If you don't like how it is after you've flown it, cut the other aileron loose, and rig up hardware to move it.
Last edited by vtdiy; Jul 11, 2011 at 09:01 PM.
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Jul 11, 2011, 09:24 PM
Future Pilot
astronaut's Avatar
Oops sorry I meant push rods! Ya have made the setup before, I use a hard plastic juice jug to make the control horns. Works well!


So before I go forward, I want to get the aileron stuff cleared up as I never have done them. How exactly should I make them? Would it be best to cut out the rectangle from the wing, and sand the parts where I cut it out from the wing (where the wing and aileron meet) so that they meet by a thin edge? I hope you know what I mean.

Or should I do what you said earlier and use foam plates? I will do the same thing either way for both the elevator and aileron I suppose.

Wow I never knew you could fly with just one aileron moving! That's amazing! How does that alter flight characteristics? Very interesting, I had never thought about this before. How come I have never heard of this technique? It sure would make things tremendously easy as I wouldn't have to build the bell crank system.

I am having a little trouble understanding the aileron push rod system you are talking about. After the part "take another 1 inch...". Do you have any pictures?

Thank you so much once again!
Jul 11, 2011, 09:52 PM
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vtdiy's Avatar
Specifically, single ailerons:

That's from Foamflyer's site, but don't miss the rest of his site. It's a real treatr:

Single ailerons work well. Single engines work well. You can fly with two engines and two ailerons. You can have twin or even three rudders. Full size gliders have one wheel. Cargo planes have truckloads. You get the idea. You pays yer money and takes yer choice.

In some cases for particular reasons some configuration makes more sense than another. In your case with a RX brick and no separate aileron servo, it would be hard and heavier to rig two ailerons and easier and lighter to rig one. So seems like a good reason to go with one.

Seeing your blank plane ready for sanding and knowing the weight, and seeing the visual thickness of the parts, it seems like it might make the most sense to make a single aileron of about the same size and outline as the original design, cut out of the wing material, rather than a separate piece of dinner plate or tray foam.

Mainly because I assume you are going to sand the back of the wing into a nice taper, so the aileron will be reduced in thickness and taper to about half the thickness of the original foam by the time you get to its trailing edge. Sand the top of the wing only. Then cut out the aileron.

You really want to limit its travel, too by having a relatively long control horn -- say about a quarter inch of travel up or down for first flights. These planes have no trouble rolling, believe me. Also you don't want to overpower the servo, and a longer arm means less back pressure. Make sure your hinges work very freely and there is no binding at the edge of the aileron with the wing cut-out. Lightweight (but sticky) tape works better than heavy weight.
Last edited by vtdiy; Jul 11, 2011 at 10:55 PM.
Jul 11, 2011, 10:46 PM
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vtdiy's Avatar
Pushrod drawing.

Note: the wing is just shown square for drawing simplicity, yours is actually cambered and tapered.

The Vee bend is a little too large in the drawing, it would bind against the drawn wing as the aileron deflected.

The control horn is shown too far back from the hinge line for a top mounted pushrod. The holes would be better lined up over the hinge line. Or ideally, a little fwd of the hinge line on a top mounted pushrod. This will give differential throw to the aileron -- more up than down.

On the other hand, if the servo and pushrod are located below the wing, the best configuration is about as shown, with the holes aft of the hinge line. This will again give more up aileron than down.

This is all getting a little technical, and I wouldn't worry about it too much.
Last edited by vtdiy; Jul 11, 2011 at 11:23 PM.
Jul 11, 2011, 10:52 PM
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vtdiy's Avatar
Tape hinges, courtesy of Foamflyer:

Note, I would use thinner tape than what he uses for your lighter plane. Your aileron servo isn't as powerful and double taping with heavy grade packing tape can produce a too stiff hinge line for a small servo. I only single taped my aileron on the P-40 on top. I did notice a little lifting of the hinge line so maybe with my 9 gram servos I should have double taped. But many smaller planes (like the Champ, I think) use only a single tape. And pretty thin stuff at that. Check yours out. Try to mimic what the Champ does.

I was able to find some thinner packing tape than Scotch brand. If you're at a store, check the size of the roll and the length of tape provided. A thinner roll of tape that says "60 yards" is obviously thinner tape than a thicker roll that says "60 yards." This saves weight, and makes a more flexible hinge.

Also 2" wide seems wide for your size model. You might want to cut it into a narrower strip before applying.
Last edited by vtdiy; Jul 11, 2011 at 11:21 PM.
Jul 11, 2011, 11:10 PM
Future Pilot
astronaut's Avatar
Ah! Wow you are amazing! I understand the keeper system now quite well! Thank you very much!

The way I understood it before the diagram led me to believe it would make it harder on the aileron servo, but I understand now. Alternatively, can't I just put some sort of stopper at the end of the L bend on the aileron? Is the purpose of the keeper only to ensure the rod does not come out mid-flight?

And excellent link for the hinge tape. I always thought I needed a special tape, but now I understand the process perfectly. Thank you so much, can't wait to continue my work on this tomorrow!
Jul 11, 2011, 11:37 PM
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vtdiy's Avatar
Yes you can put a stopper (wrapped thread anglue works there, too.) But then you can't take off the pushrod as easily and put it in a different hole to increase or decrease your throw. You'd have to scrape off the stopper, and make a new one.

With the wire keeper you can spring it outward and pull the pushrod out of the hole and move it to a new one.

It probably would work better(easier to spring) if it was a little thinner than the .032 pushrod wire. But I have done them with .032. A little hard to fumble with, but do-able. If you have thinner piano wire, use that.

BTW, all wire we're talking about is is hobby store "music" or "piano" wire, right?
Jul 12, 2011, 11:17 AM
Future Pilot
astronaut's Avatar
Yep, music wire. Thanks for the suggestion on the keeper, I will see what works best. I am using 0.032" music wire.

Just have to do some other work right now, so putting this on hold for a couple of hours. One quick question. Should I sand all parts where the plane attacks the wind to a sharp edge? Such as the front of the cockpit, LE of wing, fwd ends of the horizontal/vertical stabilizers, etc.?

Jul 12, 2011, 11:52 AM
Registered User
mrexcel's Avatar
Your model looks good.
Jul 12, 2011, 01:55 PM
low tech high tech
vtdiy's Avatar
Rounded on forward, upward, or downward facing edges is good.

Slow straight taper on aft facing edges is good.

Emulate the shape of a fish, blunt forward, sharp aft.
Jul 12, 2011, 02:13 PM
Future Pilot
astronaut's Avatar
Got it. Finished the aileron and curving the wing. Will do the other sanding stuff today, and install electronics tomorrow. Thanks!
Jul 12, 2011, 10:39 PM
Future Pilot
astronaut's Avatar
Hey, I was wondering how you decide the thrust angle on this model (or other models for that matter as well).

As well as the COG before I start installing electronics.

Last edited by astronaut; Jul 12, 2011 at 11:09 PM.
Jul 13, 2011, 12:30 AM
low tech high tech
vtdiy's Avatar
Start with just straight thrust. Usually, depending on how you mount the engine, you can later adjust that if needed. On my combat version with a BP-21 I looped out of my hand, first flight, so I rebuilt the nose with some downthrust. Next launceh she dove into the ground ten feet in front of me. My best flights towards the end were with zero downthrust.

Yours is much smaller lighter and less powerful, but I'd still start with a straight motor.

For CG, masking tape your equipment on and try to get a cg at about 25-30% of the wing chord aft of the leading edge before making holes.

A little harder to figure on a tapered wing like this one, but with your 60% size plane, I'm going to say it's at about 1" aft of the leading edge.

Or if you can find a CG recommendation by Scotta earlier in this thread for the P-40, take 60% of that. I'm too tired to look for it now.
Jul 13, 2011, 12:35 AM
Registered User
mrexcel's Avatar
I find the CG by gliding the model with some Clay on the nose. It works like a magic for my first flight. I generally do my first flight little tail heavy and then trim it little by little. Take a look at the following video of my first flight of BYOB.

BYOB 24 (1 min 54 sec)

Its tail heavy at start. But this make sure I don't break the nose in my first test.
Jul 13, 2011, 12:36 AM
Registered User
mrexcel's Avatar
In about 40 seconds, I managed to tame that beast. lol

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