My Zepron frankenstein is nearing completion, Pics and questions within... - RC Groups
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May 09, 2002, 06:50 PM
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My Zepron frankenstein is nearing completion, Pics and questions within...

As some of you may know, I've been working on a Zepron (like Fan Fold) foam plane. Nothing fancy, just whatever came to me. My goal was to build a biplane, similar to the Sopwith, Tigermoth, etc. style WWI planes but using small EDF fans.

Now that it's almost done I could really use some help figuring out where to put CG for a safe first flight. Here's a good "top" shot for someone to look at. The upper wing is 24"x6", the bottom is directly under (not offset) and is 20"x6". The airfoil is home-made, but resembles the LT-40 airfoil.

What's the best material to use for stringers? I'm not sure if fishing line or thread is better. I'd rather use thread (small, lighter and easier to use) but I'm not sure if it's strong enough to be anything other than decorative. The plane currently feels very sturdy but could stand some reinforcement to keep the wings from flexing side to side from one another.

Initial "full-power-on-ground" test scooted the thing very briskly across the floor, I'm hopeful it'll fly. The only additional weight that will be added is another HS-55 for ailerons, a little tape for hinging, pushrods and some thread/fishing line. Keep your fingers crossed!
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May 09, 2002, 06:52 PM
Registered User
Another pic, showing the airfoil
May 09, 2002, 06:57 PM
Registered User
Another view, this one from the business end.
May 09, 2002, 11:08 PM
Private Pilot, M20J Owner
Wow! That certainly is different looking. You worried about landings with that thing? Also, sorta looks like the"pilot" is going to have to do the "Flintstone" pretty darn hard for a RoG!

Any idea what you AUW is?

Thought any of trying out some of the DF performance tips that have been going around? I'd certainly love to see someone confirm the cone and duct lips make a big difference in thrust.

Let us know how it's trip into the big blue works out...
May 09, 2002, 11:35 PM
Registered User
gerico's Avatar
1/4" radius "lips" around the shroud, a tail cone, and tape to reduce the blade/shroud clearance make a 20+% improvement w/ a stock Cox/Estes ducted fan which is roughly the same size as the little GWS fan. Don't know how any or all of these will affect the GWS fan.
May 10, 2002, 08:19 AM
Registered User
ronnath's Avatar
just a thought, but for the stringers a lot of zoners use dental floss.

floss is lightweight, tough, and free, courtesy of my dentist. each cartridge has 12 yards of the stuff. that's a BUNCH of rigging.

oh yeah, it works pretty well for your teeth, too.
May 10, 2002, 08:49 AM
Plane dodger
KillerAir's Avatar
That is one different looking plane...great job. From what I have read the you take the chord of both wiings by measuring the LE of the Front wing to the TE of the back most wing .From there you move 35-40% of the total back from the Front most leading edge. But I am not an expert on biplanes or multiwing structures. I would get a second opinion before I tried to flight test. Good luck.
May 10, 2002, 09:36 AM
Registered User
Have to make a correction. "Stringers" (also called longerons) are the thin wooden strips used on a fuselage (between the formers). What you're talking about are "flying wires" or rigging; and plain old thread will work fine for the weight and stresses you'll be putting on them.

I'm concerned about the leading edges of your wings though. There's A LOT of unsupported foam ahead of your wing struts. I'd guess that, unless there's support that doesn't show in the photos, that the leading edges will flex downwards while flying. NOT a good thing.

It looks great though and I hope it flys well! If it doesn't, try reinforcing those leading edges, but don't add the weight until you try it. I've been wrong before!
May 10, 2002, 09:46 AM
Registered User
I want you to have success in your test flights. So, while looking at the photos again, I noticed something else. It appears that your wings (& maybe the horizontal stab) have a few degrees of negative incidence. If this IS the case, it will require a lot of up elevator trim to overcome. But if the negative incidence is too much, it may not fly.

Wait a minute, let me try something.....

Sorry, didn't work. But if you want, I can email a photo of what I mean by incidence.
Last edited by DBCherry; May 10, 2002 at 10:00 AM.
May 10, 2002, 12:36 PM
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Well in hopes to answer some questions.

before maiden flight, there will be some foam ribs (6 or so on each wing) made and glued to help hold the shape. I also plan to build either a skid or use some lightweight wheels for landing (it will be a tail dragger either way). As far as the incidence on the wings, I've been thinking of that for a while now. When I built the top wing you can see I made a foam rib to glue the fuselage to, then once I glued the bottom on (via the TOP of the bottom wing) I realized I made an error and the two wings were NOT at the same incidence. It was easier to reposition the top wing so I angled it down.

If you'll notice the tail is at about a 8-10 downward incidence compared to the wing, that is in an attempt to make up for the main wings awkward angle. It should fly well, but might not look level while in flight (wings and elevator are fine in relation to one another). Future frankenstein attempts will make use of this lesson that has been filed away in the "to be remembered" files.

I still havn't figured out how I want to do the ailerons, whether I want big ones or small ones, whether they will be on both wings or one. Thanks for the tip on floss, I will be using it for the flying wires as it will be white, slightly visible and I can attest to it's strength. I'm guessing first flight of next weekend (I build slow) although if I get some time inbetween all the mothers day dinners I may finish it this weekend. I'll keep you up to date.

- Joe
Last edited by Joe B; May 10, 2002 at 12:40 PM.
May 10, 2002, 03:42 PM
Get a brian, moron!
Zephyr's Avatar


I may just be being stupid (and I apologise if I am) but I thought wings couldn't just be flat (eg a piece of paper bent over) I thought they had to have a top curved surface, as yours, but also a flat bottom surface to give lift. Please correct me if I am wrong

Also I agree about folding leading edge and landing impct, possibly some sprung uc?

Sorry if I sound to critical... but it looks too good and I'm jealous
May 10, 2002, 04:03 PM
Registered User
Real glad to hear you're aware of the incidence thing. I did wonder if the stab would counter the wing(s), but wanted to mention it. (And who cares if the fuse is flying at a positive incidence? )

To tell you the truth, I think I'd skip the ailerons. From things I've heard and read, they're questionable on an uncercambered wing like this. Try it rudder only, you can always add them if it turns out you really want them on this one.

That bit of aerodynamics is only part of the reason wings lift. Think about it; many of the best flying wings are symmetrical, equal curves top and bottom; many wings are flat bottomed, why do THEY fly inverted (upside down)? If that curved upper surface thing was the only way to create lift, nether of the wings mentioned above would fly at all.

The wing in this thread is called an under-cambered wing. An awful lot of today's park flyers wouldn't be flying if they didn't work.
May 10, 2002, 09:04 PM
Registered User
No one else has answered your CG question, so I'll give you my simple advice. I believe a safe starting point will be at 25% of the top wings' chord; so say about 1.5 inches back from the leading edge.

I like to remember that, "a nose heavy plane may fly poorly, but a tail heavy plane flys once".

Good luck with the first flight.
May 10, 2002, 11:47 PM
Resident Maniac
Toaster's Avatar
A little off topic, but oh well...
How's the Zepron "feel"? I mean, is it a capable replacement for F3? apparently it's stiffer and lighter than F3 but it is a bit more expensive...
May 11, 2002, 12:09 AM
Registered User
PanzyPoof's Avatar
Joe how the fly fishing in FLA.
Ya the plane is just what the Wright~bros would have build had they ducted fans. Awsome I have to show this to the Guys @ the Biplane Hangar.

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