Post by sean on Sept 2, 2008 21:17:32 GMT 10
Thought I'd post some pics of my new Moth. As usual I made some mods to it to make it just the way I like. Aerodynamic mods involved a new larger fin, and moving the fin rearwards (both mods intended to improve yaw stability) and making the nose a touch skinnier and pointier (to reduce drag a tad, but equally importantly I wanted it to look a bit sexier). This plane will spend a lot of time DSing in ugly conditions where the bigger/longer tail will help it track a lot better through turbulence.
The wingtips have been rounded Ubermoth style - previous foamies I've built seem to benefit from this wingtip mod, plus I think it looks great.
To make the wings nice and stiff I embedded 4mm carbon rod in the top and bottom of the wings just forward of the ballast tube. The wings were covered in burly then fluoro red and matt black sign vinyl. The fuse is gooped/spackled/gooped/taped then finsihed with the matt black sign vinyl. The matt black hides any lumpiness very nicely, but only time will tell how well it stands up to abuse (not too well I'm starting to think).
The elevons are hollow carbon.... yes I know that's a bit over-the-top for a foamy but it was a good way to practice composite construction
. They look pretty trick but are also very tough - I banged a test elevon against my work bench repeatedly until it finally split at the TE, but only after some very hard hits. The resulting damage was quickly repaired with medium CA. Of course being carbon they're extremely stiff in torsion, so with a nice slop-free control setup there won't be any flutter on this Moth.
I also made a composite ballast tube using Target's most excellent ballast tube 101 build thread as a guide. It worked perfectly and saved about 40g over a brass tube, plus gave me a bit more composite practice.
The fin is 5mm balsa, sanded to an approximate aerofoil shape then covered in burly and sign vinyl. Very tough but also took a fair bit of lead in the nose to balance.
Finished it weighs about 800g... rather heavy for a 48" Moth but I don't plan to fly it in light air. Ballast should take it up to around 1100g.
It's had one outing so far and proved very fast on the front, holding energy incredibly well for some nice big halfpipes. But the fuse has shown itself to be a little fragile so it will need some beefing up in that area. Half the problem was that when I threw it off the slope, my brain flicked over into foamy mode, and I proceded to crash it into everything I could find...
It was probably a bit crazy to put so much work into a foamy but I really can't help myself
. From now on I think it's gonna be quick-and-dirty slow foamies or fast composites.
This pic shows the very rough modded forward fuse shape prior to sanding. I've cut away a lot of the upper forward section. AAA battery can be seen top-left and goes int he standard place. Rx is in wing.
Wings prior to covering. Wingtips are rounded and PUed Ubermoth style. Additional carbon spars can been seen ahead of the standard spar.
Carbon elevons. This shows the top/bottom carbon skins plus the balsa LE and end plates, prior to assembly. Carbon top/bottom skins were layed up on a piece of waxed glass then when cured cut to the right size. The layup is made from 45deg bias carbon and 90deg bias fibreglass (sorry can't remember the weights).
Carbon elevon half done. This assembly is ready to be sanded to make a sharp TE, and to make the LE the correct thickness.
This technique worked well but it had some drawbacks - both elevons warped slightly after assembly. In practice this wasn't a major prob, once hinged to the wing they straightened out (they didn't twist at all, which is the main thing). I suspect carbon bagged foam or balsa would make a stronger/straighter elevon.
Finished... well nearly anyway... these pics were taken prior to installing the elevon control rods. They're installed using the over/under technique so very little of the rods disturb the airflow (you can just make out the rod exit holes about an inch forward of the control horns). With some CA on the clevis thread and clevis bearing it makes a very slop-free setup, only slop is from the servo gears (old Futaba 3102s).
The wingtips have been rounded Ubermoth style - previous foamies I've built seem to benefit from this wingtip mod, plus I think it looks great.
To make the wings nice and stiff I embedded 4mm carbon rod in the top and bottom of the wings just forward of the ballast tube. The wings were covered in burly then fluoro red and matt black sign vinyl. The fuse is gooped/spackled/gooped/taped then finsihed with the matt black sign vinyl. The matt black hides any lumpiness very nicely, but only time will tell how well it stands up to abuse (not too well I'm starting to think).
The elevons are hollow carbon.... yes I know that's a bit over-the-top for a foamy but it was a good way to practice composite construction
. They look pretty trick but are also very tough - I banged a test elevon against my work bench repeatedly until it finally split at the TE, but only after some very hard hits. The resulting damage was quickly repaired with medium CA. Of course being carbon they're extremely stiff in torsion, so with a nice slop-free control setup there won't be any flutter on this Moth. I also made a composite ballast tube using Target's most excellent ballast tube 101 build thread as a guide. It worked perfectly and saved about 40g over a brass tube, plus gave me a bit more composite practice.
The fin is 5mm balsa, sanded to an approximate aerofoil shape then covered in burly and sign vinyl. Very tough but also took a fair bit of lead in the nose to balance.
Finished it weighs about 800g... rather heavy for a 48" Moth but I don't plan to fly it in light air. Ballast should take it up to around 1100g.
It's had one outing so far and proved very fast on the front, holding energy incredibly well for some nice big halfpipes. But the fuse has shown itself to be a little fragile so it will need some beefing up in that area. Half the problem was that when I threw it off the slope, my brain flicked over into foamy mode, and I proceded to crash it into everything I could find...
It was probably a bit crazy to put so much work into a foamy but I really can't help myself
. From now on I think it's gonna be quick-and-dirty slow foamies or fast composites.This pic shows the very rough modded forward fuse shape prior to sanding. I've cut away a lot of the upper forward section. AAA battery can be seen top-left and goes int he standard place. Rx is in wing.
Wings prior to covering. Wingtips are rounded and PUed Ubermoth style. Additional carbon spars can been seen ahead of the standard spar.
Carbon elevons. This shows the top/bottom carbon skins plus the balsa LE and end plates, prior to assembly. Carbon top/bottom skins were layed up on a piece of waxed glass then when cured cut to the right size. The layup is made from 45deg bias carbon and 90deg bias fibreglass (sorry can't remember the weights).
Carbon elevon half done. This assembly is ready to be sanded to make a sharp TE, and to make the LE the correct thickness.
This technique worked well but it had some drawbacks - both elevons warped slightly after assembly. In practice this wasn't a major prob, once hinged to the wing they straightened out (they didn't twist at all, which is the main thing). I suspect carbon bagged foam or balsa would make a stronger/straighter elevon.
Finished... well nearly anyway... these pics were taken prior to installing the elevon control rods. They're installed using the over/under technique so very little of the rods disturb the airflow (you can just make out the rod exit holes about an inch forward of the control horns). With some CA on the clevis thread and clevis bearing it makes a very slop-free setup, only slop is from the servo gears (old Futaba 3102s).
