I built a modified Sweet Vee for Ed LaCroix in 1996. Among the mods was a 32mm engine mount.
To get the 32mm mount to fit right, and to be at the proper thrustline as the 24mm mount was supposed to be, I had to cut a gouge into the top of the wing skin. So I added extra fiberglass cloth to the top center section of the wing to help to reinforce it some more.
Also, I think I used at least 2” wide, if not 2.5” wide, glass cloth on the center section joint. The glass tape in the kit is only 3/4” wide, but that seemed to be too wimpy even without the need to cut into the top of he wingskin.
The wingskins are Obechi. It is stronger than balsa (per thickness), and also cheaper than balsa. I think they chose the Obechi mainly because it was cheaper (particularly since the surface area of this wing is so much more than the Astro Blaster and Strato Blaster kits). I learned the hard way on another project that Obechi soaks up epoxy like a sponge. I kept applying more epoxy, and the skin looked “wet”, then a few minutes later the “sheen” was gone, and the skin just looked “damp”, the epoxy had mostly soaked inside of the skin.
I learned from someone else what you do about that, when I made the Sweet Vee. Use some clear dope, and apply the dope to the inside of the skin, and let it dry. The idea was to use the coat was a barrier to help keep the epoxy from soaking thru the Obechi. It worked. When I did that then applied the epoxy, it was like working with balsa, it did not soak in like a sponge.
If I did it today, I would still do the same. I do not trust spray contact adhesive to bond the wing skins.
Something else I did was to reinforce the inside of the skin a bit. I used some 3/4 ounce glass cloth for the first 6” of the wing, staring from the root. It did not add much weight. I applied the epoxy first, squeegeed most off but left it “wetter” where the glass cloth would be. So when I laid the cloth in place, the epoxy soaked into the cloth and there was still enough epoxy left to bond to the styrofoam cores.
BTW- I like to use some dry pigment to dye the epoxy. I use red, and when mixed it looks red. But when applied and then squeegeed thin, the thin layer looks pinkish. That is very useful for seeing where the epoxy has been applied and how much epoxy since the pinker it looks the more epoxy is there.
I will attach a photo showing a wingskin for a very special Cuda wing (reinforced and built for a flap to be cut out), after the epoxy, fiberglass cloth ,and thin .003” graphite spar had been prepared and was ready for the skin to be applied to the wing core. You may take note that on the root side at the left, the pink is darker, partly at the very root, then for about 1/2” along the first 6” of the leading edge, and for about 1.25” of the trailing edge for the first 6”. The pink is darker because that is where I added fiberglass cloth. The stock Cuda did not need that, but since I modified the wing for a flap to be cut out of it, the rest of the wing in that area had to be strengthened. On the core side, the other wing skin had already been applied (same exact layup) , plus a balsa insert I shaped and added to the core, where the flap would be cut out and hinged. Actually in that pic you can barely make out about a 1/16” gap between the facing trailing edges of the wing skins, where masking tape was used for “hinging” the skins along the trailing edges to keep them aligned.
I built the Sweet Vee wing to fly on, at most, a G12 reload (The Cuda wing above was built only to hold up to an E6). And the Sweet Vee flies so well on an F13 reload that a person might be pleased with “just” an F13 most of the time rather than a G12.
If a person wants to fly it on a motor with a lot more thrust, just place the kit under the left front wheel of your car, and drive forward three feet. It will save a lot of time and money in the long run to just do that instead. R/C Rocket Gliders are typically NOT built to boost super-fast. I have heard of some people getting away with lying the Strato-Blaster/Centurian on things like an E28, and the Phoenix R/C R/G was actually purposefully over-built to hold up to a G40, but the Sweet Vee is not designed for that, nor should it be (if someone wants a super-hot boost, then beef up a Strato-Blaster or get a Phoenix).
Think of the Sweet Vee as a GLIDER that happens to get into the air on rocket power. Not a ROCKET that glides down.
OK, couple of other things. The kit’s mechanical V-tail mixer design is nice in an engineering sense, but operationally it did not work smoothly enough. You could move the stick for elevator up, then let it return to center, then move the stick down, then to center, but the center would not be at the same exact place. It was biased towards the direction it returned from. Also, this bird needs noseweight and the mount for the servos did not put them as far forward as they could have been. So, I junked the mechanical mixer, and built a custom cradle to hold the two servos side by side as far forward as possible, and used the transmitter’s electronic mixing for the V-tail.
Also, the bare 1/32” music wire was a bit troubling to me. If the model lasts even a few months, music wire pushrods will oxidize. Especially the portions exposed to exhaust gases on boost. And those narrow slits cut into the boom (for the pushrods to slide thru) would then cause the music wire rods to bind somewhat. So, I replaced the music wire pushrods. I used Sullivan’s flexible cable pushrods, with the yellow sleeves that are between 1/16” and 3/32” diameter, with .030” wire cable pushrods. I had to cut out those slits in the boom not only to make them wider, but somewhat longer so the angle thru the boom would be shallow. The pushrod sleeves need to be set up to be very gradual wherever they curve, so that the pushrod cable can slide thru VERY smoothly. Otherwise, there will be the same problem with biased centering as I described for the mechanical mixer.
Try to keep the V-tail lightweight. Every excessive gram you add to the tail will require at least 2 grams, maybe 3 grams, of weight in the nose to balance it out.
For the wing finish, to keep it light, I just gave it a light coat of clear dope.
For the radio gear, put the receiver and battery pack as far forward as possible.
For the CG, try using the forward-most location, at 3”, when a burned out 32mm reload casing is in it. So that will be the glide CG. This means when loaded with a G12, the 32mm reload will cause the CG to be more to the back, but since he engine mount is not TOO far back from the wing CG, this will not be as excessive of a change as happens with models that have the engine farther back, especially in the tail (this was a big problem with the Astro-Blaster, and somewhat of a problem for my SkyDart 2X).
The issue with the CG being aft on boost is that the model will be very sensitive in pitch during boost. At least until a lot of the propellant has been burned off. But again the Sweet Vee engine mount is not too far back, so there is not a huge amount of shift. But there is enough of a shift for me to suggest to trim it for the glide CG to be a little more forward, at the 3” range they mention, as opposed to having the glide CG more to the back, which would then make the boost sensitivity worse.
For flying it on a 24mm motor, I would only recommend the E12 RC reload. Nothing bigger than that, nothing with more thrust than that. If you fly it on something with more thrust and the wing shreds, well, I already have warned about this with suggesting driving over the unbuilt kit with a car to save time and $. At some point a big enough engine will make the model boost fast enough to shred that wing. And with a 32mm casing to enable the use of an F13 or G12 reload, there is no sense in using more thrust than that.
The E6 thrust level is too low for the Sweet Vee mass. And I have something to say farther down about flying on Black Powder D or E engines.
One thing for sure. Never fly it on black powder motors. It was originally designed for the Estes “E15”, which turned out to have a high cato rate and was withdrawn, later re-introduced as the lower-thrust E9. Engine catos would often shoot the propellant grain up inside of the model, burning up the wing, the fuselage, AND the radio gear. Well, a person could risk it by making a 24mm adapter to fit into the 32mm reload casing, so if the black powder engine catos, the 32mm casing would contain the fireball. That is what I do when I make first flights with D and E sized models, using a C6 engine, where I mount the C6 inside of a 24mm RC casing just in case.
The Sweet Vee, on a G12, will boost about as high as high performance FAI S8E models do on an E6 (like the Cuda, Stingray, and modern-day FAI models). There is no need to go for more than that. And I will say that if I put “just” an E12 into an FAI S8E model that was designed for an E6, that the wing would shred on boost.
Below - Ed LaCroix boosting a Sweet Vee using an E12 reload. And a larger image of the Cuda Wingskin layup.
- George Gassaway