Big Bird

[ghost civic]

I know a 6' wingspan plane isn't really that big, but it is much better than anything I have flown or built.

I still have a long way to go on this build, but thus far it is looking achievable.

It has a 6'x6'' pink foam KFM step, and will have 6'x12'' DTFB bottom step.

The tail is 18x8

total fuse length is 55'' and it is 6'' tall.

I threw some extra pieces of pink foam, a few servos and weighed it. I estimate that AUW will be around 1600-1800g. The motor/prop should provide 1450g of thrust with the 3s lipo (4500mah)

the bottom and top of the plane will be DTFB.

Once I have the tail done and the top partly skinned, I will finalize the placement of the wing. Currently, I cannot be sure where the CG will work out, and I don't want to be too far off even tho the battery will give me a decent amount of adjustment.

The top will have a open cockpit look added to it. I bought one larger servo for the elevator, but will use regular 9g servos for the ailerons and rudder.

Im thinking of painting it red/white. Once it is fully built, I will shave and sand down the corners of the fuse as much as I can. It wont look scale by any means, but it should at least have a decent shape when in the air.



Here are some current mockup pics.

 

[ghost civic]

progress is being halted due to DT being out off foam board.

But I have re-thought my design a bit. Thinking of going with the wing on top now. Also considering using exceed rock crawler wheels...should move nicely over grass.

 

[rcspaceflight]

It looks a lot better with the wings on top. With the fuselage not being very tall, I doubt it would make too much of a difference with how to flies. I mean it would fly differently, but probably not too much.

 

[ghost civic]

yeh, gonna go with wing on top. does look a bit better and should make it a tad more stable.

 

[ghost civic]

the dollar tree had foam board in stock today.

got the DTFB added to the pink foam for the wing. Makes it a lot easier to visualize the finished product.

biggest issue racking my brain is where the CG will most likely be. I was thinking id have the leading edge of the wing around 15'' from the nose...thus hoping the CG to be about 18''. But im a bit worried that the 4500mah 3s, motor and 2.2 sized rock crawler wheels may add enough weight to the front that the wing should be a bit more forward. I have the LE of the wing about 1' from the nose in these pics.

Im wondering if I should try and mount the landing gear and tail, and then try to find the balancing point of just the fuse and then place the wing accordingly.

also, I have yet to decide what I want to use for a wing spar. normal wooden dowels ive seen don't come 72'' long.

 

[rcspaceflight]

It would be best to mount everything to the plane except the wings and mount the wings accordingly. Install the battery you're using, but not as far forward as possible. Even though it's a great idea to have the plane balance without the battery, mounting the battery in front of the wings but still giving your self room to adjust, should push the wings as far forward as possible which would give you the best performance and best looks (I think).

For the spar you don't actually need it to be as long as the wings. Even Peter in the flying sled episode said that his spar only went a few inches into each wing. Most spars are that way. Maybe even glue in a thick spar for the center part and then glue thinner spars on the wing tips. (All three spars glued to each other, of course.)

 

[ghost civic]

so a 40'' spar may be good enough then.
I was a bit surprised how stiff it was when put together. the foam board stiffened up the pink foam more than I had thought it would.
I think I will wait on the wing until the fuse is at least 95% done. I think I will have to wait on the battery tray...as I don't want to have it in the wrong place for the best CG.
I also kinda felt like the wing further forward looked better. And I would prefer the battery to be mounted in the front, rather than under the wing. Even my 13 year old daughter is excited about this build, she has said more than once that she thinks it will look really awesome if it flies.
I am thinking I will cover the whole wing in tape. This will add a fair bit of weight, but I want it to be durable and tape should stiffen it up as well.

 

[rcspaceflight]

For how simple it is, it actually is a great looking plane. Some times the simple looking planes look the best.

If you're not going for acrobatics, I think the general rule is that you should be able to lift the plane up by the center of each wing. Most planes can't handle being picked up by the wing tips, but always by the center of each wing. Once it's built you should be able to test the rigidity of the wings by having some one help you pick up the plane by the wings. Start near the fuselage and slowly work your way out to see when it starts flexing too much. If that point is past the center, you should be good to go. Or if you're really worried mock up some weight on the wings and do the same thing now just to be sure.

 

[rcspaceflight]

Oh, I had a question about the landing gear. In the pictures it's directly on the fuselage. Is that how it's going to be? Or are you adding a bracket to get the wheels lower? I think using a flexible bracket would be best. It would keep the prop away from the ground and add some bounce to cushion your landings. Right now it looks like the nose would dig into the ground a lot on take offs and landings.

 

[ghost civic]

currently im thinking I will place another 1'' thick piece of pink foam (4''x4'' square) and then a thin piece of wood to mount the axle to. In those pics it does place the nose a bit low, but I think in order to put the CG where I want, the landing gear will have to be moved back...and this will place the nose higher. Even if I pivot the fuse on the landing gear so that the fuse is level, the prop is still about 2'' off the ground.
I should make a flexible bracket as you suggest...but every time ive tried with smaller craft if failed. (either too flimsy or crocked) Maybe I can come up with a simple suspension design that would allow the axle to move up/down an inch. I would hate for a rough landing to crack the fuse because the force goes right through the whole thing.

FT's recent vid of a gasser plane they got has a similarly simple shape to it.

 

[rcspaceflight]

Even store bought fiber glass landing gear mounts are flexible. You want something rigid and doesn't really flex, but can flex without breaking.