New boost glider idea

[sj_h1]

I am always looking for some new material to work with. I saw these old file folders and just had to do something with it. So... here goes. Feel free to chime in with suggestions. First I though I would like to maximize the wing area and use the fold in the folder as a leading edge. You will notice I cut off one corner to allow a spar to go through.

 

[sj_h1]

I cut another folder identical to the first. I used painters tape to put the model to together so to allow me to change things up til I get to the final design and put the to wings together and inserted a 3/8 X 1/4 basswood spar. You will notice the spare still sticks out the back at this point because I have not decided how much spar I need at the nose for the power pod. In fact, I haven't if I will use a pop pod or just permanently mount the engine pod and just eject the motor casing. I'll trim the spar later when I decide.

 

[sj_h1]

I used a couple staples to hold the wings to the spar for now a trebled up the nose spar for about 6". That actually looks right to I cut the rear spar flush with the end of the wing.

 

[AstronMike]

I once looked at those manila file folders thinking the same exact thing you are currently doing, as in making a larger deltoid glider, thinking that material was light. Well, another look and a scale told me otherwise.

I originally intended to try to get away with one ply but it is very flimsy indeed and when I looked at the overall weight of TWO plies....it is heavier than ReadiBoard!! Plus, I still did not like its overall feel. Yea, being able to use that folded edge seemed good but the scale doesnt lie.

You also mentioned about possibly just mounting a forward motor tube and ejecting the motor, ala Astron Falcon style. Since your glider seems kind of large for that, coupled with the two plied heavier stuff, I would think that you will not get enough of a CG shift for boost with an 18mm motor, especially once the propellant burns out and it coasts. Obviously, the farther forward you can mount the fixed pod the better, but then you start looking at spar flexion as well as increasing the odds that longer body spar will break if it glides into something or even warps a bit over time (a definite no no).

Besides the delta you are already showing, what other surfaces are you looking at here? And what overall size? Darn, if I had access to a camera I would post several dozen shots of what Im sitting on that you guys dont see or hear about.

As light as Readiboard is you might be able to make a good popmotor job nice and easy as long as you size the main delta wing right. Obviously, I dont recommend this for standard convies since it usually has warpage inherently in it. Still, theres this 40" span Transwing type Im fixing to slap together.....

 

[sj_h1]

The span is 14.5" tip to tip. The overall length 21.5". Readiboard? Is that the stuff that has foam in the middle and and something like card stock on the on the outside?

 

[AstronMike]

The span is 14.5" tip to tip. The overall length 21.5". Readiboard? Is that the stuff that has foam in the middle and and something like card stock on the on the outside?

Readiboard is a cheap but very light variant of foamboard, like you would see in Staples or Walmart. Looks the same, sort of feels the same, but is WAY lighter. Just yesterday I got five more sheets and weighed one. 4.0z for a 20x30 sheet comes out to 150in sq per ounce, which is very good indeed.

You can find this stuff at Dollar Tree and no place else. Try to get the sheets compressed together in the back of the box as these have less inherent warpage. Even a warpy loose sheet isnt bad if you then use that side to side warpage for elliptical dihedral. Just make sure if you get one of these that the warpage is roughly equal on each side.

Great stuff if you are used to it, and at $1/sheet its unmatchable.

 

[sj_h1]

I'll look for it. In the mean time, I think I'll continue my experiment.

 

[sj_h1]

Now I will need a rudder so I'll cut out a 4" square from what left over from the folder material. Fold the material diagonally and cut 1/2" on the fold to make glue tabs.

 

[sj_h1]

Now lets apply the rudder.

 

[sj_h1]

Ok, I hand tossed this a few times and believe it or not it was nose heavy. 1st time that has happen to me. I added some weight to the back to balance it out. It took the 1st few crashes pretty well, much better than I hoped. It wants to turn to the side so I am thinking that maybe I need to bend up the last 2" from the wing tips for some dihedral. I am also thinking of replacing the basswood spar with balsa to lighten up the nose. Anybody got any other ideas?

 

[AstronMike]

If that is as flat as it looks in your last picture, then it does need more dihedral. You should be able to bend this in easily.

What are you using to control pitch trim on this? I dont see elevons nor any canard......are you just going to try to trim and glide a straight up delta without any of that? That is darn nigh difficult at best, and even if you think you have it trimmed it may not act it in midair, especially if it is moving rapidly nose down at ejection. Or even if the wind affects it badly if you had it trimmed to do well with calm.

You might be able to very slightly bend the trailing edges up a very limited amount, just barely enough to see, and this may get you a repeatable glide. Of course, this can affect boost, since you would need a more forward CG to offset this.

Either way, keep posting your progress on this. Always gotta try and learn something along the way....

 

[sj_h1]

If that is as flat as it looks in your last picture, then it does need more dihedral. You should be able to bend this in easily.

What are you using to control pitch trim on this? I dont see elevons nor any canard......are you just going to try to trim and glide a straight up delta without any of that? That is darn nigh difficult at best, and even if you think you have it trimmed it may not act it in midair, especially if it is moving rapidly nose down at ejection. Or even if the wind affects it badly if you had it trimmed to do well with calm.

You might be able to very slightly bend the trailing edges up a very limited amount, just barely enough to see, and this may get you a repeatable glide. Of course, this can affect boost, since you would need a more forward CG to offset this.

Either way, keep posting your progress on this. Always gotta try and learn something along the way....

I was thinking cutting a slight trim tab and just bend it up slighty. Do you think I should do a full length of the trailing edge about 1/4" or maybe just a inch either side about a 1/2 ". Your thoughts?

 

[powderburner]

You might want to look into model-airplane-type construction.

Leading edge made from 1/4 thick x 1/2 or 3/4 wide dense balsa, well rounded on front edge, 1/4 inch wide ribs & spars, 1/4 thick x 1 inch wide trailing edge (most of that 1 inch tapered down to a thin edge), covered with monocote/supercote/whatevercote on both upper and lower sides. One good solid spruce spar across the middle might be needed.

This type of construction has worked well for model airplane guys for a long time, and is one of the most practical while still giving decent flight performance.

 

[AstronMike]

I was thinking cutting a slight trim tab and just bend it up slighty. Do you think I should do a full length of the trailing edge about 1/4" or maybe just a inch either side about a 1/2 ". Your thoughts?

Since you have a 14.5" span, I would say make the tabs/elevonettes about 1.5" wide and a half inch deep. You should not deflect these up more than 1/8" if you can help it. You want just enough to induce a consistent glide.

I am also reckoning that you are going with a front motor convie poppod instead of a fixed unit. That is best for this, and dont worry if you have to add some nose weight to the pod when done for a solid boost CG.