X jet scratch build
 

Another scratch build commenced a few months back. I'll put up a few pics as the build progresses for those interested in this kind of stuff.

It is a sport jet loosely styled after some of the mid 50's X jets. It gives me an opportunity to build a circular cross section fuse which I've wanted to do for some time.

90" oal
30# target weight (I never make my targets, but maybe this time)
1330 sq in
35# turbine

RE: X jet scratch build
 

The fuse was fabricated using molded balsa shells with glass and c/f both sides to form a composite structure. I did a thread with a bit of detailed discussion on the composites forum. I'll post few pics here as well.

http://www.rcuniverse.com/forum/m_7123475/tm.htm

RE: X jet scratch build
 

Shells were glued up over a temporary form.

RE: X jet scratch build
 

The fin and turtle deck structure carries load, so it is also a composite structure, but formed differently than the fuselage shells.

RE: X jet scratch build
 

Bob and www.flyingfoam.com supplied the foam cores. Excellent work as usual. Had to prop the cores against the fuse and make jet noises.

RE: X jet scratch build
 

Very Nice!!!I would sure like to get my hands on one.:D
Steve

RE: X jet scratch build
 

Template for hot wire work; 2 lb/cu ft foam core prepped for sheeting.

RE: X jet scratch build
 

Looks fast :D

RE: X jet scratch build
 

1/8" balsa sheet; various c/f from acp and cst; quarter ton of bricks; wing panels out of the shucks.

RE: X jet scratch build
 

Bob, I have a couple questions. Is there a reason you put your balsa sheeting in the pattern that you did? I have always followed from the leading edge straight back, and you did one piece that way and the rest perpendicular to the fuse. Is there some free strength for weight gained there?

I have always cut back on the foam 3/8 both sides and installed 3/8 balsa edges for hinges. Is there an advantage to the balsa blocks you preinstalled in the foam? I assume there is cause you did it...

You put in balsa for your conrol horn, what type of horn are you going with? I have always been scared to use balsa and have been putting 1/4 5 ply for that.

Are you using carbon tissue over the gear well? My latest wings I put unidirectional carbon there and it did not work like I thought it would when I tested it :D I'm thinking of going with Kevlar there, for no other reason than I have tried pretty much everything else, and I have a lot of it here.

Looks awesome as always!

RE: X jet scratch build
 

Bob, see you put all these cool photos on here, now you're getting all these questions !
I don't see anything in the foam for a wing joiner or plug in wings. Am I missing it?

Love the build!

Jim

RE: X jet scratch build
 

Great job as usual, congrats! this technique for rounded fuselages looks excellent.. need to try it for a unusual scale jet one day of this!


Enrique

RE: X jet scratch build
 

Rob2
You are a craftsman without a doubt, full credit to you.
Paul[sm=thumbs_up.gif]

RE: X jet scratch build
 

Bob,

That's amazing. It looks like 200++++++++++++++++++mph just sittin' there.

RE: X jet scratch build
 

Hey Sean, the answer to all your questions is this: artistic license. :) Seriously though, I like to have the sheeting grain aligned with both the leading edge and the trailing edge. The ailerons and flaps should have more torsional and bending rigidity if the grain is aligned with the trailing edge, but your method obviously works quite well. The blocks for the hinges provide a bit a more surface for the epoxy to grab (I use the large dubro flat hinges), but it may be overkill. As for the horns, I make my own out of G10 which then get glued into a deep slot in the block. I use either 3.5 or 5.7 oz c/f cloth above the wheel wells - works well. See you at the field.

Jim, it will be a one piece wing - I know, arghh. There will be c/f reinforced spar joiners and glass and c/f over the wing joint. Access to the turbine will be through the wing saddle area.

Steve, SJN, Jim, Enrique, Paul, and Gary - thanks for the kind words.

RE: X jet scratch build
 

Stab similar construction to wing.

RE: X jet scratch build
 

Trailing edge stock fabricated with hardwood rear edge.

RE: X jet scratch build
 

Tested G10 control horn tear out strength in solid balsa block. Pulled 80 pounds force without failure. Equivalent to 700+ in oz torque at servo.

RE: X jet scratch build
 

Time to sand. Jet air filtration unit is mounted on a castered stand. Can be moved near the work and catches the majority of balsa dust.

RE: X jet scratch build
 

Leading and trailing edges sanded. Now ready for surgery.

RE: X jet scratch build
 

Elevators, flaps, and ailerons are sawn free on band saw. Blocks for hinges visible on cut surface.

RE: X jet scratch build
 

Nice work, Bob!

I have always arranged the sheeting as you did........For the same reasons. Additionally, it takes less wood to do the sheeting. Again, very nice, well thought out work.

Tailwinds,


John

RE: X jet scratch build
 

Two things Bob, last year I started using 10 dollar Box fans with 3to 5 dollar HVAC 20x 20 filters on the back of them. Homemade "Jet air filtration" at very low cost. Set it up just as you did with yours, close to the work, picks up A LOT!

PS, yes, you can use it in your home as well!

I love love love the fish hook test on the control horn!

RE: X jet scratch build
 

Hi Bob,

Your project is looking great!!
Question for you. In post #7 what kind of hot wire bow are you using for the hole cutouts with a top and bottom template? I've been using just a wire between two handles for quick insertion into the holes.

Thanks,
Greg

RE: X jet scratch build
 

another question Bob,

your photo shows Hysol E20-HP, is that the quicker "v-poxy" style glue?

Kirk