Deadeye

OK, I got this sexy biplane for an Xmas gift, and have the tail feathers built, and the fuselage started. I have read that this plane builds tail heavy (an understatement by some), and needs to be lightened in the tail section; aka, get some junk outta the trunk! I hope to fly mine with a Saito 100 (Magnum 120 would be nice, but cannot come up with the cash right now). Can a guy cut two large rectangles out of the rear fuse to lighten it up a bit? Just remove the balsa rectangles on the fuse sheeting that the doublers have removed already? Would I compromise strength that way? Any other suggestions? I have read every thread I could find on the subject, but nobody has done what I have proposed, near as I can tell. Only other mods I have planned is to go with a Sullivan tail wheel. I look forward to a response. *cough* Minnflyer...

aerobatixkid

I know! I know!

Take a drill and go crazy on it. Worked for me.

LSP972

My Feedback: (13)

Check out www.micromark.com

They sell a "hole saw" set quite reasonably (less than ten bucks) that will cut neat holes up to 2", I believe, with any ordinary drill.

I'll be ordering that item myself; next up on my board is a Sig SkyBolt, and that one builds tali heavy as well. This hole saw set should be just the ticket for lightening the tail feathers and rear fuselage.

MinnFlyer

My Feedback: (4)

*Cough*

Funny you should ask, I recent'y gave my old Skybolt away in that "Pay it forward" thread, and I was thinking "If I ever got another one, what would I change?"

First, this thing does NOT build tail heavy - It builds heavy - period.

I think the people with the tailweight problem are probably putting those silly little 2-strokes in a plane that should obviously have a 4-stroke in it.

So, what would I do?

First, I think I'd open up the ribs. There's a lot of balsa there that is only there so GP could sell that Wing Jig of theirs.

Next, I would cut some holes in the side like you suggested, but not two big rectangles, rather, cut some triangular holes which will keep a lot of strength. Like I did with the UltraSport I'm currently lightening - see pic)

Another biggie I would do is to use thicker stock on the tail feathers and skip the sheeting.

I think those mods would help bring the weight down without compromising the structure.

One more thing: replace any sheeting that seems particularly heavy.

Deadeye

Thanks for the replies, guys. Minn, that looks good. I think I will put a new #11 on and go to work. I've got the rear half of the fuse glued already, but I should be able to do it OK. I've already sheeted the tail feathers, but they feel light as a feather. The sheeting was light, I think. I'll post some pics of my progress.

Deadeye

Hey guys, I started my lightening project and wanted to see what ya thought about what I have done so far. This is only my 3rd kit, but I have a few ARFS and a few of my own coroplast designs under my belt. I thought it could be used as a future tutorial, as I am willing to experiment with this build. I am open for suggestions, but please don't feel offended if I don't heed somebody's - in favor for- somebody else's advice. THE FOLLOWING PROCEDURE IS PERFORMED ASSUMING YOU HAVE ALREADY GLUED THE REAR HALF OF THE FUSE TOGETHER.

I got busy with the #11 exacto, a steel straight edge, a pencil, and a couple of sanding (180 -150 grit) tools I custom made from a small dowel, and a small thin (1/8) HARD piece of basswood. I started by poking T pins in from the opposite side, right at the point where the curves start in the inside of the fuse on the doublers. This was done to make marks on the OUTSIDE of the fuse. I was generous with my marks, making my 'lattice' plenty wide, like a 1/2 inch or so. I never went any further than the doublers on the inside. Therefore, the work is done inside the doubler's hole, and any cuts must be done in a fashion where you KEEP THE STRINGERS WIDE ENOUGH inside the hole you cut.

Pic #1: I Dremeled out the round corners, keeping in mind that the stringers have to be kept wide for future sanding.

The rest are just pics of different stages of sanding. You get the idea.

I use a precise digital scale, and the fuse weighed 8.9 oz at the before stage, and 8.1 at the end (nothing ahead of the REAR wing bolt is in place yet). I lost exactly 1/2 ounce with this mod so far, and I haven't decided what to do under the tail portion yet.

CafeenMan

You did nice work on the fuselage but that's too tedious for me. One thing you could have done is built a trusswork fuselage over the side view. Every GP kit I've seen had a lot of heavy wood in it. It's not just them. That's mostly why I scratch build because if I bought kits I would take the time to cut out new parts which makes it not a kit any more.

Deadeye

Some more, notice the clamps where I broke the dang stringers!!!! [:@] I reglued with Titebond, as that is all I am using on this build so far. It is soooo much easier to sand than CA!

I thought maybe 1/16th ply in the 'X' part would help strengthen things, but then I thought I would just screw myself on the weight. It seems strong when it stays glued together.

Deadeye

MMmmmm, tedious. I actually loved every minute I was doing it. I have a thing for retro fitting. Reverse engineering is also a favorite of mine. I can understand things better that way for some reason.

MinnFlyer

My Feedback: (4)

Looks outstanding Randy!

krossk

My Feedback: (27)

I'm reading this thread with great interest as I have just bought this kit for future construction.

Are there any concerns about the "truss" portion left after the lightening holes are cut spanning longer cross-grain distances?
I'm thinking about the case where the well-intended helper picks up the plane and applies pressure perpendicular to the "truss".
Wouldn't longer holes leaving trusses parallel to the grain produce a stronger structure? Something like this:

Deadeye

I am no expert by any means, but my 'X' truss is very strong, and retained the curvature of the fuselage.

robert4u

� have built a Skybolt a few years ago,and didn't found it to be tailheavy.
I use a OS 91 FX and set the CG with the battery on top of the main gear.
It came out at 9,5lb
So I don't see any reason to lighten it up as it flys really nice the way it is.
Then again you're doing a nice job and I'm curious what your final weight will be.

Robert

Deadeye

Well, I lightened the tail, with a total of a tad over 1/2 ounce, and am now open for suggestions. I thought about lightening the cockpit floor, between the dashboard and the former. It has a structure above it anyway. Maybe an oval shape? What about the fuse sides? Should I even mess with them or will that compromise the strength?

MinnFlyer

My Feedback: (4)

I wouldn't hesitate to do both of those cuts.

As you can see in the Ultrasport pics, I removed everything inside the doubler holes.

One word of caution, I wouldn't get too close to the nose... That nose has to bend around to form a curve, lightening holes too close to it can cause problems. So I would avoid any cutting forward of the lower wing saddle.

Deadeye

I've cut the cockpit floor, lost 1/3 ounce. I have drawn on the fuse for what I think I will do for my next cut. Do you think I'm still in the safe zone?

Deadeye

The only reason I ask, is that a fellow club member (with 20+ years experience) stopped by and said tot he effect that if I cut out more of the fuse, the tail may sanp off in a hard snap roll or the like. That scared the exacto right out of my hand.

MinnFlyer

My Feedback: (4)

No problem, here's what I would do:

krossk

My Feedback: (27)

"Virtual (en)Lightenment"
Man, you're good!

Deadeye

OK, Minn, I'm going for it. Once again, a picture is worth a thousand words. I will have to adjust the cuts a little bit to clear the wing bolt plates, and I will stay behind the front plate entirely. I'll weigh before and after.

I've begun on the bottom wing. I read where you mentioned eliminating some ribs. My LE and TE pieces are 'dato'ed to fit each rib. Was your kit like that, or did they start doing this after you bought yours, I wonder? Anyway, I would have to re-dato or just skip ribs if I were going that route, right? There does seem to be an overabudance of ribs for such a thin wing. I appreciate the time you have taken with me, Minn. Thanks a bunch!

krossk

My Feedback: (27)

Deadeye,
I think the suggestion was to remove some material from the center of the ribs - not to remove ribs from the wing entirely.

Deadeye

I see, I must have misunderstood. I just weighed all the ribs for 1/2 of the lower wing, and they totaled 1.5 ounces. I'm not sure if it's worth it or not. That's only 6 oz of ribs total. That includes the plywood ones.

CafeenMan

It doesn't count if the grain direction is wrong, which in this case it is. Still probably strong enough. I'd trust it.

Deadeye

I'm not sure I understand. How is the grain direction wrong? Could you please elaborate?

CafeenMan

The grain of the diagonals should go from corner to corner. If all he did was make cut-outs in the sides, then the grain goes front to back. That makes for weak diagonals. If he were to glue some sticks behind the diagonals it would strengthen it tremendously but also put much of the weight back.

In any case, the plane is probably going to be strong enough as it is and I would just leave it alone. I was just making a point about trusses and what makes them strong.