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Dec 04, 2012, 09:32 PM
dougmontgomery's Avatar

Fuse layups and tests

Thanks for everyones help, that has helped me get to where I am at today.

Now that i have two real layups in my new fuse trying to get weights down. I am looking for some ideas about AUW weights and Fuses.

With the weights guys are coming in at, 38 to 44 grams. Does this include the Horizontal riser?

Once a riser is glued on if it is separate, what does beginning and ending weight ?

also, how much weight is it taking in the nose to balance these other gliders once all the gear and wing is installed? I want to add strength weight in fabric and not nose weight.

I have Made two fuses, #1 came in at 65g out of the mold and was rock solid 20g overweight.

#2 came In 55g with a different layup configuration using 1.7 Kevlar 0-90 full length inner, 3.7 uni to front wing bolt with a 14" 3.7 doubler at saddle area, and two layers of 3 ounce in the nose.

#3.....soon to come-
Waiting on some 4.1 HM,
I will use .75FG as a inner binder-

and should be lighter then the 3.7uni and the 1.7 kevlar as # 2 used
Last edited by dougmontgomery; Dec 05, 2012 at 04:59 PM.
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Dec 04, 2012, 10:00 PM
Just fly it!
wyowindworks's Avatar
Hey, Doug. My weights were without the stab mount/pylon/riser. My riser weighed around 1 gram without screws.
Dec 05, 2012, 09:15 AM
Father of Fr3aK, DLG Pilot
tom43004's Avatar

Worry about finished weight AND where the CG of the fuse alone is. I can make survivable fuses at 37g but they need more noseweight. Rather than dump in lead I've settled on two extra 1.7 kevlar layers up front that bring the weight to 42g or so but move the CG an inch forward. My normal fuses are around 42-44 with canopy and tail mount (1.2g with screws typical.)
Dec 05, 2012, 01:27 PM
Registered User
If you can get between 45-50 grams with the riser I would say your doing great. I think its ridiculous to strive for fuses under 40 grams not to mention crazy expensive. IMHO
Dec 05, 2012, 02:37 PM
Registered User
My lightest with hardpoints and screws, with hatch, and a tailboom perhaps 2.5" too long, was around 41.5g (from memory). This is without a tail mount. Trimmed to the length I'd use it, with tail mount added, it would be less than this. I can make lighter but not while keeping it very beefy, not without fabric changes (such as spread tow carbon which you are already using - coming in next batch).

Assuming somewhere around 1g for a horizontal stab mount would be about right. Some are lighter, some are probably heavier, but that sounds about right. I like my mount which is lighter and easy to make, but it requires testing to refine the layup. The usual sort of mounts don't need the testing and aren't so finicky of layup.

Places I shaved weight as I made more fuselages were (1) lighter screws - an easy savings (2) a fair bit less epoxy, but this did require adding a little fabric as less epoxy -> thinner layup -> less stiff (3) minor refinements of what materials I added where.

Getting less epoxy in the final product didn't require a change in how I processed, except for not closing the mold tightly for the first 15 minutes. My mold seals too well around the parting plane and it wouldn't let epoxy out!

If you are not using a very low viscosity epoxy such as MGS, you owe it to yourself to give it a try. It will make a difference as as wetout is easier so less epoxy goes in to start with, and the excess epoxy evacuates easier.

When I lay my fuselages up, I wet the mold, add fabric (dry), try to wet it out from the bottom, then add more on top to finish the job and for the next layer. This minimizes trapped air in the layup so it is stronger - but it is also a touch heavier. Air is lighter than epoxy.

I think I've published my tailboom strength test a few times. Wearing leather gloves, hold the fuselage in the saddle area, on its side (most DLG fuselages are designed to be stiffer and stronger horizontally). Hang a freeweight off the end of the boom. If it holds 5# without complaint (no creaking, cracking noises) then it might be usable. If it holds 7 1/2#, then it is probably just fine. I don't think it needs to hold more than 10# and probably not even that much. If it will, then reduce the fabric! Freeweights are available in 2 1/2# increments as small plates. That makes a convenient test - they even have a hole in the middle.

Dec 05, 2012, 04:57 PM
dougmontgomery's Avatar
I am using slow cure mgs, molds heated to 105 degrees and cured 24 hours under heat. i did leave them hand tightened for 30 minutes. then tightened.

I am making a riser mold today so I can try some polyester foam inserts that will go in the riser on top of the harpoint splooge, If I can use 1g of the polyester foam I will have a weight savings..

My riser mold for the polyester foam will be undersized for the thickness of the of the skins, I will pour 4 of these at a time for consistency.

will post some pictures and results as I get further along.

Tom, GT what are the lengths of your fuses?

Dec 05, 2012, 05:05 PM
Father of Fr3aK, DLG Pilot
tom43004's Avatar
About 40" but gets trimmed back about an inch
Dec 05, 2012, 08:15 PM
Composites guy
Doug- are you bleeding any resin out with the internal bladder? Where does it go?

Is there any internal peel ply?

Looks like nice molds.
Dec 05, 2012, 08:51 PM
dougmontgomery's Avatar
Originally Posted by sarmoby
Doug- are you bleeding any resin out with the internal bladder? Where does it go?

Is there any internal peel ply?

Looks like nice molds.
The mold is not fully closed when the bladder is inflated, it comes out the parting line. No peel ply..
Dec 05, 2012, 09:36 PM
dougmontgomery's Avatar
Ok so I seen Adams fuse tonight, it was a economy fuse 1005 or so marked 44.5 grams. The fuse was amazing- I see how you sold so many, nice work- just what I would expect from a professional.

I guess we cannot compare fuse to fuse and try to match weights of current fuses, all of them are different in diameter and different lengths.

Dec 05, 2012, 11:21 PM
Aurora Builder

For starters, I would fly anything under 50g as a prototype. 55g would probably be OK, especially with the stab mount integrated. Personally I will no longer build out a ship unless the fuselage is under 45g, otherwise it indicates the tailboom is too heavy (too much material typcially). I have an UL fuselage from Adam that weighs 38.5g w/o stab mount. I have an xxlite fuselage that weighs 38g w/ the stab mount, but it is a few inches shorter than a typical fuselage. The lightest fuselage I've seen was 32g (one off an not production) and survived very hard launches. Stobel fuselages are typically in the 36-40g range. In general however I agree with Tom that 40-43g fuselages are good weights with extra reinforcements forward rather than adding dead weight post build.

I don't see anything wrong with your shape as far as being overly large, but it is hard to say without other photos and side by side shots with other fuselages. The reality is all DLG fuselages are compared against each other and the highest strength to weight ratio wins, no matter the shape. That being said, a 45-50g fuselage with room for 4 servos in the pod will still come out at a great overall auw. Its also good to keep price in check, using HM is nice but you must have the quality to match.
Dec 05, 2012, 11:52 PM
Composites guy
Think about resin flow vs. Pressure.
If you want to get the resin out with pressure, you have to have a path for it.

P(resin) = P(atm) where flow stops.
P(bladder)= P(pneumatic pressure)

Assume resin pressure in the mold=P(bladder)

Now think of how FAR the resin will flow under pressure.

The mold line gap is your vent but as the resin advances, the flow distance is reduced.

Drip a drop of pigment on the farthest distance from the vent and asee how far it goes.
Dec 06, 2012, 12:12 AM
dougmontgomery's Avatar
In 1 hours times I get about .250 of epoxy that is outside the mold. Though I have mixed approx. 25 grams for the entire fuse. I have not weighed that material to see how much has pushed out.

My current one piece fuse Fuse I am flying is 48g. I am good with that and I looking as that as my goal.

I will not be able to make 40-44 due to these facts:

1. the circumference behind canopy at LE of Wing is 1.15 wide x 1.55 tall

2. behind my wing is 1" tall and .975 wide.

3. The aft end is .500 wide x .400 tall.

4. also the nose is 9.75" long.

to offset these weights and part of the 9.75" Nose design, My wing is also has a 7.75" Chord.

The design was so there would not be nose weight added, with the length I could use slightly smaller tail surfaces which I have been using for 3 years now without issues.

and...... I love to build.

Dec 06, 2012, 01:33 AM
Registered User
41 1/4", but for my designs I'd typically remove at least two inches.

Dec 06, 2012, 03:27 AM
Certifiable User
killercando's Avatar
Doug - Don't despair. I think you can shave some weight off. The one I have been dong is even hurkier and I have settled on a weight of 48 grams. I don't know how much lightwiegt molding experience you have but it took me at least 6 or 8 of these before I started getting the hang of it.

I think your mold is so perfect that it may seal to well, even just finger tight. Try tightening down on a feeler gauge for resin evacuation. Somethng like .050", just so the resin can move easily and the fabric will stay.

My layup is 5.7 oz twill, 3.7 oz uni laminate for the boom. 4 layers 1.7 kevlar in the nose alternating 45* - 0/90* . I have been using about 40 grams of resin research and there is a large amount pushed out.

Who made that lifetime mold for you? It is awsome


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