EJF Composite A-10 Construction

[Arthur Knowles]

Hi all,

Since I could not find one when I searched previously, I thought I'd start a new construction thread. Assuming someone else is going to want to build the Electric Jet Factory Composite A-10 kit.

In any case, mine arrived today. Kit contents include:

Composite Fuse
Composite Nacelles
Foam Wings (wire cut)
Balsa Spar, LE, and TE
3/16" Balsa Tail
1/32 Balsa Wing Skins
CD with instructions/pictures

Componets I will be adding:

2 Mega 16/15/3
2 Wemotec 480 mini fans
24 ET-1200 LiPoly batteries in a 4S6P pack
3 gear EJF Retracts
Robart Retract Kit (pump, tubing, air tank, fittings, etc.)
Hitec Electron Rx
4 Hitec/RCD HS-81 servos
Servo rods
Wing/Motor mounting bolts
Triangular stock
1/8" plywood
Carbon fiber
1"~1 1/4" Aluminum landing gear (used for mounting motors)

Art

[Arthur Knowles]

Fuse, Nacelles, and Wings

[Arthur Knowles]

Tail Section & Wing Skins

[Arthur Knowles]

I'm still working through the instruction manual. The instructions are 13 pages, and not for novices (i.e., not a series of step by step instructions). There are no printed plans. You can print the manual, but the primary plan sheet is too large to fit on a 8.5" x 11" page. If you scale it to fit, you can't read the text. Luckily for me, I have a plotter in my office so I was able to print the plans in a readable size (36" wide, so I had to scale them down a bit, but still it's much better). You can review the image files using a JPEG editor at 100% size and read the text or view the detailed images on the plans if you don't have access to a plotter/large format printer.

I do have a couple of questions for the more experianced out there:

1) I've never worked with foam wings before. The instruction state to use 3M77 spray for the wing skins. If I recall, this spray has changed and is no longer foam friendly. So, if I go this route, what should I use?

2) The instructions also suggest that instead of wing skins, I could just glass the exterior. What do you think? I am planning to paint the aircraft.

3) The plans show a balsa spar and a plywood diheidral brace, but no plywood was found in the kit. No triangular stock for retracts, carbon fiber for bottom of wing, wing/motor hold down bolts, etc. Is this a case of just using your own materials?

4) The wing shows a balsa spar 2" from the leading edge. Do I cut the wing at this point and insert the spar between the two wing pieces? Or do I carve the wing out to fit the spar?

5) The tail is composed of 3/16 balsa. Has anyone considered rebuilding the tail out of 3/16 stick? Or hollowed out the existing pieces?

I'm sure I'll have more questions as I go, but this seems like a good enough start.

Thanks for any help you can give me...

Art

[JANSSENM]

"1) I've never worked with foam wings before. The instruction state to use 3M77 spray for the wing skins. If I recall, this spray has changed and is no longer foam friendly. So, if I go this route, what should I use?"

I use the new 3M77 with the foam core for my EJF F18. It work out fine, you just have to spray it lightly on the cores and sheeting.

I notice that EJF kit is not so complete. you have to use your own stuff if you already have them or buy what you need. sorry I can't help you more. I never got to finish my A-10. I give it to my brother.

jans

[Herb]

I won my EJF A-10 inc fans & motors at a raffle . The wing on mine was weak. Too weak. I would suggest you have a nice good sized spar, reinforce the wing joints, skin the wings with balsa & probond or epoxy, and glass the whole thing with 3/4 oz ultralight glass cloth, reinforcing the joints. If you do a careful job it will add very little weight. The glass will provide you with a smooth final surface ready for primiing.

Picture of mine from three years ago, twin edf 400 units, loudest edf ever

http://aeneas.ps.uci.edu/edf/a10/a-10_mine_4.jpg

[RickG]

"1) I've never worked with foam wings before. The instruction state to use 3M77 spray for the wing skins. If I recall, this spray has changed and is no longer foam friendly. So, if I go this route, what should I use?"

Count me among those who've had less than satisfactory results fron 3M-77. I just tried ProBond and am impressed with the results. You need very little of it though, and because of the way it penetrates into the smallest spaces, you can skip pre-joining the wing skins. Just tape them together as if you planned to glue them. Works great.

[Arthur Knowles]

OK, well I have started to work on the composite parts. Sanding off the mold lines and in general just cleaning it up a bit. I've also purchased 5 meters of 3/4 oz cloth and some carbon fiber for the wings. While I was at Hobby People, I picked up some 1/8" plywood and a couple of different maple engine beams for the retracts. Not sure if I'll use 1/4" or 3/8" sq. yet.

I've also printed and read the instructions for the all balsa A-10. That cleared up a few questions, but left a few as well.

I could not find any probond, but do have epoxy. I have some pacer finishing epoxy that I was going to use for the external cloth/epoxy when I glass the wing. The main question I have is shuld I use the 1/32" wood sheeting at all? I could do as the instructions suggest and just apply the cloth directly to the foam with carbon fiber reinforcement. If I use the wood, I need to attach it using epoxy as well. Or the 3m77/probond that I don't have. Any suggestions where to find probond locally?

[Jim Phelps]

Lowes, Home Depot or any good hardware store will have the Pro Bond. There are other brands as well, the original polyurthane is called Gorilla Glue. I just started using Pro Bond and it works great. I had been using 3M-77 and thought it was too, but the PU glue makes a much stiffer wing.

Jim Phelps

[bruce ryan]

Arthur,
Just happened on your question,
my opinion is that glassing over foam is very difficult to make a good looking wing. I would use the 32nd balsa and then a light glass cloth.
Although, My first choice for foam cored wings is 1/16 balsa and then .5 oz or .75 oz cloth just for the finishing aspects. There you could use epoxy or dope, though I read people like the water based poly coatings too. If you go this method you might feel more secure with a reinforced epoxy bandage over the wing joint.
good luck
Bruce

[Ed Waldrep]

My 45" scratch A-10 has 1/32 sheeting over foam cores....it's plenty thick enough. 1/16th would work but is kind of overkill for a model this size unless you use contest weight (3-6 lb/cu. foot) wood, and glassing the entire surface will add more strength.

[hoser]

Arthur sorry I did not get to respond earlier I was out of town visiting the Mouse.


1. sheeting the wing is pretty easy I used the 3m 77 spray as recommended on some of SIG manuals for their kits use a light spray on both surfaces let sit and get tacky and then bring both surfaces together, I have also used sheeting epoxy which is very watery (use sparingly though. use the model the foam came in to sandwich the hole think flat and smooth.

2. I recommend for the retract version trim the spar so you can glue to the top and bottom some 1/4" wide hardwood strips and create a sort of "I" beam. at the wing joints definitely use a 4" strip of glass after you epoxy the 3 piece wing together and if your neurotic like me after sheeting run two 1/4" wide carbon fiber strips on the bottom of the wind from tip to tip.

3. don't forget to make al of the holes for servo leads and pneumatics prior to gluing the wing together.

4. for finishing you could use the whole wing, or use silkspan ( for non gloss finish or even clear monokote and sand lightly to accept paint


5. for the spar carve out 1/4" of foam, I forgot and mine flies fine I just move the CG back 1/4"

6. the carbon fiber and other items are up to the builder to provide, they are only needed when making a high performance set up. same issue with the retracts, the basic kit is for fixed gear and stock 480bb motors

7. I don't think you would get too much savings from building up the tail section

hope these help

[hoser]

and this

[Arthur Knowles]

I stopped by Home Depot today and bought a small container of Probond. It's a wood glue with "real" wood fibers. Looks similar ro Elmers wood glue. Is this the right stuff? Or should I be looking for something else?

[Arthur Knowles]

Hoser,

Thanks for the input. I just purchased a 9" band saw from Sears (for $70) so cutting the wing is going to be easier than originally planned. So, I have the spar thing covered.

The retract installation though is a bit different. I have ABS covers for top and bottom for the wheel covers. If I understand why these ABS pieces are in the kit. I noticed the picture you have shows balsa covers for the retract area. Is this because you have the balsa kit, or because you choose to make balsa covers over the ABS ones?

In regard to the wing, I've decided to use two servos (HS-81s). One in each wing. I'm going to run an extension from the center to the outboard panels where the airleron (sp?) will be installed. I have to check the depth first to make sure it will fit properly. This is an option on the plans so I can also use flaperons for landing.

Art

PS: Today I am going to start on the wing section (cutting and fitting of parts).