EJF Composite A-10 Construction

[Arthur Knowles]

Hoser,

I cut down an aluminum landing gear to 1 1/4" wide so it fits in the saddle area. But I see from your pictures that the motor mount has specific dimensions. If so, what are the correct dimensions and angle? Or was it just guessing for the length and angle for attachment?

Art

[hoser]

Arthur I did not use the ABS covers and built my own out of scrap.

I recommend the flaperons for the heavier set ups 3/8" max down on the ailerons and mix with 1/8' up elevator

the HS-81 are fine for the wing, I have a ton of pics I wrote the composite manual

GOOD LUCK !!!

[hoser]

the motor mount on mine was a suggestion to Robert at EJF and was not part of the kit so it will not look like yours, i just cut up some alum gear i found at the hobby store

thrust angle should be the parallel to wing, you can glue the motor mount, I used nylon screws an put a ply piece in the fuse so I could remove the nacelles if needed.

this kit is very flexible so go with what looks good to you

[Arthur Knowles]

Hoser,

Well I had planned to go with the aluminum motor mount and plywood in the fuse. I wanted to make it removable for maintence. I'll have to fudge around a bit then and figure out the overall width and angle on the mount to get it set right.

I've got the wing frammed up with the balsa spar and LE. Tomorrow I'll add the trailing edge. Then some carbon fiber and finally the wing sheeting. After that I'll glass it and cut out the airlerons. Of course, before I put the wing sheeting on I need to cut holes for servos, retracts, wires, tubes and install the framework for the servos and retracts. I suspect that'll take as long as it takes to build the entire wing. Wish I had a router! Guess my flex shaft dremel will have to do.

At least cutting the wing was easy. I got to use my new Sears bandsaw. Makes it very easy to cut wood or foam. Almost too easy.

While I was waiting for glue to dry, I decided to work on making some LiPoly assembly tabs for a 4S pack. I used a Radio Shack circuit board kit and made some boards with copper pads to assemble the pack. The circuit board is slotted so I can just slide the tabs of the cells into them and solder. I need to make 6 of them for a 4S6P pack. If I get a chance tomorrow I'll post a pick of the wing assembly and pads.

[Arthur Knowles]

Well I sheeted the top of the wing panels last night and today. Just to make it easier to work on and more ding resistant. Tomorrow I'll cut out the slots for servos, retracts, and plumbing and sheet the bottom.

In regard to sheeting. The kit came with 1/16" sheeting but the plans stated use 1/32. So, I bought some 1/32" wood to sheet the wings. Instead of following the plans (I did, but wouldn't next time) and sheet over the leading edge, I suggest you leave a small lip on the LE and sheet up to it. It'll be much easier than trying to bend 1/32" wood over a tight curve. Even in the foam beds.

[Arthur Knowles]

Here's a pic of the assembled 4S6P battery (14.8 v nominal @ 7200 mah) with a 8 cell 3000 NiMH pack next to it for size comparision.

Note: I still need to wire it up for parallel output and add connectors.

[Arthur Knowles]

Side View

[Ed Waldrep]

Arthur, I've never really looked at the plans for this kit as I don't own it but on all the foam wings I've ever done I've had a leading edge piece of balsa glue to the wing. It butts up to the sheeting on both top and bottom, and is shaped into the leading edge shape after attachment. On my scratchbuilt A-10 I used foam core wings sheeted with 1/32" balsa and after I trimmed that flush with the leading edge of the core (which was about 1/4" tall not counting the sheeting), I glued on the the leading edge "cap". After it dried I shaped it to the proper airfoil shape. You could use leading edge pre shaped balsa but that stuff rarely matches up to what you are doing.

I guess the EJF kit doesn't use a leading edge piece from what you are saying but that doesn't sound very ding resistant. Maybe they did it for lightness, but the first time you bump it on a table or a door jamb you'll get a dent. Maybe it is fine like it is, there's more than one way to skin a cat as they say (although why would you want to skin a cat...can't be too tasty).

[Herb]

I think you need a hard balsa leading edge for durability and strength...

I am curious to hear how many Amps and Watts you are pulling full throttle out of you Lion cells. I suppose you need about 400 Watts to fly the A-10 decently.

[Ed Waldrep]

My A-10 which is similar in size to this one (45" span) is pulling about 400 watts in the Kyosho nacelles and the performance is quite satisfying. I'm at 4 lb 2 oz so I'm at around 100 watts/lb which isn't super high for EDFs but it scoots quite nicely, 100 foot loops are no problem. I'm probably pulling about 43 amps off of a peaked battery, the one time I put on the wattmeter the battery had been sitting a few days. I'm using 10 x 2600 NiMH so I'm a bit fat ("I'm not Fat, I'm BIG BONED"...Eric Cartman from Southpark).

[hoser]

I use a pre-shaped trailing edge and a square leading edge that I installed AFTER sheeting the wing, I cut it with a straight edge and then epoxied the leading edge and carved out smooth and filled any gaps with light wood filler.

BTW congrats Ed i did not know you went flying allready !!! my plane is 4.25 pound and my watts are 420 the plane could easily handle 1 more cell and increase permormance so im thinkin of 13 faup 1950's since i only pull 35A on 12 cells

[Arthur Knowles]

The leading edge on the wing is a balsa block shaped before sheeting. If I were to do it again, I'd either add the balsa block after sheeting, or line it up behind the balsa LE.

As for the watts, well Motocalc predicts 44 amps at 11.8 volts (under load), but that's assuming the LiPoly cells have a .015 IR as the Thunder Tiger packs do. That's just a guess. The 4S6P pack is rated at 14.8 volts nominal (more like 15~16 with no load) and good for a max of 44 amps at 6C. I may add one or two more 4S packs and make a 4S8P. That would be good up to about 60 amps.

At it's current configuration (estimated weight) I'm looking at 130 watts per pound in and about a 30 oz/in wing loading. For a total of 520 watts. It should fly well if I can keep it within this range.

[Herb]

Originally posted by Arthur Knowles
... and good for a max of 44 amps at 6C. I may add one or two more 4S packs and make a 4S8P. That would be good up to about 60 amps....

Sorry I thought you had already tried out this setup. How many flights can you get out of the Lions at 6C? Just curious.

[Arthur Knowles]

Originally posted by Herb
How many flights can you get out of the Lions at 6C? Just curious.

Good question. The ET cells are LiPoly not LiOn and are rated at a max draw of 7C. The Aircraft World info pack (http://www.aircraft-world.com/prod_d...ets/lipoly.htm) states:

4C – The rate for highest capacity and very long life
5C – The "standard" rate at which most are using E-Tec cells
6C – The peak rate for aerobatic models using throttle management
7C - A possibility for models like ducted-fan jets - using some throttle management
.
.
.
Although many users are reporting excellent results at higher peak rates, to maximize the capacity of the pack 6C is the target to shoot for when calculating peak discharge currents in high-powered models, or 5C for longer flights.

So, I'm basing my calculations on 6C and do expect to use throttle management to lower the average rate to 5C. Although, according to Motocalc, my current power systems falls in the 5C rating at full thottle at the maximum airspeed. It's only 6C at takeoff/stalled.

I'm hoping to get long life out of these cells. At least a season of flight at a minimum. I spent about $350 on the pack. If I need to, I will increase the pack size to a 4S8P for a max amp draw of 57 amps @6C and 67 amps @7C. Of course, I can't tell if I'll need the exttra cells until after I perform some preflight testing with my wattmeter.

[Arthur Knowles]

Well, I routed out the foam 3/32 for the plywood mounting plate for the retracts. But creating the 1.25 x 1 x 3/8 hardwood for the main retract installation was a major pain. I used my bandsaw to cut the wood, but it has a tendency to creep toward one side when it cuts. I built a rip fence from some Sears parts for a scrool saw and that works really well, but still the bandsaw creeps when it cuts. I'm not sure why. Doesn't matter how slow I go or anything.

I finally created the pieces I needed by cutting oversize and sanding the excess using my new Sears sander ($88 on sale). So, now I'm ready for the assembly and mounting. Before I do, I wondered about the best way to mount the plywood to the foam to prevent it from ripping out on a rough landing.

My initial plan is to pin the 1.25 x 1 x 3/8 landing gear blocks to the 1.5 x 3 x 1/8 (I think that's the plan size, but could be off) plywood. I'll still epoxy the gear blocks, but thought pinning it with 1/8 wood dowels would make a stiffer & stronger join. But what about gluing the plywood to the foam?

Should I just glue it with epoxy? Or should I also pin in with the 1/8 dowel. I've got plenty of down and adding 4~6 pins should make it a stronger join. But maybe there are downsides I haven't thought about.

So, what do you suggest?

Art

PS: Do remember that I fly off of a dirt field. It's not the smoothest field either.