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Old Aug 28, 2012, 09:27 PM
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Comet JN4 Jenny Rubber FF----> Micro R/C conversion


So, after successfully building and flying my first micro R/C plane (The Finch- plans found on another site), I feel that I have the expertise to convert a rubber powered free flight Jenny to R/C.

I chose the Comet JN4 Jenny- plans located in the Old-timers forum. https://www.rcgroups.com/forums/show...1265873&page=2

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I have the plans ready.

I think I should be able to keep it around 1.5oz (45g).
I scavenged the radio equipment from a ParkZone P51. I will be using my Spectrum DX 6i as the transmitter.
Does anyone have any input as to whether or not the motor from the P51 and a 170mm x 30mm prop would be enough power for a 23" 1.5oz aircraft? Would a 200-250mAh LiPO make it feasible?

I will try to keep my posts limited to the modifications I made to the plans/model.

1st step... wings
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Old Aug 28, 2012, 09:40 PM
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wing time


I cut about 1/2 of the ribs from 1/32 balsa and the remainders from 1/16 balsa. I cut some lightening holes in most of them, but left the truly structural ones solid.

You will find a number of instances where I use medical equipment for hobby purposes... and the lightening holes are the first. I used a 4mm biopsy punch to make the holes. The punch is on the front of the cutting mat. Next time you are at your family physician, ask him/her if you can have one. I currently have them from 2-6mm. They dull fairly quickly, but can be sharpened easily by turning them between a folded sheet of 320grit sandpaper.

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Old Aug 28, 2012, 09:56 PM
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Upper wings


Note: There is no printwood for this plan, so I made copies of the common rib and cut them accordingly.

Modifications: The leading edge measures out at 5/32. I decided to use a 1/8 x 1/8 balsa L.E. with a 1/32 lamination on the top of it. I made the dihedral 1/2" at 6" from the center section. I made a 1/32 plywood dihedral brace and laminated it to the front of the main spar which is 1/16 x 1/8. Again, more lightening holes in the T.E. using a 5mm biopsy punch. I also added a number of gussets to the structure.

I sanded the whole assembled wing using another medical device: I have tongue depressors with various grades of sandpaper glued to them so I don't tear apart my work with my fat, not-so-nible fingers. (pictures of the framed wing to come later)
Old Aug 29, 2012, 12:25 AM
caymin last is offline
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So broke I can't pay attention
Very interesting build, will keep an eye on this one.
Old Aug 29, 2012, 01:02 AM
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Quote:
Originally Posted by ckimmey View Post
I think I should be able to keep it around 1.5oz (45g).
Does anyone have any input as to whether or not the motor from the P51 and a 170mm x 30mm prop would be enough power for a 23" 1.5oz aircraft? Would a 200-250mAh LiPO make it feasible?
P51 on a 45 gram AUW plane should work. I have a scratch built weighing 53 g with 55 sq-in wing and it flys (slow and nothing spectacular). Usually use a 180 mah battery.
Old Aug 29, 2012, 08:52 AM
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I built one of these kits up as a kid using rubber power. Flew great and lasted longer than most of my balsa tissue builds.

I use the P-51 motor and AR6400 on Dumas Walnut kits that are 17 1/2 inch WS. They fly at 1/2 throttle very nicely with full throttle getting them out of trouble. The larger Jenny should work out fine with this setup for scale like flight.

If you are taking guts out of a previously used UM you may want to look into a brand new motor. There are people using replacement brushed motors that have more power than the stock P-51 or 4-Site motors.
Old Aug 29, 2012, 09:52 AM
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Lower wing


Thanks for the advice on motors. I think my used P51 motor is going to end up in a trainer for my kids and wife.

Now, on to the lower wings.

Modifications: Similar to the upper wings, but I am adding ailerons to the lower wing. To accomplish this I started with a 3/32 square T.E and a split 3/32 thick T.E extension. I cut a chamfer in the 2 pieces of T.E. in order to accept a 1/16 copper tube (carbon fiber would work too) that will hold the aileron torque rods.

I am going to have to take a couple of days off from the workshop to catch up on work (that I get paid for), and to maintain the integrity of my marriage.
Old Aug 29, 2012, 11:06 AM
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if your getting a new motor, go brushless. an ap-05 on one cell will be close to stock p51 brushed. if you go with the gws 5043 or gws 5030 props will give you more static thrust.

looking great, i am wanting to see how this turns out, im doing the same thing with a 13 inch tiger moth...
Old Aug 29, 2012, 11:54 AM
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Great start! Looking forward to more.

From all the medical supplies you're using, appears you're a real life Flight Surgeon?

Quote:
Originally Posted by ckimmey View Post
I cut a chamfer in the 2 pieces of T.E. in order to accept a 1/16 copper tube
Sounds heavy! Considering your "large" wingspan being pushed by the micro motor, I'd be cheating to keep things as light as possible (like reducing the number of ribs). The Mustang motor with a good 180mah (or the 190mah Miniaviation) battery will give you scale-like performance - nothing prettier than a biplane slowly flying by in the early morning sun.

Quote:
I am going to have to take a couple of days off from the workshop ... to maintain the integrity of my marriage.
Smart move! (don't ask)

Gene K
Old Aug 29, 2012, 12:02 PM
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Speedy,

I considered CF tube, but didn't want to spend an hour in the car to go get some. The copper was less than 1g total. A good vigorous sanding prior to installing gave it a little bite for the CA glue and took off a few mg's.

Not FAA certified as flight surgeon yet.

Thanks for the tips. I am trying to go for a more scale look in flight. I will be making a trip to the hobby shop this weekend to look at BL motors and ESC's that will work with the spectrum micro rx.
Old Aug 29, 2012, 12:05 PM
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B.Eng.


Quote:
Originally Posted by ckimmey View Post
I cut about 1/2 of the ribs from 1/32 balsa and the remainders from 1/16 balsa. I cut some lightening holes in most of them, but left the truly structural ones solid.............Attachment 5117010
An approach I just tried is promising. I have a plane planned and want to build it using "stick and tissue" methods, but I want to use foam for the ribs. I also want to cover the plane with RAMicrolite, but the foam will not withstand the 400 degrees F that the RA needs to adhere and shrink. So this approach percolated up in my mind: Face the rib outline with strips of 1/16 balsa (of course, I narrowed the thickness of the rib). Then I found that by keeping the iron moving, the RA adhered to the balsa without deforming the Depron underneath. This is the approach I intend to use on my 13" Vought V-173 "Flying Pancake" this Fall.

I like the idea of the biopsy punches, but for about a buck you can get a single hole paper punch at $-type stores, or for upwards of $2 at Staples. For a little more, Staples also has a deluxe model with rubber grips and HydroTurbomatic transmission, Of course I'm kidding - it's manual!!! The cheaps ones cut clean holes, no splitting, no crunch, but they are fixed at 1/4" (6 mm). When they get dull, toss it out, or give it to a deserving soul and get a new one.
Old Aug 29, 2012, 12:08 PM
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Originally Posted by 356Jim View Post
I like the idea of the biopsy punches, but for about a buck you can get a single hole paper punch ....
You can also use various diameter brass tubes sharpened/resharpened with a Dremel.

Gene K
Old Aug 29, 2012, 02:48 PM
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I have built three of them with varying degrees of success.

Most used 1/32 lite weight balsa. My latest I used Bob Selmen foam wings. I am waiting for the gym season in OCT. to try this one. Most of mine weighed around 34 grams or so.

I tried ailerons but not effective. I now have only RET system with a AR6400 receiver and a P-51 motor, prop and gear box and a eflite 150 MAH battery.

My JN-4 is not scale I lengtened the nose 1/4 inch shortened the tail 1/8 inch. Now it balances with out weight in the nose. The foam wings are 3. 5 wide and the the plans I used call for 3 inch wide wings. I made templates from the plans and all 1/32 lite contest balsa and Homefly micro lite mylar.

If you want I can post a video of the my faux Jenny.

I would like to get another copy of the comet JN-4 in pdf format of the plans as my were lost in a computer crash.

John F. Clarke
Old Aug 29, 2012, 03:43 PM
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I would like to get another copy of the comet JN-4 in pdf format of the plans as my were lost in a computer crash.
How about these, John?

Gene K
Old Aug 29, 2012, 03:55 PM
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Excellant Those are the original plans I got from the same souce before.

Thsank you.

John F. Clarke


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