0-320 in a J3?

[westwind]

I have a friend whom is interested in going experimental with his J3. He has been toying with the idea of going to an 0-320 160hp, borer, pa-18 tail feathers, flaps, no electrics, wing tanks etc ....
has this ever been done before?
no doubt it would be an extensive project.........
Jerry Burr and Wayne Mackey I'm sure you would have some insight....
I know it is a bit of a loaded question but I am curious as to the logistics of it, and also what might end up weighing?

regards
Jory

 

[Fabman]

I built the exact Cub you just described, in 1992. It had metal spars and it weighed less than 1000 lbs. PM me if you have any ?'s

 

[JimC]

Be sure to beef the tail up. Even an O-200 shakes the J3 tail pretty hard.
JimC

 

[JimC]

BTW, since you are going experimental, ECI is making an O-340 stroker kit for some model O-320's, that takes them up to to 340 c.i. Using the stock 7.2:1 low compression piston gives them a 9.25:1 compression ratio and approximately 173 hp (ECI's hp estimate is a bit higher than that).
JimC

 

[Longwinglover]

Jory,

I think there are a number of Cubs like you describe being used in banner towing on the east coast. I'd look for operators around Myrtle Beach, SC and Ft Lauderdale, FL to see about operator input.

John Scott

 

[cubunltd]

Be careful taking a certified airplane into the experimental catergory. It may impose some flight restrictions on your aircraft. Since it's not a homebuilt, you 'll be placed in Demo flights or exhibition only. I would check with your local FSDO.

John

 

[citabrickr]

Be careful taking a certified airplane into the experimental catergory. It may impose some flight restrictions on your aircraft. Since it's not a homebuilt, you 'll be placed in Demo flights or exhibition only. I would check with your local FSDO.

John

He's in Canada.

 

[cubunltd]

OOPs, sorry about that.

John

 

[irishfield]

Nothing to be sorry about at all... it won't be legal at all shortly.. if not already in Canada, thanks to TC appeasing the FAA in the last little while over their "fear" of people flying "no longer certified" aircraft into the USA. If you buddy hasn't already registered his intent to build with MD-RA.. then he'd better get it in pretty fast... as the proposal is that ANY X-certified part will not be allowed to count towards the 51% assessment.

 

[Iherling]

o-320 in a j 3

i had a clipped wing j3 with an o-320 for about 15 yrs. had taylorcraft wings and I competed in sportsman. it was an awesome plane a rocketship to be exact. a few things to consider:
1. beef up the front of the fuselage where the engine mount attaches. i put a few extra tubes and gussets in each corner. the torque twisted the fuse a bit and at a rebuild i beefed it up. also i added some tubes toward the rear of the fuse. as another responder noted the rear of j3 fuse is not super strong at the best of times. i swung an aymar demuth wooden prop and it was great. I used a bc specialties lightweight starter and built a battery box toward the rear of the fuse. I probably can round up some pix of these mods if you are serious. if you do not add a battery in the rear, you will need to add around 20# of weight in the tail when you add all of the weight up front so you may as well add useful weight.
regards
Irvin

 

[JimC]

Note that adding engine weight up front and a battery or ballast weight in the tail will substantially change the spin characteristics due to the increase in moment of inertia about the spin axis. You may have to incorporate a PA18 tail for spin recovery.
JimC

 

[Lippy]

Iherling- We’re in the process of building a certified 150 hp J-3. We “repaired” the fuselage with very little left from the old fuselage. I don’t recall what the original piece is, but I do know there is an old piece in there someplace. It is now “nearly” all 4130. Would it be at all possible to get some pictures of where you strengthened the fuselage? Being a certified aircraft there are a multitude of hoops to jump through, but we’re making headway.

If you have any pictures, they would be much appreciated. Our email is:

jacksonaircraft@clearwire.net

My other J-3 is a light stock C-90-8. With the extra weight of the 150, will it still beat a light 90 off the ground… realistically?

Thanks Much,

Lippy

 

[westwind]

good stuff guys.........

thnx

 

[JimC]

Lippy, if it has a better takeoff power to weight ratio, it will. I note in passing that a stock PA18 with a 150 or 160 does not have a better takeoff power to weight ratio than an O-200 powered J3.
JimC

 

[T.J.]

Jim, not looking for a fight.....just wonder what figures you used for comparison of power/weight ratio?

 

[JimC]

>ust wonder what figures you used for comparison of power/weight ratio?<

A reasonable question. You'd use (Thrust hp)/Weight

For the 18, that would be its horspower at climb rpm (considering density altitude) multiplied by its prop efficiency at that rpm and density altitude, divided by the weight.

And the same for the J3, using the J3's relevant numbers. The highest number will win. We've run an O-200 powered J3 against a 150 hp 18 with VG's and a 160 hp 18 without. All three were carrying light payloads. The J3 got off about 110 feet shorter than either and was already about 25 feet in the air when the 18's lifted off.

JimC

 

[bob turner]

Remember that guy who said that no self-respecting Super Cub pilot would use more than 75 feet for takeoff?

Seriously, it is probably your prop combinations. A stock 160 Borer with one pilot at sea level ought to get airborne at 200 feet routinely. If you are doing 75 foot takeoff rolls, I need to find a 39" pitch prop. My 42" prop J-3 takes every foot of 200 to get off the ground. Unless the "surf's up"!

 

[JimC]

Bob, the 18's were getting off in about 190 to 220 feet. The J3 (with a 165 pound pilot -- I weigh 214) was getting off in 75 to 80 feet. Grass field elevation 310 feet, temperature about 60 degrees, and wind about 8 knots Did the 150 VG 18 one day, the 160 nonVG 18 another, and the J3 both days. 80+110=190 feet, the short end of what the 18's were doing, and the long end of what the J3 was requiring. Neither 18 was running a borer and the J3 was running a 7142. You oughta watch the J3 get off with the 7535, climbing out at about 2800 to 2850 rpm and 55 mph.
JimC

 

[JimC]

Bob, to be fair, on the crappy end of the performance spectrum -- with me on board (214 pounds), grass, no wind, 100 degrees, 310' elevation, with the 7142 prop, the J3 takes about 185 feet to get off. It'll get off about 30 feet shorter for me with the 7535. Since its AOA limited during the takeoff roll and initial liftoff, VG's, 3" extended gear, and a 6" tailwheel instead of an 8" would help a lot. Maybe someday.....
JimC

P.S. This was not using a maximum takeoff technique. It was just firewalliing the throttle with the brakes locked, release the brakes, and let the tailwheel remain on the ground with the mains lifting off first. For a maximum takeoff, I would firewall against the brakes, blow the tail off the ground with down elevator, release the brakes, add more down elevator to keep the tail up as the plane starts to accelerate, then let the tail settle back to the ground as the plane accelerates, touching the tail again as the mains lift off.

 

[Nathan K. Hammond]

Back to O-320's in J-3's...... The banner Cubs came to town this weekend for the race and 2 of the 3 were O-320 J-3's. They were obviously stripped down, but had a balanced tail, wing tanks (12gal, 18gal or a combination of the two) and a long fat prop. No flaps, but they did have 'gurney flaps.' If you need, I'll PM the N-numbers and data-plate info.

nkh

 

[Lippy]

NKH- If you could send the info that would be great. jacksonaircraft@clearwire.net

Does anybody have any pictures of a completed version with O-320? Any thoughts as to where the “beef up” would go for tubing? We’re headed down to talk with the feds in a few weeks and would like to have piles of paper worked up by our engineer relatively soon.

Thanks for your help in advance…

Lippy

 

[Nathan K. Hammond]

Lippy, on it's way plus a bunch of pics.

nkh

 

[Lippy]

You da MAN! Thanks amigo…

Lippy

 

[bob turner]

Jim - our numbers agree. I usually run a 49" pitch prop, but after reading your results put a 72CK 42 on there. RPM is up by 50 to 2250 on climbout, and I agree - 190' on a no-wind day with fuel and me. Get me 15 knots, and I am off in 65 feet!

I out-climb the Super Cubs in angle, but they are in the next county while I am still flying in one spot.

 

[JimC]

With the 1B90 7142, I climb out at about 2650, so am turning about 400 rpm more in climb. I agree about the SuperCubs. They also do a heckuva lot better with big payloads. Ain't nuthin in life perfect.