Curiosity: How Light is your Cub?

Your proposed model sounds just right for a .40 four-stroke/.25 two-stroke.

I flew the old M.E.N. Trainer 20 for a while in the early Eighties. It was first powered by a Fox .19 R/C engine that went through connecting rods like I go through popcorn. It was the old plain bearing version. It had plenty of power and would even R.O.G. I then switched to a Super Tigre G20/15, just for kicks. Had to hand launch it then, but once airborne it flew just fine. Replaced that engine with a direct bolt-in ST G21/23. Oddly enough, it flew identically to the ST G20/15. No improvement whatsoever.

Used to fly an original kit built Falcon 56 with a Fox .25. Later went to an OS .35 so it would take off without a hand launch. I liked the .35 much better, even though it was throttled back to just a couple of clicks above idle most of the time while flying.

One of the most fun models I've ever flown with a .28 - .32 sized engine was the Florio Stunt Wagon. Yeah, you could raise hell with it, but you could also throttle back and relax with it (750 square inches of wing area @ 4 lbs.). Put the surfaces on low rate and you could teach a newbie how to fly with it - 4" chord ailerons and all. An amazingly fun model to fly for just about any occasion. It wouldn't have been too difficult to do it up in

1930's blue and yellow color scheme and the big round Army Air Corps insignias on the wing, just to give it a legitimate scalish look.

Now you have me thinking of building another Stunt Wagon. I really miss that model. It would fit whatever mood I was in when I finally arrived at the field. It would do outstanding maneuvers low to the ground, or you could shoot touch and goes all day long using just throttle and rudder for control, once trimmed. I think I have one of those kits downstairs. Pardon me while I go rummaging...

Ed Cregger

plenty of 5 footers flying on 150W or less. About 2cc or a 0.15 in old money.

5lb would need at most 250W at teh right prop to fly well..that's about a .20

I don't do gassers but thats where an opverpropped 30-36 4 cycle would seem to be perfect.

If I were to go up in displacement it would be so I could swing a larger prop -- scale size would be 12 or 13", while the engine I have 'wants' a

10x4 or 9x5, and may not have the oomph if I sacrificed some power to the Big Propeller Gods.

Or I may go electric -- it's just that I keep winning these gallons of fuel at the club raffle, and a .25 doesn't use much, particularly since I don't fly a whole bunch.

That's the link to the Terrier, from the RCM plans catalog, 58" span,

550 sq. in., .25 engine. That's pretty close to what you're talking about, except your aspect ratio will be higher.

I built a couple of Terriers a few years ago and sold one to a friend. He powered his with an OS 40 LA, and I put a 40 Surpass on mine. Performance was very good, with decent vertical and good speed. Also low speed performance was excellent.

I would expect a .25 to do the trick for a plane this size, but you would have to choose the right propeller for the desired performance. Essentially you would have to drive around in first gear and sacrifice high speed performance, because the plane wouldn't be capable of going fast anyway, unless you put a 40 on it. Try a .25 and a 10x4 to start with.

Tim Wescott wrote:

I had a 7' old timer ("Ol' Reliable") that weighed in at just under 4 lb (wet) with about 6 sq ft of wing area. It had an OS .25FP, which is about as wimpy as .25s get, and the problem was *landing* - I had the idle a little high, and the thing would just putter along in ground effect for the whole length of the field. If there wasn't a headwind, I usually had to shut off the engine to get it to land.

It would do these beautiful hands-off takeoffs at about 1/3 throttle - I'd set 1/3 throttle, put the tx down, let go of the tail . . . I sure miss that plane.

Anyway, if you build it light, aren't looking for aerobatics, and build it light, a .25 should be fine, as long as the plane is light.

- Mark

P.S. build it light. For example, if it's 3 channels, a 'standard' radio with 3 std servos, 500 mah nicad, switch, and big rx will weigh about 10 oz. A small rx (say, a Berg or Spektrum) with 3 HS81s, small switch, and a NiMH battery will weigh under 5 oz. That's 1/3 of a pound savings right there.

Tim- I have a 71" SIG 1/6 Cub with about 225 flights on a OS FS26 4-stroke.

lbs with silk & dope covering (about same weight as Monokote), GWS mini servos (about 1/2oz lighter than standard servos), standard Futaba rcvr & battery. Flies great, even on floats! Most flying is at 1/2 throttle, but I use full throttle for takeoff & getting out of binds. I'd like to try an OS FS20, but the 20 is not as tall and I'd have to cut the cowl some to clear the exhaust - and I don't think the FS20 would be a good choice for floats.

If I were to use a 2-stroke, I'd go with a .20 or mild .25. I'd save a .40

2-stroke for the FJ-3, the fighter version of the Cub.

-Dave

WHAT????

"fighter version of the Cub"!!!!!!!!!!!!

I almost choked on my coffee over this one.

Dave Plumpe wrote: (top posting fixed)

The OS-Max (pre- LA, FP, QX, whatever) is definitely a mild engine. It's just a plain-bearing loop-scavanged, cast-iron in steel sport engine.

So I think I'm set.

FJ-3 -- I like that. I've seen a few of them. When you have to sheet the wings against flutter, then you know the engine's too big...