blackbaron

My Feedback: (92)

I have never owned anything larger than a 40 class RC Airplanes before and I just bought a 60/90 class ARF. I picke up a Great Planes 1/4 Scale Spacewalker ARF and a brand new O.S. 91 Surpass II 4-stroke engine. This seemed to be the most recommended engine on this board so I bought it. My question is, what size prop should I use to break-in the engine and make my first initial flight with? Next, what would you recommend for aerobatics? And lastly, what would work best for scale flying?

Thanks Guys.

swooper

I'm flying that airplane and a Surpass .91 (no pump) with the APC 14x8 turning about 9000 rpm. We're at 6300 ft., though.
The engine idles low, pulls hard, and never misses or sputters...at all. Don't know where you are, but I'd prop it to stay below 10,000 rpm. I'm not an engine expert, though!

Break it in with O.S.'s recommended prop and keep plenty of juice squirting out the exhaust for a couple of tanks. Gradually lean it and don't be in a hurry, run a few tanks on the ground. You'll be rewarded with a slow, reliable idle and steady response.

I like the loop size. Mostly fly around 5/8-3/4 throttle, trying to go just fast enough to make nice shaped patterns while keeping the scale-like slow impression. With the Spacewalker's slow roll rate and general smooth stability, it's easy to keep it looking more like a real aircraft and less like a bug flitting around. With the muffler inside the cowl, it's nice and quiet, too. One of the quietest models at our field.

Nice choice, BTW, on both airplane and engine.

kqutob

I have the same (GP SW / OS 91 pump) . With this combination your best friend is the 14x6. This is the only prop that allows the Spacewalker to fly and handle the way it should (like a cadillac). No other prop with a different pitch will give you those smooth easy landings.
The only other choice you can try once you perfect those landings is a wood 15x6.
For aerobatics I dont think the .91 will be much help no matter what prop you use because of the size & the wingspan of the SW which I dont think was built for aerobatics. But I do know that many of the guys out there are using 1.20s 1.50s and even 1.80s . It will be interesting to hear what those engines do to the spacewalker.

blackbaron

My Feedback: (92)

Thanks for the info:

The engine manual does not state what size prop to use during break-in. Does it matter? If not I will just use a 14 x 6 prop that you guys suggested. Someone also suggested a 13 X 8 prop too.

carrellh

Ann-Marie Cross posted in one of the usenet groups that the best prop, based on much testing, for the .91 is a 14x6. She wrote that many overprop their four strokes and that the .91 should be propped to turn about 9500 rpm on the ground.

swooper

My I respectfully disagree? I love flying Cuban 8's, inside and outside loops, and all the other loop-and-roll combinations. Mine's very easy to fly inverted and I like making a half-dozen inverted figure 8 passes around the field before slowly rolling back upright. The .91 pulls mine through nice, big, slow, smooth reverse Cuban 8's with plenty of time to complete each manuever. Given our 15-20 percent loss of power and lift compared to sea level, I think the .91 would be enough for scale-like flying although I don't know how much inverted performance the full-scale Spacewalker is capable of. Any more engine would ruin the scale-like qualities but still not transform it into an Extra. Within the Spacewalker's scale-like flight envelope, it provides graceful and flowing aerobatics that are a real pleasure.

Some observations:
1. Mine had the wing at a high positive incidence as assembled out of the box, about 3 degrees positive relative to the stablizer. (The wing's leading edge was high.) It wasn't pleasant to fly like this with the c.g. at recommendation. I filed the notch in the fuselage former that the leading edge keys into to drop the leading edge about 3/16-inch. This put the wing at about 1 degree positive incidence and made the plane fly better.
2. With the .91 Surpass engine you'll probably need nose ballast if you mount the servos in the provided tray. For our altitiude I wanted to keep the plane as light as possible so the servos went as far forward as possible. If you're down near sea level, though, don't sweat a half-pound of nose ballast, the plane will easily carry it and might even handle wind better.
3. The nylon wing mounting bolt anchor blocks failed early (along with the wheel pant mounting pieces) and were replaced with oak. Keep an eye on the wing anchors, a failure there would make a real mess.
4. I think some aileron differential improves the shape of rolls and helps the plane turn cleaner. Mine's now at nearly 2:1 up aileron:down aileron.
Best wishes with this lovely airplane! I've put my order in for the Sig 1/3 scale Spacewalker for next winter's build!

waagbuck

My Feedback: (1)

Good suggestions. I made no modifications to my gp spacewalker and it flies beautifully. I have an os 91 four stroke with a 14 x 6 master airscrew prop.

kqutob

Swooper
Thanks for the valuable info. I'm going to try the aileron differential on my next flight and see how it feels.
You got me worried about the wing mounting bolt anchor blocks and you're not the first to warn me.
What precautions or modification do you suggest ?

Richard L.

My Feedback: (24)

Well, mine happily swings a Graupner 13.5x8 at 9600 rpm on the ground:



Granted this prop is a faster prop than a 14x6 (I prefer speed). A 14x6 prop should also work well for your application.

Speaking of smooth easy landing on a prop other than a 14x6: [link]http://whitetyphoon.com/rc/kyosho_corsair/landing.mpg[/link]

swooper

Hi kqutob,
I should have given more information. The nylon wing bolt anchors on mine broke on the first landing, which was a nose-over into the snow. I was flying off snow with skis, so it was a cold day. The impact into the snow wasn't bad, but bad enough to break the cowl bottom and break the wing anchors. The plastic anchors were more like shattered into lots of small pieces instead of one big simple break, it looked maybe like bad plastic. Once again, the cold may have had an effect.

Anyway, I made new blocks of oak, epoxied them to the fuselage sides, and drilled them for the screws provided to attach the plastic anchors. Then they were drilled and tapped for the wing mounting bolts in the usual fashion. This was at least 4 years ago and no more problems.

That's my experience. This ARF has been around long enough that if the anchors were a problem, it would be general knowledge by now. So, I'm not claiming they are faulty, just a potential weak spot that will definitely destroy the airplane if they fail in the air. Even if they work fine for 99 percent of their owners, it's about the weakest wing anchor design I've ever seen.

Harry Lagman

I'm getting good results with an APC 13x10 on my .91 S2-P. I'd recommend this if you need a little more speed than a 14x6 will yield. Mine's pulling 9,400 rpm on the ground with this prop.