Building a sig 1/4 scale cub and have an o.s. 91 4 stroke engine laying around and was wondering how good it would fly this cub, anybody flying this combo?

As a matter of fact, I have flown something very similar...with a Saito 91 4 stroke. We ended up adding quite a bit of lead (12 or 14 oz if I remember...) to the firewall to compensate for the lighter engine. The cub flew just fine with that engine, although going up was not its' forte. I was able to do loops, hammerheads, wingovers, even inverted flight with that engine. But I have to be honest, it was not very exciting to fly. I swapped that engine and the ballast for a G-20Ei and it is much more energetic, and fun...
Normal power for these birds is a 120 4 stroke, or a G-23 / 26......but there is flexibility in both directions..

I would think a 120 four stroke would be about right for scale like flight. Maybe a 150 for a little more umph and peace of mind! The OS 91 would work if the airplane was built extremely light and would probably be pretty close to the 40 hp type power on the full scale version but it would be pushing it (comfort level) on the model IMHO.

Hi all
I Put a 120 four banger in my Sig Cub and if I was doing it again I would chose the 91.
If you like, a scale like flight the 120 is much more than necessary. On my aircraft, the throttle seldom goes past half, even on take off.
It is a J3 after all, so hauling all the extra weight around is pointless..... bert

I had a OS91fx then a OS120 twin in my 1/4 Cubs. For scale flight the 120 twin was a bit much but lots of fun. A 91 would fly it but then I don't think it would be quite as much fun. Its a great rudder plane!!

Carl

Hello! I just got back from the flying field with my 1/4 Cub. It is powered with a Saito 91 spinning an APC 15x4 prop. The plane weighs 13 3/4 LBS. ready to fly. As far as the comments on "scale power" goes........ The 91 is WAY more power than a full size Cub! I have about 34 hours in the full scale Cub. I am a Private Pilot. With the 91 it takes off in about 35 to 40 feet and climbs at about a 20 degree angle at a pretty decent speed. It does loops and rolls at half throttle. It also (much to everyones suprise at the field) does knife edge from one end of the field to the other without losing altitude! The knife attitude is at about a 45 degree angle. I have maximum throw on the rudder and quite a bit on everything else. Also the CG is at almost 5 inches back from the leading edge. I know you will not believe it but those are the facts. Some people at the field thought it was imoral to see a Cub do that! So, to anyone who does not think a 91 will power a 1/4 Scale Cub and do a good job at it...... you are dead wrong! I think it is the correct engine for the plane. This is a Balsa USA kit. ............... Jeff

Interesting and a little confusing for me...[sm=spinnyeyes.gif]

I am building the Clipped Wing Sig Cub at 1/4 scale, and have a Magnum 91 already fitted nicely.
This decision is based on my Precedent Aeronca Champ that at 108" span and 10.5 Lb., flys great on an old OS 61 FSR two stroker with a 13-5 APC. Takes off with authority, needs 50% to maintain level flight.

However, I've read quite a few posts indicating I may be pushing it a bit...so I started considering a Magnum (?) 120 in place, though wouldn't realy like to fit a new engine...

So now I understand that maybe I am OK with the 91? I might add I build rather light (started in the hobby with free-flight sailplanes...) and fly off asphalt. The CWC will be covered with Dave Brown's Skyloft (after happy experience with it on my Sig Smith Miniplane).

Comments?

It will fly just fine....Mine was built extremely light, and I ended up adding a ton of ballast in the nose with the smaller engine. It still flew fine. I was trying to think back on all the 1/4 scale cubs that I have flown, and I think only 1 had a 120 on it, and it was on floats... the others were anywhere from a Saito 91 to a G-38 ...........

It will fly just fine with that engine. A 120 would make it climb straight up at a very light weight. Mine is the 108" cub at about 13 3/4 pounds and it does real well on the Saito 91. The CWC at 11 pounds should be good. Jeff

A .91FS! Drat! Am I going to be WAAAAAAYYYYYYYYY overpowered! I have a Saito 1.50 that I am currently fitting to the nose of my BUSA 1/4 Cub. I do plan on spinning a scale 18" prop. Mine might come in heavier as I am adding scale gear and an interior plus pull-pull on all the surfaces. Even still I think I have too much engine. I was thinking about starting my competition career with this plane. Sounds like I would be better off with a 1.20 since mine will spend a fair amount of time on floats. I am just not sure a .91Fs would pull a 14lb Cub + floats off the water very well.

Since I am very much interested in scale flight I think I need to reconsider engines. What do you think? For a competition Cub that will be on floats ditch the 1.50 for a Saito 1.20 or a Saito 1.00?

There is also a used OS FT-160 at my LHS. Has the stock carb replaced with a dual needle carb, on-board glow etc for $369! The engine was originally bought from the same shop and has had two owners. Both take excellent care of their gear. Probably too much engine but it sure is tempting!!

Doug

If you are going to fly on floats, leave the 150 on...it is not that much more power than a 120, (and the 120 does have have that much more than a 91) we are talking fractions of a horsepower here.
The 150 would allow you some flexibility of swinging a bigger prop at lower RPM..If you compete at higher elevations, or hotter climates, you won't be hurt so much by the power loss..... Remember the throttle works in both directions....!

Thanks! It is true the throttle works in both directions ;-) Surgery is required to get the 1.50 on. While it isn't difficult to do, a 1.00, 1.20 or the OS-160 Gemini all wuld most likely fit without and changes. The lowest pitch prop in an 18" size I can fine is a 6. Wish someone made a 18 x 5 or an 18 x 4.

That OS-160 twin sure is tempting!

Doug

What about a Fox Eagle 74 for power?

I ask because my father has a Balsa USA 1/4 scale Cub that he has been working on and that is the engine he is using. The Cub is nearly done and needs only a couple more hours of finishing work before it is ready for its maiden flight (only took 13+ years to get there) I have my doubts about the Eagle 74 having enough power to fly anything beyond scale like and am concerned that at a critical moment the lack of power could spell disaster. I'm thinking a Saito 125 or 150 would be a better choice however, it is going to require some 'surgery' for sure to change over to a Saito power plant which would delay the Cub's completion even more[]

Anybody have or know of a BUSA (or equivalent) 1/4 scale Cub powered by a Fox Eagle 74?
I would like to hear about how well it performs. Thanks!

Mike

I'm afraid I don't have any good success stories with that engine... If you have one that runs well, it may well fly, but don't expect any spirited performance..... a lot will depend on the weight of the finished cub.

We have one at our field with the os twin nice set up sounds cool.
If money were not an issue I would like to try something like this...
It would look real scale. LOL

Does anyone have any experience with this engine for the Sig 1/4 scale J-3 Cub.
"Gemini-160". FT-160 Twin-Cylinder 4-Stroke Engine from O.S.
It is Scale-Like in Appearance when Installed in a Piper Cub.

I have an OS 160 twin in a Sig Spacewalker and it is one of the sweetest running engines I have ever run. WHen the Spacewalkers time is up I have a Sig 1/4 scale cub its going in. Very smooth engine!

Jeff

Give me a minute here and I will dig out a nice picture of one...... The owner says it is not a very powerful engine...I think he mention that the single cylinder 120 had more power...... Sure flew nice and sc...er.....realistic...with a very nice exhaust note...

A guy in our club has a clipped wing 1/4 scale cub with the Hazel Sig paint job. Looks real nice and flies very well more than enough power as long as you are not trying hovers and knife edge. Sounds real nice in the air!

For what its worth, heres my exp. I built and still fly a SIG 1/4 Clipped Wing Cub. Its fitted with G26 with rudder servo tail mounted.
5" Du Bro pneumatic wheels. 6.5 kg digital on elev. Weighs 16.1 lbs and required no ballast. Slightly heavy, but the scale speed AND sound are for me (and others) purrrfect. It will struggle to loop without a slight speed build. Touch n goes are somthin else!! It can really bounce!
If I built another, I'd go for a G38........
Terry

I can save you a lot of heart ache and effort....I've done it, and it is not worth it.....
It is a heavy overpowered beast that loses all of it's cub-like qualities, Having said that, it is fun to fly, but it took me about 3 seasons to get a handle on it and it's various handling quirks - like holding right aileron while doing a left had turn!

guys we always powered our cubs to go straight up but here in the last few weeks i built a g.p. arf cub, put a new 52 magnum. it was so much more fun with the smaller engine, you have to use full power to get it moving so it has the straining sound like the real ones do. my friend that i putt-putt around with pulled his o.s. 70 and put an old saito 45 on his. lot's more fun and it really gets the wing loading down.


hey iron eagle, the wrights did crash!! orville crashed during an army trial while carrying lt. thomas selfridge who became the first person ever killed in a plane crash. i spend too much time reading!!!

this my sig clipped with magnum 160

Jeff,
It sounds like you have about scale weight to power with that 52 magnum.
Is your cruise about half throttle or so?
What is your flying weight with that setup?


The Wrights never called them crashes they called them as hard landings....

And you are correct Lt. Selfridge was killed during a demo flight.

Orville described it later: "Quick as a flash, the machine turned down in front and started straight for the ground. Our course for fifty feet was within a very few degrees of perpendicular. Lieutenant Selfridge up to this time had not uttered a word, though he took a hasty glance behind when the propeller broke, and turned once or twice to look into my face, evidently to see what I thought of the situation. But when the machine turned headfirst for the ground, he exclaimed 'Oh! Oh!' in an almost inaudible voice. Suddenly just before reaching the ground... the machine began to right itself rapidly. A few feet more, and we would have landed safely."

hear, hear !!!! I've always maintained that anyone can fly fast...it takes a real pilot to fly slow!

I flew my 105" Sig 1/4-scale Cub with a Saito 91 for an entire season, and had a ball with it. Plenty enough power for scale-like flying. When the front bearing finally gave out, I moved my Magnum 1.20 four-stroke into the Cub. It now has plenty of reserve thrust for climbing out aggressively. I spend most of the time flying with the throttle cracked open somewhere past idle. Cubs should be flown on the wing, not on the engine, and the Magnum does a great job of putt-putting all day long at partial power. My 20oz tank lasts a long time at these power settings.

BTW, true Cub fans know about the Cub Nuts event next month in Oregon. Come and be part of the "yellow swarm"!
http://www.cubnuts.com/