I've finished the World Models Super Chipmunk 90S, with an OS .91 4-stroke. Anybody else who has this combination, please give info on what prop you are using, and how it performs. Also, if anybody has experimented with different props on this combination, please tell differences between props re: performance. (verticals, slow flight, etc.) Thanks.

I just finished mine with YS91. Using 14x6 prop for engine breakin. On first flight attempt last Sunday, retract gear on one side collapsed just before lift off. On inspection I discovered that I had not properly set up the gear so that it was locked out. Only the servo was keeping it out. My first experience with retracts. Minor damage, wing tip scuffed. Lesson learned.

I have this model and have had both an OS .91 & a Saito .91 in it. My personal preference for all around sport flying with either of these 4 strokes is an APC 13 x 8. For a little more grunt and a little less forward speed I would try a 14 x 6. Great model by the way (flies like a Chipmunk), can't beat the fit and finish.

I have one with a YS .91/APC 14X10 combo on it. Great flier and looks great with the gear retracted. Only real problem so far is that I fly off grass & it likes to nose over on taxi, takeoff, & landing. Other than those 3 areas, it does fine on the ground.

Hello Kirk,

Did you weigh your plane? Mine weighed about 8.5 lbs. by bathroom scale. It seems kinda HEAVY.

thanks,
Jerry

Never weighed it. Bathroom scales depress me. Bottom line is that the YS .91 lets me do everything I ask of this model. I spent a career flying fighters in the Air Force & I tend to fly aerobatics the way I did in full scale F-100, A-7, F-4, & F-16 aircraft. Maybe I'll get into 3D some day, but for the time being I'm satisfied with what I'm doing at the moment.

Just weighed mine with my new 10 lb. digital postal scale.
8# 3.2oz. with a TT FS91 and 15X6 Zinger.
(I made some lightweight foam tires for the WM wheels. They're lighter, bigger, and softer.)

I was using a 14X6 Zinger but it didn't seem to be enough prop for the engine.

Most people with the O.S., Saito, and TT engines are running one of the following:
13X8
14X6
14X8
15X6

The 14X6 is probably the best place to start.

You will absolutely LOVE to fly this plane!

Jazzy

Oh yeah, keep your control rates down at first - it is very responsive! And to keep the nose-over problem down, put two or three small washers or 3/32" angled ply under the trailing edge screws of the retract gear. This will increase the angle of attack but will not affect their ability to retract into the wheel wells.

Hey Jazzy - Thanks for the tip on the nosing over problem. I also put on the biggest tires the wheel wells could accept and that helped a bit. I'm considering enlarging the wells to accept even larger tires.

Kirk, I thought about makin' them bigger too but, I just couldn't bring myself to cut into such a beautiful wing!
WM makes a 58mm wheel, (2 1/4"), that is a little wider than the tiny ones that come with the kit. The foam on the 58mms is just as hard as it is on the smaller ones.
BTW, I fly off of a somewhat rough grass field. It seems smooth enough until you drop a 8+# plane on it with dinky little wheels.
It isn't too pretty of a sight. Gets laughs though!
One more thing. Did you balance yours a little nose heavy? I did at first to be cautious then put a red painted flat disk of lead right under the rudder. Slightly tail heavy-SLIGHTLY mind you. This also helped keep the wood props from breaking.
Jazzy

Hi Jazzy - Like you, I started just a bit nose heavy for safety's sake. After a dozen or so flights I started adding lead to the back a little at a time. I trashed the supplied tailwheel setup in favor of an Ohio Superstar/Sullivan combo. Easy to strap bits of lead to that until I get exactly the right amount. Then I'll cut into the rear belly and make a permanent lead injection. What a great flying and looking model!!

Would an O.S. 120 fit and fly well in the WM Super Chipmunk?
I have a 120 not a 90 sitting around.

My chipmunk weights 8lb. Saito 91, best prop for today is 13x8 MA scimitar or k-series (9600 - 9900rpm).
14x6 isn't good.
I am using recommended rates and 30% expo. 120 4- stroke will be to heavy (8-9 oz more).

My Chippie is still in the box, sigh ... hope to start building it this week! Are the most of you running your engine sidewinder or inverted? I know an inverted set up keeps the cowl looking great.

Kirk - I envy you ... not only for the YS91 but that you got to fly so many nice real planes!

Osprey - you will need to relocate the firewall mounting hole with a 120 I think. Bet she will do unlimited verticals.

Thanks for the imput, I guess I need more than just the plane now.

I think you will be better off with a nice 90 4C for easy flying ... unless you wanna get more power with the Saito 100 or even a yummee YS!!!

I took everyones advice and got an OS 91 4C.
There isn't much to the instruction. What servos are you guys using and wear?

Mine got side tracked and she has gone back into the box ... So many planes and so little time and money!!!

You'll have no problem using standard servos. As far as I remember World Models do not recommend high tork for the Chipmunk. I use standard ballbearing Futaba 3001s and just one 9202 on the elevator.

I got around to building my Chippie, was about to get a TT 91 4C into it but then I came across a literally new YS 110 at a really good price. Any comments about the YS110 in the Chippie? I know the YS is one heck of an engine but then I really do not want to go out and get another 90 sized 4C. Also, I had bought a ST91 ... I am thinking of using that over the YS110. Any comments please ... thanks!

ST91 is better, YS 110 and TT90 are to heavy.
I am not agree regarding standard servos. On ailerons you would like to have 645MG. Otherwise the aileron servos will strip on hard landings. I have JR 90oz servos on mine and replaced gears three times this year (150 flights). I had once JR 517 servo on aileron and one gear broke in half.

UK - thanks for the advice ... you are correct on the weight issue, its 7 oz heavier for the YS or TT. I will go with the ST90. Why do your servos strip? I mean I thought if you do not pull any hard manouvers the gears should not strip.

My TT .91 weighs about the same as my ST .90, maybe a tad more. But then this is an older one with the bolt on bearing case, so it may weigh more than a new ST .90. My TT .91 weighs 26 oz, just two ounces more than my old OS .91, but a lot more power. That said I would consider the YS 110. But then again that engine probably has more power than I would use most of the time and it probably would eventually get swapped to a larger plane.

Sport ... my YS 110 will go into my pattern plane ... a nice GSP Swallow. I'll settle for the ST90 for the Chippie.

Hi There Guys!!

Kirk Brimmer - you say you are using a YS 91 in your S/Chipmunk...

I'm in the middle of building my WM Super Chipmunk 90S and have an engine mounting problem!

I'm mounting a YS motor (FZ91 type) and have trouble with the location of the throttle pushrod exit through the firewall. The throttle linkage on the motor does not line up with either of the optional pushrod exits (upright mounted or side mounted).

Also, the throttle linkage is obstructed by the gusset of the plastic engine mount (once the engine is fixed in the plastic mounts).

Does anyone know a solution to these 2 problems?? Can you email me at [email protected] ?? I'd really be grateful!!

Thanks

Adam Rickenberg