CRAZYRYAN

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i have posted before on this forum and wonder what the right brand of pittstyle muffler i can get for my magnum 91 four stroke im installing in the hobbico sukhoi su31. does it require to cut more of the cowl out? since you have the header? this will be side mounted for better performance than upside down mounted engines. help please i still had no responses.[]

bubbagates

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Ryan,

I can tell you this much, I'd stay with the stock muffler on that engine. But if you really want the pitts muffler it looks like Bisson makes it. I just found it on their web site. I cannot tell you about the cowl as I have never seen that plane but if you can find out the dimensions of the cowl and look at the dimensions of the engine, specifically how tall it is from the mounting ears to the top of the head then get the muffler specs you can determine pretty closely how much of the cowl will need to be removed.

Also I have a feeling that a muffler for an OS 91 Surpass 4-stroke may just fit. They are very very close to being the same engine but you would have to verify the thread sizes

http://www.bissonmufflers.com/en/muf...imageField.y=8

Also, it's the weekend and a really nice one so be a little patient while waiting for replies, they will come

CRAZYRYAN

My Feedback: (1)

ok well thanks anyways fast reply

jbloom

I've got that aircraft, it'll be maidened today. I have a Super Tigre .90 under the cowl. Completely under the cowl... There is about a 1/2 inch from the top of the head to the side of the cowl. I measured mine and it's about 7 1/2" wide at the widest point. I've installed a Bisson Pitts muffler on it. While the cowl is flexible enough, I cut about 1/2 an inch off the tubes just to give me a bit more room. I installed the dummy radial and that makes slipping the cowl on and off a bit tricky has the prop shaft has to clear opening before you can get it on far enough to get the down tubes to the exhaust opening. So I enlarged the opening in the front. If you don't use the dummy radial, there probably won't be an issue. Also, just for looks, I cutout between each of the dummy cylinders. I think it looks better than just cutting an opening for the engine head.

jbloom

Well, the maiden flight when great! Today was slightly breezy, pointing the plane into the wind and advancing the throttle brought the tail up almost immediately. A take off run of about 15 feet and she was up. No surprises as she climbed out strong. I gave it two clicks right aileron, and three clicks down elevator and she was straight and level. I made a note to self to add about 25% negative exponential, that elevator was really sensitive. The rolls are quick and on the mark, no straying from course. Inverted flight required only a breath of down elevator to hold altitude. The knife edge was a bit more tricky. The plane wants to veer towards the wheels when rudder is applied. However, a little practice and it was holding fine. At one point, with the throttle at full and the rudder at full, I did a half knife edge loop. The Super Tigre .90 is plenty of engine for this plane, and the rudder carries a lot of authority. The standard cuban eights, split-S's, loops and rolls are on the money, with only a slight straying to the left when doing a full power verticle climb.

Landing are nearly effortless. Wings level and let it settle down. Anyone at our field, young and old could have out run that plane as it settled down to the runway. In short, it was a great day of flying.

Here are a few pics from the day.

CRAZYRYAN

My Feedback: (1)

thank u sooo much for posting that!!! i know from the looks and construction it will be a beautifull flying plane!!! next time if you can barrow someone's video camera and take the video. does the .90 two stroke have more power than the four stroke? let me know im installing a .91 it should sound awesome with a pittstyle once i can find the right thickness and thread for it so far no luck!!![8D]
oh one thing to note if your really picky like me i would spray paing the engine firewall that way when you look through the dummy cylinder radial you wont really see the bare wood in my opinion it will look better thats what im going to do.

jbloom

Yea.. I probably will paint the inside of the cowl and the firewall black. The wood is well fuel proofed right out of the box, but you're right, painting the inside would look much better.

As a rule of thumb (and I'm no scholar), a two stroke .90 will pull stronger than a four stroke .91. At least that's my understanding based on recomended engine sizes on the kits. I.E. .50-.75 2 stroke, .70-.91 Four Stroke. But, since the .90 two stroke is much more than required, I think you're .91 will be fine. As a personal note, the smallest engine I'll put on a plane, is the largest one listed in the recomended sizes.

CRAZYRYAN

My Feedback: (1)

well the reason i think that the two stroke is stronger is that it does not have the pushrods and valves that the kenetic engergy has to go through. thus the four stroke has less rpm while the two stroke has more wich makes it pull stronger. the reason the four stroke has all the mechanical moving parts is mainly for sound. so i guess i answered my question. will you take a video of your plane? i would really appreciate that!!!

redfox435cat

as a rule 4 strokes have more usable power in the form of torque. if you notice a 4 stroke will swing a biger prop than the same sized 2-stroke. 2-stroke have more HP and do have more power on the high end. With a plane like your suiky were you'll be using mid range alot for vertical manuvers a 4-stroke will perform better since it has more pulling power and a more linerar throttle response.

As far as a muffler. Go for the flexable tubbing. It works great and you can mount it and put the exuast anywere you want.

jbloom

I will take video as soon as I find someone with a video camera. I wouldn't mind have it myself.