What type of exhaust - Can/Pitts/Tuned Pipe?
04-28-2010, 03:31 PM
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What type of exhaust - Can/Pitts/Tuned Pipe?
Being new to IMAC... I'd like to ask the expertsopinions on what type of exhaust to use on planes intended for IMAC. I've got a couple I'd like to set up, but not sure which way to go...
I have 30cc, 50cc, and 100cc engines to put exhaust on. ...the 30cc seems small enough that a Pitts would be fine (not much for options there anyway???). For the 50cc and 100cc... Are pitts mufflers generally okay for those too? Does the necessity for canisters and/or tuned pipes really come into play with the bigger planes... i.e. 150cc and up?
I have 30cc, 50cc, and 100cc engines to put exhaust on. ...the 30cc seems small enough that a Pitts would be fine (not much for options there anyway???). For the 50cc and 100cc... Are pitts mufflers generally okay for those too? Does the necessity for canisters and/or tuned pipes really come into play with the bigger planes... i.e. 150cc and up?
04-28-2010, 04:02 PM
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RE: What type of exhaust - Can/Pitts/Tuned Pipe?
One thing to remember is that IMAC does judge sound and the noisier the plane, the lower the sound score. Now I know people are going to come on here and say it does not mean much but in all my years of flying IMAC in the NE region, I've seen tons of contests that came down to the sound score.
Besides, if you look at the RCP's being voted on by the SACB and AMA for 2011, most of them make the sound score more important in one way or another. Besides it's prudent to be as quiet as possible, also in IMAC, you should be thinking about contests at another field where there might be limits imposed by the hosting club.
On my Da100L I used MTW75K cans and a 25x10 3-blade on a 30lb Comp-Arf 260 and I consistently showed 92dB at full power on grass at 9 feet and still had loads of power to easily do the Advanced sequences. Toss on a 28x10 two blade and I went to 96dB and could then do Unlimited. In either case, I could go to the local field and glow planes were louder than me on factory supplied mufflers and at times it was hard to hear my plane at all.
Now if you want even more power, a pipe is the way to go and still be quieter. Just be sure to find out the proper header length with your engine/prop combo. The Grieves pipes are just as light or even lighter, depending on the application, as almost all of the canisters I've looked into so balance will not be much of an issue.
Another sound producer is the plane itself. Open bay wings tend to "drum" if the covering is slightly lose, lose fitting hatches, wires bouncing around in the wings and fuselage and believe it or not, a prop out of balance will also exaggerate all of what I just mentioned
Besides, if you look at the RCP's being voted on by the SACB and AMA for 2011, most of them make the sound score more important in one way or another. Besides it's prudent to be as quiet as possible, also in IMAC, you should be thinking about contests at another field where there might be limits imposed by the hosting club.
On my Da100L I used MTW75K cans and a 25x10 3-blade on a 30lb Comp-Arf 260 and I consistently showed 92dB at full power on grass at 9 feet and still had loads of power to easily do the Advanced sequences. Toss on a 28x10 two blade and I went to 96dB and could then do Unlimited. In either case, I could go to the local field and glow planes were louder than me on factory supplied mufflers and at times it was hard to hear my plane at all.
Now if you want even more power, a pipe is the way to go and still be quieter. Just be sure to find out the proper header length with your engine/prop combo. The Grieves pipes are just as light or even lighter, depending on the application, as almost all of the canisters I've looked into so balance will not be much of an issue.
Another sound producer is the plane itself. Open bay wings tend to "drum" if the covering is slightly lose, lose fitting hatches, wires bouncing around in the wings and fuselage and believe it or not, a prop out of balance will also exaggerate all of what I just mentioned
05-03-2010, 01:54 AM
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RE: What type of exhaust - Can/Pitts/Tuned Pipe?
The stock exhaust is still ok on the 100 cc but you cant use a horribly loud prop. I had stock DA exhaust w/ mezjlic 27x10 prop on my 35% H9 extra260 last year and scored 5 on the sound score some times 10s never had any zeros. most the time i was under half throttle except on 45° and 90° uplines and even then didnt have to go to full power. The plane was 27.5 pounds. Having the extra power help a lot. If the plane is IMAC only then tuned pipes are great but if you want to fly 3d with them you will have to get used to the lack of transition.
Im in the 40% planes for my imac now and run a DA170 on re3 tuned pipes and mis the perfect throttle transition of canisters or stock exhaust but on this sized engine it gets to loud to use stock exhaust. My current plane is to heavy for canisters so the tuned pipes extra power stays, but on my future plane that will be under 40 pounds i will use canns for the transition.
Im in the 40% planes for my imac now and run a DA170 on re3 tuned pipes and mis the perfect throttle transition of canisters or stock exhaust but on this sized engine it gets to loud to use stock exhaust. My current plane is to heavy for canisters so the tuned pipes extra power stays, but on my future plane that will be under 40 pounds i will use canns for the transition.
