Not enough Thrust with Saito 100
05-19-2007, 10:51 PM
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Not enough Thrust with Saito 100
Hello all, I am having a problem with a Saito 100. I have been breaking the engine in per instruction using a 14-8 MA prop in my Hanger 9 Spitfire. I tached the engine at about 9000 rpm today as the engine has about 3/4 gallon through it so far for breakin. The low needle is about 5 turns open it came to me set 7 turns open. The top i have varied from 5 originally down to 3 and now it is at 4. My tach may be wrong but it was reading 9000 rpms and the air it was pushing back did not even seem as much as my OS 46 pushes. No way that thrust will fly a 9 pound plane. Any ideas would be appreciated. Thanks, Kevin.
05-19-2007, 11:15 PM
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RE: Not enough Thrust with Saito 100
Yes i know that this rpm is suppose to be a pretty good one, but what I am concerned about is the lack of air being pushed back. I know it sounds crazy but it just does'nt feel like it will fly the plane. This is my first four stroke and I may just be looking for something that is not suppose to be there anyway.
05-19-2007, 11:49 PM
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RE: Not enough Thrust with Saito 100
ORIGINAL: crashproof
...My tachometer may be wrong, but it was reading 9,000 RPM and the air it was pushing back did not even seem as much as my OS.46 pushes. No way that thrust will fly a 9 pound plane.
...My tachometer may be wrong, but it was reading 9,000 RPM and the air it was pushing back did not even seem as much as my OS.46 pushes. No way that thrust will fly a 9 pound plane.
I believe you may be misjudging the prop-wash speed as thrust...
Your OS.46, even with a 6" pitch prop, at 14K will be pushing air back at a significantly higher speed than the Saito at 9,000 with an 8" pitch. But you are ignoring the prop disk area, which is twice as large for the 14" diameter prop, as it is for a 10" diameter prop.
Connect a spring-balance/laundry scale/Etc. to the tail of your model and you should be seeing more than 9 lbs. of thrust.
Besides, everyone is using a similar setup; it can't be wrong only for you...
05-20-2007, 03:29 AM
#6
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RE: Not enough Thrust with Saito 100
Your first 4stroke, huh? I think you are getting fooled by the sound. At 9000 rpm the engine fires 4500 times a minute (every other revolution) and therefore it may sound like less "work" is beeing done, as opposed to your familiar 46 screaming at 12-14000 rpm. Firmly hold your plane vertical, full power with the prop ABOVE your head and you should be able to feel that the engine will pull your plane upwards
05-20-2007, 08:35 AM
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RE: Not enough Thrust with Saito 100
Thanks for the replies guys, I will keep at it and continue to learn about these 4 strokes. It just had me worried, but all of your opinions seem to be basically the same and I feel much better about it. Thanks, Kevin.
05-20-2007, 12:37 PM
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RE: Not enough Thrust with Saito 100
I have a 9lb RV3 with a saito 91 and a 14x8 APC; goes like stink. Download "aero design propeller selector" on google and have a look. I compared the reading with a fish scale on this 91 setup and the two came out virtually the same.
05-20-2007, 12:38 PM
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RE: Not enough Thrust with Saito 100
It'll fly great with the Saito 100 and an APC 14-8. I have the same combo in a H9 P-47 and it flies great with plenty of power; it jumps off the runway before I can get to full power. Try it, you'll like it.
05-21-2007, 07:46 PM
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RE: Not enough Thrust with Saito 100
As usual you all were correct. Maidened the plane yesterday, and it flew just fine. Thanks for the replies, I am learning these 4 strokes and more importantly am willing to admit it. Thanks again, Kevin.
