GASSER VIBRATION
03-30-2009, 12:36 PM
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GASSER VIBRATION
Hi, I have finally ventured into the petrol scene and purchased an Extreme Flight Yak 74" and a Roto 35VI engine, fired it up for the first time yesterday and was amazed how much the model vibrated with the engine on tickover.
Is this normal for a gasser or do i need some sort of anti vibration mount as my engine is mounted directly to the firewall.
thanks for any replies
Is this normal for a gasser or do i need some sort of anti vibration mount as my engine is mounted directly to the firewall.
thanks for any replies
03-30-2009, 12:59 PM
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RE: GASSER VIBRATION
The bigger the motor the more they shake. Try raising the idle up out of the high shake rpm range, most gassers idle lower than you need for flying. You did balance the prop? You might want to try a lighter or heavier prop to find one that doesn't have max shake at your idle speed.
03-30-2009, 04:42 PM
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RE: GASSER VIBRATION
You might try tuning the needles. Factory settings are generally adequate to get the engine running, but often are on the rich side. Rich low end has more vibration than a properly tuned low end.
03-31-2009, 08:37 PM
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RE: GASSER VIBRATION
Agreed.
Wings will act as a vibration dampener and smooth out the engine pulses on the rest of the airframe.
Rich low end usually makes it thump quite a bit at idle. Tune it properly and fly it.
Wings will act as a vibration dampener and smooth out the engine pulses on the rest of the airframe.
Rich low end usually makes it thump quite a bit at idle. Tune it properly and fly it.
04-01-2009, 08:49 PM
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RE: GASSER VIBRATION
I fussed with this quite a bit lately. Make sure the prop is balanced, orient it vertical when you are at TDC, make sure it is not running rich. They tend to want to run rich in the midrange and consequently shake a lot. There are articals on the net on how to get optimal mixture through the full throttle range.
My latest engine conversion was a bear to get the prop hub dead true with the crank. I started with the prop tips up to 1/4" out of 90-deg, in other words, on prop was higher than the other as you rotated the engine. You could clearly see the as the engine ran on the test stand. I ended up setting it up in a lathe and trueing the prop hub and prop nut stud. Once everything was dead true it all got better. I also selected a carb with no third jet. This makes it run at a near optimal mixture acrtoss the RPM range. After all that, with the wood prop oriented to TDC is does not skake and shimmy. Watch out for glass filled plastic props. They are heavy. You get them a little out of wack and all that mass pulls the engine all over the place.
My latest engine conversion was a bear to get the prop hub dead true with the crank. I started with the prop tips up to 1/4" out of 90-deg, in other words, on prop was higher than the other as you rotated the engine. You could clearly see the as the engine ran on the test stand. I ended up setting it up in a lathe and trueing the prop hub and prop nut stud. Once everything was dead true it all got better. I also selected a carb with no third jet. This makes it run at a near optimal mixture acrtoss the RPM range. After all that, with the wood prop oriented to TDC is does not skake and shimmy. Watch out for glass filled plastic props. They are heavy. You get them a little out of wack and all that mass pulls the engine all over the place.
04-05-2009, 12:57 AM
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RE: GASSER VIBRATION
Thanks for all the replies, I have tried some of them and the vibration has lessened some what.
yesterday I swapped the 4 cell nicad for the ignition to a 4 cell Nimh of higher capacity but now i get a fast ticking noise from the ignition unit?
Any ideas?
yesterday I swapped the 4 cell nicad for the ignition to a 4 cell Nimh of higher capacity but now i get a fast ticking noise from the ignition unit?
Any ideas?
04-05-2009, 03:18 PM
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RE: GASSER VIBRATION
90% or more of gasser vibration issues is due to the low end beeing too rich.
Fiddling with the needles is definatly a part of this hobby.
Just note where the needles are now and start messing with them. Be sure you adjust the correct needle when making adjustments to either idle/midrange or full throttle.
If you get lost, just set it to the "factory preset" and start over.
Start with 1/4 in on the low end. And if it gets better, continue with 1/8´s until it starts to hesitate or respond slower to throttle input from idle (1700-2000rpm). 1/8 Out when you get no response to the last change or hesitation/slow reaction.
The same goes for full throttle. Get a tach and start messing.
Lars.
Fiddling with the needles is definatly a part of this hobby.
Just note where the needles are now and start messing with them. Be sure you adjust the correct needle when making adjustments to either idle/midrange or full throttle.
If you get lost, just set it to the "factory preset" and start over.
Start with 1/4 in on the low end. And if it gets better, continue with 1/8´s until it starts to hesitate or respond slower to throttle input from idle (1700-2000rpm). 1/8 Out when you get no response to the last change or hesitation/slow reaction.
The same goes for full throttle. Get a tach and start messing.
Lars.
04-05-2009, 03:28 PM
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RE: GASSER VIBRATION
ORIGINAL: chunk111
Hi, I have finally ventured into the petrol scene and purchased an Extreme Flight Yak 74" and a Roto 35VI engine, fired it up for the first time yesterday and was amazed how much the model vibrated with the engine on tickover.
Is this normal for a gasser or do i need some sort of anti vibration mount as my engine is mounted directly to the firewall.
thanks for any replies
Hi, I have finally ventured into the petrol scene and purchased an Extreme Flight Yak 74" and a Roto 35VI engine, fired it up for the first time yesterday and was amazed how much the model vibrated with the engine on tickover.
Is this normal for a gasser or do i need some sort of anti vibration mount as my engine is mounted directly to the firewall.
thanks for any replies
If the prop is balanced, your shaking is the result of the low needle being a bit rich.....even a rich high needle will cause rough running... Some other responses here will confirm this....sometimes, two clicks of the needle will make a big difference..
04-05-2009, 06:55 PM
#10
RE: GASSER VIBRATION
I'm not pointing fingers. Everyone seams to be in agreement here. The engine needs to be tuned in addition to the other standard practices such as balancing the prop and spinner.
It still just completely BAFFLES me that guys will take a new gas engine and run it without bothering to tune the engine properly. Why all the fear? Perhaps the old timers of years ago made it out like tuning gassers was witch craft? Those old fears still carry through today? Who the heck knows?
The fact is a gas engine tunes the exact same way a glow engine does. There just aren't any "clicks" on the high speed needle. Run it to full RPM and lean the HS needle until it sags. Richen it back up to peak RPM and then continue to richen until you see about 200-300RPM drop. Now set the throttle to idle speed and lean the low speed needle. It will speed up. Lean to peak RPM. Lean the sucker out and watch the RPM's go up as you lean it. Just like a glow engine. If you continue to lean you will see it eventually hit a max RPM and then begin to stumble or die if you go any further. You simply back the needle out until it gets back to the spot where it was at max RPM. Now richen it until it drops 100RPM. One Hundred - not 1000. Just like you would tune any glow carb. Now go back to full throttle and reset the high speed needle. Richen it until it is visibly/audibly slower. Now peak it to max RPM until it stumbles or sags. Back it up rich to the max RPM and then richen 200RPM more for safety on a new engine.
Go fly it. No witch craft. No secrets. No black magic.
If you can tune a glow engine, you can tune a gasser. If you haven't learned to tune a glow engine yet, well............. [sm=lol.gif]
It still just completely BAFFLES me that guys will take a new gas engine and run it without bothering to tune the engine properly. Why all the fear? Perhaps the old timers of years ago made it out like tuning gassers was witch craft? Those old fears still carry through today? Who the heck knows?
The fact is a gas engine tunes the exact same way a glow engine does. There just aren't any "clicks" on the high speed needle. Run it to full RPM and lean the HS needle until it sags. Richen it back up to peak RPM and then continue to richen until you see about 200-300RPM drop. Now set the throttle to idle speed and lean the low speed needle. It will speed up. Lean to peak RPM. Lean the sucker out and watch the RPM's go up as you lean it. Just like a glow engine. If you continue to lean you will see it eventually hit a max RPM and then begin to stumble or die if you go any further. You simply back the needle out until it gets back to the spot where it was at max RPM. Now richen it until it drops 100RPM. One Hundred - not 1000. Just like you would tune any glow carb. Now go back to full throttle and reset the high speed needle. Richen it until it is visibly/audibly slower. Now peak it to max RPM until it stumbles or sags. Back it up rich to the max RPM and then richen 200RPM more for safety on a new engine.
Go fly it. No witch craft. No secrets. No black magic.
If you can tune a glow engine, you can tune a gasser. If you haven't learned to tune a glow engine yet, well............. [sm=lol.gif]
04-10-2009, 04:14 AM
#13
RE: GASSER VIBRATION
I am amazed at one can find if you just spend the time to look throught the forum...I was going to post a question about this very same subject,now i have my answers!!
Thank you!!![sm=thumbs_up.gif]
Thank you!!![sm=thumbs_up.gif]
04-10-2009, 07:20 AM
#14
RE: GASSER VIBRATION
ORIGINAL: Rcpilot
I'm not pointing fingers. Everyone seams to be in agreement here. The engine needs to be tuned in addition to the other standard practices such as balancing the prop and spinner.
It still just completely BAFFLES me that guys will take a new gas engine and run it without bothering to tune the engine properly. Why all the fear? Perhaps the old timers of years ago made it out like tuning gassers was witch craft? Those old fears still carry through today? Who the heck knows?
The fact is a gas engine tunes the exact same way a glow engine does. There just aren't any "clicks" on the high speed needle. Run it to full RPM and lean the HS needle until it sags. Richen it back up to peak RPM and then continue to richen until you see about 200-300RPM drop. Now set the throttle to idle speed and lean the low speed needle. It will speed up. Lean to peak RPM. Lean the sucker out and watch the RPM's go up as you lean it. Just like a glow engine. If you continue to lean you will see it eventually hit a max RPM and then begin to stumble or die if you go any further. You simply back the needle out until it gets back to the spot where it was at max RPM. Now richen it until it drops 100RPM. One Hundred - not 1000. Just like you would tune any glow carb. Now go back to full throttle and reset the high speed needle. Richen it until it is visibly/audibly slower. Now peak it to max RPM until it stumbles or sags. Back it up rich to the max RPM and then richen 200RPM more for safety on a new engine.
Go fly it. No witch craft. No secrets. No black magic.
If you can tune a glow engine, you can tune a gasser. If you haven't learned to tune a glow engine yet, well............. [sm=lol.gif]
I'm not pointing fingers. Everyone seams to be in agreement here. The engine needs to be tuned in addition to the other standard practices such as balancing the prop and spinner.
It still just completely BAFFLES me that guys will take a new gas engine and run it without bothering to tune the engine properly. Why all the fear? Perhaps the old timers of years ago made it out like tuning gassers was witch craft? Those old fears still carry through today? Who the heck knows?
The fact is a gas engine tunes the exact same way a glow engine does. There just aren't any "clicks" on the high speed needle. Run it to full RPM and lean the HS needle until it sags. Richen it back up to peak RPM and then continue to richen until you see about 200-300RPM drop. Now set the throttle to idle speed and lean the low speed needle. It will speed up. Lean to peak RPM. Lean the sucker out and watch the RPM's go up as you lean it. Just like a glow engine. If you continue to lean you will see it eventually hit a max RPM and then begin to stumble or die if you go any further. You simply back the needle out until it gets back to the spot where it was at max RPM. Now richen it until it drops 100RPM. One Hundred - not 1000. Just like you would tune any glow carb. Now go back to full throttle and reset the high speed needle. Richen it until it is visibly/audibly slower. Now peak it to max RPM until it stumbles or sags. Back it up rich to the max RPM and then richen 200RPM more for safety on a new engine.
Go fly it. No witch craft. No secrets. No black magic.
If you can tune a glow engine, you can tune a gasser. If you haven't learned to tune a glow engine yet, well............. [sm=lol.gif]
