I had a starter on my engine. I wanted to save weight and removed it, ring gear and all. I found after removing the starter ring gear I had a vibration I did not like. I replaced the ring gear and she is silk smooth again.
My 1/2 VW has no vibration what so ever. I even have a video to prove my point. Actually a couple video's.
http://www.youtube.com/watch?v=TVl6Afk9iuQ
http://www.youtube.com/watch?v=wN5rz5pM8ZA
Tony
MY counter weight is in the correct position.I also tried running up without it but really couldn't feel any difference, also I have removed the spinner to eliminate any balance issues with it as I have had 2 spinners crack from vibration. The prop index is a great suggestion as it is indexed differently than before. I will try all three positions when the flying weather improves. Also I am trying another prop ( with the help of Hummel Aviation ) less pitch will put me in a different RPM range. Have run static, still to much vib but need to fly to see if I can find a quiet spot to fly in. I will post any improvements, thx for your suggestions
Robert
Nice looking plane, Robert...congratulations!Originally Posted by lasermanro
One question out of curiosity, though... the pictures seem to show a lot of space open behind the pilot. Is this just a function of the camera angle, the slant of the rear bulkhead, or just the position of the seat? Most of the pictures online include the canopy, and it might be that my eye was thrown off your al fresco shot.
I've always like the Hummelbird; it seems like a good basic aircraft using modern materials. Well-suited to the tin bashers among us. Had a couple under construction in locally here, a while back, always got a kick out of poking my head inside.
Ron Wanttaja
Back to that broken crankshaft. Where did it break? These torsional vibrations can create a major fatigue problem with the crankshaft. Or he may just be lucky and not operating at a critical rpm.
From another later post above, if there is any sort of flywheel (or starter ring) on the back of the engine, a nasty torsional vibration issue could be happening, with the max stress probably between the front crank throw and the prop hub. I know the writer of that post said it ran much smoother with the starter ring gear on the back, but the problem with torsional vibration, is that its presence isn't apparent at all to the pilot.
Years ago a local Dragonfly owner did something remotely similar (i. e. inertia on both ends of the crankshaft) & the failure was immediate. There was extensive charring of the wood/prop flange interface and the propeller bolts were breaking with alarming regularity.
Last edited by nrpetersen; 02-15-2014 at 11:43 AM.
Starter ring gear is mounted to the prop hub. Not to the rear of the engine.
Tony
I highly suggest that you find someone with either a MicroVib II or ACES system and have your rotating mass balanced. The rotating mass consists of the crank, prop, spinner and anything else connected to that which spins. I do prop balancing several times a month at my shop on all kinds of aircraft and I can tell you that it will make a big difference in most cases. The A&P/engineer that does the balancing should be able to work you down to a value of at least .030" ips (inches per second). Values lower than that are possible but as you get closer to zero the need for accurate placement and the amount of weight needed goes up exponentially. If you get a lower value great, but don't let them spend to much time as it just ends up being not worth the time invested. Weight will be added to your spinner screws during several runs. When the value is as low as the operator can get it, he will move that weight combo from the outer screws to the spinner backplate. He should check it after moving to assure that the value did not change to much.
Broken crankshafts, cracked oil coolers/baffling/brackets/exhaust etc....are many times attributable to a poor distribution of mass about the centerline of the crankshaft. Prop balancing will go a long way to improving this issue.
Remember, with a wooden prop always leave the aircraft with the prop in a horizontal position. If left vertical, moisture will tend to migrate towards the bottom blade and can significantly effect your balance.
Arnold Holmes
AV-Mech LLC
EAA 519850
av-mech: great info. I always keep my prop horizontal as you say.
By the way, My grandmother was a Holmes and I live at Holmes airfield owned by Dave Holmes.
Small world.
Tony
The prop on my RV-6 has been dynamically balanced and I agree it can make a significant difference in smoothness.
But I have a question. Where would weights be placed on the prop of my Legal Eagle?
There is no prop spinner and the prop bolts are very close to the prop shaft. I suppose a prop tip could be trimmed but that sounds a bit extreme. Suggestions?
Sam,
Engine configurations like yours are difficult to do for the stated reason that you have nowhere to hang weights. It is possible to add heavy washers under the prop bolts. A number of problems arise doing that including: needing a longer bolt(which changes weight on it's own), the weight added not being very far from the center line of the crank, which in turns requires more weight that if you could add at a location farther out (think lever arm). You most certainly DO NOT want to trim the tips. Blade length being equal on both sides is critical, as is blade tracking. That is something I did not mention to the original poster and will make a difference as well.
To: 1600VW, make sure that each blade tip passes in the exact path of the other blade tip. An easy way to do this is to remove spark plug from cylinder so engine is easy to turn over. place prop in vertical position and place a cardboard box (or anything else you like) under the lower tip. Try to get it within 1/4" or so. Using a good sharpie marker, place it on the face (back side if looking at the aircraft from front) and gently lower it down until you make a mark on the box top. Next, gently rotate prop so opposite blade is in the lower position, use your marker again to make a mark on the box top. the two marks should be within 1/16" of each other. If one is displaced forward or aft of the other, retorque your prop bolts until the tips are marking at the same point. You may need to loosen one side of the bolts while torquing the other side. Go slowly and don't get aggressive, just use baby steps.
Its not a tracking issue. Don't get me wrong you need to check tracking but this is not the problem with my setup.
The weight goes on the prop bolts in the front of the prop, you will need two longer bolts for this. Bring the piston, does not matter what one they both are at TDC together. Bring the piston to TDC and mount the weight at the 9: o:clock position. This is standing in front of the airplane looking at the engine.
If you have never seen one of these weights its a piece of steal about 3inch by 3 inch by 1/4 inch.
I left mine on my engine and Scott at Hummel has it. Call Scott tell him what you need and he will help you. Washers is not the way to do this, they will do nothing.
Tony
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