cliffy Posted January 27, 2017 Report Share Posted January 27, 2017 Came back from TUS yesterday 8500', DA close to 8500', full throttle, 2550 RPM, leaned to 9.8 GPH. Smooth conditions, TAS 145-146 for quite some time for a good check (used a wiz wheel). 64 D/C 1200 hrs on engine, 3 blade prop, very smooth engine with no 3 blade vibration issues. Day before had to go to 13,500 for a short while to get over cloud deck. The short body works just fine for us. 6 Quote Link to comment Share on other sites More sharing options...
par Posted January 27, 2017 Report Share Posted January 27, 2017 I attempted a full power run like you are describing and I also have a 3 blade prop. I noted an increased amount of vibration at full power. Is this a common issue with a 3 blade prop? If so, what is the solution? Quote Link to comment Share on other sites More sharing options...
KLRDMD Posted January 27, 2017 Report Share Posted January 27, 2017 5 minutes ago, par said: I attempted a full power run like you are describing and I also have a 3 blade prop. I noted an increased amount of vibration at full power. Is this a common issue with a 3 blade prop? If so, what is the solution? Most (not all) three blade props on four cylinder engines seem to vibrate more than their two blade counterparts. Quote Link to comment Share on other sites More sharing options...
carusoam Posted January 27, 2017 Report Share Posted January 27, 2017 (edited) Power strokes vs number of blades causes a bit of vibration under certain conditions... Combine that with blade angle and air speed while the plane is moving or accelerating through the air. Where does the power stroke occur compared to the angle of attack/attitude of the airplane...? If there is a solution, add a pair of cylinders to go with the fancy prop... keep in mind that some vibrations may be caused by something else like worn or broken parts. PP thoughts only, not a mechanic... Best regards, -a- Edited January 27, 2017 by carusoam Quote Link to comment Share on other sites More sharing options...
Cyril Gibb Posted January 27, 2017 Report Share Posted January 27, 2017 52 minutes ago, Hyett6420 said: How can that be so if the diametric distances between the blades is the same and rhey are dynamically balanced? All crankshafts bend and twist during normal operation. Typically in a 4 cylinder car engine there are 5 main bearings. (each crank throw is supported on both sides). On a 4 cylinder aircraft engine, there are only 3 main bearings. That allows much more flex in the crank. Depending on the orientation of the prop blades to the crank throws, there can be more (or less) twisting which causes vibration. If the vibration is a crank/prop resonant frequency under high power, things can break. That's why we usually have an rpm range we should avoid. Propellers don't act like a flywheel. I'm still trying to get an opinion from Lycoming or Hartzell if it's advisable to reclock the prop on my F to reduce vibration as specified in SB M20-206 for early Js. 2 Quote Link to comment Share on other sites More sharing options...
TTaylor Posted January 27, 2017 Report Share Posted January 27, 2017 1 hour ago, KLRDMD said: Most (not all) three blade props on four cylinder engines seem to vibrate more than their two blade counterparts. I have found the opposite, most 3 bladed I have flown have been smoother. Quote Link to comment Share on other sites More sharing options...
Mcstealth Posted January 27, 2017 Report Share Posted January 27, 2017 2 hours ago, Hyett6420 said: How can that be so if the diametric distances between the blades is the same and rhey are dynamically balanced? Because.......... Quote Link to comment Share on other sites More sharing options...
Hank Posted January 28, 2017 Report Share Posted January 28, 2017 5 hours ago, TTaylor said: I have found the opposite, most 3 bladed I have flown have been smoother. Digging through my logs during annual last weekend, I found that my 3-blade Hartzell was last balanced in June 2002, when it was installed. My new IA (2nd annual with him) has a side business balancing props, so we checked mine. Cold start on a 70° day, hasn't run in a couple of weeks, fired off and running on the 2nd blade. Warmed at 1000, then 1200, 1500, 2000 and 2700. Needed more braking pressure for the last. Found my mechanical tach (replaced at the same time as the prop by the PO) was reading low by 22 RPMs, and the balance read 0.01, so I shut down, pushed her back inside and started greasing and lubing under the belly. Not bad for an old, shaky 3-blade prop! Quote Link to comment Share on other sites More sharing options...
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