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aarongleixner(at)sbcgloba
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 Posted: Sun May 06, 2007 10:19 am Post subject: Engine Mount and Propeller Impacts on Airframe Vibration |
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I am at the point of ordering my engine and prop for the RV-10 and need to make a decision. My RV-8A has an O-360-A1A with Hartzell CS Prop, and the airframe vibrates in flight more than I would like, so I want to make sure it will be better on the RV-10. I have three questions that I'm hoping someone can answer:
1) I've heard that Lord engine mounts do a better job of damping vibration than the mounts that Van's sells in the FWF kit for the IO-540. Anyone have experience with this on the RV-10? The Lord mounts cost more, but if they improve vibration, the extra cost would be worth it.
2) Is there any back-to-back data on the Hartzell 2 blade vs MT 3 blade? I saw Van's comparison, but it wasn't really back-to-back. Do you really loose 5 kts with the MT 3 blade? Does anyone have a subjective feel for the vibration difference between the two?
3) For those flying the IO-540 with the Hartzell 2 blade, how good or bad is the vibration level? Do you ever find yourself wishing you had traded the 5 kts and lower cost for the lower vibration of the MT prop?
Aaron
[quote][b]
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rv10builder(at)verizon.ne
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| Posted: Sun May 06, 2007 11:02 am Post subject: Engine Mount and Propeller Impacts on Airframe Vibration |
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Aaron;
Great questions! Search in the vansairforce.net forum and the archives for other answers, but from what I recall since, I myself asked these questions here is the responses.
Consider getting the blade on your RV-8 balanced, may make a world of difference.
2) * Is there any back-to-back data on the Hartzell 2 blade vs MT 3 blade?
I followed up with the builder of the 3 blade of this test last year- here is the fact of the results:
Just because an engine is stamped 310 hp doesn't mean it is producing that hp. allegedely mine dynoed 310 hp (at) 2800 rpm. I don't run it at 2800 rpm. It might even be 350 hp at 3000 rpm. I've limited it to 2700 RPM because that is the propeller limitation. When Van and I flew side by side at 8,000' and WOT, the fuel flows were within .3 gph and mp was within .5", so I believe we were actually matched. The factory a/s indicator read 7 mph faster, but our GPS were within 1 kt of each other. I have 2 independent a/s indicators and they were equal, and I have had them calibrated to 20,000. I can always count on 166-170 knots TAS. I assure you if I were 12 mph slower I wouldn't settle for it.
*Does anyone have a subjective feel for the vibration difference between the two?
We notice we are not fatigued at the end of the trip as we have been on our other airplanes over the years (Rv-4, RV-6, Kitfox, Bonanza, C-182). The only annoyance is getting the lower cowl on and off, but after the 1st 100 hours it doesn't need to come off as much. No regrets here. 
3) I gather you'll get a whole lot of information on this. Tim olsen has his blade balanced and I believe he even mentioned why he chose the 2 blade- check out his great site (although as history shows, I guarantee he'll respond in detail for you anyway) http://www.myrv10.com
My experience, as I was blessed to get a ride in the 3 blade MT RV-10, is the comfort is far more important to me, (and my family) than any speed I may get- so I see a 1-2% increase, at 177kts I am quite happy with a smooth running airplane, and as the builders I have spoken to who own the 3 blade each comments on the comfort flying and after landing (in the form of fatique). I just started looking at the plans but I knew from the start that I was going 3 blade.
What is more important to you? do YOU want that extra few knots or that extra comfort to maybe go a little further on those cross countrys without the added fatigue? is your intention to stay local? than 3 blades will get you higher sooner than a 2 blade, and cruise is rather insignificant in the big scheme of things anyway.
Oh and is cost a factor? more to buy that MT, let alone an Aerocomposite prop than a Hartzell. So it does come down to is comfort and climbing performance worth the extra bucks?
Pascal
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Tim Olson
Joined: 25 Jan 2007
Posts: 2879
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| Posted: Sun May 06, 2007 3:17 pm Post subject: Engine Mount and Propeller Impacts on Airframe Vibration |
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A couple things...
Re: #1) I think the mounts that come with the kit ARE Lord mounts.
They seem to be fine.
Re: #2) I don't really see there being a big enough difference in
speed or any other things to matter, depending on your preference.
The two props to have a completely different feel in the airplane
though, but I wouldn't say one is better than the other. I prefer
the lower pitched sound of the two blade to the more high pitched
sound of the 3, although I won't argue that the 3 isn't smooth, because
it's very smooth...it's just different, and it gets to be a personal
preference. Advice...fly in 2 -10's with both props, if you can.
Re: #3) If you take the time for dynamic balancing, you should be
happy with either choice as well. The 6-cylinder engines are far
smoother than the 4-cylinder modesl, so even an IO-540 with a
slightly out of balance prop is probably smoother than most 4's
that you've flown in. If you balance either, then I think either
would make you happy. It's all personal preference, including the
looks, and the relative ease of cowl removal with a 2-blade...to
each, his own.
Tim Olson - RV-10 N104CD - Flying
do not archive
Aaron Gleixner wrote:
| Quote: | I am at the point of ordering my engine and prop for the RV-10 and need
to make a decision. My RV-8A has an O-360-A1A with Hartzell CS Prop,
and the airframe vibrates in flight more than I would like, so I want to
make sure it will be better on the RV-10. I have three questions that
I'm hoping someone can answer:
1) I've heard that Lord engine mounts do a better job of damping
vibration than the mounts that Van's sells in the FWF kit for the
IO-540. Anyone have experience with this on the RV-10? The Lord mounts
cost more, but if they improve vibration, the extra cost would be worth it.
2) Is there any back-to-back data on the Hartzell 2 blade vs MT 3
blade? I saw Van's comparison, but it wasn't really back-to-back. Do
you really loose 5 kts with the MT 3 blade? Does anyone have a
subjective feel for the vibration difference between the two?
3) For those flying the IO-540 with the Hartzell 2 blade, how good or
bad is the vibration level? Do you ever find yourself wishing you had
traded the 5 kts and lower cost for the lower vibration of the MT prop?
Aaron
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