Lose 5-10 knots with a 3 blade prop on a 10?

Subwaybob · #1 03-04-2019, 07:30 PM

Spoke to Vans support today. They (one guy) thinks I'll lose 5-10 kts with the Hart 3 blade prop over the two blade. Is this true? My RV10 will have a Thunderbolt 260hp and POSSIBLY a 3 blade. I sure as snot don't want to lose 10 kts! Any truth to this?

dmaib · #2 03-04-2019, 07:36 PM

True with the MT. Not sure about any other brands.

Subwaybob · #3 03-04-2019, 07:37 PM

Quote:

Originally Posted by dmaib

True with the MT. Not sure about any other brands.

So you lose that much? 5-10 knots??

dmaib · #4 03-04-2019, 07:41 PM

Yep. I'm afraid so.

rocketman1988 · #5 03-04-2019, 07:55 PM

I am very skeptical that there is a 10 knot loss with a 3 blade compared to the two blade. I would believe 2-3 knots...maybe.

If you have definitive, not anecdotal data, please share it...

paul330 · #6 03-04-2019, 09:01 PM

Quote:

Originally Posted by rocketman1988

I am very skeptical that there is a 10 knot loss with a 3 blade compared to the two blade. I would believe 2-3 knots...maybe.

If you have definitive, not anecdotal data, please share it...

Absolutely correct. Couple of knots at most. Verified by racing my 3-blade MT against 2-blade Hartzells at last year's Race for Rhinos. At one stage I spent the best part of an hour 100m or so behind a 2-blade. Tried everything I could to close the distance but couldn't. Eventually he just drew away - maybe 1/2kt. There were a total of 6 -10s at the race and I was the only 3-blader, Results showed us all within 2kts apart from one who was about 4-5kts faster than anyone else - no-one could work out why (supposedly stock aircraft

). He ended up on the podium.

On the plus side - super smooth and (supposedly) better TO and climb performance. Plus the cool factor

Only real downside is getting the lower cowl on and off. Some mods needed to the lower cowl. After a while, you get the hang of it.

BobTurner · #7 03-04-2019, 11:23 PM

Posts like Paul?s above mean nothing; there?s too much variation from plane to plane. The only good test is A-B on the same plane. I?ve only seen one such post; that owner put his 3 blade up for sale after trying a 2 blade and gaining 5 knots, iirc.

paul330 · #8 03-05-2019, 01:34 AM

Quote:

Originally Posted by BobTurner

Posts like Paul?s above mean nothing; there?s too much variation from plane to plane. The only good test is A-B on the same plane. I?ve only seen one such post; that owner put his 3 blade up for sale after trying a 2 blade and gaining 5 knots, iirc.

A little harsh, I think ......

It was a reasonably sized sample so I think the comparison has merit. Again, apart from the one aircraft, not only were we within a knot or 2 of each other, we were also within a knot or 2 of our handicap speed.

Having said that, 2 knots would be worth some 2 minutes over the race. I'd like to try a 2-blade to see what benefit it gives and then swap out for the next race. Full time though, I wouldn't want to give up my MT - love it.......

mike newall · #9 03-05-2019, 04:04 AM

+1 to harsh

Our 3 blade MT 7 will keep up with a 2 blade Hartzell without any issue.

Besides, how often are you running flat out ?

Ultimately, you look at what you want out of your aeroplane and look at the pro's and con's of 2 or 3 blade props. 3 blade is smoother and in our case, the MT has phenomenal acceleration and deceleration, it's smooth and quiet and I cruise just fine at 145kts at 23/23.

vic syracuse · #10 03-05-2019, 04:44 AM

To each their own.

Saying the other airplane was faster because one had a 2 blade and one had a 3 blade means nothing.

The only way to verify for sure is to take the same airplane, at the same weight and power settings, and fly it under the exact same atmoshpheric conditions (pressure/temp/altitude, etc). Period.

BTW, we did that with my RV-10 (swapped props) and noticed no measurable difference in speed. We even took my RV-10 back to the mothership and let Van fly my airplane right next to the factory RV-10, with both Van and I in mine (Van doing the flying) and Ken Krueger flying the company RV-10. At 8500' and full throttle, we were neck and neck. The GPS's on each airplane were within 1 knot of each other. Everyone was surprised.

Without swapping the props it still didn't mean anything except it put to rest all of the hullabaloo that the MT is 10 knots slower.

There are advantages and disadvantages to each prop. one might be smoother, have more ground clearance, and better climb performance. The other might be more durable on unimproved runways, easier to get cowling off, cost less, etc..

Racing is a totally different arena.

Build the airplane for you.

Vic