AeroComposites - 3-Blade - TMX-O-360

Hey folks,

I would like to get feedback on expected performance for a 3-blade prop and any recommendations on moving to a larger blade diameter. The situation is I originally ordered a 72-inch 2-blade Aerocomposites prop, and due to a number of issues, ended up with a 3-blade 68-inch prop. I'm turning the prop with a TMX-O-360 Red-Gold, RV-7, tip-up;

At 75% cruise, the best I can do is about 184 MPH TAS, 65%, 177 MPH TAS, WOT, maximum speed is 197MPH. Airplane is flying straight, balanced, etc..

A few questions:

Are these cruise speeds in the ball park?
Can I push a larger diameter 3-blade prop, say 72 inches with 180HP?

Reason for asking is we were expecting to loose 2 or 3 knots with the AC 3-blade prop, versus 2-blades, from the book numbers, but, we're down 10-15 knots (or so it appears). In a side-by-side comparison with an RV7A, I need to run about 2 inches of MP higher to obtain the same speeds, until I run out of throttle.

The disconcerting aspect is the AC propellor is NOT custom designed for the 68-inch, as I understand it, they start out with a 78-inch prop, and simply lop off the tips to get the desired diameter. I have about a four inch wide prop tip, looks like the end of a canoe paddle.

I have not been successful in obtaining a 2-blade prop from ACI up to this point in time, it has been nearly a year of lobbying.

I am running the MT 3 blade MTV-12-B/183-59b (72'') on my RV7A powered by an Aero Sport Power IO-360M1 with dual Lightspeed 11 EIs
On a 5 hour flight yesterday in good calm conditions at 8500 ft, OAT 3 deg C, QNH 1014 mb I was acheiving a TAS of 163 knts running 22/24 and 40 deg LOP at a fuel useage of 29.5l/hr. Running ROP best power it TAS's out at about 173 knts at 40 l/hr at that altitude.

bondiRV7A

bondiRV7A said:

I am running the MT 3 blade MTV-12-B/183-59b (72'') on my RV7A powered by an Aero Sport Power IO-360M1 with dual Lightspeed 11 EIs
On a 5 hour flight yesterday in good calm conditions at 8500 ft, OAT 3 deg C, QNH 1014 mb I was acheiving a TAS of 163 knts running 22/24 and 40 deg LOP at a fuel useage of 29.5l/hr. Running ROP best power it TAS's out at about 173 knts at 40 l/hr at that altitude.

bondiRV7A

Click to expand...

Thank you!

I generally cruise about 0.5 inch below maximum MP at any given cruise altitude, 2350 RPM and ROP about 25-50 degrees seems to give me the best cruise performance, fuel flow 10.5 GPH, 40l/h, between 8-9K,

Based on your numbers I'm 10-12 knots slower.

Do you have any issues with turning maximum RPM for T/O? I realize we really don't need that much power for T/O, the plane literally leaps of the ground as it is.

Cheers

Your numbers are very much in line with what I've personally seen on probably 7-8 different 7s... (give or take a knot or two)... so in a way I wouldn't be too worried..

I use full RPM (gov set to 2710) and throttle to the stop for take off until settled into the climb at about 400-500ft and ease back to 25/25 for the climb to criusing altitude. Not a bad idea to reach a safe manoeuvring altitude and airspeed ASAP. The MT prop has a max RPM of 2800 and no speed restrictions. I usually lean progressively to cruise altitude keeping the EGTs, CHTs, and Oil temp in the correct zones.

BondiRV7A