Electric CS prop not recommended for acro

[agent4573]

So the RV7 read ahead plans and the MT prop order form both say that electric constant speed props are not recommended for aerobatic maneuvers. Can someone point me to the supporting evidence for this statement? I'm trying to decide on the major components for an upcoming build and would just like more info on why you cant just set an electric prop to the climb position and go do your routine. Is there a safety concern somewhere or is it just a performance issue? Thanks in advance.

[FORANE]

They are slower to change pitch. I suspect you would be at risk for overspeed if using one in acro.

[Southern Pete]

Yes, the pitch change mechanism is too slow to motor the blades from full fine to coarse (or the other way) when the throttle is moved quickly. The alternative is to select manual and fly as a fixed pitch for a few minutes, or fly only gentle aerobatic figures and don't move the throttle very quickly. MT recommendation somewhere in their documentation.
Pete

[49clipper]

I talked to AirMaaster at OSH and they informed me the new drive motor is faster and it has been flown aerobatic. I am done with aerobatics at this point in life, but I am putting one my current build. (not an RV)

[breister]

Originally Posted by 49clipper

I talked to AirMaaster at OSH and they informed me the new drive motor is faster and it has been flown aerobatic. I am done with aerobatics at this point in life, but I am putting one my current build. (not an RV)

Bud is a great guy, but he is also owner and chief salesman for his product. My guess is that he said something VERY similar to what you said and that his statement is literally true - their props probably do pitch faster than MT props (their only real competitor for higher horsepower electric props).

When you do a loop, in the downward portion your speed can build VERY quickly. Hydraulic props change pitch so fast you are unlikely to overspeed; electric ones would likely require you to yank the power to prevent that, then push it back in approaching the bottom of the loop.

I've done some aero with both fixed and C/S hydraulic props. Treat it like a fixed and you will >probably< be ok.

[agent4573]

Pete, do you have a link to the MT documentation you referenced? I looked through their site but couldn't find anything specific about it.

Anyone know how fast a hydraulic prop changes angle? 2 degrees a sec, 5, 10? I know it's based on oil pressure and temp, but let's assume both are in the green on an average engine. The MT service manuals don't say much in the way of real numbers, and I don't have access to those overhaul manuals to look through them.

The only real difference I could find that's documented is that normal hydraulic cs props will go flat with oil pressure loss, acro hydraulic cs props will go full forward, and electric cs props will stay exactly where they are when they failed.

[mike newall]

Group in the UK bought an RV8 with an MT electric prop. Now having to set it manually and fly aerobatics almost as a fixed pitch prop.

The electric prop is great, but for touring, not stunting.

We have a hydraulic 3 blade MT on our RV7 and it is absolutely faultless, great take off and landing performance, super smooth, looks great and sounds awesome as you run in at 200kts 25/25 before you start your twirls....