fixed pitch vs. constant speed

[JonJay]

Originally Posted by mlwynn

Hi all,

I recently converted my RV 8, IO360M1B from a three blade Catto to a Hartzell composite. There have been a number of pluses and and number of minuses.

On the plus side, markedly better acceleration. Much shorter take off run. About 20 kts improvement in top speed (I would overspeed the prop with much more than 19" MP at cruise). Aerobatics work better as it climbs better and the flat prop also provides a little more wind resistance in the down line. I can make substantially shorter landings now with a giant air brake in the front.

On the minus side: Definitely louder, especially at cruise speeds. More vibration although not uncomfortably so. My CG moved quite a bit forward, which sometimes a plus and sometimes a minus. I usually keep #25 ballast in the rear luggage compartment if I don't have a passenger or baggage.

In general, I thought the airplane was more ladylike with the FP prop: smooth, maneuverable, easy to land and take off. With the CS, it is much more of a tiger. More torque on take off to adjust the rudder for, need much more care in landing as I can't tell how much power I have by listening to the engine--the RPM is pretty high until the throttle is way reduced. Also, if you come completely off the throttle at speed, there is kind of a backfiring that goes on. Doesn't sound like it could possibly be good for the engine. Glide ratio was better with FP.

In the final analysis, I am glad I made the transition. I think the overall performance improvement was worth the time and expense to make the change. The actual installation with pretty simple and straightforward.

I think you summarized the positives and negatives very well. Assuming you are injected, it is typical to have that "popping" when dumping the throttle. I don't think it hurts anything.

[Michael Henning]

Get it balanced to smooth it out. Two blade has a larger diameter than a three blade configuration, so a higher tip speed equals more noise. I have the WW150 three blade and am loving it. I too get the popping if I come off the throttle at a high speed, but as the plane slows down the popping goes away.

[bret]

Did you pull the prop back when comparing the glide ratio? not flying my 7A yet but our 172 would accelerate when I pulled the prop to course pitch from an idle setting when I would practice power out landings.

[mlwynn]

Hi all,

I did dynamic prop balancing before the first flight with the new propeller, so I think that issue has been addressed. I have tried glides both with the propeller in high RPM (where it would go with engine failure and loss of oil pressure to keep it closer to feather) and with the prop control pulled back. Makes a really big difference to have the prop pulled back, but I can't necessarily expect that to be possible in an engine failure situation. So, there are really two best glide speeds. Still working on defining those. The folks who make my AOA indicator say that the best glide speed is one green bar. That seems to be pretty accurate, in so far as I have been able to measure thus far. The nice thing about AOA is that it takes into account weight as well as drag. Anyway, more data to follow.