Low Speeds out of my O200 in my 750?!?

Purchased a Whirlwind 2 blade GA prop and solved my low RPM issues, still only getting 70-75 mph (on Dynon and GPS) in cruise at 2600 RPM. Looking for someone in the Hannibal, Mo area that could offer assistance. We are the 3rd owner on this aircraft with 90+ hours on the airframe and engine but running out of ideas and $$$.

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Permalink Reply by Chris Aysen on June 24, 2014 at 9:26am

 Darin - Did you reduce prop angle setting to get higher rpm?

Permalink Reply by Darin Logue on June 24, 2014 at 10:16am
Yes, slightly but even at a higher angle, the airspeed hasn't changed? I'm confused as all get out. Could really use some help and would like to find someone in my area to take a look at her.
Permalink Reply by Chris Aysen on June 25, 2014 at 7:03am

Darin- If you haven't already. When you get a chance, on a calm day, take it up to about 2500 ft. and adjust elevator trim until you can drop the nose without a decay in altitude. Even a slight nose up attitude can affect forward speed. We can talk about a load of variables but those two, prop and trim, would probably be the biggest.

Best of Luck

Chris

Permalink Reply by Jesse Hartman on June 24, 2014 at 12:29pm

I have heard that they cruise MUCH slower than advertised . You might be close to the true cruise speed.  What did the other owners claim for speed?

Permalink Reply by Darin Logue on June 24, 2014 at 1:03pm
The builder has since passed away and the 2nd owner was no help. Once he got his cash he disappeared. The plane is solid inside and out...just a few minor things I need help with. And....getting her to fly faster than the speed of smell. Ha!
Permalink Reply by Timothy Aanerud on June 24, 2014 at 9:02pm

Keep the ball centered. There's a 5-10 mph difference when you are in a slight skid versus truly straight and level.  The full flying rudder requires more attention to keeping the aircraft level compared to aircraft with a fixed vertical stabilizer.

Permalink Reply by Paul Bonasera on June 25, 2014 at 5:57pm

Ck the Timing on the engine?   Have you Checked the compression???

Permalink Reply by Wayne Tyson Jr on June 26, 2014 at 8:19pm

Does the O-200 manual recommend cruising at 2600 or ? I've heard that Continentals "like" to run a little hot to keep the crud off the valves. I've been advised to keep the CHT on the upper end of the range with my IO-240, and to avoid low power settings, but I still have a lot of reading and learning to do.

The comments on trim and close attention to the rudder has raised a question in my mind about the usefulness, desirability, and feasibility of adding cockpit-controlled adjustable rudder trim.

I have found the electric elevator trim too coarse and incapable of a fine enough adjustment for true hands-off level flight, but then, I have a lot of learning to do yet. But, as a low-time 750 flyer, I find that I have a tendency to climb, possibly because of the exceptionally great visibility over the nose. I hope that I will soon get to the point where I am fully capable of flying this airplane "perfectly." Meanwhile, I'll wait a while to worry too much about the airspeed--unless it is deviant enough to indicate one or more problems in the system. But I'll watch this discussion closely to advance my knowledge as rapidly as possible.

W

Permalink Reply by John Austin on June 27, 2014 at 7:48am

Wayne

I installed an adjustable Ray Allen trim speed control and reduced the trim speed. My trim was too "touchy" and slowing it down made it much easier to precisely trim.

John

N750A

Permalink Reply by Wayne Tyson Jr on June 27, 2014 at 4:31pm

John, thou art the Oracle of the 750 world (not to mention your other contributions), and I am, again, profoundly grateful.

Yr. Ob't. Sv't.,

Wayne

Permalink Reply by Timothy Aanerud on June 27, 2014 at 5:44pm

Here's some real numbers on a CH-750 with an O-200, no slats, vortex generators, 2 bladed ground adjustable prop, empty weight ~830,  two people in the airplane, the ball is not quite centered. 2300 rpm

Permalink Reply by Wayne Koski on September 4, 2014 at 1:00am
Looks like it may need a few speed mods...

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