CS FP tradeoff

[N941WR]

Originally Posted by pierre smith

Climb probably suffers a little, we're getting 1500FPM at 140 MPH and a little more at 130.

1500FPM on a climb prop! That is outstanding! Ever flown a fully loaded 65 hp T-Craft on a 95 degree day? I think you would be lucky to see 200FPM.

[gmcjetpilot]

Originally Posted by osxuser

You post on this topic so much George, there ought to be a sticky:

Perception VS. Reality, GMCJetPilot on FP Vs. CS, which brands, and why.

I have no Idea what you are saying or why, but I just thought the picture was a good one and the write up was also good. I did not say if FP or CS was better. As for Brand's, I do think the Sensenich and Hartzell are the best value, best performing, best supported and lowest maintenance props you can get, and these opinions are based on facts. People who have no facts tend to divert the discussion with nonsequitors or make personal comments. Deal with it.

When a companies with the expertise and experience of Sensenich and Hartzell decide to go after a specific market, making props optimized for our (RV's), you can expect them to dominate.

If you have something intelligent to say about the topic and not about me and my many "sticky" posts(?), great; I would like to read them. Other wise your opinion is noted. Have a nice day and a Great Christmas. George

Originally Posted by Kyle Boatright

One item the original poster mentioned is that a C/S prop is better for climb, cruise, and economy.

If you choose a fixed pitch "cruise prop", that prop will perform just as well in both economy and speed in the cruise portion of flight. The trade off will come in short field and climb performance. KB

Kyle exactly, and since Sensenich is optimized for RV's (HP, RPM's, speeds, altitudes) they are pretty awesome. That is my point, it is hard to beat props made by companies that have been in business for 70-80 years, who put their effort into making special props just for RV builder/pilots. There are many props out there and one size does not fit all, to each their own. However metal props have an edge in efficiency due to thinner blade thickness. 10-15 years ago I thought the CS prop was the only way to go. With the Sensenich the choice is harder. For me I prefer a CS prop. With the RV-7 I need the weight on the nose and can afford the exter cost. However I got a $2,500 used rebuilt Hartzell and $500 Woodward governor. So for about a grand more than a fixed pitch I have a CS prop.

There where just no acceptable FP metal props years ago and the only acceptable FP props where wood, although good, they are just not quite up to the efficiency of metal. With purpose built Sensenich FP props, documented excellent performance, the FP vs. CS is more a matter of $$$$, weight and complexity and less about performance.

As far as FP vs. CS cruise performance / efficiency, with the Sensenich it is no longer as big an issue, since Sensenich has good cruse efficiency, although as you say t/o, climb and landing will suffer a little (landing because the fixed pitch has more residual idle thrust). Also CS props are better for Acro and formation flying, but this kind of flying is not an issue from many RV pilots. Another advantage of the Sensenich FP over wood is it can be re-pitched. Still wood based props will always be "smoother", however a well made balanced metal prop (FP or CS) on a balance engine has very acceptable smoothness, but this is subjective. George

"all opinions are mine and for entertainment purpose only, based on 25 years in aviation including building 2 RV's, aerospace engineering and pilot experience. I am not personally familiar with any other brand of prop than the ones I address, so take it or leave it."

[LessDrag]

In response to the original topic;
MT counterweighted blade CS propeller starts at a coarse pitch with oil pressure from the governor moving them to fine pitch. In the event of an engine failure, or even just a loss of oil pressure, the propeller blades go to a coarse pitch.

According to MT Propeller, feathered blades reduce the propeller drag by 88%.
The counterweighted blades in coarse pitch reduce the propeller drag by 67%.
When compared to the standard configuration low pitch CS propeller.

Regards,
Jim Ayers

[whifof100ll]

Originally Posted by Kahuna

And there is no way I would put glide distance in any top 10 list for either prop. The difference is minisquel and the issue remote.
Best

I have been one of those lucky guys who has flown about 2000 hours with no engine failures. This means that I am due. Engines will fail. When this happens, depending on where it happens, reduced drag might become a higher priority than cruise speed, climb rate, fuel efficiency, sex appeal, money, hair loss, or world peace.


IMO it ranks among the top one.

Regards,
Dale

[whifof100ll]

Glen Thompson

Thanks,

I did not mean to fuel a debate on which prop to buy, but wanted to explore glide performance issues.

This was exactly what I was looking for.

Regards,
Dale

[whifof100ll]

Originally Posted by LessDrag

In response to the original topic;
MT counterweighted blade CS propeller starts at a coarse pitch with oil pressure from the governor moving them to fine pitch. In the event of an engine failure, or even just a loss of oil pressure, the propeller blades go to a coarse pitch.

According to MT Propeller, feathered blades reduce the propeller drag by 88%.
The counterweighted blades in coarse pitch reduce the propeller drag by 67%.
When compared to the standard configuration low pitch CS propeller.

Regards,
Jim Ayers

Thanks Jim,

Worth looking into!

I guess MT prop governors with Hartzell props do not act as you describe correct?

[osxuser]

Originally Posted by whifof100ll

Thanks Jim,

Worth looking into!

I guess MT prop governors with Hartzell props do not act as you describe correct?

Not quite sure what difference the governor would make. Any governor that uses oil pressure to decrease pitch should work as described. If i'm not mistaken, Hartzell, Woodward, and McCauley all make governors that fit this description. Any prop in the course pitch configuration should create less drag, the numbers may not be exact, but should be close to those quoted by MT for any brand. Hartzell's composite Aerobatic prop uses oil pressure to decrease pitch, as do ALL multiengine props.

[Kevin Horton]

Originally Posted by LessDrag

In response to the original topic;
MT counterweighted blade CS propeller starts at a coarse pitch with oil pressure from the governor moving them to fine pitch. In the event of an engine failure, or even just a loss of oil pressure, the propeller blades go to a coarse pitch.

Sorry about coming into this late - I just found this thread.

I'm puzzled as to why the MT would go to coarse pitch following an engine failure, if the engine's oil system is still functional (e.g. failure due to fuel starvation). The engine will be windmilling, so the engine's oil pump will deliver oil to the prop governor. The prop governor's internal oil pump will boost the oil pressure to allow it to govern the prop. If the windmill RPM is lower than the governor's set point, then the governor will drive the prop to fine pitch. Am I missing something?

[penguin]

AFAIK the MT props with counter weights are primarily designed for aerobatics. When flying aeros a common scenario is to lose oil pressure at the top of a vertical climb (when your inverted oil system is improperly set up). In this case the throttle is wide open, the last thing you want is for prop balde pitch to decrease, and engine rpm to go wild, with no oil pressure. It's preferable for the prop to go to coarse pitch, briefly bogging the engine, curtailing your vertical excursion. You then have no choice but to get to pointy end toward the ground, restore oil pressure, and engine well being.

Pete

FWIW to avoid low oil pressure the firewall oil valve should be mounted at a 10 or 15 degree angle from the vertical (bottom sticking out), so the system transitions to inverted mode (pick up at the back & top of the engine) in vertical up lines and normal mode (pick up at the front of the sump) in vertical down lines.

[Vern]

Although my experience was not in an RV, I once had a chance to either eject or land gear up in a North American OV-10 Bronco due to a mechanical failure. The procedure required feathering both props and shutting down both engines about 1/4 mile out. After practicing the approach a few times, I shut 'em down.Man, was I surprised when the Bronco shot ahead, gaining 30 plus knots rapidly as the props feathered.

Ancient history!