CS FP tradeoff

Since I have not yet selected a prop, I have been reading about the FP/CS tradeoff issues. I understand CS is better for climb, ecomony, cruise, ect. FP better for cost, weight ect. One disadvantage that I have recently considered came to light when interviewing a freind after an engine failure in his Hartzell equipped RV. He said he came down like a rock. The same thing that gave him very good control of decent speed and short feild landing performance, costs him in glide performance. Since these props do not have a feather position like a twin, I would think they would flatten out on loss of power trying to maintain the RPM. Has anyone experimented with pulling the black knob all the way out, then pulling the blue one to see if it improves glide distance.

I think here a wood cruise prop would have the advantage since it would maintain it's high pitch, and has low intertial mass which combine to allow the prop to stop windmilling at a higher airspeed.

I know that stopping a CS prop would greatly increase glide distance, but I would not want to think about that in an emergency situation. Also I would worry about departing too much from best glide speed.

Relevant experiences would be appreciated.

Regards,
Dale
RV-6 finishing kit.

Pulling prop knob

Yes, pulling back the prop control lets the plane surge forward as the drag goes away. I don't know when you lose control of the prop but as long as the prop is windmilling there seems to be enough oil pressure to control the blade. Surely somebody on the list has the particulars on this, but by simulating an engine out the effect is pretty dramatic.

Bryan 9A "Flyin the Flag"

If it doesn't weight to much more, a full feathering prop will increase your glide a LOT .

ahh. not exactly

whifof100ll said:

Has anyone experimented with pulling the black knob all the way out, then pulling the blue one to see if it improves glide distance.Dale
RV-6 finishing kit.

Click to expand...

It does nothing on a 540 with a "Check" governor. Prop cycle rmp is above 2200rpm and the windmill rpm is not close to that.
Rats.
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

FP vs CS props

Ours was a money issue. We decided to go with a Catto 3 blade, pitched for max cruise on our 6A. Without gear fairings or wheel pants, our 0-360 carbed Lyc yields 172/174MPH (GPS verified) at 2550 at 2000' or so (We're running 75% to seat rings). The airplane flies like a dream...just absolutely incredible little airplane at 1046 lbs empty. It is hard to slow down for sure and glides really well considering the short postage-stamp sized wings!
I noticed that the elevator is down a little bit at speed (about 1/4 inch at the counterweight) and we'll probably shim the stab and gain yet more speed. The reason is 1) A light prop instead of a heavy CS on the nose 2) Incorrect stab angle, even tho' built to plans. I don't know what speed we'll gain, if any, by raising the stab but I really like the characteristics of the FP Catto so far........and smoooooooth as silk! Climb probably suffers a little, we're getting 1500FPM at 140 MPH and a little more at 130. Haven't done all the various airspeed combos yet, just enjoying the Sojourner every time we can,
Pierre

Fixed vs. Constant Speed

http://www.hartzellprop.com/kitplane/kitplane_certified_prop.htm


Select Performance or scroll down just past the top box to performance and there is a short write up on fixed vs. Constant Speed. My recommendation:

Here is a pitcture: http://www.hartzellprop.com/new_images/prop_eff_big.jpg

Fixed: Sensenich
C/S: Hartzell Blended Airfoil

George

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.

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

Actual flight testing...

As I was testing a friend's RV6A a couple of years ago, during my engine out testing ( Yep, except for Jims' 10, per his request, I test ALL my planes in the "glider" mode) I found the following...Actual flight testing!....
****RV6A, 1150 empty weight, 1550 test weight. O-360 A1A with C/S hartzell, altitude 10,000' over Pahokee airport, Fl.
****Cooled down engine slowly....80MPH, idle gave 750 fpm decent rate, RPM, 1200.
****Pulled mixture, no noticable sound change,or feeling whatsoever!!!! Just a rapid A/S decay at same pitch attitude. Note also, RPM stayed at 1200, (8.5 compression pistons, higher comp. pistins IMHO will spin at slower RPM) BUT,then, VVI went to 1050 fpm to maintain 80 MPH!, Yep, guys, if you have a failure, you will not sense it (C/S propeller) until the A/S drops, and sink rate develops, hence the "RV sink" when engine fails...
****Pulled prop control full aft, yep, as I assumed, at 1200 RPM, prop will not govern (hartzell govenor) and there was NO CHANGE in RPM or sink rate. Prop remained at low pitch stop regardless of prop lever setting.
****Tried to stop prop next. This proved to be very hard, as the plane stalled before the prop would completely stop spinning. I found that I had to pull the nose up and get down to less than 40 MPH by a 0 G pushover to get the prop to stop. And, it stopped rotating verrrrryyyy slowly, as in, I had to push over, get like, 120 MPH, pull the nose WAYYYY up and 0 G for quite a while (as in not just quickly push over) to get the prop to finally, actually stop spinning.

****VVI now settled in at 700FPM with prop stopped.!!!!!!!!! This is VERY important for all to note re. this thread topic. C/S vs. FP are 2 different animals with engine off.!!!!! BTW... . IMHO, my best unobserved guess, the FP RV will be somewhere between 800 and 900 FPM deadstick unless you can get the prop stopped, which IMHO will be even more difficult due to the higher pitch of the FP blades. Note that my Kitfox with an 0-290 and a warp drive prop set at 14 deg, the prop can be stopped but will not stay that way at my best glide speed. YMMV.

****Next, I made sure the engine would start easily with the starter. Started like a champ on the first blade.

****Next, engine shut back down (still 6000' to go, and time to even do some "glider" stalls and acro!!!), Prop stopped again...as I approached 100 MPH, the prop started to slowly turn against each compresion cycle and at 100 MPH engine was back up spinning again.

****Engine was this time restarted at idle and full power with prop spinning. Immediatly after pushing in mixture the engine lit and was back to life.

Bottom line to all, if engine quits, prop still spinning and you do not have around 1000 FPM, your A/S will be decaying rapidly, and a very dangerous "RV sink" will be in your immediate future! This should apply to the 3,4, 6,8...A little less to the 7,..Even less to the 9, and the 10? Well, it is just a pussycat all around, like a 4 place Cub IMHO and observation during testing.

I hope this has shed some light on those too timid to actually experience their first engine failue as a planned, controlled, high altitude experience. This, as compared to a Linen soiling 300' AGL during takeoff, life altering experience, as a desceased friend found out during his first and last fatefull engine failure on takeoff.

Parting comment, ...Engine failure?????? GET THAT NOSE DOWN RIGHT NOW !!!!!!!

Glen

pierre smith said:

I noticed that the elevator is down a little bit at speed (about 1/4 inch at the counterweight) and we'll probably shim the stab and gain yet more speed. Pierre

Click to expand...

I was considering doing the same thing on my RV6 but if you read the section on flight test procedures in chapter 15 of the manual, you will see that Van's recommends about a 1/4" at the counterweight in cruise configuration. This apparently helps with pitch stability. I'd think twice before reducing it.

Doug Meloche

pierre smith said:

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

Click to expand...

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.

Thanks for your opinion

osxuser said:

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.

Click to expand...

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

Kyle Boatright said:

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

Click to expand...

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."

CS FP tradeoff - an alternative

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

Glide distance

Kahuna said:

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

Click to expand...

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

RE, Glen Actual Flight Testing RV6A

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

LessDrag said:

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

Click to expand...

Thanks Jim,

Worth looking into!

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

whifof100ll said:

Thanks Jim,

Worth looking into!

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

Click to expand...

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.

LessDrag said:

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.

Click to expand...

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?

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.

Feathered Props

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!

Another reason to stop the prop..

I'd like to recognize and thank Gregory Young for his July 14, 2001 sincere report on his first and last RV flight. An excerpt is as follows.. (http://www.vansairforce.net/gregyoung.htm)


"....It wasn't slow and it wasn't pretty. I was
worried about maintaining speed during the turn and avoiding a stall/spin.
The descent rate was enormous with a windmilling CS prop......"

One more eye opening reason and justificatoin for stopping the prop (if able and you are capable) and/or knowing how an aircraft flies when the fan stops working....... in a CS engine failure situation.
Any questions?

Glen

Hartzells and acro

Penguin: We've flown a Pitts S-2A for many years in a lot of acro including advanced competition. The plane has an angle valve 200HP Lycoming and a Hartzell CS prop. Despite all that acro, including much negative G and lots of transitions as well as zero G parabolas just for fun, the Hartzell never once showed any overspeed tendancy. Even with the Christen inverted system, oil pressure drops substantially for brief periods, one time being during any transition from pos to neg G and the worst in right knife-edge flight. We've also experimented with moving the prop control to coarse pitch (low RPM) and found the prop RPM on the Pitts does decrease (at 100 mph IAS) and so does the sink rate. It's still pretty high - a friend says he figures where he can throw his car keys and plans to land there - kidding a little! Have not stopped the prop on the Pitts S-2A but have done so on S-1S Pitts and Cessna 150's and 172's. In all cases the perceived decrease in drag and descent rate was striking. In all three airplanes it was necessary to really stall to stop the prop. The Pitts took 175 mph indicated to start the prop again. The Cessna's were restarted with the starter. The only attempted stopping of a CS was on a T-34A. The nose gear failed on TO and I orbited for over 2 hours while the authorities quarelled about who was going to foam the runway - so there was plenty of time to think. The T-34 has a special extra coarse (semi-feather) postion accessible on the prop control by going past a detent. The plane accelerates when you move to this position and rpm slows quite dramatically. Even so, I couldn't get that prop to stop at the forward CG condition of that flight, with a full stall. I wanted to stop the prop so it could be put in a horizontal postion before a dead-stick landing as this would avoid prop damage. As it turned out, the only damage was to the prop tips, the nose gear doors (minor) and the augmentors. I wonder what my RV-8 with Hartzell Blended Airfoil and Hi comp pistons will do when and if it's finally done? Bill

Q

Bill Dicus said:

Penguin: We've flown a Pitts S-2A for many years in a lot of acro including advanced competition. The plane has an angle valve 200HP Lycoming and a Hartzell CS prop. Despite all that acro, including much negative G and lots of transitions as well as zero G parabolas just for fun, the Hartzell never once showed any overspeed tendancy. Even with the Christen inverted system, oil pressure drops substantially for brief periods, one time being during any transition from pos to neg G and the worst in right knife-edge flight. We've also experimented with moving the prop control to coarse pitch (low RPM) and found the prop RPM on the Pitts does decrease (at 100 mph IAS) and so does the sink rate. It's still pretty high - a friend says he figures where he can throw his car keys and plans to land there - kidding a little! Have not stopped the prop on the Pitts S-2A but have done so on S-1S Pitts and Cessna 150's and 172's. In all cases the perceived decrease in drag and descent rate was striking. In all three airplanes it was necessary to really stall to stop the prop. The Pitts took 175 mph indicated to start the prop again. The Cessna's were restarted with the starter. The only attempted stopping of a CS was on a T-34A. The nose gear failed on TO and I orbited for over 2 hours while the authorities quarelled about who was going to foam the runway - so there was plenty of time to think. The T-34 has a special extra coarse (semi-feather) postion accessible on the prop control by going past a detent. The plane accelerates when you move to this position and rpm slows quite dramatically. Even so, I couldn't get that prop to stop at the forward CG condition of that flight, with a full stall. I wanted to stop the prop so it could be put in a horizontal postion before a dead-stick landing as this would avoid prop damage. As it turned out, the only damage was to the prop tips, the nose gear doors (minor) and the augmentors. I wonder what my RV-8 with Hartzell Blended Airfoil and Hi comp pistons will do when and if it's finally done? Bill

Click to expand...

This is what I/we/lurkers are looking for in posts!! Great info!!! Question though... When you said................" ...We've also experimented with moving the prop control to coarse pitch (low RPM) and found the prop RPM on the Pitts does decrease (at 100 mph IAS) and so does the sink rate. It's still pretty high - a friend says he figures where he can throw his car ...".................. Was that engine off or on?? Also, in the T-34 incident, did you try to stop the prop with the prop lever towards high RPM also? It appears to me the less the prop pitch, the harder to restart the prop..
Glen

Props

Glen: Relative to Pitts glide, it seemed steep either way, just a little less so with engine stopped. The pitch attitude to maintain 100 mph IAS was not as nose down with the engine stopped as it was at idle. Neither Pitts of ours has a VSI, so these are really gross estimates. The T-34 - I never thought to try stopping the prop in low pitch/high rpm. I thought it would be harder to stop that way. Should I have tried that? Seemed to me it would be easier to stop it while in the lowest rpm mode (high pitch). Anybody have thoughts on that? Bill

Yep, flat pitch, hihg drag, but...

Bill Dicus said:

Glen: Relative to Pitts glide, it seemed steep either way, just a little less so with engine stopped. The pitch attitude to maintain 100 mph IAS was not as nose down with the engine stopped as it was at idle. Neither Pitts of ours has a VSI, so these are really gross estimates. The T-34 - I never thought to try stopping the prop in low pitch/high rpm. I thought it would be harder to stop that way. Should I have tried that? Seemed to me it would be easier to stop it while in the lowest rpm mode (high pitch). Anybody have thoughts on that? Bill

Click to expand...

Yep, flat pitch is the high drag reigime if engine is stopped, and course pitch impinges upon the prop in a more "torquing fashion". I proved with experimintain in my Kitfox (warp drive ground adjustable), that the prop is almost impossile to keep stopped with the higher cruise pitch setting (15 deg. at tip) as compared to the less pitched, power setting of 11 deg.

Glen