CS FP tradeoff

[whifof100ll]

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.

[Bryan Wood]

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"

[osxuser]

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

[Kahuna]

Originally Posted by whifof100ll

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.

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

[pierre smith]

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

[gmcjetpilot]

http://www.hartzellprop.com/kitplane...ified_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

[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.

[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

[glenmthompson]

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

[dmeloche]

Originally Posted by pierre smith

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

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