Observed RV-10 flying qualities

[w1curtis]

>Not necessarily true. With constant throttle, there is an optimum RPM that produces the highest ratio of thrust:drag. A higher RPM will decrease this ratio so that the prop acts like somewhat of a speed brake.

Yes, this will happen at low power as I sometimes do on shot final. High RPM sets the blade to a flatter pitch which causes more drag and thus reduces your speed. This is not the same thing that's happening at high power. Again, look at the power charts for most propeller aircraft, highest power (and speed) is with highest RPM.

 

[flyeyes]

If you are seeing an increase in cruise speed at maximum RPM compared to cruise RPM, then you are not optimized for the full range of flight ops.

Ummm, no. I think several things are getting comingled here and causing confusion.

That's why a fixed climb prop is pitched lower - more thrust/drag at low speeds, but its efficiency suffers at higher speeds.

prop efficiency is a factor here but has more to do with the prop planform, airfoil and twist than the average pitch. Fixed-pitch climb props are better for takeoff and climb because they have less pitch, and allow the engine to turn more RPM at low airspeed which means more power available. They are inferior in cruise because you have to limit the throttle to avoid exceeding the engine's RPM limits in cruise. Another factor is that for a given power setting, the lowest RPM that is usable for that power setting is generally the most efficient.

A fixed cruise prop is pitched higher - more thrust/drag at higher speeds but decreased takeoff performance

Similarly, the main reason for the decrease takeoff performance is that the FP cruise prop is pitched too steeply which prevents the engine from turning its full rated RPM (and therefore full power) on takeoff

A FP prop can really only be optimized for a single altitude/power/load. The ideal cruise prop would be one that allows you to just reach full rated (continuous) RPM at your desired cruise altitude, WOT, and your typical load.

A CS prop is better compromise, because it allows the engine to make all the available power, regardless of airspeed or altitude. Prop efficiency does suffer somewhat with increasing RPM, but I'm somewhat sceptical that Hartzell is making a prop poorly suited to the speed range of the RV10, since it is similar to many other airplanes.

The deceleration noted when pushing the prop control forward at low power settings is expected and one of the benefits of a CS prop (it's much easier to land with the extra drag available). This is a different case however when the prop is being driven by the engine rather than the other way around.

Glen, is your piston/prop time mostly in turbocharged aircraft? That might explain the lower observed airspeeds for a given power setting, if you were below the engine's critical altitude.

Most of my time is behind normally aspirated engines and CS props. I have always used the lowest possible RPM for a given altitude and power setting, but have generally found max continuous RPM necessary to maintain reasonable cruise speeds and climb at higher altitudes (above 10-12K)

James Freeman

 

[Bryan Wood]

Engine RPM and Horsepower

Good evening all,

Just thought I'd throw in another factor to muddle things up. If you haven't read any of the "Pelicans Perch" articles on Avweb they are fantastic. There is one that addresses power settings for cruise that is informative and would seem to factor into this discussion. It deals with operating oversquare and the losses that come from running high rpms in cruise. The charts that are used in the articles are for a Continental six in a Bonanza, but the theory should transfer to other engines. Using the graphs generated by the engine manufacturer on an engine test cell the big Continental loses 20hp to friction internally by turning it faster. With similar displacement the same could be true at some level with the Lycoming IO-540. Using the cube root formula this should account for about a 2-3 knot loss. Just a thought. Anyway, if you are interested go to Avweb, use their search for Pelican Perch, and then look for article #65 Cruise. Since I've started running oversquare my plane is just as fast, quieter, and uses slightly less fuel.

Also interesting is another article he has there on oversquare and how most of us were taught not to do it. He gives clear explanations, photos of journel bearings, and how it only pertained to the old radial engines and why. Anyway, the guy seems like a genius from my vantage point.

 

[Mike S]

Guys, think of how and what a C/S prop does---------------it controls the enging RPM by placing a load on the engine by adjusting the pitch.

If Glen is at or close to max power output, and tries to increase the RPM, then the only way for that to happen is for the prop to flatten a bit, unloading the engine. If the lessened pitch creates less thrust at the new, higher RPM, then guess what the plane will do.

Remember that speed is a very complex formula, but if you take drag and effeciency etc out of it, it all boils down to basicly RPM times Pitch.

Still, I do like all of the various comments that have been make here. Keep it up.

Mike Starkey

 

[rv6ejguy]

There is a point where prop airfoil angle of attack is optimal and operating at its best L/D however depending on blade twist vs. rpm and forward speed, this may not be so at all stations along the blade. Thrust will vary accordingly. If we could have a prop with variable pitch, twist and sweep, then we could really get the best performance at all rpms and speeds in all flight regimes. A C/S prop may be no more or even less efficient than a well designed FP prop and indeed we see this with the latest ones offered for RVs in the cruise regime but then of course there is no comparison in the takeoff and climb departments.

If max hp is developed at 2700 rpm, it matters not that frictional losses are higher at 2700 than 2500 as they certainly are. Hp is measured at the prop hub and is what is left over after all losses sap their given amount. SFC will be highly affected by frictional losses and difference in volumetric efficiency with rpm. This is generally why oversquare operation is more efficient in cruise but may not be the fastest.

It would be interesting to look at Lycoming's power/ rpm charts and to do some testing at the same % power using different MP/RPM combos with the standard Hartzell C/S prop. One combination will likely deliver best speed and another maybe a few knots less but lower fuel flows. Van's is rating their cruise speeds at 75% and 65% but don't say at what rpm/ mp they used.

 

[glenmthompson]

RV 10 4 sale now!! (QB kit)

First ladies and gentlemen...Brian, Mike and RV6 guy, Fly Eyes... Your comments are incredibly eloquent and informative. Although you speak in generalities, they are most informative and yuz guyz bring in great info and food for thought.

This plane stuff, is just hard to understand sometimes, and does not always follow conventional wisdom. I guess this is why some of the biggest brains (outside of Vans of course) cannot seem to build a descent plane that goes fast, for good value! I love every comment here, but these comments are the most informative in general terms, IMHO. I am still waiting though, for other 10 numbers either similar to mine (for comparison) or like a post in the general section by a 7 driver I believe,... he gave performance numbers at 7500 ft, WOT and TAS in incriments of 10 RPM. His plane varied only a couple of MPH. Interesting and, yet quite confusing as well. haha
Hey, lets have and aeronautical engineer give us a platform to follow, and have every 10 driver throw in his numbers! We are still in the test phase, and I am absolutely more than motivated to be a part of some good ol?RV 10 research! Come on, lets GO!!!!

RV 10 QB, ready for delivery to YOUR house! Listen up!!!!!!!!!!!!!!!!!!!!

Any way, listen, if some one does not hurry up and get that 10 QB ready for delivery some guy has in the classifieds here, then I am going to be forced to sell my 6 kit and spend 47K that I do not have! My goodnes ladies and gentlemen, this plane is soooo awsome, it really will make all the other RV?s obsolete! (SORRY, just an opinion of another 6 builder...DOOHHH!)< Ok, well, maybe it won?t make the 3, or maybe the 4, or no...ok, maybe not the 6, oh, 7, or 9 or 8? Ok, we need them all, but remember, some of us have kids and they need to see OSH too, so get off your A__!!!
Jim and myself, part time in less than 20 months, put together his 10.( With an extra 75 hrs spent beating heads against a wall installing the Efis 1,,,,well, thats another story, read it in glass vs steam guages) An EXPERIENCED RV builder can have this QB ready in under a year easy, sans paint...Imagine, hmmm Sun N Fun 2007, in YOUR RV 10!!!! Why is it still on the market? CALL HIM! You WILL NOT regret building this plane! (hint, insulate the CRAP out of the tunnel floor before closing!)
Glen

 

[mgomez]

If Glen is at or close to max power output, and tries to increase the RPM, then the only way for that to happen is for the prop to flatten a bit, unloading the engine. If the lessened pitch creates less thrust at the new, higher RPM, then guess what the plane will do.

Mike Starkey

It's not quite so simple...if the engine is at WOT, then letting it rev a little faster will also let it produce more power. Up to a point, of course...at some point the torque drops off faster than the RPM rises, so the power starts to DROP with RPM.

 

[stewartj]

Finally Baited

Well guys here goes. First with my apology. This is my first post on this sight as wonderful as it is. I have been spending my time building on my airlplane with a wonderful kit I purchased from Vans. Installing a Lycoming engine IO540C4B5, which I overhauled myself. Installing the Hartzell "blended airfoil" constant speed prop, completely painting, wiring, and upholstering my RV-10. Now as a result I have an airplane that is lighter than the prototype, and after Ken at Vans crunched the numbers faster as well. Not by much. According to the power point presentation at Oshkosh probly 1-2 mph. I fully attribute this to building a STRAIGHT, LIGHT, RIGGED PROPERLY, airplane. As to my qualifications, a lot of time was spent trying to figure out why my RV-6A N799HS was so fast when it was completed in 1997. I still maintain Vans numbers to be accurate. Both RV-10`s built here in Burlington CO. seem to perform as advertised if not better. In a loose formation with power settings (tracked by VM1000C) set the same, these two 10`s will cruise several hours and not deviate distance from one another worth speaking of. Come on guys, Van has given you everything you need. Spend your time in the shop, instead of debating one another and we will have a cool one at a fly in somewhere!!!!! John Stewart
Flying "Pair of Tens"
N104ME,
N104LJ

 

[glenmthompson]

TAS update.

Ok ladies and gentlemen, now that we have some semblence of life back after that bitch Wilma blew through here (ie. power, phone and cable), we are resuming the testing of Jim's plane, 331JH.
I have read some opinions/observations that maybe the TAS and even wind readings in the E-1 might not be dead on, so I flew the "box" just now and have the following to report based on GS from GPS.
Box was flown E,N,W,S at 7500 feet, OAT 19 deg C, WOT, 22.5 Inches MP was obtained. Leaned to best power, 2400 RPM (will try 2300 next flight, the sunset caught me today). Test was done at 7500 feet based on another's recommendation. 175 lb pilot with 20 gallons on board and all fairings installed. Got the following numbers off the GPS....176, 168, 157, 173 knots.
Assuming my math is right, that gives 168.5 KTAS, or 193.8 TAS in MPH. This is 2.8 higher than I got off the E-1 TAS readings. Still short of Van's numbers I am afraid. Engine now has 16 hrs.
Now, another 10 pilot reported on a long X-country, he got identical speeds.
I would like to suggest to as many 10 flyers as possible to run the "box" also with these parameters, so we can all compare and see just how fast the 10 really is. Remember, hartzell blended CS prop, O-540, 35 lbs under empty factory weight, no paint.
If yuz guyz don't mind, I am asking for real numbers, not "seems to be", Or "about", or "I think". There are many people very curious as to what numbers we builders are acheiving in this awsome new Van's product!
Comments? Challenges? Requests? Additions? Corrections?
Glen

 

[glenmthompson]

Vne.

During the last flight of which I just posted with my parachute strapped to my back, I took the plane to 3 mph over VNE, that is 233 MPH IAS. Can you say stable, stable, stable!!?? Had power set at 24 squared, and pointed way nose down. Has any other 10 driver dared to go over that magic number by any more than 3 IMPH?
As a side note, with feet on the floor the ball was way out of the window, needed quite a bit of left rudder to center ball at that speed, at 175 IAS, it is a feet on the floor plane, with centered ball.
Glen