Interesting (?) Climb Speed results

[Ironflight]

And winner for the best rationale has got to be Kevin! I knew that sooner or later, we'd smoke you out and into the conversation...You're right - a 3 second difference means about 10%, which really is reasonable. Of course, you had to bring math into it....

And Allen wins for the best description of how to do a sawtooth climb test!


Paul

[Kevin Horton]

Originally Posted by mlw450802

I wonder if this observation changes between C/S and F/P props (asked in genuine ignorance)?

-mike

The rate of climb depends on excess power (and aircraft weight). Excess power is the difference between the power available from the engine, and the power required to maintain level flight at the climb speed. The power requried vs speed will be the same no matter what prop you have. The power available is equal to the power produced by the engine times the prop efficiency.

With a C/S prop. the engine should be producing max power (for that altitude and temperature) no matter what the climb speed is, so the only thing that affects the power available is the variation in prop efficiency with speed.

With a F/P prop, the engine rpm goes up as you increase speed, so the power available will increase with speed. This will affect the climb rate vs speed curve. I would expect the air speed for best rate of climb would be slightly faster for a F/P prop than it would be with a C/S prop.

[Bill Dicus]

Paul: When you did your sawtooth climbs (for the -8) did you do so at full throttle or did you set a percentage of power before each segment? I thought the latter method might give more accurate best rate and angle of climb results. Thanks for any advice you can give me. I've found the climb of my RV-8 amazing!

[humptybump]

If I combine Kevin's description with the question of FP vs CS, I would assume that us FP guys would benefit from flying the faster end of the spectrum - especially if we are flying a cruise optimized propeller. This assumption is based on the fact our engines are not producing optimal RPMs in a climb and this is exacerbated by a cruise optimized FP propeller producing lower RPMs as slower speeds.

Would someone [in]/validate my assumption ?

[spatsch]

Here what I got with my RV-8. The pic shows one run. Did multiple of them at different altitude and they all looked similar (large flat spot on top). Note my speeds are in mph.

So I think your measurements are in line ... .

Oliver
p.s. Just noticed a typo in the picture column K is ft/min not Mph... .

[rzbill]

The test chart for my 7A looks the same as above between 70 and 110 Kts. Flat.

Glad this thread popped back up. I had done two runs and wanted to do a third but I see it is a waste of time since I will get more of same.

I was trying to find best glide on the descent during the sawtooth but that data was equally flat.

I remain very unsure of best glide speed.

[vic syracuse]

I have seenpretty much the same results in many RV's I have tested. My conclusion is that RV's are not that sensitive to "nailing" the airspeed to get the best performance in climb. They are wonderfully-behaved airplanes, with a very wide envelope, making them very great performers on both ends, and especially on the low end where safety is paramount. I'm sure Van must have realized that when he built the first one, and the rest is history.

I think we all have learned the same thing regarding cooling, too---they all seem to cool better around 120 knots in a climb. And the over the nose visibility is enhanced without a climb penalty.

VIc

[jdearborn]

Interesting thread.
I?d like to expand from speed for best ROC, to most efficient speed/ROC combination. That is; getting the most ?miles down the road? per pound of fuel burned. This includes the climb phase. Usually it is a tradeoff between going fast and time/fuel to get up to one?s most fuel efficient cruise altitude. Hence the old adage of ?fly fast into a headwind and climb fast with a tailwind?.
A constant IAS climb is not the most efficient method. The IAS for the best ROC will decrease with altitude. AOA will help in this endeavor. It maintains the optimum airfoil variable and generates your climb schedule regardless of weight and CG. It'll work for glide schedule too. That theory assumes a no wind condition. Factor in the climb winds for best results. . . YMMV

[Bill Palmer]

How about Best Sustained Climb Angle? (at gross or calculated weight[s] adjusted for wind, altitude, temperature, etc.) In other words, forget rate and efficiency; it?s Show Time! . . . or there is a tall canyon wall just past the end of this short runway. Has anyone taken a measured look, including engine/prop configuration, at this terrain performance parameter?

[David Paule]

Look at the curve on post #15, and draw a line from the bottom left corner where the rate of climb and speed are both zero to the point on the curve that gives the highest line, that point on the curve is your best angle of climb. It is for that airplane and that engine/prop and that altitude.

Just from looking at it, it sort of looks like it's at the low-speed end of the curve.

Dave