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Rates of climb, 9 vs 14 vs 7

Vansconvert

Well Known Member
So the 7 is the king of climb. I get that. The 9 at 160 horse and the 14 at 210 horse are within 100 feet per minute of each other per Vans published figures; stating that is with a fixed pitch on the 9, and assuming a constant speed on the 14. Why is the rate of climb that close with 50 horsepower less and a fixed pitch at that?
 
King of climb?

The -7 king of climb? Really?
I would have thought that the additional 3ft of wing would give the -9 the edge, all things considered. Guess you learn something everyday. :)


So the 7 is the king of climb. I get that. The 9 at 160 horse and the 14 at 210 horse are within 100 feet per minute of each other per Vans published figures; stating that is with a fixed pitch on the 9, and assuming a constant speed on the 14. Why is the rate of climb that close with 50 horsepower less and a fixed pitch at that?
 
So the 7 is the king of climb. I get that. The 9 at 160 horse and the 14 at 210 horse are within 100 feet per minute of each other per Vans published figures; stating that is with a fixed pitch on the 9, and assuming a constant speed on the 14. Why is the rate of climb that close with 50 horsepower less and a fixed pitch at that?

The two biggest factors are span loading and excess power. The -9 stacks up well on both counts.
 
2450 fpm advertised on the 7A with a 200 horse and constant speed. The 14 with 210 horse is at 1900, about the same as a 9 , fixed pitch, 160 horse. Those are the specs on Vans website.
 
2450 fpm advertised on the 7A with a 200 horse and constant speed. The 14 with 210 horse is at 1900, about the same as a 9 , fixed pitch, 160 horse. Those are the specs on Vans website.

Also consider the weights of the three and estimate the power to weight ratio and the excess power available at Vy.
 
As for fixed pitch vs constant speed ? you want the engine to give max power which usually means max RPM. You can get that with either a c/s or a fixed pitch. But the you need to convert that power to thrust, and there?s a zillion factors, including prop diameter. There?s also helix angle as a major factor (sorry, go look it up.)

As in so many other things, it depends.
 
Thinking apples to apples-

The 9 and the 7 share everything except the wing, so a meaningful comparison could be made with identically equipped airplanes carrying identical loads. I?m betting the 9 would decisivly outclimb the 7 in that contest, with the 9?s advantage increasing with altitude.

That said, I chose the 7 because it has so many more ?hot-rodding? and maneuvering options. I love the thrill of a composite Hartzell pulling 190 HP at max ROC and I love boring odd-shaped holes in the sky, but I also have deep respect the wing John Ronce designed for the 9 and the efficiency and economy it imparts to Van?s airplane.
 
The 9 and the 7 share everything except the wing, so a meaningful comparison could be made with identically equipped airplanes carrying identical loads. I?m betting the 9 would decisivly outclimb the 7 in that contest, with the 9?s advantage increasing with altitude.

That said, I chose the 7 because it has so many more ?hot-rodding? and maneuvering options. I love the thrill of a composite Hartzell pulling 190 HP at max ROC and I love boring odd-shaped holes in the sky, but I also have deep respect the wing John Ronce designed for the 9 and the efficiency and economy it imparts to Van?s airplane.
Well there is the rudder, the elevator, oh yes, and the flaps. All very different too. Quite a few important differences actually.
 
I believe rudder and elevator are same 9 and 7, no?

And flaps are definitely part of the wing, but not used during such climb comparisons. Minor differences in empannage would have little influence on climb in any event. Differences in power, prop, and weight are what need to be controlled to make a meaningful comparison.
 
apples n oranges

....nobody has mentioned the airfoil on the -9, which is quite different from the others.....so you can't just say 'with 3 more feet of span, it's gonna climb better'.
Those that have mentioned the 'fixed pitch' are correct, but WHAT pitch?
Mine certainly didn't turn 2700 rpm in climb, so it's only making 120 hp, not 150 or 160, or 180 or 210 etc etc.

jus' sayin'
 
The 9A is no slouch in climb, I'm a bit heavier than others but I also carry a few more horsepower with an IO360. I can hold better than 2000 fpm off the runway until there is no doubt that I might have been doing it by accident, even with two butts in the seats and full standard fuel.

Those kinds of climb rates are not the sort of thing you do to an engine you love though - temps can get elevated even when you're running slobbering rich. More realistic "normal" climb rates are 1000 fpm and 110KIAS.

7 or 9 or 14 - there's no replacement for displacement.
 
I agree, I would say that climb rates are more about the time of year and temperature, more than what airframe.
 
I believe rudder and elevator are same 9 and 7, no

Otis, no... You might recall my plane to have the smaller -8 rudder. The earlier -7's came this way and I never built my larger -9 rudder. Later -7's came with the -9 rudder as standard.

The -9 tail is absolutly ENOURMOUS compared to our -7's. I dare say that the reason is so that it will keep flying at slower speeds that the Roncz airfoil of the -9 can and does.

:) CJ
 
Well guys, my comment was based upon this statement:
The 9 and the 7 share everything except the wing, so a meaningful comparison could be made with identically equipped airplanes.
this statement is simply not true. The 9 and 7 do NOT share EVERYTHING except the wing.

Not meaningful to climb rate, which is the discussion topic.

And flaps are definitely part of the wing, but not used during such climb comparisons. Minor differences in empannage would have little influence on climb in any event. Differences in power, prop, and weight are what need to be controlled to make a meaningful comparison.
Regardless of what discussion topic you choose to discuss, a false statement is still a false statement.
 
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