Doubting the speeds posted
06-11-2010, 04:08 PM
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RE: Doubting the speeds posted
Actually.. the difference in pitch angle at 5" radius between 7" pitch and 8.5" pitch is about 2.5 degrees, at 4" radius up towards 3 degrees. Hmm, that is right in the general ballpark for the difference between lower surface datum line (like a pitch gauge measures) and zero lift angle for common airfoils like the Clark-Y. Maybe this is not such a mystery after all. The question is how APC rates their pitch numbers, but again, a couple minutes with a pitch gauge would tell a story. I can measure up a 10-7 using other means tonight maybe. Got me curious!
MJD
MJD
06-11-2010, 11:40 PM
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RE: Doubting the speeds posted
For racers, its not just about the top speed, the plane also has to fly perfectly neutral in all angles. Designing that yourself and building the molds and learning the composite technology behind it is much more expensive.
Its not just about going fast, but controlling the speed perfectly.
Its not just about going fast, but controlling the speed perfectly.
06-13-2010, 09:57 AM
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RE: Doubting the speeds posted
Folks thanks for all the info, my flying partner still is doubting the speeds, so I'm building another Screamin Demon with an onboard airspeed indicator just to prove him wrong.
06-14-2010, 08:19 AM
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RE: Doubting the speeds posted
Well, if you ever get the chance to fly one you'll know right away why we spend the money on them.. Like daven said, it's not just about the speed with those aircraft, they have to do other things as well, like turn 3 times a lap and maintain the speed..
I was wasn't saying every speed posted on here was incorrect, simply that I understand how some might be skeptical..
Here's one I just test flew last night.. Fastest one I've had.. (no, I don't have $1600 into it!!)
I was wasn't saying every speed posted on here was incorrect, simply that I understand how some might be skeptical..
Here's one I just test flew last night.. Fastest one I've had.. (no, I don't have $1600 into it!!)
06-14-2010, 08:02 PM
#32
RE: Doubting the speeds posted
That's nice!
Racing is a whole different game from just doing speed passes for sure but the name of the game in both is all fun. Once a sport flyer drinks the kool-aid it becomes crystal clear. Also as we, er me, make the steps up in classes it gets even more fun for sure.
Racing is a whole different game from just doing speed passes for sure but the name of the game in both is all fun. Once a sport flyer drinks the kool-aid it becomes crystal clear. Also as we, er me, make the steps up in classes it gets even more fun for sure.
06-21-2010, 09:15 PM
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RE: Doubting the speeds posted
ORIGINAL: MJD
Doesn't matter. It strictly represents a geometric distance based on the pitch angle of the blade and the helical path it would scribe if rotated one revolution with no slippage. The possibility of getting close to this number in real life is dependent on aerodynamics (of the aircraft and the prop) and power.
If it helps anyone, I recall my eyes opening and thinking ''aha!'' when I began to understand and visualize relative wind as it affects the prop's angle of attack. The angle of attack of the blades changes with airspeed and rpm, think about it. It's easier to first forget rpm change, just think about a prop moving along at ever increasing airspeed, constant rpm, and the angle of the relative wind. When that clicks, you'll suddenly appreciate better the significance of the term pitch speed and the issues surrounding it.
This diagram ain't bad. Here, the prop shaft runs horizontally, and you are looking at an end on view of the prop blade, i.e. the engine is pointing to the right.
So you can see how a high pitch prop can end up operating at the same angle of attack in flight as a low pitch prop - but it has to be moving faster to do so.
MJD
Doesn't matter. It strictly represents a geometric distance based on the pitch angle of the blade and the helical path it would scribe if rotated one revolution with no slippage. The possibility of getting close to this number in real life is dependent on aerodynamics (of the aircraft and the prop) and power.
If it helps anyone, I recall my eyes opening and thinking ''aha!'' when I began to understand and visualize relative wind as it affects the prop's angle of attack. The angle of attack of the blades changes with airspeed and rpm, think about it. It's easier to first forget rpm change, just think about a prop moving along at ever increasing airspeed, constant rpm, and the angle of the relative wind. When that clicks, you'll suddenly appreciate better the significance of the term pitch speed and the issues surrounding it.
This diagram ain't bad. Here, the prop shaft runs horizontally, and you are looking at an end on view of the prop blade, i.e. the engine is pointing to the right.
So you can see how a high pitch prop can end up operating at the same angle of attack in flight as a low pitch prop - but it has to be moving faster to do so.
MJD
Are you saying that if we have a "x" prop at "x" rpm working at 30,000 feet and -20°C it would behaves equal than at sea level and 40°C??? it would advance the same distance in both cases ??? does not matter the density of the mean in wich the prop is traveling ???
Lets suppose that we are talking just from a prop , so we dont have to consider the coefficient of drag of an airplane.
Everything is in a good way bro .
Thanks.
