Gyro/Heli V -
Propeller
Overview:
Mounted on planetary ring gear or planet holder.
Propeller:
59" diameter
16 degrees
4 blades
280 lbs static thrust
2425 rpm
|
Ken Rehler |
30/10/00 |
|||
|
Larry Neal |
30/10/00 |
|||
|
|
Ken Rehler |
31/10/00 |
||
|
|
|
Larry Neal |
31/10/00 |
|
|
Ken Janulewicz |
31/10/00 |
|||
|
carl schneider |
31/10/00 |
|||
|
Ken Rehler |
31/10/00 |
|||
|
|
CA BEATY |
31/10/00 |
||
|
|
carl schneider |
31/10/00 |
||
|
|
|
Ken Rehler |
31/10/00 |
|
Date: 30-Oct-00 19:20
Author: Ken Rehler (rehler@stic.net)
Subject: Best tip speed for a gyro?
I read somewhere that the optimum tip speed for a prop is from 576 to 630 feet per second. Is this correct? Is it different for a gyro than a fixed wing, since a gyro needs maximum thrust all the time due to the drag of the rotor?
Specifically, I have a 65" three bladed ground adjustable Sport Prop which at 4000 rpm (cruise) spins at 2121 rpm which makes the tip speed 600 feet per second. The most I will spin it at takeoff is 4700 rpm engine, 2492 rpm prop, 705 fps tip speed. My blade pitch now is 12 degrees (at blade tips).
Someone has recommended that I change my reduction from 1:1.88 to 1:2. This would spin the prop slower requiring a higher blade pitch setting. If I make the change then cruise at 4000 rpm engine would make the tip speed 564 fps. Takeoff at 4700 engine rpm engine would make the tip speed 663 fps.
Which is best - the 1:1.88 reduction or the 1:2 reduction?
Date: 30-Oct-00 23:10
Author: Larry Neal (nhc@compuwise.net)
Subject: Propeller tip speed.
Ken, When we calculate the tip speed for our New Horizons Components PSRU we choose the ratio that puts the prop tip as close to 70% of the speed of sound as we can get or about 760ft/second. After this speed the efficiency seems to be less. Running the tips slower than this will cause the prop to run quieter and will require more pitch but we have found that the thrust is also less. Your ratio is fine as it is.
Date: 31-Oct-00 09:53
Author: Ken Rehler (rehler@stic.net)
Subject: What rpm?
At what engine speed should you measure - at maximum engine rpm, or at crusie rpm?
Date: 31-Oct-00 11:01
Author: Larry Neal (nhc@compuwise.net)
Subject: Prop tip speed.
Ken, We always set the reduction ratio around 760 fps tip speed at maximum RPM. This should give you maximum thrust for take off and climb out, then when you throttle back you will still have good thrust for cruise speed. As you know with a heavy ship we need all the thrust we can get especially on 110 degree Texas summer days.
Date: 31-Oct-00 13:36
Author: Ken Janulewicz (kensandyeggo@msn.com)
Subject: My detailed answer
Ken R.,
I read your post quite thoroughly regarding maximized prop-tip speed and redrive ratio, and just in case you were wondering about my detailed thoughts on this, the answer is that I wouldn't have sno-cone's chance in hell (or August in southern Texas), of even guessing the right answers. Hope you can use this info as I am always eager to help those of us in the gyro community who may be less informed......Counselor Holmes! Where's my insurance binder? Doc? The shipment is late again.
Date: 31-Oct-00 10:01
Author: carl schneider (carltoni@interl.net)
Subject: prop tip speed
i have been flying gyros over 33 years. i have no letters behind my name. so anything i say you have to take with a grain of salt. my prop rpm on takeoff is less than 1500. tip speed is around 500 fps. i still get 700 to 1000 fpm rate of climb. top speed is 105 mph. at 100 mph i can move my control stick fore and aft 6 in. it is very comfortable crusing 90 mph. my thurst line is 7 in below the cg. i too have many dead friends. i am greatly sadend by the many poorly designed gyros still being sold and flying.
Date: 31-Oct-00 10:24
Author: Ken Rehler (rehler@stic.net)
Subject: Carl,
Your gyro sounds like an outstanding one. I'm sorry I can't remember what type of gyro you fly. What type is it?
Also, what is your prop pitch and engine HP?
Date: 31-Oct-00 11:10
Author: CA BEATY (cabeaty@worldnet.att.net)
Subject: Carl
Don't mean to speak for Carl, Ken R.; his gyro resembles but is not a Dominator. The fact is, both evolved at about the same time.
Carl and I had numerous telephone conversations about CG a number of years ago, so Carl, logically, decided to find out for himself. He had a Bensen sort of gyro with Rotax 447 to which he added a dummy keel and on which was mounted seat and rudder pedals. It was attached so that it could, by loosening some clamps, be slid up and down. Carl said that the higher the dummy keel was elevated, the more stable the machine became. He quit at about the point where he was getting a rotor blade haircut.
If my memory hasn't failed me, Carl had this machine at the Hearne, Texas 1990 PRA flyin.
The fact is; with CG above the propeller thrust line, the machine has better angle of attack stability than dead on, much like a nose heavy fixed wing airplane.
Of course there is a downside to having CG above prop thrust line. If everything is on center, changing the throttle setting will not affect airspeed; if throttle setting is increased, the machine naturally noses up and climbs at the same airspeed, and if throttle is decreased, the machine noses down and descends without a change of airspeed.
With CG above the prop thrust line, the machine noses up more and airspeed decreases with an increase in power, requiring a cyclic input. The long period oscillation that most people don't even notice unless they lock the stick and look for, takes longer to die down. Same as a nose heavy fixed wing airplane.
Date: 31-Oct-00 13:03
Author: carl schneider (carltoni@interl.net)
Subject: engine hp
ken single hp-50 pitch 17 degrees two place hp 65 pitch 19 degrees the two place performance is about the same as the single except it is about 10 mph slower on the top side. carl
Date: 31-Oct-00 13:21
Author: Ken Rehler (rehler@stic.net)
Subject: Blade pitch
Carl, thanks for you help.
I (and others) can use you numbers for comparison.
It looks like you are getting good results with slower turning props (500 plus fps) with high pitch settings (17 to 19 degreees). In comparison, mine is faster turning (600 plus fps) with less blade pitch (12 degreees), which may be less efficient.
Also run Prop20 program
Back to top | Return to Home Page
Last Revised: February 2, 2001
