pre rotater

Butch

Newbie
Joined
Jun 18, 2020
Messages
13
Location
Jackson Ca
Aircraft
Bensen Gyro
Total Flight Time
50 hrs
I just purchased another bensen and it has a small motor at the top of the mast and it utilizes pulleys to turn the roter. Does anyone have experience using one of these?
 

Smack

Re-member?
Joined
Nov 3, 2013
Messages
635
Location
Georgetown
Aircraft
Kitfox IV / F1 Rocket / Magni M-16 / Beech 18
Total Flight Time
500+
PLEASE post detailed pictures.
That pre-rotator option has been discussed, but I've rarely seen pictures.
It seems that only the 'old-timers' (I mean that in a reverent way) know of it.
Bensen wrote of a 'Big Bertha' option wherein the rotor was powered by a small (or multiple) motor such as you describe.
YES, pictures, please.
Brian
 

Butch

Newbie
Joined
Jun 18, 2020
Messages
13
Location
Jackson Ca
Aircraft
Bensen Gyro
Total Flight Time
50 hrs

Butch

Newbie
Joined
Jun 18, 2020
Messages
13
Location
Jackson Ca
Aircraft
Bensen Gyro
Total Flight Time
50 hrs
PLEASE post detailed pictures. That pre-rotator option has been discussed, but I've rarely seen pictures. It seems that only the 'old-timers' (I mean that in a reverent way) know of it. Bensen wrote of a 'Big Bertha' option wherein the rotor was powered by a small (or multiple) motor such as you describe. YES, pictures, please. Brian
 

Butch

Newbie
Joined
Jun 18, 2020
Messages
13
Location
Jackson Ca
Aircraft
Bensen Gyro
Total Flight Time
50 hrs

Smack

Re-member?
Joined
Nov 3, 2013
Messages
635
Location
Georgetown
Aircraft
Kitfox IV / F1 Rocket / Magni M-16 / Beech 18
Total Flight Time
500+
A belt appears to be missing. Is that roundish upward-pointing brown object the muffler?
Is there a separate throttle linkage?
Have you tried to start the little engine?
Does it list a Hp for the pre-rotator engine?
 

Butch

Newbie
Joined
Jun 18, 2020
Messages
13
Location
Jackson Ca
Aircraft
Bensen Gyro
Total Flight Time
50 hrs
A belt appears to be missing. Is that roundish upward-pointing brown object the muffler?
Is there a separate throttle linkage?
Have you tried to start the little engine?
Does it list a Hp for the pre-rotator engine?
I have the belt. I just purchased this gyro and I finally have the time to get into it. I plan to remove the upper unit from this one and install it on my original Bensen. My only concern is with the added weight to one side. am still new to this but if I am correct it does not matter where you add weight because a spinning object wants to stay balanced. A good example is when you hold a bicycle wheel by its axle and spin it it is hard to tilt it. I hope that I am wright about this but I am not sure. It sure would be nice if this was a proven system because this little motor should spin that rotor pretty fast. I will try and find out the hp. I am now going to look at it in detail and try and start the motor. Any help with this from a more experienced Bensen guy would really be appreciated. I will post my results once I start the motor
 

Smack

Re-member?
Joined
Nov 3, 2013
Messages
635
Location
Georgetown
Aircraft
Kitfox IV / F1 Rocket / Magni M-16 / Beech 18
Total Flight Time
500+
Do you have or have you read Igor Bensen's book "A Dream of Flight"? He does write of this type of prerotator.
Should be a very exciting learning experience. Please post the milestones.
 

jany77

Member
Joined
Jul 13, 2008
Messages
545
Location
central california
Aircraft
cessna 150,172,182,trikes,ul
Total Flight Time
over 300
That is Ohlsson and Rice engine rated 1 hp ,it just run full power ,there should be lever on carb ,i used to had one of those
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,390
That unit was Bensen's "deluxe" offering for many years. The O&R engine is not terribly powerful, but would bring Bensen blades (small and light) up to about 150 RPM. At this RRPM, you still have to begin your takeoff run with partial power, lest you flap your blades.

Most prerotators add more weight to one side of the head than to the other. The effect on the controls is there, but is slight.

IIR, there is no engage-disengage control. Once the O&R engine is started, it engages and the blades begin to spin. For that reason, you don't start it near a hangar or spectators; wait until you are near the point where a clear taxi run to your takeoff point is possible. The reach up, yank the cord and hope for a start. A shutoff switch is optional.

Because you start your main engine first, and then reach up to pull the O&R's start cord, it can be hard to tell when the prespin engine has actually started. The guys in our chapter who had one would touch the engine body to feel for vibration.

The 2-stroke O&R engine found other uses in tiny motorbikes and powered concrete finishers.
 

Smack

Re-member?
Joined
Nov 3, 2013
Messages
635
Location
Georgetown
Aircraft
Kitfox IV / F1 Rocket / Magni M-16 / Beech 18
Total Flight Time
500+
Doug, I would think a cut-off switch would be mandatory.
So, the O&R engine remained engaged and supplying power to the rotor during and AFTER takeoff ?
Brian
 

Butch

Newbie
Joined
Jun 18, 2020
Messages
13
Location
Jackson Ca
Aircraft
Bensen Gyro
Total Flight Time
50 hrs
That unit was Bensen's "deluxe" offering for many years. The O&R engine is not terribly powerful, but would bring Bensen blades (small and light) up to about 150 RPM. At this RRPM, you still have to begin your takeoff run with partial power, lest you flap your blades.

Most prerotators add more weight to one side of the head than to the other. The effect on the controls is there, but is slight.

IIR, there is no engage-disengage control. Once the O&R engine is started, it engages and the blades begin to spin. For that reason, you don't start it near a hangar or spectators; wait until you are near the point where a clear taxi run to your takeoff point is possible. The reach up, yank the cord and hope for a start. A shutoff switch is optional.

Because you start your main engine first, and then reach up to pull the O&R's start cord, it can be hard to tell when the prespin engine has actually started. The guys in our chapter who had one would touch the engine body to feel for vibration.

The 2-stroke O&R engine found other uses in tiny motorbikes and powered concrete finishers.
Thank you so much for the info. Now my final question. Would you use it ?
 

Kevin_Richey

Yamaha gyro...Oregon, USA
Joined
Nov 16, 2003
Messages
2,294
Location
Oregon, USA
Aircraft
Sport Copter gyroplane
Total Flight Time
300+ gyroplane, 11 airplane, 1.5 PPC, AND... a ZILLION hours of flying in my dreams!
Former Texas PRA Chapter president Steve Weir used a lightweight weed whacker 2 stroke engine mounted up on his mast. He was filming me & Danny Whitten flying back from Rochester to Mentone back in 2012. I still had my Sport Copter powered by a Rotax 503.

His little 2 stroke engine w/ clutch got his Dragon Wings up considerably fast (possibly in excess of 200 rrpms) in approximately 25 seconds, as he demonstrated @ the beginning of his video. I suspect his was likely patterned after what Matt Pearson had on his Butterfly-copy gyro.

 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,390
My earliest gyro training was done on a SxS car-towed gyroglider with the O&R prerotator. I would, and did, fly with it. Of course, it wasn't mine; it belonged to my nearest Bensen dealers, Clyde Gordon and Ron Menzie. Using a noisy little 2-stroke on a gyroglider did kinda degrade the otherwise quiet gyroglider experience. I never did buy one of my own, instead learning how to hand-spin my blades.

I don't know the exact clutching setup, but it was (or was something like) a centrifugal clutch. It allowed the rotor to overrun the engine once autorotation was established. The engine was not powering the rotor at that point -- a Bensen rotor turns some 400 RPM in flight, far more than the prerotator's engine could keep up with, much less add to.

The engine would continue running harmlessly during flight until the little tin-can gas tank ran dry. Some people did add a prerotator kill switch.
 
Top