Tandem gyro plans

[davh12]

You could always cut them down a bit. Requires you to re-balance the blades, but the symmetrical airfoil blades I had to cut down had a metal leading edge spar so I was not overly concerned about chord wise balance. Span wise was easy enough to re-balance. The blades I have on my helo now do not have a leading edge spar.

[joe nelson]

Dave,

I will cut them down if the rrpm is too low. Right now, I just want to get it altogether so I can do some testing.

I saw a video of a simular size gyro with two coaxial rotors flying. The rotor blades appeared to be about a foot long but had four blades each. The only reason that I can figure the builder has this set-up is for higher rrpm. I'm also guessing he's getting about 50 ounces of lift in this configuration. The important thing about this is he's flying and flying well! It appears that he has no SAS or gyro stabilization...that's what I want!! If you want to watch the video it's on U-tube and it's the HUP gyro.

[joe nelson]

Today, I tested the model in front of the fan. As expected, the rrpm was slow due to the system friction. I have the front and aft rotors coupled with a speedometer cable which uses bushings. The rrpm was only about 200 rpm as measured by my electronic tach. 600 rrpm seems to be the number that I had the most success before it was coupled.

I'm going to attempt to smooth out the fiction in the system and if I have no success, I will switch to bearings throughout. I still have my small gearboxes if the speedometer cable falls short!

[joe nelson]

Bearings have been added to the rotor heads on both the front and the rear rotors. Two bushings have been removed to decrease the system's friction. Overall the friction is less as I turn the rotors but the true test will come when it's in front of the fans.

[davh12]

Where did you get you electronic tach?

Got my parts from hong kong.....my state side supplier fell short. Net issues. Been working on another project for someone else so I was not left sitting on my hands. Take care.

Dave

[joe nelson]

Dave,

I got it at the NAPA auto parts store. I can't remember the price though.

Cross your fingers cuz I'm going to the Hobby Lobby test range in the AM. I'll give you an update when the dust settles, lol.

[joe nelson]

Today was a bust! I taxied all over the parking lot and never had enough rrpm to fly. There's too much drag in this system for good rotor rpm performance. I'm guessing that I had 2-300 rrpm when I need around 600 plus.

Monday, the speedometer cable will be changed to a bevel gear setup.

[joe nelson]

I have looked at a video of a tandem gyro using a dual coaxial setup. It flew pretty well, as far as I could tell.

The shorter rotor diameters made for a good rrpm and having two head on the same shaft makes it equivalent to a larger lifting surface.

[joe nelson]

Yesterday, I spent a lot of time in front of the fans. I was able to gain about a hundred rrpm by lubricating the speedometer cable with bees wax.

The landing gear was changed to a lighter weight, wider stance version for ground stability. The rear gear was moved to a position of 15 degrees behind the CG like a fixed wing aircraft. I think that this will make for easier take off rotation and a lower front rotor angle. My best quess the aft gear "was" too far to the rear which required a large angle on the front rotor for rotation. I'm hoping that the lower rotor angle will reduce the tendancy to loop on take off.

[davh12]

Keep trying Joe. I finished up the gear assembly for the tail rotor input shaft. Looks a bit like Wylie Coyote threw together an acme rocket, but it works. I could not afford to start over on that part of the airframe at the present time, adding a more efficiently fabricated gear box. Got my first patent maintenance fee coming up in July. A lot of bones to shell out, even for being small entity. When I get my upright mill (hopefully next year) gear assemblies will be easier to fab. I think these gyrocopter guys on this site don't like powered rotors...lol
Dave

[joe nelson]

Dave,

Thanks for the encouragement. I am back testing in front of the fans in my shop. This seem to be where I get the results quicker than running to the Hobby Lobby parking lot on Sunday mornings.

RRPM, or the lack of it, seems to be the key to solving my problem. Recently, I found a couple of tandem designs using coaxial rotors on the front and rear. I assume that this was done to have the required rotor area with short enough spans to have good rrpm and good lift.

I think that these guys, on the forum, like any rotors! Powered or not they just like to hear the whop whop...lol!

Keep up the good work my friend...it'll pay off in the end.

[joe nelson]

This morning, I was tinkering with an unusual drive system. I began using surgical tubing as universal joints with two small gearboxes connected by carbon fiber rods. This wasn't connected to an airframe but just a jig to see if I could improve the rrpm in front of the fan. Sunday, my speedometer rig wouldn't turn at all while in front of the fan where a week before I was getting about 300 rrpm...I'm confused!

[All_In]

Originally Posted by joe nelson

... Sunday, my speedometer rig wouldn't turn at all while in front of the fan where a week before I was getting about 300 rrpm...I'm confused!

Oops something is jammed in the gears, or bent, out of alinement or something?

[joe nelson]

John,

Everything looked OK. The parts are so tiny it's really hard to tell if something is wrong! The system couldn't be any simpler. It's just a speedometer cable connecting each rotor through a series of bushings lubricated with bee's wax.

I would like to be able to determine the amount of torque it takes to turn the system. It couldn't be very much but when you're dealing in ounces a little means alot!

I have read where there's as much as 30% loss of HP when driving through a gearbox. If this is true, this thing won't fly with two gearboxes.

[joe nelson]

In comparing the feel of the two systems, the speedometer cable requires more "finger torque" to turn than the double gearbox system to turn. The double gearbox is about 4 ounces heavier than the speedo cable but is much smoother and easier to operate. The change will be quick and may be done by Sunday's trip to the Hobby Lobby test range.

Next major question is how much plane and how much gyro will be needed to my this gyroplane fly? In most of the test flights, the front rotor operated as it should but the aft stayed on the ground. This resulted in a loop followed by a crash. This might have been lower rrpm on the rear rotor generating less lift or a need for a horizontal stab. for longitudinal trim.

At this point, I don't believe that a tandem rotor gyro can fly using just helicopter type control systems. My idea of having "rudder type control" come from just the lateral movement of the aft rotor may not be correct. I think that a horizontal stabilizer and a rudder may be required.