Control rods

[GraemeClarke]

I'm haveing trouble with my control rods being to close to the engine. How much clearance should be allowed from the control rods. The rods are 3/4 * 1/8 606 t6.

Graeme Clarke

[rehler]

Graeme,

They should not touch anything when moved up and down and have enough clearance to allow for any vibration.

Unless yours are rather short, 3/4" seems small. 7/8" is probably the most common size for the "average" gyro - around 4 feet long push rod x .065 wall thickness. 3/4" seems good for about 3 feet or less (1/2" for 3' is NOT adequate as I learned when I got blade flap in an attempt to take off too soon - bent one of the 1/2" control push rods). Longer than 5' or so should probably be 1" diameter.

The wall thickness is not as important as the diameter. The diameter greatly affects the amount of flex.

Most gyro that have the engine in the way use two push rods rather than one running all the way from bottom to top. They have a short pivot arm near the center with a short push rod running up to it and another one from it up to the top. There are many examples of this.

[Doug Riley]

Bensen's plans call out 3/4 x .065 6061-T6 for pushrods. These were, of course, used with Bensen's 60" masts. Typical lengths were in the low-mid 50's (of inches). Even so, they did flex sideways an inch or more each way if they happened to get into resonance with the engine. Therefore, they ought to be kept at least an inch or more away from other airframe parts. 2" would be better.

People went to 7/8" as masts got longer. Some have increased this to 1". The use of idler arms ("scissors") as Ken relates results in shorter and much stiffer rods... but does increase cost in money, weight and possible failure points.

[gyropilot]

Examples of "scissors" used to clear the engine on a GyroBee.

John L.

[GraemeClarke]

Thanks for your help. My rods are 56 & 57 inches long. I will probably change to 1' dai.

Graeme Clarke

[johnbenham]

Examples of "scissors" used to clear the engine on a GyroBee.

John L.
The idea of an IDLER ARM is a good one for any rod less than 1" in diameter and length over 4ft. Greatly reduces the tendancy for the rod to develop a resonance with the gyro.
The comment on wall thickness is correct to a point as the wall needs to be thick enough to allow the total load on the rod in tension to be taken by ONE RIVET at the rodend. I run stress analysis all day at work and see that this is usually the influencing factor in wall thickness selection.
A note to John Landry, I have been trying to e-mail you but get blocked, Your telephone number is no longer current. I need to know where you got those ear plug headphones and the small mike?
John Benham N945JB(Dominator)
Camarillo, CA
johnbenham4725@hotmail.com