Trim Spring

[rotorman890@hot]

I am a bit puzzled by the issue of trim springs. Do I need one on my semi-gyrobee? Exactly what does it do, and why

Also, I see alot of Gyro photo's and I've noticed that most of them don't have an N number. Can you fly without it? Is it legal?

I appreciate any help...Jim

[gyropilot]

Jim,

Trim springs...

With an offset gimble rotor head (the normal type of rotor head used on most gyroplanes with a 2-bladed teetering rotor), you will usually need a trim spring. The reason is this:

The rotor head is designed so that the rotor usually lifts the gyro at a point somewhere behind the rotor head pitch pivot. If there were no trim spring to counter this upward pull, the rotor head would tilt forward and the pilot would have to hold the cyclic stick aft (and this could require a lot of force on the cyclic stick while in the air).

Why is the rotor head designed this way? Simple... it creates rotor stability and feedback into the cyclic control system to suggest to the pilot where the cyclic needs to be. For example, if the gyro encounters un updraft, the rotor "pulls" upwards on the rear portion of the rotorhead (against the trim spring) causing the rotor head to tilt forward, thus "nosing" the spinning rotor downward into the updraft. The reverse would occur if the gyro encountered a downdraft.

The trim spring is normally adjusted so that the gyro will maintain cruise airspeed in straight and level flight (if the cyclic were released by the pilot).

There are some combinations of rotor head offset, rotor blades, and airframe weights that will require little or no trim spring to compensate. As I understand it, this is not necessarily a good setup as rotor stability and control feedback to the pilot can be reduced. Conversely, there are some rotor head offsets, rotor blades, and airframe weight combinations that require very heavy trim spring pressure to compensate. This isn't good either because if the trim spring were to fail, the pilot would be subjected to heavy, unexpected, and possibly violent cyclic stick forces (forward) he/she may not be prepared to deal with. I could imagine a sudden loss of control... or even worse (like in flight blade flapping)... as the result.

N-Numbers...

If an aircraft qualifies as an ultralight and is operated under FAR Part-103, then no registration (N-Number) is required. If not, an N-number and an airworthiness certificate are required.

Regards,

John L.

[rotorman890@hot]

Thanks for the response on the trim spring issue. I have the Wobbly Flyer rotor head. Should I do the trim spring just as Tagart shows in his plans?

[gyropilot]

Yes... if you're building a GyroBee, you'll want the normal trim spring setup Ralph used with the Wobbly Flyer rotor head.

It's wise to have a very experienced gyroplane pilot (preferably one familiar with your particular type of gyroplane) conduct the initial test flights and adjust the trim spring for you. That way when you start flying, you're not distracted by fighting heavy stick forces due to a mis-adjusted trim spring.

Best regards,

John L.

[rotorman890@hot]

[QUOTE=gyropilot]Yes... if you're building a GyroBee, you'll want the normal trim spring setup Ralph used with the Wobbly Flyer rotor head.

It's wise to have a very experienced gyroplane pilot (preferably one familiar with your particular type of gyroplane) conduct the initial test flights and adjust the trim spring for you. That way when you start flying, you're not distracted by fighting heavy stick forces due to a mis-adjusted trim spring.

Best regards,john l

Does the trim spring bracket fit tight on the mast? In Taggarts plans, it is to be 2 and a quarter inches wide. At that rate, it would slide up and down the mast at will. Can you clarify this...Many thanks...Jim

[banaari]

Hi Jim,
studying the documentation and the Photo Tour on Dr Taggart's website... the friction isn't generated side-to-side. It's generated fore-and-aft. The frame rides at an angle on the mast, in such a way that the more tension on the frame from the spring, the tighter it clings to the mast... That and the vinyl tubing generate enough friction to hold it in place, while still allowing you to adjust it.
Presumably by pulling down on the spring-attach point to release the tension and let it slide.


cheers,
John

[Doug Riley]

The trim spring CAN have another function... on a pitch-stable gyro. A pitch-stable gyro frame will "weathervane" nose-up or nose-down to meet down- and up-drafts. The spring forms a soft link between the frame and the rotor so that the rotor "knows" what the frame is doing. Of course, you can overpower this link manually, but if you maintain the standard cool gyro pilot's gentle grip, the spring will do its thing and the rotor will follow the frame as it should.

A gyro airframe that's unstable will compromise or defeat this helpful function.

[Texas Armadillo]

Sometimes you'll see two trim springs. (like mine)

I put a second spring on the right side of my rotorhead. Without it, my gyro slowly turns to the left. (probably because my pre-rotator cable puts presure on the rotorhead.)

[gyropilot]

the friction isn't generated side-to-side. It's generated fore-and-aft.
John,

I can't speak for Ralph's experience with his mast spring bracket... I assume it worked well for him... but for some reason when I tried to use the very same design on my GyroBee, mine kept slowly creeping up the mast! It sure was simple and convenient to adjust, but the friction created between the bracket and the mast apparently just wasn't high enough. Maybe it was because I used glossy paint on my mast... dunno.

Anyway, I wound up narrowing my bracket to "clamp" the sides of the mast in addition to the original wedging effect Ralph used. This makes it more time consuming to adjust, but it doesn't move once set.

Now what I really would like to have is in-flight adjustable trim... but maybe that's for a different time and a different gyro. I have to keep reminding myself to keep it simple and keep it light!

Regards,

John L.