What Is Best- Springy Or Stiff Trim Spring??

[mikeconcannon]

My trim spring on my single seater is pretty stiff, in fact very stiff. The last machine that I used to own, also a single seater, had a fairly springy trim spring. Does anybody know how the decission is made about what amount of springyness to choose in a trim spring and what are the consequences of to stiff a spring (or to soft a spring)
The reason that I am making this post is because my trim spring is very stiff, I turn my trim all the way off rather than pulling against the spring when Im coming in to land (with the engine on low revs I must put the stick forward) I have in fact a double spring, a spring inside a spring. My gyro is made by one of the best manufacturers in the world, Magni, so I have no reason to think that they would get it wrong. If I change to a softer spring, will the characteristics of the trim be compromised for normal straight and level flight when we most need the trim to work effectivley?
Eg. What happens as far as the action of the spring is concerned, when a gust or a thermal pops the rotor disk up (or down), as the disk is setteling back to normal trim position, will a soft spring allow the rotor to mominteraly nodd and return to trim or will the stiff spring preform a better action.
Anybody know??

[Fl90]

For my control set, long spring (springy?). To release the trim, completely, for landing, seems odd to me.

Phil.

[mikeconcannon]

I release the trim because when I back off the power the speed also drops, so Im approaching the runway holding the stick forward to get a bit of speed on for coming in through the gradient. If I dont release the trim to fully off, I am pushing against a stiff trim spring and the force needed is not light to do this. Gone is the nice light control stick. I would really like to replace my trim spring for a lighter one but Im woried that in doing this, I may mess up the way the trim spring acts in normal cruise, when we really use it for what it is meant for. And.. I doubt if Magni would have got it wrong.

[Passin' Thru]

Mike, if all Magnis fly as you decribe yours, then Magni got it wrong!
I don't mean to be offensive, but if you need that much forward pressure on the cyclic to maintain airspeed for reduced power decent, something is very wrong. More than just the spring rate of progression.
Did you purchase your Magni new or used? I ask because I wonder if a previous owner may have "improved" something? Hopefully Greg Gremlier(sp?) is around and can point you in the right direction.
Good luck, I do wish you well.

[Harry_S.]

IMO...A trim spring is what it is, a trim spring. In our application I would not consider it a safety of flight item unless, as you stated, it takes a bit of muscle to over ride the spring.

A suggestion would be to remove the present spring and scale it...how many pounds does it pull? Say it pulls 30 lbs, get another comparable size spring and pull it. Say it pulls 25 lbs. Install it on your machine and fly it. If that spring suits your needs better, great, if still too tough, try anpther till you get what you want.


Cheers :)


PS I understand a probable cause of the Citation tragedy yesterday was possibly a "runaway trim." That's not in our realm of flying.

[Fl90]

I'm with Pete on this. Trimmed is trimmed. After trimming for a desired airspeed, the only thing the throttle controls is altitude. You should ascend and descend at the trimmed airspeed. Need to call Magni and get their recommendation.

Phil.

[mikeconcannon]

Do you think so? That would be an ideal set up, where the throttle setting controls only climb or descend and does not alter the trimmed airspeed atall. Are there gyros out there that act in the way that you have described? I have never owned one like that (although I did have a weight shift ultralight that had true centre line thrust and no matter where the throttle was the speed always stayed at 55 mph , I think it was the Chaser if I remember correctly).

[Timchick]

Mike,
At cruise speed what happens if you let go of the stick? Does your gyro pitch up? Decend? Or stay fllying level?

[Fl90]

"I have never owned one like that"

Mike, I've never owner one that wasn't like that, and all I've flown are the HTL machines that are seen with negativity. What kind of rotor heads have you flown? Do they have a gimbal design or straight? I'm very curious, forgive the number of questions, but my experience is rather limited with large gyros.

Phil.

[Passin' Thru]

Do you think so? That would be an ideal set up, where the throttle setting controls only climb or descend and does not alter the trimmed airspeed atall. Are there gyros out there that act in the way that you have described?

Mike, every gyro I have ever owned, and every deciently set up gyro I have ever flown, trimmed to air speed. Cruise, decend, climb by changing power setting with hands off the stick. I have never flown a Magni, but I have flown a lot of others. That is why I say you may have other problems.
Tim Chick ask:
Mike, At cruise speed what happens if you let go of the stick? Does your gyro pitch up? Decend? Or stay fllying level?
Good question. What does it do? If you reduce power without moving the stick, what does it do?

[mikeconcannon]

If I reduce power from cruise without altering the trim position, the machine will slow right down. Next time I go flying Im going to bring a pen with me and make a note of the speeds for different throttle settings, with a fixed trim setting which would give me 55/60mph in cruise.

One important point. My Magni is the single seat version and I believe that they are a bit different to the two seat in this aspect. Now that you have reminded me, I do now remember flying the two seat and the speed was the same no matter what the throttle position, to within afew miles per hour. I think that mine being the single seat and with the tailplane more close coupled than on the 2 seat, that maybee this is a trade off for having a more manouverable machine than the 2 seater

Anyhow, we are getting away from the point that I made the original post about. I dont mind having to use the trim in different positions for different amounts of power, its not that difficult. What I was asking about is, does anybody know if the action of the trim spring will help return a gyroplane to normal attitude flight after it has been disturbed, by say a thermal for instance, or is the trim spring tension of no significance here. If the trim spring tension has no influence on the return to normal atitude, then Im going to replace mine with a softer one as I feel it would be easier to push against it when I want to get a bit of speed on, without having to adjust the trim.

[gyrogreg]

Mike,

I would really suggest conferring with the Magni factory. I've not flown the single seat, but it does sound to me that the spring rate of the trim spring is too much - needs a softer spring.

I don't want to speak for Magni here. There may be some things that are not correct on this gyro - but maybe just the trim spring. But, here are my thoughts:

The airspeed reaction to throttle setting will be the same no matter what spring rate trim spring you use - soft or hard. The airspeed reaction to power setting sounds like the HTL is not balanced by the HS reaction to propwash. The M18 single seat is an older Magni model - and may not be as "balanced" as their 2-seater models. Some would argue gyros should be more balanced so as not to require so much stick input when changing power - but typically, older model HTL gyros, with or without HS, have this characteristic. Some would argue that this characteristic makes the gyro easier to land - flares itself upon final reduction of power in the flare!

Trim spring rate: with a soft or hard spring, to trim for a specific airspeed, the adjusted pull of the spring will have to be the same - so it will trim for the desired range of airspeeds. It is my opinion that a softer spring rate will allow more correction of the offset gimbal for turbulence and G-Load disturbances. Such a heavy spring rate does not allow for as much negative feedback from the G-Load to the corrective rotor disk AOA. I would rather you confirm this with the Magni factory, but I can't see it doing anything but good to put a softer spring on it. You need to choose a spring so that it won't overly stretch the spring or break it when you stretch it as much as necessary to provide the same overall force. The spring will stretch over a larger range if it is softer, but it will also allow the rotor AOA to change over a larger range from G-Load disturbances - thereby giving a stronger negative (corrective) feedback with the softer spring. To my way of thinking, this should be better for G-Load stability and turbulence!

The installation of such strong springs could have been done if the offset gimbal were the wrong leverage at the rotor head. You should try to verify the rotor head is arranged properly per the factory - same spindle to pitch pivot offset, and same trim spring lever arm length.

The 2-seater trim spring is a strong double spring as you describe. I do not know what the factory installs on the M18. Perhaps it is not supposed to be the double spring, and someone just installed a "Magni trim spring" on this single seater too! My guess is that the single seater would not require such a strong spring - but you should consult the factory.

I believe the M18 has a cockpit manually adjustable trim spring - electric is an option. On the 2-seat electric trim systems, after landing, it is necessary to push hard against the spring to keep the rotor level. The trim spring on the 2-seaters is the double spring - like you describe! So, it does also require a strong push on the stick against the spring to hold the rotor level after landing. Normal practice though, is to relax the trim spring upon landing as you move the control stick forward so you don't have to push so hard. I'm not sure if you can do this manually on the M18.

- Greg

[mikeconcannon]

I would just like to say this in a public way so that you all can see it, about Greg.
I live in Ireland, he is not ever going to sell me anything, but he is always right there with help and advice about my Magni anytime I need it. Thanks.