Trustline offest in TS?

barnstorm2

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I know that my Twinstarr seems much more stable then my HTL aircommands (which all had HStabs).

How can I tell (or estimate) how many inches my thrust line is high?

Is there a simple method to estimate?:noidea:

Do I just measue up from my belly button?

Am I allowed to suck in my gut? ;)
 

gyromike

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Tim,

You'll have to do a double hang test to find the CG at your All Up Weight, and see where the thrustline passes.
 

Doug Riley

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Tim, check out the varous descriptions of the double hang test here on the Forum.

I did an article describing it in Rotorcraft a couple years ago, too.

Tandem gyros in general feels more "stable" in the sense that they ptich more slowly when first disturbed. It's more difficult to "catch" one once it gets pitching, though.
 

barnstorm2

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Thanks guys!

Doug, Do you know what issue/year?
 

gyromike

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Tim,

I'll try to get the rest of the Twinstarr article scanned for you tonight.
If you don't hear from me in a couple of days, shoot me an email.
 

Friendly

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Doug

Doug

is the hang test the only way to figure this out? If so would you please try to expain it here again? Or Mike could you scan it to me in an email as well?
 

raghu

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My experience with the twinstar in the few flights I have is that it certainly is unstable in pitch but not to a degree that cannot be managed with some training. The instability is not so obvious in calm conditions but becomes readily aparent in gusty conditions. More than the pitch instability though the directional instability is obvious and requires active rudder control in gusts.

I have never hang tested the twinstar but suspect it has a slightly high thrusline with two people loaded and has very limited pitch damping due to short tail arm. One would have to test though to be sure.
 

Caribean_gyro

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Raghu

How many hours do you have in the twinstar?
What is you consideration of gusty conditions.

My experince with just a few hours in it and in winds of 20 to 30 miles is that she is not pitch sensitive. she is yaw sensitive whne it comes to strong head wind. The big tail have a domain on the fusalage that counter react the engine torque. making a new person over control the rudders du to the strong engine torque.

I take very peaky when it come to the twinstarr. She is not a rocket but she is a strong work horse in wind tolerant and sloopy pilot at controls.

ChuckP
 

chuter

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Paul Bruty posted the 2-pic method a while back but I'm having trouble finding it with a search.

Here is a link to a thread where I posted pics of my double hang test.
thread
 

barnstorm2

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Currently, I have no way to hang my Twinstarr.

Can I in the short term make a rough estimate by measureing thrustline from belly-button?

I would also like to mention the Greg Gremminger has made some stability test proceedures.

Has anyone tried these on a Twinstarr?

Thanks everyone!!
 

Caribean_gyro

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Tim
just curios why the concern abouth center line thrust.

I beleived Woody mentioned the distance in one of his last mail.

ARe you experiencing some thing strange in you machine
 

barnstorm2

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Tim
just curios why the concern abouth center line thrust.

I beleived Woody mentioned the distance in one of his last mail.

ARe you experiencing some thing strange in you machine
Woody stated it somewhere? Please let me know if you find it.

No big reason. Just with the recent RAF going down it got me wondering about the Twinstarr thrustline.

I was thinking that with our V-Tails we could lower the engine a few inches and possibly make a CLT Twinstarr kit?

I have flown a number of CLT and HTL machines and while I am FAR from an expert and I only have about 200+ hour time (100UL/100+N#logged) the Twinstarr seems VERY stable.

It occured to me that the Twinstarr might be considerd NCLT?

If you draw an imagineary line through the prop it is I guess about 4-6" above my belly button.

If you draw that line on a magi it seems much higher and on an RAF it looks like it could be over your head!

I respect the machine and I don't intend to perform any manouvers that close-in on 0g or unload the rotors on this or even a CLT machine for that matter.
 

Chuck Roberg

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Tim, I have Chuck B. program on how to do it by weighing it. I tried, to no avail, to upload it to the Chapter 34 site.

If you give me your email, I'll send it to you. It's in Excel.
 

Udi

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Here is a method for estimating your gyro vertical CG without a hang test. This spreadsheet was written by Chuck Beaty and I have made some minor improvements to it. All you need is some weigh scales, an accurate angle measuring device (like a Smart Tool) and a helping hand. Follow the directions, it is self explanatory. Let me know if you have any questions.

Udi
 

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Doug Riley

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Tim, the PRA mag article was in the September 2005 issue.

You can do a CG calculation entirely on paper the same way designers do it. There's little bit of arithmetic involved, but just the pocket-calculator kind. This method is taught to fixed-wing students in connection with finding CG along the horizontal axis, but it works the same way in the vertical axis. Pick a convenient datum --say, the ground when the gyro is on is gear.

The "belly button" method makes no sense, since the pilot's seat height varies in different aircraft. Your navel is a good guesstimate of your PERSONAL CG, though.

If you're not familiar with this method (and don't have a Jeppesen student manual handy) let me know and I'll try to post a quickie version.
 

GyroRon

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Tim, you can buy a chain fall hoist at Northern Tool that could lift 4 of your gyro together, for under 100$. Go get one and then surely somewhere on your airport there is a hangar with a truss that is 13-15 foot high.... tie the chain fall to that truss and lift away. Don't say you can't, just say you don't want to..... nothing can't be done!
 

barnstorm2

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Ron,

I have a hoist but the hanger nazi's would have a $:censored:Fit.

We can't even work on our machines unless the on-airport maint facility gives us a note saying they won't do the work.

I am really excited to try the spreadsheet.

At some point I may fly it somewhere to hang it but taking the 30 foot rotors off and back on takes several people and alot of work.
 

Doug Riley

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It's been done with a backhoe, too. You need a calm day if hanging gyros outdoors.

The challenging part of the double-hang with an enclosed gyro is finding a hard point up front from which to rig a sling.
 

barnstorm2

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Spreadsheet Questions!

Spreadsheet Questions!

Data: "Main axle height above floor"

Ahh.. my axels measured where they meet the wheel or frame or?




Results:

AUW
HOrz CG
Vert CG

And I get thrustline offset from??

Do I measure the height of the probeller hub and subtract from the intersection of Vert CG and Horz CG?
 
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