Trim spring force

Kitty Hawk

Newbie
Joined
Oct 21, 2011
Messages
38
Location
Roskilde
Aircraft
Dominator Tandem
The Dominator has finally come out flying, but I need a lot of effort to keep the nose up, hang test is fine, but at least 85 kg in the front seat, so I probably can not move the rotor head farther forward..
Spring trim is pulled far, alternatively, should I use a heavier spring, but can it fit? it was after all this that was in the kit .. I made a little spreadsheet to figure out how many kg I need to pull the rotor head back, but does it looks correct? it seems to be many kg I need?
:help:
Best regards
Martin
 

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Gyro28866

David McCutchen
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May 8, 2009
Messages
1,892
Location
Dickson, Tn. USA
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Benson B7m & B8m, Dominator II; Kolb Mark III Classic
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750 combined FW & Gyro
During my recent annual inspection. I replaced my single spring to two springs one larger I.D. Than other smaller O.D. One spring is inside the other spring. Just tweaking the mast clamp for location to allow best tension for solo and dual when adjusting electric trim in flight.
 

Kitty Hawk

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Oct 21, 2011
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Location
Roskilde
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Dominator Tandem
Thank you for your reply..
Ok so I should switch to a stronger spring? do you have any idea how many kg you pull? do you have a picture of your setup? :yo:
 

helipaddy

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Jun 5, 2005
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005'N 005'E
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Dominator, ELA 07, B206L4 and B407
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Around 250 days
What was your hang check measurement at the mast? Did you get 0 to 5 degrees nose down as Ernie said?

Where is the stick positioned during cruise flight?

Post a photograph of your trim spring setup
 

Kitty Hawk

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Oct 21, 2011
Messages
38
Location
Roskilde
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Dominator Tandem
Yes 0-5 degrees nose Down
I have to pull hard in the stick to cruise..
About 32lb tension on the spring, and not enough, is that normal?..
 

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helipaddy

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005'N 005'E
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Dominator, ELA 07, B206L4 and B407
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Around 250 days
I've seen a few tandems with 2 springs.
I'd go with a bit more spring tension and see if it helps.
 

Passin' Thru

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Jan 15, 2006
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Naranjito, PR
Yes 0-5 degrees nose Down
I have to pull hard in the stick to cruise..
About 32lb tension on the spring, and not enough, is that normal?..
There are so many variables that can affect trim spring tension that its hard to know where to start.
First, are you sure your horz stab is not nose up and lifting the tail? The yard arm set can affect that.
How much offset does your rotor head have? All else being equal, the more offset the more spring required to counter balance.
Blade pitch can affect cyclic "flapping". The greater the "flapping", the less spring required to counter balance. (so called "blow back".) Blade length affects it.
The all-up weight of the machine affects it.
The distance from the pitch pivot to the teeter bolt affects. The amount of undersling affects it.
I say all this to point out that there ain't no "one size fits all".
A stock / standard Bensen BM-8 with Bensen metal blades required 2 springs about 3/4" diameter and the tension was really quite high. (I don't remember the number) But just changing to RotorDyne blades you could remove one of the springs and reduce the required tension by roughly half.
There ain't no easy answer!:lol: I'd try Helipaddy's suggestion first.
 
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Kitty Hawk

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Oct 21, 2011
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Roskilde
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Dominator Tandem
Great I got solved the problem, I "borrowed" a spring from my daughter's trampoline, it fits perfectly :) it's just a little tighter than the original, thank you very much for your help friends :wave:
 

Gyro28866

David McCutchen
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May 8, 2009
Messages
1,892
Location
Dickson, Tn. USA
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Benson B7m & B8m, Dominator II; Kolb Mark III Classic
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750 combined FW & Gyro
I am going to have to check, but I think the two springs I used were each rated at about 3 or 4 pounds. I have one inside the other.
I have to go by Lowes and I will check and see what the data tag states.
Got my curiosity up now?
 

Kitty Hawk

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Oct 21, 2011
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Roskilde
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Dominator Tandem
uhh I thought maybe not this looks just fine? maybe that's why I need as powerful a spring? : Ohwell:
 

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Gyro28866

David McCutchen
Joined
May 8, 2009
Messages
1,892
Location
Dickson, Tn. USA
Aircraft
Benson B7m & B8m, Dominator II; Kolb Mark III Classic
Total Flight Time
750 combined FW & Gyro
Is it me or the photo, but this machine looks really long.
Is this a Dominator or a Dominator "CLONE"?
It might be that the head needs to be moved forward on the mast to better align the CG?
Just asking???
 
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Kitty Hawk

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Oct 21, 2011
Messages
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Location
Roskilde
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Dominator Tandem
Actually, I do not know if it is longer than the "original" Dominator from us, this is from Niel in New Zealand .. I've moved the head part back when we did hang test as it is reasonably heavy in the rear, but it seems that the tail pointing too far down?
 
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