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HelicopterHIROBOOther › Near Freya Mishap
03-12-2003 03:01 AM  14 years agoPost 1
JPBIII

rrApprentice

Birmingham,Al

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I got lucky today with my Freya 91. Just after bringing it back into a hover the heli would not stay trimmed, the controls were very slugish. After I landed it , I found that the (2) 4x14 button head bolts that go through the dampners in the yoke and thread into the center hub fallen out. This allowed the yoke to tetter back and forth on the center hub.
I learned my lesson, now I will more closely inspect it before each flight.

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03-12-2003 03:06 AM  14 years agoPost 2
z11355

rrMaster

New England

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I lost a Freya due to loss of exactly
that bolt.

Folks at home, don't skimp on the
Loctite.

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03-12-2003 03:35 AM  14 years agoPost 3
Dave_D

rrKey Veteran

Philippines

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Happened to my a couple of times as well....

Luckily there were enough bolts left on the yoke to let me land it in one piece.

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03-12-2003 03:40 AM  14 years agoPost 4
irq

rrKey Veteran

San Diego, CA

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I checked that bolt on my stock Freya a couple of weeks ago and noticed it was a bit loose...

I imagine that because it pivots on that bolt it can weaken the effect of threadlock after a while...

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03-12-2003 11:53 AM  14 years agoPost 5
JPBIII

rrApprentice

Birmingham,Al

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I will definitely use more thread lock on those bolts. Are there anymore bolts that have a tendancy to work loose?

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03-12-2003 12:12 PM  14 years agoPost 6
z11355

rrMaster

New England

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those seem to be amongst the most
common ones to loosen. One
observation is that button head cap
screws almost always NOT 12.9 grade
hardness but rather something like 8.8.

You could certainly replace those
button heads w/ SHCS's as long as
they do not interfere w/ the seesaw or
flybar operation.

I replaced all the Phillips head screws
w/ SHCS's & locknuts or use lockwashers and set the powerdriver to clutch setting #2

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03-13-2003 12:15 AM  14 years agoPost 7
bravoh

rrNovice

South America

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Happened to me just yesterday...luckily I only lost one of them.
It seems the problem is that only the tips of these bolts are actually screwed in, so the loctite doesn't have much surface area to work on.
I was wondering what if I used one long bolt all the way across. Using loctite, there would be more surface area for that one bolt to hold on to. With a locknut on the other end as added insurance it would seem to solve the problem.
Will this affect the helis flying in any way?

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03-13-2003 12:31 AM  14 years agoPost 8
z11355

rrMaster

New England

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The dampers are 9mm thick and the
screw is 14mm giving you a screw
depth in the center hub of 5mm.

While you could make the argument
that maybe an up to 18mm screw would
be better, I don't see where you're getting
the 'only the tips' statement from. 5mm
isn't an insignificant amount.

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03-13-2003 05:48 AM  14 years agoPost 9
bravoh

rrNovice

South America

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Well maybe the phrase "only the tip" isn't the most accurate, I think the phrasing is a bit of a mood point. The real issue is that only 5mm of a 14 mm bolt are doing the work. By using a bolt that goes all the way across, that area can be increased to 10mm to hold 1 bolt in place (using loctite). This plus a locknut on the other end would most likely solve the problem.
My question is will this have an effect on the way it flies. In other words is there a reason 2 bolts are being used here?

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03-13-2003 08:04 AM  14 years agoPost 10
heliz44

rrApprentice

Southern california

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The elevator toque lever also has a tendancy to come loose. I lost all control of my elevator and crashed once and another time i caught it on the bench.


Chad

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03-13-2003 12:27 PM  14 years agoPost 11
z11355

rrMaster

New England

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Point taken. Sorry for my misinterpretation.

I can't honestly see much if any
negative effect by using a longer
screw.

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03-13-2003 03:29 PM  14 years agoPost 12
darrenjet

rrApprentice

Springdale, AR - USA

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bravoh, I think you're using some flawed logic here.

"The real issue is that only 5mm of a 14 mm bolt are doing the work. By using a bolt that goes all the way across, that area can be increased to 10mm to hold 1 bolt in place (using loctite)."

Surface area of the threaded part has little effect on the holding power of a bolted joint. I know it seems initially contrairy to logic, but it's true. Think about it, why aren't nuts more than a few thread lengths long? - because there is nothing to gain by making them longer. Adding loctite forms a chemical bond that increases friction, reducing the likelyhood that the bolt preload will be reduced by vibration, load cycling, etc. A 20 mm long 14mm bolt in a threaded hole has the same holding power that a 5 mm long 14mm bolt in a threaded hole has, assuming they are tapped the same, made from the same materials and are preloaded the same way. Even if loctite is applied uniformly to both. Loctite increases friction, but friction is independent of surface area.

Some of what I said was not entirely accurate. There are a lot of variables in a bolted joint. The length CAN have an effect, but it is not to produce more friction. A longer bolt in a completely tapped hole is different that a bolt and nut combination. The longer bolts in a tapped hole have the advantage of reduced likelyhood of relaxation, embedment and other flaws that affect the joint integrety. So, depending on exactly what is causing the failure, a longer bolt can have positive effects.

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03-13-2003 04:09 PM  14 years agoPost 13
Brian Bennett

rrKey Veteran

Dugway/Tooele UT, USA

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Pics Pics Pics !

Which is the elevator yolk bolt? I have a "mini Freya" (Sceadu) with the SV-IV head and I believe it is quite similar to the Freya head in configuration. Recently I read that Volkul may have had a loose bolt on his and I am wondering which ones to red flag and monitor real close.

--Gi

Team MRC-Hirobo and Model Avionics Rep

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03-13-2003 04:19 PM  14 years agoPost 14
MRC-Hirobo

rrKey Veteran

Edison, NJ

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Been there, seen it, expereinced it, red loctited it, fixed it. Just make sure to not get any of the red stuff on the threads where the dampner goes to save a headache later, or let it get in there so the two are joined and repalce the screw as preventive maintenance when the dampner is repaced. Either way works. Just make sure the oil

A quick check before flying just to make sure it is tight and off I go.

As long as the Elevator torque pivot set screw is on the flat spots and the 3mm lock nut is used as well. You should be probelm free there.

jeff G

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03-13-2003 04:27 PM  14 years agoPost 15
z11355

rrMaster

New England

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yea but do you have the T Shirt!

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03-13-2003 08:25 PM  14 years agoPost 16
Daniel Santana

rrApprentice

Tampa, Fl

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"As long as the Elevator torque pivot set screw is on the flat spots"

First crash on my first day out... forgot to locktite this? Maybe I just never tightened it?

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