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HomeAircraftHelicopterAerobatic FAI F3C F3N Contest › F3C Head Problem
05-04-2005 05:14 PM  13 years agoPost 1
GM1

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Tallahassee, Florida US

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I have three "identical" Tempest FAI rotor heads. Two of them will hover at 1400rpms with no problem. The third will bump until I reach 1500 rpm where it also smooths out like the other two. They are all built the same way, same dampers, same shims, same mixing ratios, same flybar paddles, same length flybar, same blades (brand, length, weight), same blade axle support. I have interchanged blades and it is rotorhead specific, that is, changing the blades doesn't stop the bump. I have measured runout on each head on the same shaft and they are all within .001 of each other.
Do you F3C guys have any ideas what is going on and why it occurs on one head but not the other two?
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-04-2005 05:43 PM  13 years agoPost 2
RotarSoft

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St Leonards On Sea UK

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Gordie,

I would guess some kind of sticking damper. Or even a bad thrust race.. might be worth putting a fresh set of bearings in and some new lubricated dampers. Got to be an easy relatively straight forward swap... they're the only items that can make the difference if everything else is identical!

Cheers

Mark

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05-04-2005 06:25 PM  13 years agoPost 3
Wayne Mann

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United States of America

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Gordie run the model up into a hover for a minute, sit it down, kill the engine and let the head stop on it's own. Then set the collective at half stick, sit the transmitter underneath one of the blade tips and adjust the antenna so that it is just underneath the corner of the blade tip. Now rotate the head 180 and check the other blade. If they are not within lets say a quarter of an inch I would say that something is holding the axle tilted. You might want to check your other models to get a reference for where they are at. If the static tracking is off it will cause the model to keep bouncing off the dampers.


Wayne

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05-04-2005 06:30 PM  13 years agoPost 4
GM1

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Tallahassee, Florida US

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AHA!!
I will try that this afternoon. Great thought. I did not check static tracking.
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-05-2005 01:15 AM  13 years agoPost 5
GM1

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Tallahassee, Florida US

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My Hero
Hey Wayne.
I went out this afternoon and flew the model with no problems, checked static tracking, about 1/16 inch for a norm reference. I flew the problem head, checked static tracking 1/4 inch+. Since the head block bolts together with zero lash and the main shaft is clamped, there is no adjustment available other than replacing the head block, which, while a pain in the tail, is actually pretty easy to do. I think I even have a head block here somewhere that was left over from the Tempest 3D head experiments.
I will change it out and see what the differences are.
thanks,
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-05-2005 04:38 AM  13 years agoPost 6
cfranks

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Adelaide South Australia

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Another possibility is that the Thrust bearing in one of the Blade Holders has been installed reversed. It will jam until a certain load is applied. This of course assumes you have thrust bearings in the blade holders.

Charles

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05-05-2005 12:55 PM  13 years agoPost 7
GM1

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Tallahassee, Florida US

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LOL
I wish I could say that I had never installed thrust bearings backwards.......... but I'd be lying if I did. I have done it and it does indeed cause some strange stuff in flight. In this case though, that wasn't it.
I'm curious to see if fixing the static tracking problem cures the ills of this head but I won't get to it today as it's really raining hard and the forcast says it won't stop until late tonight. Maybe tomorrow................
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-05-2005 01:37 PM  13 years agoPost 8
vetrider

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Daleville, AL (Ft.Rucker)

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Very interesting post. It's nice to learn something new early in the moring. Wayne's tip is one I'll have to put in the memory bank.

Nolan

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05-05-2005 02:28 PM  13 years agoPost 9
tim tompkins

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Boston, Georgia sw Ga. Thomas County

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flood of old memories
Wow a flood of old memories. Back several years ago, Schluter heads had no blade axle as such and we had to adjust the static tracking. The old transmitter ant. trick was the favorite method to check this. Cool thought about fun times! TimT

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05-05-2005 03:15 PM  13 years agoPost 10
GM1

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Tallahassee, Florida US

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Old times
Tim,
I bet you remember when we took a piece of wire, clamped it next to a fan and eyeballed the fan alignment on the crankshaft with no dial indicator. It was cheap and worked surprisingly well.
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-05-2005 05:01 PM  13 years agoPost 11
tim tompkins

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Boston, Georgia sw Ga. Thomas County

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dial indicator
I first saw the process in the schluter building plans. How about the cg test with a pencil? or the balancer made with two water glasses? I said a flood of memories. TimT

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05-05-2005 06:26 PM  13 years agoPost 12
Dr.Ben

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Richmond, VA, USA

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A round pencil and two water glasses can STILL give you a pretty smooth head.

The Achilles heal for a lot of newcomers is that many of these classic diagnostic or setup techniques have been lost over time. These models are the same basic animals that they've been for two decades, and even with modern designs and machinery, problems crop up which look just like they did in the old days. There is no sustitute for experience in these cases. Thank God, I came along after models had started to be half decent, but BEFORE all these techniques were no longer needed. A priceless file in my memory bank.

We'd all been queried by Gordie for months about his head issue. I'm not surprised that Wayne came up with the best possible cause to date.

Ben Minor

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05-05-2005 08:51 PM  13 years agoPost 13
Wayne Mann

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I have had the same problems that Gordie as described with a few of my Caliber heads and it turned out to be the dampers. The dampers for the Caliber 60 and 90 are rather large donuts and unfortunately they are not as concentric as small o-rings therefore they will hold the axle crooked in the head yoke if I do not insert them in the proper orentation. So anytime I'm having problems like Gordie described I check the static tracking.

The real problem with basically all model rotorhead designs is the fact that we use rubber o-rings for dampers. First of all a rubber o-ring is not a damper, it is a spring. The shock absorbers in your car are dampers. Helicopters need dampers for the axle or head yoke. I have often thought of putting a R/C car shock on the rotorhead to act as damper, but I have been told that a fluid damper would not be able to pass fluid back and forth fast enough to work. We need some type of friction device or jelly like substance for the axle to work against instead of rubber springs.

Full scale helicopters with off center teeter hinge heads like on RotorWay's Exec's have preload applied to the hinge bearings to provide stability to the body of the aircraft as opposed to using rubber dampers like we use. At least this is the information I was given. Anyone have any ideas?


Wayne Mann

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05-06-2005 04:18 AM  13 years agoPost 14
Helipilot01

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ColliervilleTn

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Gordie,

It's been a while since I've had a MA head apart and I'm really not familiar with this one. If it's a solid axle head this is my thoughts.

Since it's only on the one head,it leads me to beleive it's the blade axle. It sounds like to me it's too short. If it's only a few thousands too short it's the same as a shim that's the same few thousands too thick.

May try installing a new blade axle or to be for sure,with one from the other heads. If that's not it,leave blade axle in place and swap both blade grips from one of the known good heads. Maybe one of the inner bearings cavitys is not deep enough or one inner bearing is not fully seated putting too much pressure on the dampners.

Maybe this will help.

Mike Fortune

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05-06-2005 08:18 AM  13 years agoPost 15
Optech

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San Diego, CA.

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We need some type of friction device or jelly like substance for the axle to work against instead of rubber springs.
In the early days of full-suspension mountain bikes, the vast majority of shocks and suspension forks were built with elastomeric compounds. They provided both the spring and damping rates. You could even "tune" the forks or shocks with multiple rates in your "Stack". With the advent of lightweight metal compounds to offset the weight of oil damping systems, and/or new air shock technology, elastomerics are no longer used. However, maybe they would work for our purposes. You could troll some bike shops and see if they have any old stock. You'll have to devise a way to cut them up into "O-rings" but I'm sure it could be done, like with sharpened brass tubes or something. Maybe you could get samples from manufacturers.

Keep in mind though that one of the cons of the elasto's was they tended to change rates with temperature. Especially as they got a little worn.

Mike

Viva La Airtronics!

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05-06-2005 12:06 PM  13 years agoPost 16
GM1

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Tallahassee, Florida US

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Good thoughts
Hey Mike,
The new MA heads with the metal grips are different than the old ones with plastic grips. The blade axle goes in and all the bearings go on and the end cap screws are in place so you can check the fit and feel of each. The grips slide over the whole bearing stack and get bolted to a collar in the middle of the bearing stack. It's a good system as you can pull just the grip to inspect the bearings (and squirt some grease into the thrust bearings) or pull the stack grip intact to change dampers or a blade axle.
I did check the axle length as you suggested but that seems to be nominal. While I was at it, I mic-ed the shims to be sure I had what I thought I had.
I have another head block that I will install and see if I can get the static tracking within 1/16 or so and will see if that makes the difference.
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-09-2005 02:39 AM  13 years agoPost 17
GM1

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Tallahassee, Florida US

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After testing.
I did quite a bit of testing this weekend and had some mixed results. I replaced the upper hed block with a spare I had lying around and checked static tracking and it was much improved, about 1/8 inch. I hovered the model at 1500 without problem, a big plus as it would occasionally wiggle in a heavy crosswind before. I got it down to 1440 before the wiggle returned in earnest but something is still not right. My other good head will go to 1350rpm or so with this same setup. I choose to run a little stiffer damping in it to help in the wind so it runs about 1460rpm but this problem head would never tolerate that set up. At least now I can run 1480 in the wind and be OK. I have a few other things to try before I give up completely on this one. The first thing I'll try is a known good head block, one I know has hovered below 1400 in the past. I checked the runout on the existing head block and it seems OK but maybe I'm not measuring something that we need to measure.
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-09-2005 04:40 AM  13 years agoPost 18
tabbytabb

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seattle

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Watching this thread with much interest as I had a similar experience with a Fury Ion with Tempest FAI head. It would bump periodically with cross winds at HS's under 1550.

Great info on the static tracking!

Tabb

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05-09-2005 07:05 PM  13 years agoPost 19
GM1

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Tallahassee, Florida US

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Bumping
I have figured out that the softer you run the o rings, the lower the head speed you can run BUT if it gets too soft, the model sux in the wind, which is why I want to know what's causing this. When it is DEAD CALM, a really soft head hovers really well. God help us all if the wind is blowing.
Gordie

On a dog sled team, if you're not the lead dog, the view never changes.

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05-10-2005 04:04 AM  13 years agoPost 20
Wayne Mann

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United States of America

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Gordie I finished Ray Powells's helicopter setup today with the 14MZ. He has the ball on the center of the axle. We are using two soft dampers or the one's with two yellow dots along with one thin shim on each side. I also have the long Miniature single ball on the pitch arm which gives 9mm of uncorrecting delta. The head damping is fairly soft, but the delta stops the problems with windy weather with soft damping. Plus the soft damping with the delta make the model track like it's on rails upstairs and takes all of the touchiness out of it.

I'm fairly sure that the reason you were having wiggle problems when increasing the delta is because you didn't have a ball on the center of the axle. Tomorrow I will be trying some more delta on Ray's machine.


Wayne Mann

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