Rotor Head problem discovered

I’ve never paid any particular attention to a SparrowHawk rotorhead but would guess the adjustable spacer was to adjust end play by springing the towers in or out by a few thousandths. Nothing wrong with that and allows plastic spacer washers to be punched from standard thickness sheets.

Certainly, the bearing block can be machined to a close enough tolerance to allow a fixed length 3” spacer otherwise.

I don’t know what all the fuss is about.

The Rotordyne rotorhead, designed by Art Weillage, had no teeter bushings, just a plain 3/8” bolt running through plain 3/8” holes in both towers and teeter block. There were .050” plastic washers on the inside between teeter block and towers which worked fine as long as the teeter bolt was kept greased and just finger tight. Worked just like a floating piston pin and never seized or galled. The Rotordyne bearing block was the same as Bensen with 2.6” inside between towers. These things were ubiquitous 30 years ago and no one ever crashed and burned from worn out or broken teeter bolts.

The spacer washers were a bear to install; many people made up plastic washers with handles.

The Bensen rotorhead was the first with hats and bearings. Aluminum hats of all things and the bearings were some sort of heavily graphited matrix of babbit. They worked just fine but the imitators, believing they were making an improvement, substituted Olite bushings and stainless steel hats. Teeter bearing seizure was nearly instantaneous if the teeter bolt was torqued sufficiently to lock the hats against the bearing block. But I never heard of any crashes as a result; you’d get lots of stick shake and the stick would be forced hard left.

In fact, the first rotorhead I made used steel hats running on Delrin bushings and even this combination had a tendency to seize. The wear surface of the Delrin would acquire a steel coating. That’s when I started using Torrington needle bearings.
 

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I just went an looked at the rotor head in the kit I am building now. The spacer did not have the torque stripe on it nor was it locked into place. I would bet that Sport copter did not find it necessary to do that for the SH as it used a different rotor head than where the blades were originally mounted. Later ones probably just got done that way as it was part of the Sport copter process. I don't believe that we should fault Sport copter or GBA for this adjustment problem. The instructions are clear in my opinion.

You mentioned deaths as a result of this problem but I know of none that can be attributed to this adjustment problem. I am well aware of the two deaths in the SH as are most other regular readers of this forum. Speculations have been made as to the real cause of this accident but I don't believe that the cause was ever substantiated. Updates were made to the pitch control just to be sure that it could not be the cause of a future accident. I did not see any nose fork updates but did see the needed update to the main gear after some non injury collapses due to rough landings.

I think the best option is to make information like this public as GBA has done in the past and as you have done in your post. Past this we need to stay objective.
 
Points

Points

Mike,

I was not saying this problem led to the deaths of any pilot that I know of. But I would not bet my life or that of anyone else's all things considered. The pitch bolt coming out was most likely the cause and it was known about by several CFI's here and elsewhere. The only reason they are here is because they flew a short enough flight to the point where they did not lose enough back stick. THe lack of aft stick lead to rather harsh and unexpected landings. Talk to CFI Steve Mcgowan and CFI Rick Abercrombie for additional details.

Chuck, I am sure that given enough grease and enough slop a bolt might survive if you in fact knew that you had to check such a setup. I guess if your blades were spot on in tracking the wear would be minimized. Not sure how an ungreased bolt would fair on the heavy 2 place gyro though, and something tells me you are referencing single place light gyros. Not lead sled class 2 place ships ? . Given that the galling and seizure of the teeter hats occurred on an earlier design I built that only used teflon coated bushings instead of bearings I know for a fact that the bolt would become the wearing element in a critical safety of flight system. There is a lot of turkey stuffing that has passed for flying gyros and our safety record proves it. I have seen a set of smoking / melted teeter towers on a gyro from a pilot that did not regrease the teeter pivots and installed them dry, so I know there is some load up top.

The delrin bushings appear to be turned from stock not punched as they have tooling marks indicating so. But that is neither here nor there had the delrin spacers been made to .050 thickness instead of .060 "I would not be wasting time here about it. . I made new ones and the all should be well.

Lastly Sport Copter has nothing to do with this other than they supplied the hub bar that came with the setup, their specs were spot on @ ~2.500 on the hub bushing.

I GBA made updates to any of their instruction / construction manuals I never received any and they have my contact information......and this was before they closed / suspended operations.


out

J
 
The later kits came with an assortment of thinner bushings to allow the builder to get the clearance a bit closer. I don't know but you may still be able to get them from GBA. The instructions that I have are newer than my kit so I can not say what problems the old instructions may have had.
 
Correct Jonathon

Correct Jonathon

The difference is approx. .030 clearance in the top hats and the adjustable thimble bolt on Sport Copter blades..

The Adjustment/takeup bolt on the top has torque seal applied. That being said, The plastic washers are there for cushion and wear,, NOT Torque value.

I have taken two(.015) shims and added it to the inside between the horizontal adjustment bolt on the hub bar.. one on either bside, Then adjust the top clearance bolt and retighten the locking nut.

Chuck,,

As of yet there hasn't been a failure in this area that I am aware of.

HOWever,
I have inspected machines and found worn thru bolts and even bushings that were cracked due to slide lashing of the hub bar on the area mentioned.. And that was with less than 100 hours on the machines.

This can also be on any gyro witha similar head system..

Thanks again Jonathon....I'd much rather be safe than sorry..

Steve

PS.. and as Mike has said,, different thickness ring spacers are the best way to correct this.
 
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Let me ask you a question, Steve.

You probably have more time in a Parsons 2-place than anyone.

If it still has the original stainless steel hats and Olite teeter bearings, do you torque the teeter bolt down enough to lock the hats against the undersling block?

On second thought, you most likely replaced the Parsons head with a RFD needle bearing rotorhead.
 
Chuck,
The head on my Parsons is an Air Command DBL. bearing , and the bushings are teflon coated, not the needle bearings such as Earnie has in the Dominators.

The teeter as you are aware of only travels some 20-30 degrees front to back.. as all gyros do.
I inspect them and apply a thin film of grease. Either way they're replaced if the teflon is broken down. And Yes I do tighten, (not torqued,) the Stainless top hats,( which have been replaced many times) and are locked in with a snapp ring.. Side motion is also controled with the plastic shim rings.. again which are replaced when needed.

Red Neck Torque Wrench is to tighten the castle nut, and two castelations later apply/insert the keeper pin.

I know your way ahead of me on the proper procedures..
 
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anyone willing to post an Idiots Guide to checking your rotorhead with photos??

I think it would be of great value to me and other less non-machine shop savvy pilots/owners.

.
 
I’ve used Teflon coatings in the past, Steve, for microwave tuners where electrical contact had to be avoided..

Generally, it’s a powdered Teflon in resin that’s sprayed on in an electrostatic spray booth and cured at 350º-400ºF. It doesn’t hold up very well under high pressure. That's the reason for plastic spatulas in Teflon coated frying pans.

If you have a phobia against needle bearings, a satisfactory alternative is DU series bearings which are woven Kevlar with interwoven Teflon fibers bonded to the bearing shell.

I’ve never ever had to replace needle bearings. But they should be the caged type and need glass hard inner races for good durability.

**
Vance: You say that needle bearings aren’t the greatest thing for oscillating motion; Have you ever seen 2-stroke connecting rods that had anything but needle bearings at the small end? Well, years ago, $39 lawnmowers had plain bearings at the small end. Good for one summer and throw away.
 
idiots guide 101

idiots guide 101

Not done yet.

I assumed that the teeter towers were .500 thick during my calculations to make the proper thickness delrin shims / washers. I was wrong since I did not measure them. Garbage in + garbage out = no flight . Machined flat bar to some spec I have never seen, or expected.....

Assume: (ass)...out a u-&me

Should we have a contest to see if anyone can guess how thick the teeter plates are ?

No flight tonight...... arrrrrrrr.....

J
 
Spoke with Dan Banks.

Spoke with Dan Banks.

While Dan is no longer with GBA he took the time to call me out of his busy schedule....He informs me that while he was not involved in the early or initial kitting of the SPH 1. He did in fact address some of the rotor head issues / kit information or lack there of in later versions. Shimming the rotor head is / was a procedure REQUIRED in all builds until the 3 version whereby GBA supposedly produced a ready to install rotor head assembly, where no measuring or shimming was required. The builder was required to assemble and measure the space between the rotor hub bushing and the teeter hats with a feeler gauge and measure and math out the required shim thickness via trial and error. Shims were sanded to proper thickness. (yikes). The upper spacer was to be adjusted to fitment as Mr Burton indicated, by placing the spacer in the bottom of the bearing block / teeter plate inside spacing.

While the proper machinist's tools to do the job with any precision would cost several hundred dollars, Inside mic, caliper set, depth mic, etc and a lathe and delrin bar stock to turn a finished product could cost even more... It would give more accurate results and I am quite sure a much smoother finished product at least from the get go. Another route might be to cut out sheet as Chuck suggested was the case might save some tool requirements and overall $$. While there are many paths to the same destination I feel that a precision / critical / component such as a rotor head should be a finished piece and should not require the builder to "finish" the part except to mount it.

Plus some rotor tracking, and minor adjustments.... But that is only my opinion. I have built several rotor heads and while the materials to build one are nothing special, adherence to tight tolerances and accurate machine work is the real challenge. Plus the tooling and equipment to check said work. I know early bensen plans and even kits had builders make their own rotor heads and even rotor blades, but after several deaths even bensen stopped making rotor head plans available due to liability issues....the question in my mind at what point or what degree do you make the builder the engineer and what kind of tools and skill does the builder have to make sure a safe product is turned loose for flight....

It is evident to me the early kits had no such documentation and required builders to figure it out on their own.

J
 
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