caution to RAF 2000 owners to inspect rubber bushing

Luc De Keyser

Member
Joined
Mar 22, 2004
Messages
97
Location
Belgium
I was passed along this email today. George Mitchell is very experienced. Hopefully RAF and GBA will warn all of their customers ... Luc
(emphasis mine)
... I recall that two people were killed during the last Benson Days Fly In, while flying an RAF 2000 gyro. From an eye witness report, it seems the gyro went into a gradual nose over maneuver until it contacted the ground in a near vertical position. Speculation was, the flight control linkage may have broken at the control stick, resulting in loss of fore and aft control. Now there seems there may be another possibility. I am in the process of overhauling and modifying an RAF 2000 that has been hangered in high summer heat for several years. While disassembling the two piece rotor mast, I discovered that the rubber vibration dampener that is located near the top of the lower mast assembly, was deteriorated to the point that it was about 90% dissolved into liquid and had run down the side of the lower mast, between the upper and lower mast attaching cheek plates. This liquid rubber was not visible on inspection until the cheek plates were removed. Leaving the cheek plates in position and removing the lower adjustment bolt that is normally used for mast/rotor cg positioning, would not indicate a problem, and would not have been noticed in a normal preflight cg adjustment. However, if flight had been attempted with two heavy people on board and the rotor mast cg ground adjusted accordingly, it is doubtful that recovery from a nose heavy condition after takeoff would be possible. Normal rotor mast cg adjustment for the RAF 2000 is accomplished by loosening the upper rotor mast adjustment bolt, removing the lower bolt and then rotating the solid, predrilled lower mast adjustment insert appropriately to position the the upper mast for best aircraft cg position. Full adjustment will swing the rotor head fore or aft, through a range of about 3-4 inches. If the rubber dampener in the fatal RAF 2000 crash was also badly deteriorated, and the mast cheek plates were snuggly torqued after ground cg adjustments, the gyro could have taken off and flown normally for a while, until vibration would have moved the rotor mast to the full aft position due to rotor drag and engine thrust. The pilot would not necessarily have noticed anything was wrong until the cyclic control began to bump the aft cyclic stop. The normal pilot reaction would be to reduce throttle and resolve the problem. This, of course, would have only aggravated the problem and caused the nose of the gyro to pitch forward rapidly into a diving attitude without possibility of recovery. As the aircraft was destroyed by fire after the crash, it is doubtful a dissolved rubber mast mount would have been discovered or noticed. This rotor mast rubber insert installed in the RAF 2000 appears to be a custom made factory supplied part, and is of an amber colored, semi translucent rubbery material. I would caution all owners of RAF 2000 gyros to remove the mast cheek plates on their machines and inspect this rubber mount before their next flight.

George Mitchell
 
Last edited:

Rando

Gold Member
Joined
Oct 30, 2003
Messages
769
Location
Mesa, AZ
Luc De Keyser said:
...while flying an RAF 2000 gyro. ].George Mitchell
The gyroplane that crashed was a SparrowHawk, not a RAF 2000. I am not disagreeing with what George Mitchell said about the rubber mount, I just wanted to correct the type of gyroplane that crashed at Bensen Days.

Does the SparrowHawk have the same type of mast setup?
 
Last edited:

Harry_S.

Gold Supporter
Joined
Oct 30, 2003
Messages
5,649
Location
Ocala, Florida
Aircraft
RAF2000
Total Flight Time
2000+ hrs.
Rando said:
The gyroplane that crashed was a SparrowHawk, not a RAF 2000. I am not disagreeing with what George Mitchell said about the rubber mount, I just wanted to correct the type of gyroplane that crashed at Bensen Days.

Does the SparrowHawk have the same type of mast setup?

No...the SH does not have an adjustable mast such as on the RAF.

The *donut* in the mast of the RAF is definitely a problem as noted by Luc and George. I experienced the same reversion of that bushing. I posted it in the RAF thread, with some pics.

I am currently using a *cushion gum rubber* bushing, through the courtesy of a special man...who shall remain nameless, unless he consents to being named. If you look up the postings on this problem in the RAF thread...he can't hide.

I would suggest that all RAF owners physically pull this donut out of the mast hole and check for any signs of the material reverting to it's liquid state. At least once every year and replace it every year if you are operating in a hot and humid environment.

.
 

Aussie_Paul

A reforming stirrer!!!!!
Joined
Oct 30, 2003
Messages
4,441
Location
Ballarat Australia
Aircraft
None at the moment.
Total Flight Time
Since 1982 Gyro 5000+ mostly instructing, and approx. 200 fixed wing in the late 1960s.
Gary_in_Orygun said:
Sounds like Icarus flying too close to the sun.:rolleyes:
No, I have experienced this occuring in a RAF with the semi opaque neoplrene type material "magic" bush. This machine had been in the tropics for a couple of years while being finished. The bush had gone into a jelly like state.

A few years ago Birdy rang me and told me that his andjustable hang test had changed from position 3 to position 2 in flight. I told him that I had never heard of this before. It appears that Birdys and many other Rafs are not set up correctly re the 1/2" bolt that goes thru the hang test adjuster adjuster alloy bush.

If the bolt does not tighten the upper mast plates to the alloy bush then the "magic" bush is taking the weight of the machine allowing the alloy bush to rotate as none of the 1/2" holes are in the center.

In Birdy's case he pulled enough "G" (I can't see Birdy flying to that extreme can you??!!!!!!!) to allow the "magic" bush the compress enough to allow the eccentric alloy bush to turn 180 degrees and end up with the top of the mast moving back into position 2, resulting in a small change in hang test, and the stick position moving forward to lower the now additional AoA of the rotor disc to maintain s/level. In Geoges scenario the machine would be trying to raise the nose, due to an increased disc AoA, and the pilot would have to apply more forward stick to stop climbing or reduce power and fly slower. It maybe possible to reach the front stop and still have a disc AoA that is behind the power curve and a mushing landing would be the end result.

This alloy bush is not usually wide enough when arriving in the kit and the machine is being supported by the "magic" bush and we have to add a spacer betwen the alloy bush and the upper mast plates to be able to have the correct bolt tension and have the upper mast plates tight against the alloy bush.

This cannot happen in position 4 because the movement is too far for this to occur. The "magic" bush cannot compress enough to allow the "magic" bush to rotate enough.


In this situation the "magic" bush cannot do its job correctly as it is now supporting the weight of the gyro and cannot allow the mast to move fore and aft as it should to remove the 2 rev shake.

I hope that I have explained this very important topic clearly enough.:eek: I don't have a Raf manual, due to lending it and it not being returned,:eek: to scan the pages for a clearer picture of what happens.

Aussie Paul.:)
 

Chris Burgess

GYRO-CFI
Joined
Oct 30, 2004
Messages
767
Location
Winter Garden FL 34787
Aircraft
Many makes and models, prefer open frame, Sold my SnoBird Tandem
Total Flight Time
3400+
I had one of these bushing tear out completely back in 1997. It virtually cut the bushing in two. We actually did not pick up on the problem until the student went to put his gyro in the trailer/hangar. It was flyable with no detectable problems. However, I think I did notice a slight change in the control stick position. Once the gyro was in the trailer, he couldn't close the ramp/door to the trailer. We checked, and the gyro was in the correct position to allow the ramp/door to close, but it would not because it was hitting the rotor. That's when we started checking and found the problem. The mast was now leaning further back than it should.

One suggestion, check them for sure, but also mark the mast plates so you know where the mast should be (use a felt tip permanent marker). That way at least you will know if it has failed. At the time, RAF said they were trying to manufacture the rubber parts, but that they did not have much success in that area. I think they sent a good bushing for replacement. I made one out of some VERY hard rubber I had so we could continue training until arrival of the correct material.
 

paulp

paulp
Joined
Oct 31, 2003
Messages
259
Location
Edmond, OK
Aircraft
Taylorcraft mod 19=RAF2000
Total Flight Time
3800+
Howdy All,

I beleive that checking the rubber bushing is listed on the 25 hour inspection schedule for the RAF. Along with a bunch of other items such as rod ends, fuel filters, torque settings and bearings and so forth.

I just finished a fifty hour inspection and it took a day and a half. Covered everything.

In addition, I drilled the rear stop limit bolt and it is now safety wired to the torque tube so it can not work loose and limit the aft tilt of the gimble head.
Not a big deal but I feel more comfortable.
 

Aussie_Paul

A reforming stirrer!!!!!
Joined
Oct 30, 2003
Messages
4,441
Location
Ballarat Australia
Aircraft
None at the moment.
Total Flight Time
Since 1982 Gyro 5000+ mostly instructing, and approx. 200 fixed wing in the late 1960s.
Chris Burgess said:
I had one of these bushing tear out completely back in 1997. It virtually cut the bushing in two. We actually did not pick up on the problem until the student went to put his gyro in the trailer/hangar. It was flyable with no detectable problems. However, I think I did notice a slight change in the control stick position. Once the gyro was in the trailer, he couldn't close the ramp/door to the trailer. We checked, and the gyro was in the correct position to allow the ramp/door to close, but it would not because it was hitting the rotor. That's when we started checking and found the problem. The mast was now leaning further back than it should.

One suggestion, check them for sure, but also mark the mast plates so you know where the mast should be (use a felt tip permanent marker). That way at least you will know if it has failed. At the time, RAF said they were trying to manufacture the rubber parts, but that they did not have much success in that area. I think they sent a good bushing for replacement. I made one out of some VERY hard rubber I had so we could continue training until arrival of the correct material.
Chris was that one in 1997 black or the later semi opaque one? The RAF uses I think 50 durometer material.

If the rubber bush is carrying the weight of the gyro they will begin to be cut by the 1/2" bolt that goes thru the centre of it. Correct instalation of the lower alloy bush is critical to the success of the rubber bush. The construction manual and construction videos did not explain it at all back in 1997 to 2002 when I was a Raf rep.

I hope that they have improved the manuals etc to make sure that they are assembled correctly. Every Raf that I have inspected has not been correctly assembled as the builder did not know!!!:eek:

Aussie Paul. :)
 

GyroRon

Former Gyro know it all
Joined
Oct 29, 2003
Messages
16,505
Location
Fort Mill South Carolina
Aircraft
Dominator gyro, Titan Tornado plane
Total Flight Time
1300+
Harry_S. said:
The *donut* in the mast of the RAF is definitely a problem as noted by Luc and George. I experienced the same reversion of that bushing. I posted it in the RAF thread, with some pics.


.
Not to be a trouble maker as I know this is a sore point with you Harry, but this is exactly why I said months ago that you should break that one long " RAF " thread up into smaller individual threads dealing with specific items of concern. Unless someone has alot of time on their hands to read through all those pages of posts, they will most likely not see some of the good info that was posted there. It is easier to go to the RAF section and look up specific threads.
 

Harry_S.

Gold Supporter
Joined
Oct 30, 2003
Messages
5,649
Location
Ocala, Florida
Aircraft
RAF2000
Total Flight Time
2000+ hrs.
Aussie_Paul said:
No, I have experienced this occuring in a RAF with the semi opaque neoplrene type material "magic" bush. This machine had been in the tropics for a couple of years while being finished. The bush had gone into a jelly like state.

I deleted the rest of your post Paul.

The above portion of your post is the most relevant. The bushing is made of poor material...PERIOD...believe me, please.;)

I've been thru this problem with the bushing and I believe one of our mentors has come up with the solution.

I suggested a while back, that with the rotor removed, the lower cam bolt should be positioned in all four positions and a felt pen marker, used to indicate on the teflon plate, the position the upper mast should be, when in the proper cam hole. This to be checked after every flight.

I have from experience, had my mast, in flight, move from #4 to #1 position, solely because of the failure of the bushing reversion to a plastic state.

This present state bushing, needs to be replaced with a more stable compound. When this material discrepancy is resolved, then we can discuss adjustments.


Cheers :)
 

Harry_S.

Gold Supporter
Joined
Oct 30, 2003
Messages
5,649
Location
Ocala, Florida
Aircraft
RAF2000
Total Flight Time
2000+ hrs.
GyroRon said:
Not to be a trouble maker as I know this is a sore point with you Harry, but this is exactly why I said months ago that you should break that one long " RAF " thread up into smaller individual threads dealing with specific items of concern. Unless someone has alot of time on their hands to read through all those pages of posts, they will most likely not see some of the good info that was posted there. It is easier to go to the RAF section and look up specific threads.


It can be broken into sub-parts Ron, by adding the subject in the TITLE section of the header. I believe this would make it easier in a search. I may be wrong on this point tho. I'm not sharp on computer functions...dull, in fact.

I have been guilty of not doing this in the past:p


Cheers :)
 

gyromike

Administrator
Staff member
Joined
Oct 29, 2003
Messages
3,731
Location
Abbeville, Louisiana
Aircraft
Bensen B8MG
Harry,

It really would be better to start a new thread for these kinds of topics instead of tacking on to the current thread ( I mean the other RAF thread, not this one).

I usually just click 'New Posts' when I logon to the Forum, and a new thread with a new title will catch my attention, whereas a thread that runs on forever tends to get lost in the background along with any good stuff in it.

At least it does for me, anyway.
 

route66

Gold Supporter
Joined
Oct 12, 2004
Messages
902
Location
Parks, AZ
Aircraft
c-182/ RAF AAI Mod.
Total Flight Time
2000
This past week I watched a mechanic during his inspection on a RAF check the magic bushing and while it seemed to be a little soft he kept scratching his head as something was not right as he could see from the movement marks on the Teflon sheet. He pulled the lower cam alloy bushing and from an eyeball look could not determine a problem. By a chance of luck while pondering the problem he put the bolt through each hole of the cam bushing only to find the outer hole would not accept the bolt. Upon measurements and a closer inspection it seems the cam bushing had collapsed a few 100ths and was a little out of round. Could have been caused by the high hours on the machine or could have been an oversight from a hard landing a long time ago. Guess why I am posting this is it might be a good idea when you look at the rubber bushing take the time to run a bolt through both cam bushing holes to make sure there are no problems which you might not see on a visual. If I read correctly the magic bushing is to be inspected for deterioration after every 5th flight and all I found was it was a Time Change component, could not find the times for change though. Mine have a manufacture date on the original package, anyone know any more as to the time on the bushing for removal or non use?
 

Aussie_Paul

A reforming stirrer!!!!!
Joined
Oct 30, 2003
Messages
4,441
Location
Ballarat Australia
Aircraft
None at the moment.
Total Flight Time
Since 1982 Gyro 5000+ mostly instructing, and approx. 200 fixed wing in the late 1960s.
Harry_S. said:
I deleted the rest of your post Paul.

The above portion of your post is the most relevant. The bushing is made of poor material...PERIOD...believe me, please.;)

I've been thru this problem with the bushing and I believe one of our mentors has come up with the solution.

I suggested a while back, that with the rotor removed, the lower cam bolt should be positioned in all four positions and a felt pen marker, used to indicate on the teflon plate, the position the upper mast should be, when in the proper cam hole. This to be checked after every flight.

I have from experience, had my mast, in flight, move from #4 to #1 position, solely because of the failure of the bushing reversion to a plastic state.

This present state bushing, needs to be replaced with a more stable compound. When this material discrepancy is resolved, then we can discuss adjustments.


Cheers :)
Harry in the weather environement I fly here I have done over 500 hours on the Raf bush, and it was still ok. It seems that the high humidity areas wreck the bush.

For Firebird the diameter of the bush is 1 1/4" with a 7/16" bolt through it. It appears that I will have to get advice from CB about making my own.

I take it you are happy with what CB made for you. I remember the posts at the time.

Aussie Paul.:)
 

Harry_S.

Gold Supporter
Joined
Oct 30, 2003
Messages
5,649
Location
Ocala, Florida
Aircraft
RAF2000
Total Flight Time
2000+ hrs.
Aussie_Paul said:
Harry in the weather environement I fly here I have done over 500 hours on the Raf bush, and it was still ok. It seems that the high humidity areas wreck the bush.

For Firebird the diameter of the bush is 1 1/4" with a 7/16" bolt through it. It appears that I will have to get advice from CB about making my own.

I take it you are happy with what CB made for you. I remember the posts at the time.

Aussie Paul.:)

That's right Paul...high temps coupled with high humidity will ruin that donut.

So far, the CB donut is perfect. Of course it hasn't *aged* any yet, but CB said it would be good for, what was it, a hundred years?!:D

Rudy Raffeo is also using one now.


Cheers :)
 

Harry_S.

Gold Supporter
Joined
Oct 30, 2003
Messages
5,649
Location
Ocala, Florida
Aircraft
RAF2000
Total Flight Time
2000+ hrs.
gyromike said:
Harry,

It really would be better to start a new thread for these kinds of topics instead of tacking on to the current thread ( I mean the other RAF thread, not this one).

I usually just click 'New Posts' when I logon to the Forum, and a new thread with a new title will catch my attention, whereas a thread that runs on forever tends to get lost in the background along with any good stuff in it.

At least it does for me, anyway.


OK Mike...I get your point and I was thinkin' last night, this would make for easier *searches* as well, if the proper thread title is used.

Can a thread title be changed...if need be? I mean to aid in *searches* for example.


Cheers :)
 

rgraffeo

Gold Member
Joined
Nov 16, 2003
Messages
914
Location
Gonzales, Louisiana
Aircraft
RAF 2000 GTX/SE
Total Flight Time
~500
My rubber bushing was hard as a rock & the bolt hole was torn so that the bolt was touching the mast. It had 250 hrs on it & was 5 years old.
My instructor told me to replace the RAF bushing every 2 years in our part of the country.

I used a new bushing that Harry sent me. I looks superior in every way, the man that made it did a good job.
I also followed Paul's advice & used washers on the bolts for the pre-rotator sheath support to add space to both sides of the cheek plates.
 
Top