View Full Version : Xenon Rotor Head Issue
03-18-2008, 04:14 PM
I would like to start off by saying that I am a big fan of the Xenon gyro. I think it is one of the nicest looking machines out there and I don't want to come off like I am bashing them in any way. But I have some issues with the type of hardware used on the rotor head. All the bolts are coarse thread hardened bolts with allen socket heads. I have not put them under the rockwell tester yet to compare them to AN bolts, but they look like standard hardened screws. I'm sure they are plenty strong for the job they are doing. I am a tool and die maker and use these kind of bolts in situations they are not intended for and they rarely fail. But if everyone else is using AN nuts and bolts, why isn't Xenon. I pulled the rotor head off the black Xenon in Valpo, IN last week to fix a wallered out hole in the towers.(that story can be saved for later) The thing that really bothered me was that even though the bolts had nylock nuts on them, I found one of the critical nuts loose. So loose that I unscrewed the hole inch of thread with my fingers. The nut is pictured below. Both of those lower bolts have cotter pins on the ends, but the current setup doesn't seem right. Now I don't claim to be an engineer of any kind, but common sense tells me that don't look right. Changing over the head bolts to at least a fine thread metric rather than coarse may help the abuse of the nylock, but maybe you experts could chime in a little here. Maybe you Xenon pilots should double check these in your preflight.
03-18-2008, 05:07 PM
You bring up some very good points and great observations. I can say from my own dealings with Allen head bolts that they are very strong. We used them on all wind tunnel model due to the strength factor of the bolts. I know they look like screws but they really are bolts. At least I hope so- a bolt has a shank and a screw does not so if parts are joined and there is no shank - that's bad for the part.
As far as being used on aircraft, I personally think that aircraft hardware is the best material to use in aircraft. They are hardened but not so hard so as to be brittle. Aircraft hardware also has much more protection from corrosion. I fully agree with your conclusion from your findings that aviation grade hardware would be better in this application.
Now from the standpoint of fit and or strength, the manufacturer or engineer may have found that the standard AN/MS hardware would not either meet the strength requirements or that an even more expensive NAS bolt would have to be used to meet the needs of the application. NAS hardware can get rather pricey quick but like evertything else in life - you get what you pay for.
FYI the new RAF bolts for the last RAF blade and bar change- those RAF stamped bolts are actually a special NAS grade bolt designed specifically for RAF. Yeah, they paid big bucks for added owner/operator safety.
Nick, it would be interesting to see what the hardware would look like in five years (with the current hardware used). I would really recommend doing regular checks for corrosion and promptly replace any corroded hardware no matter what the extent of corrosion is for any of the allen head hardware.
Holes being elongated or worn out is a definate sign of a bad fit or hardware arrangement, the hardware is to hold all the "goodies" together not damage them. I would seriously contact the kit manufacturer and let them know what you have found, the hours on the components and what can be done to prevent further damage. Also check with them to make sure that the damage to the major components is not excessive, they most likely have not given the criteria for how out-of-round those holes can be and my guess for this application is that the tolerance is going to be very small.
Good work, Good find and thanks for informing others of your findings,
First of all, congratulation to Xenon USA for their first anniversary of operation!
I haven't had the pleasure of seeing a Xenon up close yet, but one of the first things I have noticed (in pictures) when the black Xenon showed up in BD 2007 (http://www.rotaryforum.com/forum/showthread.php?t=12327) was the funny-looking fasteners. If the Xenon in question is the same black one from BD 2007, it is possible that it's fasteners are different than those on newer machines. Still, I think this bolt application in a critical part as a rotor head is unwise, to put it mildly. Aviation fasteners must have the correct length shank. Bolts that act as hinges, like the pitch pivot bolt above, should use a castle nut with a cotter pin located correctly. I don't see the logic in using nylock in this application - and a cotter pin located miles away...? Looks like an afterthought to me.
p.s. I just noticed the teeter bolt has no washer on the bolt head side and no castle nut.
03-18-2008, 11:49 PM
I fully agree, Udi. The Nylock with pin is in fact very dangerous. Obviously the nut loosens, thereby exposing thread which can then come under shearing load, once the bolt decides to use its new freedom.
That is a disaster waiting to happen!:Cry:
03-19-2008, 06:26 AM
The coarse thread will loosten a lot more than a finer thread if the fastener turns even a tiny amount , say to the limits of the cotter pin in its slot etc.
03-19-2008, 06:43 AM
In the UK we would insist on at least two threads showing through those nylocks. Doesn't seem to be much 'aviation practice' going on here !
03-19-2008, 11:58 AM
Self locking nuts and castlelated nuts do serve different purposes, but NEVER allow bolt threads to be within the bolt hole of tensioned adjoining components.
If you cannot acquire, or use a bolt with the proper grip length, add washers under the bolt head or the nut.
03-20-2008, 12:42 PM
Wow, seems like a problem in my eyes. These machines have not been fully vetted and this is some proof. Bringing issues like this up are good things that have to happen to sometimes help make a safer machine.
03-20-2008, 07:51 PM
Fully "vetted" ? Is this some young, hip slang? Snow again, I didn't catch your drift.
The Xenon rotor head problem in this thread was caused by the previous owner replacing the factory teeter bolt with a new bolt that was too short, allowing the threads to "machine" the hole every revolution.
03-20-2008, 09:08 PM
vet1 vɛt - Show Spelled Pronunciation[vet] Pronunciation Key - Show IPA Pronunciation noun, verb, vet•ted, vet•ting. Informal.
–verb (used with object)
2. to examine or treat in one's capacity as a veterinarian or as a doctor.
3. to appraise, verify, or check for accuracy, authenticity, validity, etc.: An expert vetted the manuscript before publication.
–verb (used without object)
4. to work as a veterinarian.
Tom, see definition 3.
03-22-2008, 09:56 AM
Thanks Adam you can be helpful sometimes. I did a little research to debunk Tom's notion that the word is "young, hip slang" Turns out that the word "vetted" has been around and used since 1860–65; and is a short for veterinarian]
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