Greasable fitting on landing gear strut bearing?

[DBeaulieu]

The XAM-7 called out in the plans can be purchased through vendors with a greasable fitting (Zerk or flush), though it does reduce the load capacity of the bearing. I've made a call to the Aurora engineers for a value on that. Meanwhile,does anyone see any real benefit to having this particular bearing being greasable assuming it meets required load spec per Bob? I think it would be beneficial over the long term, but not sure if there is any downsides. Chime in with thoughts and opinions

 

[AKKen07]

Why would you accept a reduced load capacity? Assuming Bob chose the bearings based on engineering (safe bet!), and with his practical nothing-extra mindset, I can’t see an upside. My guess/opinion is that it would be a measurable increased risk with a likely negligible advantage. If you are really concerned, I think a talk with Bob would be a useful. Or, alternatively, buy an extra set of standard parts and replace in 20+ years?

 

[jaredyates]

SERVICE BULLETIN
AviPro Aircraft, Ltd.
23 June, 2005

MANDATORY COMPLIANCE

Inspection of Landing Gear Shock Strut Rod End Bearings


Background:
One AviPro aircraft equipped with the Spherco ARE720N rod end bearing on the landing gear shock strut (Heim HMX-7G is designated in the plans) had a failure that resulted in relatively minor damage to the airplane. In investigating that incident it was found that Spherco bearings with the grease fitting, as designated by the “N” in the part number, are deficient in strength and should not be used. At least one major aircraft catalog supply house is sending these bearings out as equivalent, when the Heim HMX-7G is ordered.

Aircraft Effected:
ALL Bearhawk Aircraft, AviPro and otherwise.

Remedial Action:
Verify that the shock strut rod end bearings are not Sphercos with the grease fitting.

It is recommended that aircraft currently flying be inspected immediately for grease fittings in the rod ends and, if they are found to be Sphercos, they should be replaced as soon as possible. If the builder elects to continue flying, landings should be approached in a very cautious manner and at lighter weights until the change is made.

The Heim HMX-7G, which has a grease fitting, has been flown in Bearhawk N6890 (Proto I) for 950 hours and landed at gross weights many times, plus the designer conducted an engineering analysis of the bearing that indicates it has sufficient strength, so he feels it is an adequate bearing. However, the ideal bearing would be a Heim HMX-7 or Aurora XAM-7, neither of which have grease fittings. The Aurora bearings without grease fittings will be available from either Bob Barrows or AviPro in the near future.

It is also extremely important that the tread of all aircraft be checked at gross weight. Until further testing is done, the tread should not exceed 74”, center of tire to center of tire, as it affects the overall geometry, therefore the loads, in the landing gear. The rod ends should be adjusted to give that tread.

The strength of the landing gear is also heavily affected by the amount of air in the shock strut. It must be kept FULL of oil or the shock absorbing function of the system is compromised. The fill port for the shock strut needs to be located at the high point of the strut with the airplane sitting in the three-point position to facilitate filling it all the way.

Call Bob Barrows, 540-473-3661, if you would like to discuss this subject in more detail.
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[jaredyates]

The 2005 Q3 Beartracks had this note:
In the service bulletin concerning the replacement of the rod end bearings it was mentioned that the landing gear geometry must be such at the tread is 72” (measured center of wheel to center of wheel) when at normal weight and maximum 74” at gross. These dimensions are critical because the loads on landing gear components increase dramatically as the wheels are allowed to splay out. They absolutely must be held.
To check the spread, you can load the airplane then roll it forward and back, giving the gear time to equalize. Another method is to take two pieces of old Formica counter top, place them face-to-face with grease between them. Then this homemade “slip plate” is put under one wheel and the airplane rocked by the wing tip a few times until everything settles out.
DO NOT UNDERESTIMATE THE IMPORTANCE OF KEEPING THE GEAR TREAD WITHIN THESE LIMITS. ALSO REMEMBER THAT THE ONLY ACCEPTABLE ROD END BEARING FOR THE SHOCK STRUT IS THE AURORA XAM-7M. This magnafluxed bearing can be purchased from AviPro.

I think it may be referencing this safety update?
http://bearhawksafety.com/4-place/changejul04.html

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[jaredyates]

I found this in the old email archives, I don't think it is currently published in the usual safety update channels but wish it was.

 

[jaredyates]

Update to the update:

SERVICE BULLETIN
From: AviPro Aircraft, Ltd.
Dated: 23 June, 2005

MANDATORY COMPLIANCE

Replacement of Landing Gear Shock Strut Rod End Bearings

Background:
Subsequent to the issuance of the earlier Service Bulletin, it was determined that there has been a manufacturing design change in the Heim HMX-7G rod end bearing, which is called for on Drawing 25, Landing Gear Shock Strut, such that it is now the same as Spherco ARE720N making it inadequate for the shock strut application.

Aircraft Effected:
ALL Bearhawk Aircraft, AviPro and otherwise.

Remedial Action:

1) Rod End Change:
The best bearing to be used in the shock struts is the Aurora XAM-7. A lot buy is being made of this bearing and they will be made available through AviPro.

Bearings now being manufactured (and for a number of years past) by Heim/Spherco with the lubrication port, do not meet the strength requirements for this application.


2) Landing Gear Geometry Check:
The bearing needs to be screwed into the shock strut tube far enough that the tread of the aircraft (72”). as shown on Drawing #23, does not exceed 74” center-of-tire to center-of-tire, at your aircraft’s gross weight.
The lock nut is not needed IF Loc-Tite (Blue) is used on the threads. This should give sufficient thread length for adjusting the landing gear tread. Do NOT use red Loc-Tite, as it is permanent and can’t be removed without applying heat (350 degrees F.).


Call Bob Barrows, 540-473-3661, if you would like to discuss this subject in more detail.

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[DBeaulieu]

Good info...thank you Jared! I'm kinda new to the BH party and having access to "Corporate Knowledge" like this is very beneficial.

Cheers! --- Dave


Edit--- Just to add a bit of closure to this thread! Got a call back from one of the engineers at Aurora ---

The reduced ultimate radial load capacity of the XAM-7 with a grease port is 18761 lbs versus 23452 lbs without - a 20% reduction. Based on the info above and in addition to seeing these numbers, I will be sticking with the non-greasable XAM-7