Fixed Gear Replacement Bumper

Old versus new part

For those of us that fly with the gear “down and cured” …  If you have worked on the nose gear of the FG, you probably know there is a rubber bumper used as a shock absorber on the nose gear.  Like several other parts, this was a “found part.”  It is an automotive engine mount that seemed to fit the bill.

I have not flown yet, so I can only relate what I have been told.  The rubber portion of the mount is sandwiched between plates of steel.  When compressed, the steel will deform and does not relax to the original shape. The bent steel introduces slop.  Over time, possibly a lot of slop.  I am told that Velocity has recommended replacing the shock, or shimming from behind.  Shimming will remove the slop, but not the original problem.  The steel may deform even more.

A small group of builders/owners has taken up the task of finding a new option.  The original research was done by Jorge Bujanda.  http://www.jbujanda.com   He located an industrial bumper.  It is not a sandwich.  It is a rubber pad mounted to a steel plate.  Jorge’s son is an engineer and ran the numbers for suitability.  His analysis showed it would be an excellent replacement.

Damaged Part

Since it was not a proven solution, we didn’t think it wise to recommend it to anyone.  We wanted to get our hands on it and try it first.  The new part was ordered and installed by Kevin Steiner (SELW/FG) and Bruce Topp (XL/FG).  The new part mounts vertically on the canard bulkhead.  The retaining strap on the current bumper is discarded.

The pad is hard but flexible.  Taxi tests revealed the new shock must be installed under compression.  Both Kevin and Bruce fabricated shims and adjusted the force so the gear leg would stay firmly held with a two passenger load in the front.  Kevin did this by standing on the canard bulkhead and checking for any gap.  I couldn’t to this.  I’m pretty sure I would shoot a knee cap across the shop.  I’ll have to find another way.  :)

Once installed, the new shock has taxied, flown, and landed beautifully.  There has been no sign of deformation or slop.  It appears to be just the right thing.  The manufacturer of the bumper is an industrial supplier.  Unfortunately, the smallest run they make of the product is in the thousands.  At the time the part was located, they had just 17 left on the shelf with no plans to make more.

Gary Paxton (SE/FG) ordered the last of the bumpers this weekend.  He reported back that the manufacturer said this has become a “hot item” and they were going to tool up and make more.  :)  There should be enough for anyone that wants one.Jorge spoke with Scott Swing and they will be getting one.  If they see them same results, this might become the standard part.

If you are interested in making this modification, here is the info:
ADVANCED ANTIVIBRATION COMPONENTS
2101 Jericho Turnpike
New Hyde Park, NY 11042-5416
Tel:   516 328-3662

Desc:  Rectangular Bumper
Part Number V10Z 7-1011

Their catalog can be found here: http://www.punchtools.com/PDFSupplies/V100.pdf (6 MB download)
The part is listed on page 126. There is a picture. Dimensions are also given.
You can call and order it directly. The cost is around $50 (including shipping).

Andy Millin

Instructions

Jorge

1. I opened 3/8” holes on the canard bulkhead
2. I used a 3/16” aluminum spacer between the canard bulkhead and the rubber shock’s steel plate.
3. I inserted a couple of wide area washers between the bulkhead and the spacer, on the top bolt, to ensure a flat support for the spacer against the uneven surface of the canard bulkhead
4. I used 3/8 x 16 bolts and nuts
5. I inserted a couple of wide area washers between the aluminum spacer and the rubber shock on the bottom to increase compression and ensure that the strut be tight in place against the captivator.
6. I had to place 140 lbs on the nose compartment to compress the rubber shock enough to allow installation of the captivator back in place
7. Once unloaded, the strut sits in place tight against the captivator.
8. I may have to adjust the level of compression before flying.

Andy

1. Remove the captivator plate.
2. Remove the upper cross bolt.
3. Remove the old bumper.
4. Place the new bumper vertically. Center approximately over the old bumper bolt hole.
5. Drill the top hole. 3/8"
6. Remove the shock from inside the keel.
7. Bolt it to the forward face of the canard bulkhead through the new top hole. Make it as close to plumb as you can.
8. Drill the bottom bolt hole.
9. Remove the shock.
10. You will need to shim new shock. It is looking like 5/16" is the right number. You will need to verify what is right for your airplane.
11. I followed Kevin Steiner and made a microglass pad for a shim. Bruce Topp and Jorge Bujanda fabricated a shim out of aluminum. Builder's choice.
12. I used Grade 8 bolts 3/8x16, 1-1/2" Also purchased Grade 8 Nylock nuts. Can be purchased at the local hardware store. If you want to use AN hardware, you'll probably want AN6-14A or AN6-15A.
13. Bolt the shock in place with the shim.
14. Put the gear leg in and put the cross bolt in.
15. Install the nose gear fork and tire.
16. Turn the fork backward (point to the nose).
17. Remove any sawhorse or other support; placing the weight of the aircraft on the nose gear forcing it to compress against the new bumper.
18. Put enough weight in the front end to compress the shock. (on the canard bulkhead, on the floor close to the canard bulkhead, you in the nose, etc.)
19. When you have enough weight, you will be able to bolt the captivator plate
back in.

You're in business.

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  Old versus new part

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  Replacement Part

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  Installed Shock

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  Installed with Gear Leg

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  Shock Shown Pre-compressed

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  Damaged by a few landings N44VF

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  This bumper had only 15 flight hours N44Vf