As you all know by now I am going to install a Corvette LS-1 Engine in my RV-10. I have chosen the conversion package from Geared Drives and will be receiving my engine package next summer.
In the mean time I have been working on all of the systems that need to be in place to support this beast. One of those is the cabin heater. I now have the use of hot liquid coolant from the engine to heat the cabin so I have made a heater box that its in the center tunnel just forward of the fuel valve.
I called the fine people at British American Transfer (BAT Inc) and ordered a 4 in. SPAL slim line puller fan, a 115mm 13 row oil heat exchanger and a couple of 8AN banjo fittings. I then crafted a plenum that enclosed the fan that is placed on top of the heat exchanger. This allows the fan to pull air upwards through the heat exchanger and the plenum has 2 in. outlets pointing for and aft towards the front and rear seat distribution tees.
I mounted the heat exchanger on a couple of long rectangular, looped mounting brackets that hold it about 8 in. off of the floor. I did this for a couple of reasons . First, I needed to allow air access to the underside of the heat exchanger and this was accomplished by rasing it up. Second, I needed to get the outlet positioned so that there were essntially straight runs to the distribution tees.
I have it mounted in the tunnel and haven’t taken pictures yet so they will have to come later. I will also talk about the hook ups for this heat exchanger in another post.
For some time now I have been hearing of problems intrinsic to Van’s front wheel design in that there have been instances of wheel shimmy and the loss of preload on the front wheel bearings. My investigation into the problem has led me in a couple of directions.
First, there is the issue of the bearings spinning on the axle and the subsequent damage that is caused to the yoke. Van’s has tried to fix the initial problem due to a spacer that was too thin. At 1/16″, the spacer would bite into the bearing race and start to spin on the axle shaft. The spacer would then start cutting into the aluminum yoke and all bearing preload would be lost. This results in front wheel shimmy and all of its inherent risks.
Van’s tried to fix the problem with a thicker spacer made of aluminum which was 1/4″ thick. This has lead to the second problem.
The thicker spacer now contacts and preloads on the seal of the bearing which is leading to seal breakdown and the resultant spinning of the spacer, galling of the yoke and ultimately seal separation from the bearing. I have seen this personally and it is quite disconcerting.
To understand this all we need to revert back to the design philosophy of the Matco wheel that Van’s uses in many of its home built kits. This wheel and bearing set-up requires a preload to be placed against the cone so that it stays seated in the cup and bears the load of the aircraft. When pre-load is lost for whatever reason the cone can come away from the cup slightly with the ramifications being wheel shimmy, bearing damage and ultimately bearing failure.
The wheel/bearing system from Matco is designed to operate in the following manner:
The bearings are made up from two parts called the cone and the cup. The cup is pressed into the wheel hub and the cone is forced against the cup by the sleeve that is installed between it and the yoke. In this design it is very important that the sleeves that provide the pre-load on the outer steel portion of the cone be of a specific length.
The axle that supports everything has to be just a little shorter than the sum of the wheel, bearings and sleeves so that when the outer bolts are tightened the axle does not mate to the yoke. This allows the compression forces to be placed against the outer portion of the sleeves. These compression forces constitute the pre-load that forces the cone to mate properly with the cup in the hub of the wheel. When looking at the wheel while it is spinning, theseal should be stationary.
Now the sleeves have to make good contact with the steel portion of the cone so that it is forced to remain stationary. Both the steel portion of the bearing and the seal should not rotate if the system is set up correctly. The fundamental problem we are seeing with this wheel/bearing/sleeve system is that the contact with the steel portion of the bearing is not being made correctly.
When the 1/4″ thick sleeve of Van’s is used it contacts the inner 1/16″ of the seal and not the steel portion of the bearing. With the preload on the rubber surface of the seal it deteriorated quickly and the proper preload on the bearing is lost. This sleeve needs to be 3/16″ thick to do the job properly.
Compounding this problem is the fact that the steel portion of the cone that the sleeve contacts is curved. It presents a challenge in transferring the compression force from the flat face of the sleeve to the curved face of the cone. The result of this is the propensity of the cone to spin on the axle. This in turn causes the sleeve to spin on the axle and damage the yoke.
Clear as mud I know but it is important to get technical in this explanation as there are many misconceptions out there right now.
Here is how I approached fixing the problem:
First there needed to be a way of getting a consistent preload on the bearing cone without relying on precise measurements in the length of the sleeves. To do this I proposed that an adjustable sleeve on one side of the wheel and a fixed-length sleeve on the other be employed. These sleeves have a profile cut into the face that contacts the cone that matches their radii. It is cut to the proper diameter so that no part of it can touch the seal rubber.
What this does is allow the axle to yoke joint to be more robust by having a properly torqued bolt on both sides. The adjustable sleeve is both a bolt and a nut with a hole through the bolt for the axle. The head of the bolt rests against the yoke and the nut rests against the outer steel face of the bearing cone. When you loosen the nut away from the bolt it tightens against the bearing and preloads it against the bearing cone. Once you attain the proper preload you simply tighten set screws to affix its preload.
A big bonus to this is that the preload can be set without taking the wheel off. This eases maintenance and allows for quicker adjustments.
The second area I tackled is that of the spacers spinning and causing damage to the inner part of the yoke. Here I decided to have a small round milled out of the flanges of the spacers where they contact the yoke. You measure out from the center of the front wheel bolt hole and drill a hole. You then tap it for a 10-24 socket head cap screw. This screw head nests into the milled half round in the flange to keep it from rotating.
Together, these two approaches should solve the problem with the seals being damaged and the loss of preload on the bearings.
I will be offering these for sale through Cleaveland Aircraft Tools and possibly through Van’s and Aircraft Spruce in the future.
I invite your comments and I will add pictures to this post a little later.
I have been working on my RV-10 and have added products to my line offered through Cleaveland Aircraft Tools. I currently have 6 products that I sell through Cleaveland and I am always looking for more. If you have an accessory that you have designed and don’t want to market but would like to see successful. Send me a e-mail at dhertner@kitaircraftmods.com I would be happy to discuss it with you.
The latest product I have designed is a replacement spacer set for the RV-10 nose wheel. This spacer set consists of a solid spacer on one side of the wheel bearing and a two-piece threaded spacer on the other. You assemble the wheel, tightening the bolts in the axle to the proper torque specification. Once complete, you turn the outer sleeve to set the proper preload on the bearings and set the set screws.
Once the wheel is assembled you will not have to disassemble it again should you need to adjust the bearing preload.
I will write another post describing it in detail shortly.
Thanks for taking the time to read my musings on the modifications of kit aircraft and do not hesitate to send me your modifications to include on this site.
