Kit Aircraft Modifications

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, the seal 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.

Dave

Hi Everyone,

Been away from this site for way too long

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.

Dave

I saw that there was a listing today on eBay for an RV-10 that has a 600hp Corvette LS7 engine shoehorned into it. I went and saw the listing. What can I say. If this person has designed the firewall forward system in the same fashion as he has built the airframe then I hope he never sells the thing. Especially to someone who doesn’t know all of the facts. Someone bedazzled by the sexiness of having the Corvette emblem attached to the aircraft.

You can go to the listing here and have a look for yourself. I don’t know about you but I don’t think that the side skins of the RV-10 are attached with 1/8″ rivets. All of those clecos are supposed to be silver aren’t they? There’s a whole lot of head scratching going on here!!

I personally have looked long and hard into the Corvette conversion and have had extensive conversations with experts in the field. I even flew out to meet Jack Kane who owns EPI Inc. in Washington state. We looked at the many many many variables in converting an automotive engine to aircraft use and simply couldn’t make the math work out without making a whole slew of compromises. Jack is a pretty smart cookie with the degrees and experience to back up his opinions.

I tucked my tail between my legs and headed home. I will put it very simply. There are precious few alternatives currently available for the person building an RV-10 when it comes to an alternative to the venerable Lycosaurus. This is not to say that there aren’t some exiting developments in the works.

I am working on an engine project of my very own. One that uses a proprietary compressor/effector technology that has been developed by a company in Texas. It will use the Brayton cycle which is the same cycle used in turbine engines but it will use a different and more efficient compressor and effector than the axial turbines used today.

My primary goal is to have the new engine fit into the space that existing Lycoming takes up. No new cowl, no new engine mount. It will directly replace the Lycoming.

It will be able to burn almost any type of fuel. Gasolines, naptha, diesels, kerosenes and bio-fuels. The problem for me is that it is going to take a pretty big chunk of cash to make it happen.

Anyway, I digress. It is a wonderful thing that we can invent and implement these inventions within the framework of the experimental category. It is very important though that we do things in the safest and most professional way so that those who are building the plan-jane version are not adversely affected by the insurance industry and the relentless pursuit of the ambulance chasing lawyers.

Thanks for tuning in. Link to me if you can.

Dave

This is something that you don’t see every day!!

I had a fellow in the yesterday having a look at the fiberglass parts that Van’s sends with their kits. This guy lives, eats and breathes everything composite. From America’s Cup boats to custom canoes for children. I have seen his work and I am glad that he came over.

When we had a moment to talk, he told me that Clamar Floats, whom he does a lot of work for is going to be installing a set of their beautiful composite floats on a Van’s RV-7. Talk about a conversation starter. Apparently this fellow lives in the Pacific northwest and is quite an accomplished float plane pilot.

This isn’t the first Van’s aircraft to receive the float treatment. A fellow from British Colombia installed a set a number of years ago and successfully flew them on a Van’s RV-6. His name was Eustace Bowhay. You can read about his installation by clicking here.

I don’t know about all of you out there but I think that I would have a bit of a hard time with the thought of having to extract my 6 foot 200 lb self out of the aircraft to dock the thing.

Dave

When it comes to Van’s aircraft lighting there is a number of choices that you have to make before closing out the wings. I have touched on the very cool wing tip position lighting from Jeff Bordelon but you have to make a decision on the landing and taxi lighting as well.

There are two schools of thought here. You can either put them in the wing tip with the position lights or you can install them in the leading edge of the wing. The wing tip lights are small compared to the leading edge lighting and they tuck neatly into the wing tip lens. This is about all I think that they have going for them.

I have purchased the HID lighting kit from Duckworks Aviation. Don and Janet Wentz developed the lighting kits for Van’s aircraft and have done a wonderful job of lighting our path forward.

Over the past couple of days on the list I follow there has been a number of questions regarding the Duckworks HID landing lights and how they compare to the lower power lighting in the wing tips. I have gathered that there is a lower power draw for the HID system and much higher performance. One posting indicated that the pilot had no problem landing at his home strip at night with only reflectors along the edge of the runway. Wouldn’t that be something to try!

I think that if you can get over the jitters of cutting a big hole in one or both of your wings, this is the system you should install. It is rugged with no filaments to break every few hours and miserly with the electrical power. I am putting two of them in my RV-10. I expect that I will be using the landing lights fairly frequently. We own some property on a small island in Lake Erie and I would hate to leave without roasting at least a couple of marshmallows.

Dave

Hello Everyone,

News coming across the wire in the last couple of days is that David Carrigan from Prince Edward Island, Canada has flown the first RV-10 to be built north of the 49th parallel.

I had the opportunity to talk with Dave on the phone the other day as he had seen a post of mine and called to find out where I was in the construction of my ‘10. He hadn’t flown his yet when he called so I would like to publicly say congratulations to him for getting his new bird into the sky.

Dave has what I think is going to be a popular modification made to his airplane. He has swapped out the standard Van’s cowl for the new James Aircraft Holy Cowl. This is a cowl patterned after the successful designs of Ray LoPresti. It has the round inlets that have a significantly smaller inlet area. This along with the engine cooling plenum that they sell significantly reduce the drag on the airframe.

Here is a picture of Dave’s RV-10.

This cowl and plenum have just been made available for the RV-10 but they have been popular with the other models of RV. From the posts that I have observed on the Matronics RV-10 forum there has been some difficulties in getting the cowl installed and the majority of the issues revolved around the lower cowl exit louvers. There seemed to be trouble in integrating the Van’s produced louvers into the new bottom cowl. I have only got this second hand so I need to hear more information on this. I will post any comments I get to this page.

We are all hoping that the speed numbers will be better than the original and that the engine has good cooling. Dave has said that he will post some numbers as he gets more time on the aircraft.

I am working on a way to get you higher resolution photos to you. In other posts I have been able to link to another site but I received this photo via e-mail. I should have it available for you to link to very soon.

Dave

I haven’t posted for a day or so because I have been actually working on my airplane.

I have had a local upholsterer here at in the garage taking measurements for the wonderful leather and fabric seat covers that I have designed. He is also taking the measurements to make templates for the side panels and carpet sections.

I can’t believe the cost of an upholstery job. I am lucky though that I found someone local who has experience with aircraft. I am having him make all of the templates so that I can offer an upholstery package that is less expensive. This might mean that we will have to put out a standard set of colors to keep the cost of inventory down. Whay do you think of that?

I am hoping to have my seats at Oshkosh this year at my Distributor’s booth along with examples of a line of seat foams that will be very competitively priced.

I would like to hear from some of you readers. I have received only a few comments on the tail strobe mount ring in the comments section. I would very much appreciate any comment you might have regarding this blog. I am into it now for a couple of weeks and I want to know firstly, if the content is what you are looking for and secondly, I would like to hear about the modifications that you have made to your aircraft.

Send your comments to davehertner@kitaircraftmods.com I would love the feedback.

Dave

Van’s recently posted a Service Bulletin regarding the modification of RV-10 engine mounts. The problem with the engine mounts is that they will not accommodate certain variants of the venerable (I)O-540, A crossbar that runs near the induction sump interferes with certain models of cold air sumps such as those offered by Barrett Performance.

In the SB Van’s says that “it is the builders responsibility to assure that any NON-Lycoming engine (including ‘clones’) be dimensionally equal to that of the stock 260hp Lycoming (I)O-540.”

Van’s has always held firm on the insistence that 260hp be the limit for this aircraft and there have been some who have increased the performance of the (I)O-540 D4A5 engine through the addition if different ignition systems, higher compression pistons etc. I am unsure as to what the driving factor is for this close adherence to a horsepower rating. Is it weight and balance, VNE, risk of litigation?

It seems to me that the builder should have the unrestricted choice as to which power plant he/she puts in the aircraft. The rules under which we build these EXPERIMENTAL aircraft allow us to put any type of power plant in the aircraft as long as the installation meets acceptable building practices and standards.

It is the pilot who is controlling the higher horsepower engine via the throttle that keeps the aircraft under the VNE speed. It is the builder who compromises when it comes to weight and balance. The heavier engine up front will extort a price when it comes to the weight needed in the rear to balance the aircraft.

As for the litigation, I think that there have been too many instances where the spouse of a pilot/builder has brought a law suit as a result of an experimental aircraft crashing. Wasn’t that spouse in full awareness of the construction of the aircraft and the implicit risks involved? Maybe its me and I just don’t get it.

Van’s is doing it correctly when it comes to producing a kit aircraft. They should offer only one engine mount. The one for which they have done the testing prior to bringing the aircraft to market. Let the market produce the modified engine mount that supports other engines. Then let the builder do the verification testing in a 40 hour test schedule. That is what it is there for.

I am all for making modifications to aircraft. That is what this blog is dedicated to. We need to design test and bring innovative products and processes to help with the evolution of kit aircraft. We will modify them to meet a specific mission. The reality is that the mission is subtly different for every builder out there.

Dave

It is funny how you can have this perception as to how a product needs to be manufactured and then you talk to someone who offers up a completely different and better way to do it.

I had another look at my tail strobe mount ring the other day and was talking to an engineer that has experience in CNC and other manufacturing technologies. Here I was thinking that I would need to set up a bar of aluminum and have a 2 axis CNC milling machine mill the shape out. I would then take the remainder of the bar and simply cut the parts off from it using a band saw. This vision defaulted to my usual way of approaching the manufacture of things I design. High complexity and high cost.

My engineer acquaintance looked at the napkin that I was drawing on and said why don’t you just cut it out using a water jet cutter? DUHH!! Now there’s a good idea. This means that can get the parts cut out for a great deal less money and will therefor be able to pass the savings on to the people who are interested in it.

I should know in a couple of weeks where and when it will be available. I am working on getting a US distributor so that largest market is served well and won’t have to deal with the border and its shipping fees.

Happy Building

Dave

Many builders are talking about installing electric rudder trim. The RV-10 is a very capable cross country machine that could benefit from rudder trim during those long flights. The problem with a fixed rudder trim tab is that it performs best in a narrow range of speed. With the capabilities of the RVs in general and especially the RV-10 there is a need to vary the angle on the trim tab.

I initially heard about trim system that Vic Syracuse installed on the Matronics list. Vic did a very nice job of shoehorning a Mac servo into the rudder on his RV-10. I have heard that you can install this system after the rudder has been built. It takes some careful cutting and the installation of an inspection cover kit but it is definitely doable. The actual flying surface of the trim system is not all that big. It extends from the rudder trailing edge a little more than the width of half a piano hinge. It gives the rudder a more complex look with the control arm extending from the small fairing that protects the exit hole.

Vic did a great job of making it look like it was designed with the airframe. This is always the true test of the person designing a modification.

I’ll post some pictures below for you to get an idea of how it looks and functions. You should be able to click on them and you will go directly to Tim Olson’s site where the higher resolution photos are stored. Thanks Tim.

Have a great time today building and modifying your aircraft.

Dave