Keep those first flights short
 

Well, today didn't turn out as I had hoped.

I went to the hangar mid-day, to pull the cowlings and do a good inspection ahead of the firewall before going flying to do some more engine break-in. But, I discovered two significant issues that needed dealing with ASAP, and another issue that will need correcting eventually.

1. The alternator pulley had been touching the lower cowling, and put a pretty good gouge into it.

2. The throttle cable showed signs of heat stress where it passed close to the exhaust system. I had thought that there was enough clearance, but obviously not. The damage doesn't look too bad after 20 minutes of running. I think the cable would have been trashed with an hour of high power running time.

3. There were signs of a bit of rubbing on the upper cowl from part of the oil cooler mount. Also, four of the screw heads that hold the plenum chamber cover on showed signs of rubbing on the cowling - three of these were very minor rubs, but one was more significant.

Tomorrow, I'll pull the prop and change the alternator belt for a shorter one. I'll put a piece of tape over the gouge in the cowl to act as a witness for future clearance issues. If I still have a clearance problem with the 7355 belt, I'll have to fabricate some sort of pad on an arm to prevent the lower cowl from being pushed closer to the engine by the ram air pressure. Once I am sure the clearance problem is resolved, I'll fill in the gouge.

I'll put a heat shield on the exhaust where the throttle cable passes by. That'll be a quick, easy fix.

As for the oil cooler mount, today I removed a bit of metal from the mount in the affected area. I'll put a piece of UHMW tape on the cowling, and see how it does. I can remove more metal if needed. As for the screws that touched, eventually I'll replace those four with flush head screws. For now, I'll remove those screws, as there should be enough other ones to hold the cover in place. I'll put some UHMW tape on the cowling to act as a rub guard. In the end, it may be necessary to rework the contours of the plenum chamber cover to move the outer edges closer to the engine. This would be a big job, so I am hoping to avoid it, if possible.

I'll do another 20 minute flight to see how things are doing. Maybe late tomorrow, or maybe some other day if the work takes too long.

Originally, I had planned to fly for an hour on the first flight, in order to minimize the low power running time. But, Ron MacEwen, the local Aircraft Maintenance Engineer and EAA Flight Advisor suggested that it would be better to only fly for 20 minutes or so, and then do a big firewall forward inspection before flying again. I am very glad I took his advice - I believe that the alternator pulley would have completely worn through the lower cowling if I had flown for an hour, which would have necessitated a lot of fibreglas work to fix. As it is, I only need to mix some resin and fibre to fill the gouge - that'll be a quick fix, and it can wait for a few flights.

Moral of the story - keep those first flights short, to minimize the risk of undetected small problems quickly becoming big problems. A lot can happen in the course of an hour.

Yup
 

Just ask Howard Hughes about that one..:)

Frank

I Certainly Agree
 

My first flight was once around the pattern then it was inspected for problems and failures. It took a good part of the 25 hour test flight period to get all of the bugs out.

I don't think the pulley problem is operational time driven but instead it is operational/flight cycle driven. That is a common problem with RVs. Mine included. Mine never cut through but it would have with enough flights. Some people put larger pulleys on the alternator to reduce the RPM and the resulting cut cowl is predictable. I have the small pulley on my 60 amp alternator but I still saw the contact marks. Under static conditions there is significant gap but even with the small pulleythere is incidental contact in some operating mode (landing, starting, shut down? who knows?). I fixed the problem several hundred hours ago by cutting a blade off of one of my wife's stainless steel butter knifes and bonding it to the inside of the cowl with structural adhesive as a strike plate. The pulley still marks it but there is no damage.

Do you know what the EGT is on the pipe that caused heat damage to your cable? Early in my flight testing the timing of my LASAR system from the Lycoming factory was approximately 65 degrees ahead of the specified 25 deg. BTDC of the compression stroke of cylinder #1 (approximately 90 degrees BTDC in other words). The engine would run but the EGT was very high and I had to throttle back to get the EGT needle off of the peg. I flew it to the test area but flight was not comfortable. I call Van's and I was told that Lycoming runs all of the new engines in a test cell (I had the test cell data sheet) and it should run properly right out of the box. I worked with Unison the west coast tech rep for Lycoming and Pecision Airmotive via telephone for some time before I ordered a LASAR timing box through Van's and fixed the problem.

I use the inside of the upper cowl as the top closure of the plenum so no information there.

Bob Axsom

No need to be up any more than 20 minutes on the first one. You never know what the gremlins can get into. They've been waiting for some time to screw with your new creation.

I can think of two cases where rather large oil leaks developed on first flights and in a couple more minutes, very bad things would have happened. As it was, it took a good hour for these guys to clean the belly and it oozed from all the skin laps for another 6 months afterwards.

I removed the cowlings after every flight for quite some time on mine and checked everything very thoroughly. Of course mine was all non-standard FF.

Pilots doing 90 minute first flights are just asking for it IMO.

Kevin,

Congrats on your first flight.

As for the alternator pulley rubbing on the cowl- I think the shorter belt should do the trick nicely. I had the same trouble until I went to a shorter belt. I don't know why Van's continues to recommend the 7365, it is just too big for most installations, and there is no downside to going a size or two smaller. Fortunately they are commonly available locally.

Here's a little fitting info from PP...

* The supplied 15355 Dayco V Belt will fit the 9 3/4" diameter ring gear support pulley, for applications which have a 7 1/2" diameter ring gear support pulley locally purchase XL7300 Gates V Belt or equivalent.

http://www.plane-power.com/images/Al...5%20Pulley.pdf

http://www.plane-power.com/images/Al...5%20Pulley.pdf

Throttle Cable
 

Mayday.... there have been several instances of the throttle cable fusing and "freezing" in the last position. You might consider sheathing the entire cable with heat protective tape or "heat shield" hose. Van' refuses to publicize that this is occuring.... anyone else with such an experience?

Tim Morris
N187TM
Rv-8/ "Betty Jane"

Kevin, congratulations on your first flight! I can see the engineer in you-- all technical reporting and stuff! Tell us how it felt! After almost 11 years of building, I'm sure it brought a smile to your face.

Any pics?

Vern

I'm not sure what state the inside of the cable is in now, but the outside sure has a large bubble in the green plastic. It feels normal when I move the throttle, but to be safe I will order a new one, and replace it at a convenient opportunity. Better to do this now, than have it fail when I am on the road some day in the future.

I replaced the alternator belt today with a shorter one, and put a heat shield between the exhaust system and the throttle cable. I did a 25 minute flight, then pulled the cowlings - the alternator pulley no longer touches the cowl, and the throttle cable looked the same as it did before the flight. I think I am now ready to launch into longer engine break-in flights. But, I'll be on the road from Wednesday until October, so testing will take a pause.

Not just 1G
 

I know it is a different airplane, but my RV-6 alternator pulley was fine at one G but when I started pulling 3 to 6 in testing is when my pulley started contacting the cowling. In my case, there was no alternative but to make a bubble in the cowling.