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Q-talk 153 - Kuhlman & Dirks Q2

by Charles Kuhlman

Our Q2 is doing O.K. We added dual brakes, so ground handling is MUCH better. (No more ground loops.) We use a 3 bladed warp drive prop and it works well. So, the airframe is fine, but the Revmaster engine is definitely the weak link. We seem to have continual valve leakage problems, so compression is never as consistent as we’d like it to be. We also have the usual VW oil leaks from the case bolts, the cylinder to case joint, and shaft seals.

We had been using strictly 100LL Avgas, but when we removed the heads we saw significant buildup of lead. When Avgas hit $6.29 a gallon, it sealed the deal, and we’ve started to use premium auto gas at only $3.80 a gallon. We’ll let you know how that works out, but so far so good.

We are (were) concerned about the auto fuel affecting the epoxy. So we’ve been doing a fuel soak test for several months now on some fiberglass/epoxy coupon squares. The only noticeable change is on the coupon in the Ethanol blend. We will NOT use ethanol in the Q2. Although I like it in all my other engines, (car, pickup, mower, snow blower, etc.) it causes the weight of the sample to increase, as expected. 100LL and Regular unleaded (no alcohol) have had no effect on the samples, but we will continue to use the Premium grade as we do in the Cessna 150 that I also 1/4 own.

My Building/Flying Partner Harold Dirks.

We have "detuned" the compression to make the case last longer, so we only fly it solo now. With full fuel, a 120 lb passenger, and me @ 160 lbs it has an uncomfortably low rate of climb. This adds up to a gross weight of about 1055 lbs. ( 675 lb empty wt. + 160 lb pilot + 120 lb passenger + 100 lbs fuel ) We have managed to put 310 hours on the engine so far though.

We have the T-tail, aileron reflexor, belly board, forward hinged canopy and dual throttle controls, (for the days back when we used to fly it dual.) Not much else to add. She’s fun to fly and fairly inexpensive at only 3 or 4 gph.

Thank you for your good work, Dan. We all like to read and see what others are doing, but don't feel worthy to share what we have or are dealing with.

For example, the last time I flew the Q2, (about 2 weeks ago), as I was washing the bugs off the cowling, I noticed the Exhaust wrap we put around the #4 exhaust pipe was frayed and coming unwrapped. [We put this exhaust wrap on to help keep the oil temperatures cooler].

At first glance, I thought the clamp holding the wrap had come undone. Then I saw the whole exhaust pipe was broken completely in two, between the exhaust pipe flange that bolts onto the head and the larger diameter resonator.

So now am considering brazing the pipe back together. We successfully brazed shut a hole on the #3 exhaust pipe that was due to the heat muff we put on that straight section of #3 exhaust pipe, just below the #3&4 head.

But I’m concerned that brass (or whatever a brazing rod is made of) may not be a high enough temperature filler metal. I don't want to steel weld it, due to corrosion and the thin wall of the pipe. I am sure it would burn or blow through during welding. So I’m hoping that brazing will work. It should have pretty good cooling as that part of the pipe is right by the air inlet hole in the front of the cowling. So whenever the engine is running, it will have air blowing over it.

I think it is worth a try. I’m not sure what the EGT is at that point, but it’s probably in the 1300°F range? That is what I see during the "lean to peak" times on the #3 exhaust pipe where we have the EGT probe mounted.

I would definitely appreciate any comments or thoughts from the group.

P.S. Since this article was written the exhaust pipe was brazed and is working fine. We have an hour of flight time on the repair, and the brazed joint is solid and intact.

I spoke with a metallurgist where I work and he said the typical brazing rod may begin to soften at about 1,000F. So given that the exhaust gas could easily be 1,000 °F +, the fact that the joint is right in the blast of the prop, in the cowling inlet hole, must make a big difference.

Charles Kuhlman (and Harold Dirks)
builders of Q2 - 32DK

These are 3 of my favorite photos. The all important seconds just before touch down: