| Bill,
I don't feel a surge in speed when going from takeoff mode to cruise mode. You can hear the engine slow down, but since I usually start dialing back the prop rpm's shortly after takeoff, I am still in climb mode when I do this. The M/T prop changes pitch very slowly, so that would work against feeling a boost of speed when changing prop settings.
My best guess on the smoking rivets is that it may have been caused by running the engine at around 5100 rpm for long periods. This is possible at full throttle with the c/s prop set to 1700 rpm. When running at that rpm (cruise), I can feel a slight vibration in the airframe. Run the engine faster and the vibration goes away, but the fuel burn goes up too. So this may be a harmonics issue caused by running the engine too slowly. Solution is to not run at less than 5500 rpm. We'll see how that works out.
I have been fabricating a new intake and slide-throttle for the new p-port motor, along with a new inconel tangential exhaust, and installing an MSD ignition on the leading plugs. I've also removed the water cabin heater in favor of a heat muff, and CO detector.
I had a setback with my new engine when I noticed portions of the #3 rotor TES o-rings "oozing" out from between the seams on the cold side of the engine. Upon disassembly it appeared that the o-ring got pinched during assembly. I believe this was caused by me using too much Hylomar during assembly which reduced the available area for the o-ring to squeeze during torquing. I have reassembled the engine with new TES o-rings, using a minimal amount of Hylomar. I have run the engine about 1/2 hour now and it looks to be good to go. Lesson learned!
I'm very pleased with the new inconel tangential muffler. It is discernibly quieter than my old exhaust system (with DNA muffler). The entire exhaust weighs 17.4 lbs, but the fact that it also replaces the water cabin heater makes up for about 6# for a net weight savings. The big improvement is in noise reduction. I'll take some measurements and post them later. I should make it clear that my tangential muffler uses a slotted tube that runs down through the length of the 5" tube. This tube is also inconel and is welded to both ends, thereby adding strength to the flat ends. I utilized Lynn's coupling design to allow for movement between the muffler and the engine.
I'll post more on my MSD conversion later, but it is set up to provide multi spark throughout the entire rpm range. I hope to get lower fuel burn at cruise altitude from the MSD ignitions.
I hope to be back into the air this weekend.
Mark S.
On Wed, Apr 7, 2010 at 5:00 PM, Bill Bradburry <bbradburry@bellsouth.net> wrote:
Hi Mark,
You have several projects in works…getting your drive plate back
together, building the PP 20B. How are you progressing? How about
an update? On both projects.
Regards the rivets loosening. You are one of the few with a
constant speed prop. I am assuming that when you dial from takeoff prop
to cruise prop, the plane would surge forward with acceleration and the engine
would reduce rpm as the prop starts to bite. That would have put a lot of
force on the rivets. This, along with you more powerful engine, could
have been a player??? If so, those quarter inch bolts should move the weak
spot up the chain to wherever the next weakest link is. That, hopefully, may
be above your operating envelope. :>)
Bill B
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