Mark S are you having any problems landing due to the poor idle?
Are you using a 2.85:1 PSRU ratio. I forgot if I ever knew :)
I am building a 3.12:1 box for the extra power at 8500 RPM (800 prop
RPM) so 2500 engine RPM idle should be no problem in this regard.

If you blow compressed air into the rotor housing between the
exhaust port and intake port it will idle better as it will keep the
contaminated exhaust gases out of the intake. The path for these
gases is the depression in the rotor flank.

Paul Lamar


Paul,

I'll send $60 for three pressure taps.  I may also need to use the PVC
pipe trick.  I'm heading out to the airport shortly to check the
vacuum system for leaks per Tracy's suggestion.

Mark


It's common to put a restriction in the line between the MAP tap point
and the MAP sensor..  I suspect your check valves leak, but also act
as restrictions, so you're getting the desired effect..  Carry on.  ;)

Here's some relevant verbiage from the Megasquirt tuning page:

<http://www.megamanual.com/v22manual/mtune.htm>

About 3/4 down the page:

"Another tip you can try if you have a large overlap cam is to pinch
off the MAP hose slightly while the engine is idling, and see if the
idle quality improves. If so, then try a restriction in the MAP vacuum
line. This has the effect of damping the vacuum pulses that the MAP
sensor sees. Start with a ~0.040" (1.0mm) restriction in the line. You
may have to experiment with restrictor sizes to see what works best
for your system."

So, a restriction and a can.

I know we've talked about this before on here...


Regards,

Matt-


Matt,

Lots of good info on that page.  I'll keep the restriction trick in
mind, but first I want to gather some data with my Hytek data logger so
that I know if there really is a problem with fluctuating vacuum.  I
tried to do some data logging today, but when I went to look for the
file it wasn't anywhere to be found.  Time to read the instructions.

Don't know what I did with the post from Bob Mears, but that makes more
sense than anything I've read so far.  Basically, it idles like the
thoroughbred that it is.  If I had wanted to fly behind a plow horse, I
should have left the side ports alone.  ;-)

Mark

Bob is right about p-ports not idling well. It is not so much a timing difference as it is a port overlap problem. Port timing is more or less the same. I think your idling expectations are bit high. It will never idle as well as a 13B let alone an RX8 with no port overlap. It is those nasty exhaust gases coming up from the exhaust port through the pocket in the center of the rotor that causes the problem. It can be solved by the NSU trick of using two p-ports per rotor. One tiny one for idle only.

I have not flown your airplane but a slipping approach is advisable for an airplane that does not idle well. In a slipping approach the airplane ALWAYS has enough altitude to glide to the runway with the engine totally off and the prop rotating or not rotating. It matters not. In the traditionally 1/4 mile approach where you are coming in on a 3 degree glide slope angle if the engine quits or stumbles you are not going to make the numbers. Some small amount of power is always needed for a traditional approach. Some call it "dragging it in". Airliners do it all the time.  Best to practice slips at altitude until one becomes comfortable with the technique. Over the years I have developed  the habit of doing it on all landings much to the chagrin of my relatively inexpericed biannual check pilots :)

We had a crash here in SZP on a just completed canard crashed on approach when the Lycoming engine quit. He was not slipping. People were injured on the ground.

Don't send money for the taps. I will send them to you. If they do not help send them back. If you want to keep them then send the money.
Send me your mail address by putting the word "private" in the subject box.

Paul Lamar