|
|
|
Tracy;
I set the static timing as per your EC-2 instructions, it started and ran great at low power. I checked it at 3000 RPM with a timing light, and it was about 35 BTDC. The pulse counter was near the back of the travel limit so I moved it back a gear tooth and set it about 23 BTDC @ 3000 RPM (tight against the advance stop). I reread your EC-2 manual, and set it back some more. Now it runs better at low RPM, but needs to be richer. So the next chance I had was yesterday, when I checked the timing as I mentioned.
How much advance occurs across the RPM spectrum? It seems to me there is a retarded timing point at idle (or 0 TDC), then above some number, maybe 1500 RPM it advances about 10 degrees? then about 2500 rpm it starts to advance some more, about 5 degrees more @ 3000 RPM?
It would be helpful to know what to set the base timing at while cranking over the engine with the injectors turned off.
Also what the advance is at various RPMs, along with knowing the vacuum advance (5 degrees below 22" Hg)
-----Original Message-----
From: Tracy <rwstracy@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, Sep 9, 2013 6:36 pm
Subject: [FlyRotary] Re: First Flight jitters
If your ignition timing measurement was accurate at 3000 rpm and 16" mp, it's way too retarded. What did you set the static timing to? Remember that that has nothing to do with actual ignition timing. It's just a reference point for the computer.
Tracy
Sent from my iPad
Thank all of you for the constructive comments.
My Prop is a Catto 68X74, the same as for a 180 HP Lycoming O-360, except it's left turning due the Tracy's 2.19:1 reduction gear. I should expect to get 2200 static RPM with it, 4818 engine RPM.
The turbocharger is a Turbonetics 60-1 with a TO4-E turbine, with P trim .81 A/R on center housing.
Although I did briefly throttle up to 37" Hg, I'm not sure what the RPM was at that moment. Before I blew up the first version of the engine. I did get above 4800 RPM on a tethered trial. The oil temp rose quite rapidly. The manifold pressure for that run was 44" Hg. I'm concerned that as the aircraft speeds up, the propeller will unload and the RPM will increase, as it will, causing an increase in exhaust flow, increase in boost, increase in intake temp, and another detonation incident.
The run where I described checking the timing maxed out at 3000 RPM, where my hat blew off, is where I saw 11 degree BTDC and 16" Hg. My wife was in the driver's seat while I was using the strobe light on the pulley. So these numbers are ballpark numbers. I had the top cowl off to read the timing. Last time I ran to 4000 RPM with the top cowl off, the oil cooler air diffuser flew off.
I'll do better next time. I have fastened the air diffusers so the next time I should be able to run at the 4000 RPM mandated in the EC-2 manual, where I will be above the mode 6 set point of 22" Hg. I'll find out what the current timing actually is, verify the Mode 8 timing is set to the mid point, and do another run to set the final timing to the 19 degrees recommended or something a little less to be on the safe side. If I am too retarded now, I'll feel the difference in the following full cowl trial to the previously tested settings and if all goes well, higher power. I'll also follow that advice to vary power to make sure the engine performs well and won't quit due to transitions.
-----Original Message-----
From: Tracy < rwstracy@gmail.com>
To: Rotary motors in aircraft < flyrotary@lancaironline.net>
Sent: Mon, Sep 9, 2013 1:58 am
Subject: [FlyRotary] Re: First Flight jitters
You are either over propped or something is wrong with the engine or tuning. At 37" mp you should be in the 5500-6000 rpm range. You didn't give the rpm at 16" mp and 11 deg BTDC so I can't tell if timing is in the ballpark or not. Is that the same rpm as your hat blew off (3000)? If so, you may be too retarded.
And of course we need your prop numbers to make a guess about anything. Prop chord at 70% on blade is good to know too. Do you have one of those wide chord airboat type props?
Tracy
Sent from my iPad
I've been slowly building my RV-8 with 13BT engine for about 14 years...!
On June 13th 2013 it received the coveted Airworthiness Certificate. That same day I detonated my engine due to the trailing spark plug holes being machined oversize in an attempt to improve the single spark plug power, should the leading plug ignition fail. This, and possibly advanced ignition, and possibly over-boost detonated my engine on it's first high power taxi test. That took about 2.5 seconds.
Now I've rebuilt the engine with new unmodified rotor housings, and it runs better than ever. I've re-marked the timing marks on the pulley, and reset the timing, though not to 4000 RPM yet. today I checked it. At 3000 RPM my hat and hearing protection blew off. 11 degrees BTDC, and 16" manifold pressure.
I've been taxiing around at modest RPM, it's great. I've consistently been idling at about 1600 RPM, (730 prop RPM) and sometimes as low as 1490, (680 Prop RPM) smoothly. That is slow enough to keep the brakes from getting too hot.
I've done run ups and brief bursts of power to 4200 Engine RPM, (1917 Prop RPM) which is about 32" manifold pressure, and seen 37" manifold pressure briefly. I know this is not enough power to take off, although I have done a Pre-take off to 50 MPH with this power before powering down with roll out to the end of the runway. I suppose it would fly off and maybe clear the trees at this power. I've lifted the tail, and rocked the wings with the ailerons. It steers well and the brakes work.
The water level in the engine stays up between flights as does the oil, and the water temp today was consistent 163 F oil about 173 with the highest observed 183F. I did about 4 pre-take off passes with taxi back, with excellent temperature control and throttle response.
A couple of oil fitting were tightened looking for an oil seep.
7.3 hours engine running time on the EM2, about 2 hours since the engine overhaul.
I don't think I'm at all ready to fly this thing. I'm missing something, so offer up some advice, I'm all ears!
|
|