Mailing List flyrotary@lancaironline.net Message #2720
From: Tracy Crook <lors01@msn.com>
Subject: Re: [FlyRotary] MSD injector test results
Date: Thu, 28 Aug 2003 10:10:58 -0400
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Message
The other posible reason for the big difference in apparent flow rate is injector response time.   When running at low manifold pressure, a small difference can make a big difference.  Most injectors take about 1 millisecond to open.  At idle, the injector on time is only about 1.4 ms.  A difference of only .1  ms  would look like a 25% difference in flow rate even if the injectors were perfectly matched at 100% duty cycle.
 
Another reason to use same brand of injectors in all the holes!
 
Tracy
 
----- Original Message -----
Sent: Wednesday, August 27, 2003 7:55 PM
Subject: [FlyRotary] MSD injector test results

Greetings,
 
RC Engineering seems to be a very fast and efficient operation.  They just got my injectors today, and have already called with test results.  I sent 4 very slightly used Mazda 550's, and 2 new MSD-2013's, which are supposed to be 50 lb/hr (525 cc/min).  They said all 6 injectors were clean, and needed no service at all.  The MSD's flowed less than advertised, but not by nearly as much as I figured.  Here are the  results:
 
MSD- 498, 503
Mazda- 547, 549, 551, 551
 
I'm sure these are static flow rates, and I think they also do pulsed flow tests, but I forgot to ask about that.  I'll get them back in a week, so I'll check the results when I get the data sheets.  50 cc's difference only represents about a 10% difference in flow, and doesn't really explain the large difference in mixture that I see on the EC-2.  I have to wonder if maybe there's more effect than the number would indicate, since my MSD's are at the throttle body, with about a 20 inch run to get to the rotors.  I can see how this reduced efficiency might make them seem smaller than they are, but I would also think that Ed would see the same thing, and maybe he is. 
 
If you guys (Ed and Al) don't mind, I'd like to propose a test.  At your convenience, and I'm not kidding- don't make any special trips, or go to any real effort.  Could each of you run at low power, below the staging point, maybe 1500 rpm, and enable only one set of injectors at a time.  I'd be interested to see what position on the mixture knob you have to use for each set.  On mine, I have to turn the mixture knob to about 9:00 for the Mazda 550's, and about 3:00 for the MSD's.   
 
The test will be interesting, since (as I recall) Al has Mazda 550's as primaries, and also has the same MSD's that flow about 500 as secondaries.  I can't recall if I've ever seen the physical layout of these though.  Are they all the same distance from the rotors?
 
Ed, I believe, has matched injectors, with a large distance between the secondaries and the rotors.  Any difference in his mixture setting will indicate a loss of efficiency resulting from the large distance. 
 
Sorry to keep dragging everyone through this, but the difference bugs me.
 
Rusty (T minus 3 days to liftoff)
 
PS- speaking of fast, efficient operations, I sent my ailing Lightspeed Thirty-3G headset for repair Monday via next day UPS.  Lightspeed got it Tuesday, fixed it, and shipped it out the same day, via next day UPS.  The repaired headset is back in my hands today, and they threw in a free holder for the battery box that I told them I wanted to purchase.  Bummer that it broke, but mighty friendly folks, and GREAT service! 
 
  
 
 
Subscribe (FEED) Subscribe (DIGEST) Subscribe (INDEX) Unsubscribe Mail to Listmaster