Just wanted to give an update. I have IO 540 Barrett with cold air induction and James Cowl and was not able to get LOP until Performance Aero Dons group placed turbo fuel rails and injectors. The James Cowl was pulling air from the injectors and the plane would lurch violently when trying to get LOP with stock injectors. All is well now. Maybe this will help someone in the same situation.
Van's Air Force
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LOP with Sam James Cowl
- Thread starter Hoss
- Start date
Don at Airflow
Well Known Member
Injector Nozzle Operation
Well, you need to understand how aircraft mechanical fuel injection works. The injector nozzles on Airflow Performance, Bendix (Precision) and Continental mechanical fuel injection systems are what are called ?air bled? nozzles. That is air is introduced to the fuel at the injector nozzle to atomize the fuel, which is then sprayed under pressure into the intake port. A miniature carburetor at each intake port if you will. This is unlike an EFI nozzle that requires relatively high pressure to atomize the fuel with a pintle valve.
So with some designs of pressure cowls the plenum pressure can get lower than the manifold pressure. This will siphon the fuel out of the vents on the injector nozzle causing rough operation when leaning. The solution is to fix the cowl so that the pressure in the area of the injector nozzles is equal and higher than the intake manifold pressure, or a more common way is to reference all the injector nozzles to ram pressure via Bleed Air Rails to the nozzles. So it is not un-common on these applications to see Turbo Injector Nozzles and Upper Deck Rails used on turbo charged engines to accomplish the feat
Don
Well, you need to understand how aircraft mechanical fuel injection works. The injector nozzles on Airflow Performance, Bendix (Precision) and Continental mechanical fuel injection systems are what are called ?air bled? nozzles. That is air is introduced to the fuel at the injector nozzle to atomize the fuel, which is then sprayed under pressure into the intake port. A miniature carburetor at each intake port if you will. This is unlike an EFI nozzle that requires relatively high pressure to atomize the fuel with a pintle valve.
So with some designs of pressure cowls the plenum pressure can get lower than the manifold pressure. This will siphon the fuel out of the vents on the injector nozzle causing rough operation when leaning. The solution is to fix the cowl so that the pressure in the area of the injector nozzles is equal and higher than the intake manifold pressure, or a more common way is to reference all the injector nozzles to ram pressure via Bleed Air Rails to the nozzles. So it is not un-common on these applications to see Turbo Injector Nozzles and Upper Deck Rails used on turbo charged engines to accomplish the feat
Don
Thr Sam James Cowl has had alot of heat issues. I put in 4 louvers and added an extra oil cooler. 2 days ago I was taking off in Mississippi and I had full fuel, baggage, 4adults and runway temp 103 degrees and had A/C running and had no problem. Oil temps in low 200s (201-206) in cruise and maybe 212 in climbout. CHTs all under 380. What an amazing plane.
You also asked about even temps of cylinders. The real question is are they balanced when you reach peak. Ie. all cylinders reaching peak in .2 or .4 gallons of fuel. Don and Kyle at Airflow Performance did the fuel flow balancing and they are awesome. They are located in Spartanburg SC.
You also asked about even temps of cylinders. The real question is are they balanced when you reach peak. Ie. all cylinders reaching peak in .2 or .4 gallons of fuel. Don and Kyle at Airflow Performance did the fuel flow balancing and they are awesome. They are located in Spartanburg SC.
hevansrv7a
Well Known Member
SJ Cowl Thoughts
The SJ cowl is supposed to be used with the SJ plenum. Mine is. My cooling is so effective I have to block the rear side of my Van's oil cooler and my CHT's never get to 390. I wonder what the differences are between my installation and the ones that have heat issues? It also follows that the pressure on top of the engine - where my injectors are - is at least as high as for a non-SJ installation and probably higher.
I don't dispute what Don says about the results if the pressure is lower, but in a SJ plenum, it should be higher and likely is.
The SJ cowl is supposed to be used with the SJ plenum. Mine is. My cooling is so effective I have to block the rear side of my Van's oil cooler and my CHT's never get to 390. I wonder what the differences are between my installation and the ones that have heat issues? It also follows that the pressure on top of the engine - where my injectors are - is at least as high as for a non-SJ installation and probably higher.
I don't dispute what Don says about the results if the pressure is lower, but in a SJ plenum, it should be higher and likely is.
Don at Airflow
Well Known Member
Plenum Pressure
There are no substitutes for facts. And I have yet to see any plenum pressure data VS MAP or a pressure map across the plenum VS air speed from any manufacture of these pressure cowlings or data from any builder that has these issues. Believe me, we?ve asked the question when this issue arrives. But the fact remains that if you see blue stains on the cylinder fins and you know you don?t have any fuel leaks or the engine runs OK when throttled but has a miss at high altitude at the same MAP then you know there is something going on with the nozzle venting. Hey, it?s never and ignition issue.
I guess what I?m saying is that until you actually run data don?t assume anything. Plus your results for a four cylinder engine may be completely different than for a six cylinder engine.
Don
There are no substitutes for facts. And I have yet to see any plenum pressure data VS MAP or a pressure map across the plenum VS air speed from any manufacture of these pressure cowlings or data from any builder that has these issues. Believe me, we?ve asked the question when this issue arrives. But the fact remains that if you see blue stains on the cylinder fins and you know you don?t have any fuel leaks or the engine runs OK when throttled but has a miss at high altitude at the same MAP then you know there is something going on with the nozzle venting. Hey, it?s never and ignition issue.
I guess what I?m saying is that until you actually run data don?t assume anything. Plus your results for a four cylinder engine may be completely different than for a six cylinder engine.
Don
AlexPeterson
Well Known Member
Van's standard cowl - actual pressure recovery data
Years ago, I installed a pressure manometer in the cockpit, with lines running out to the area just above the crankcase, as well as one behind the engine, just in front of the firewall. The pressure recovery was almost perfect, meaning that if one put an altimeter on the line to the area above the engine, it would agree with the one from the pitot tube. This isn't how I did it, but the result was the same. I measured pressure differential, in inches of water, from the line above the engine to cabin static. I used Bernoulli's equation, together with the TAS, to get this data.
My conclusion from these tests is that there was nothing meaningful to do with the top portion of the cowl to improve cooling or significantly reduce drag.
There could indeed be some misbehavior in the SJ cowl - two 7A's in this area have them, and both have fought high temps. Non-complete pressure recovery is what will cause what Don is referring to, together with WOT.
Someone needs to instrument the SJ cowl the way I did the standard one. I'll talk to my hangar mate about doing this.
Years ago, I installed a pressure manometer in the cockpit, with lines running out to the area just above the crankcase, as well as one behind the engine, just in front of the firewall. The pressure recovery was almost perfect, meaning that if one put an altimeter on the line to the area above the engine, it would agree with the one from the pitot tube. This isn't how I did it, but the result was the same. I measured pressure differential, in inches of water, from the line above the engine to cabin static. I used Bernoulli's equation, together with the TAS, to get this data.
My conclusion from these tests is that there was nothing meaningful to do with the top portion of the cowl to improve cooling or significantly reduce drag.
There could indeed be some misbehavior in the SJ cowl - two 7A's in this area have them, and both have fought high temps. Non-complete pressure recovery is what will cause what Don is referring to, together with WOT.
Someone needs to instrument the SJ cowl the way I did the standard one. I'll talk to my hangar mate about doing this.
hevansrv7a
Well Known Member
Curious
Alex, I'm curious about your post regarding the two 7A's with SJ cowls. Do they have the plenum, too? I really am puzzled by the difference between their planes and mine. Mine has cooling that is almost too good. If I did anything "right" I don't know what it was. I do have the plenum. I did everything as prescribed. The plenum is attached to the standard Van's baffle kit but, of course, it is cut down at the top to accommodate the plenum. That also meant installing the oil cooler lower, but otherwise behind the left rear cylinder just as in Van's plans. Are they running Lyc's or Superiors or other?
Thanks.
Alex, I'm curious about your post regarding the two 7A's with SJ cowls. Do they have the plenum, too? I really am puzzled by the difference between their planes and mine. Mine has cooling that is almost too good. If I did anything "right" I don't know what it was. I do have the plenum. I did everything as prescribed. The plenum is attached to the standard Van's baffle kit but, of course, it is cut down at the top to accommodate the plenum. That also meant installing the oil cooler lower, but otherwise behind the left rear cylinder just as in Van's plans. Are they running Lyc's or Superiors or other?
Thanks.
