My cowl is divided into three compartments 1- the normal plenum (formed by baffles and upper cowl), 2- The lower cowl under the engine extending to the lower cowl outlet, 3- the area between the engine and the firewall and the upper cowl outboard of the baffles and valve covers.
In preparation for the AirVenture Cup Race I blocked off ever penetration of the rear baffle except the oil cooler and picked up approximately 2 kts.
There is a small vent at the bottom of zone 3 that provides an exit flow path for all of the air coming through the rear baffle with all of the other holes blocked this was reduced to the oil cooler air flow. I increased this small vent by half and the aircraft speed was reduced slightly. I put the size of the vent back the way it was for the race.
For the 2 hour flight the Manifold Pressure was 28, the hottest CHT was ~337, the engine speed was 2720 rpm, the EGT was kept just under 1300 on the hottest cylinder, the oil temperature was ~190 and the oil pressure was ~80. I flew just over the 2,000 MSL floor for the entire race except where we were required to fly higher by the rules and the low passes at Kankakee, Ill. and the finish line. My speed was 207.13 mph. That was much faster than I have flown in the past (2005 = 184.04 mph , 2006 = 193.42 mph) but seven planes in the RV-Blue class were faster and that mitivates one to look at ways to increase the speed.
When I placed my hand on the cowl the zone 3 area was hotter than 1 or 2. This tells me the the heat from the oil cooler is being dumped into zone 3 and the area in there is hot but not unreasonably so.
There are a lot of parts to this system and every change in one place affects the system somewhere else. I have seen photographs of John Huft's oil cooler ducting after the cooler which turns the air and routes it down to the cowl outlet. His system looks very clean and he won the AirVenture Cup for the RV-Blue class at 235 mph so anything he does has instant credibility. However, I simply do not have room for the kind of duct work he employs. Alan Judy uses a whole different path for his oil cooling air flow with its own variable in flight inlet. A thermal/mechanical engineer friend Berry West tells me that the velocity of the air downstream of the oil cooler will be low. With these pieces of information in mind the thought of putting a oil cooler exit port in the upper cowl keeps popping up in my thinking.
Some positive and negative thoughts I have are:
1 - The heat on all of the components in zone 3 will be reduced.
2 - The airplane is performing so well right now that I hesitate to disturb the setup.
3 - The increased flow efficiency will increase the air mass flow through zone 1 and could increase cooling drag. Some form of fixed or variable control will be required to get the air mass flow down and the airplane speed back up. This may be a good reason for the isolated oil cooling system used by Alan Judy.
I will keep thinking about this for quite a while I'm sure before I cut into the cowl that I know and love but any thoughts on the idea would be appreciated - especially if you have tried something similar.
Bob Axsom
In preparation for the AirVenture Cup Race I blocked off ever penetration of the rear baffle except the oil cooler and picked up approximately 2 kts.
There is a small vent at the bottom of zone 3 that provides an exit flow path for all of the air coming through the rear baffle with all of the other holes blocked this was reduced to the oil cooler air flow. I increased this small vent by half and the aircraft speed was reduced slightly. I put the size of the vent back the way it was for the race.
For the 2 hour flight the Manifold Pressure was 28, the hottest CHT was ~337, the engine speed was 2720 rpm, the EGT was kept just under 1300 on the hottest cylinder, the oil temperature was ~190 and the oil pressure was ~80. I flew just over the 2,000 MSL floor for the entire race except where we were required to fly higher by the rules and the low passes at Kankakee, Ill. and the finish line. My speed was 207.13 mph. That was much faster than I have flown in the past (2005 = 184.04 mph , 2006 = 193.42 mph) but seven planes in the RV-Blue class were faster and that mitivates one to look at ways to increase the speed.
When I placed my hand on the cowl the zone 3 area was hotter than 1 or 2. This tells me the the heat from the oil cooler is being dumped into zone 3 and the area in there is hot but not unreasonably so.
There are a lot of parts to this system and every change in one place affects the system somewhere else. I have seen photographs of John Huft's oil cooler ducting after the cooler which turns the air and routes it down to the cowl outlet. His system looks very clean and he won the AirVenture Cup for the RV-Blue class at 235 mph so anything he does has instant credibility. However, I simply do not have room for the kind of duct work he employs. Alan Judy uses a whole different path for his oil cooling air flow with its own variable in flight inlet. A thermal/mechanical engineer friend Berry West tells me that the velocity of the air downstream of the oil cooler will be low. With these pieces of information in mind the thought of putting a oil cooler exit port in the upper cowl keeps popping up in my thinking.
Some positive and negative thoughts I have are:
1 - The heat on all of the components in zone 3 will be reduced.
2 - The airplane is performing so well right now that I hesitate to disturb the setup.
3 - The increased flow efficiency will increase the air mass flow through zone 1 and could increase cooling drag. Some form of fixed or variable control will be required to get the air mass flow down and the airplane speed back up. This may be a good reason for the isolated oil cooling system used by Alan Judy.
I will keep thinking about this for quite a while I'm sure before I cut into the cowl that I know and love but any thoughts on the idea would be appreciated - especially if you have tried something similar.
Bob Axsom
