Re:Corvair Engines - The Justification Series - Performance
Posted: Thu Apr 05, 2018 3:27 pm
I would like to reiterate that this series on justification is to answer the question of why I followed the path I did by installing a Corvair engine on this air frame. Remember that the views in this series are mine. Should anyone decide to follow a similar path they must understand that the choice and consequences are theirs. What has been successful for me isn’t a guarantee for anyone else. Having said that; I did follow a well-trodden path in my journey to find and build the best experimental, light sport compliant, airplane I could afford. My airplane is a very close clone to previous Cleanex models. I tried to duplicate all the things that had been shown to be highly successful on previous builds. Not only what parts to use, but the placement and coordination of the parts and how they worked together. My engine choices were limited by my budget. This caused me to work to find the best fit, the greatest reliability, and the highest performance my budget would allow. Enter the 3.0 Corvair conversion built by Dan Weseman.
We talk about safety and that must be the number one factor in our approach to building. The key factor in safety is reliability. Regardless of money savings, visual appeal, ease of operation, no maintenance required, latest & greatest, or any other attraction … if it’s not reliable it’s not worth flying behind. One of my favorite safety reminders is a William Wynne quote; “There is no characteristic more important than reliability. Anything you could get in trade for reliability isn’t worth it.” Very close to this is consistency. A great trait for humans as well as flying machines is that they will continually do their work on a reliable, dependable, and consistent basis. Working within those parameters means that changes are a warning that something is wrong and requires an investigation. That’s why it’s important to me that my engine never stumbles on the take-off roll. If it does, something is wrong and we go back to the hangar and investigate.
Real performance! As we approach safety from a different view another ‘justification” is realized by the performance data of the Cleanex showing improved capability with the greater horsepower available from a 3.0 Corvair conversion. My earlier VW version of this air frame would climb solo at a rate of ~750 fpm, and at gross of 1100 lbs. at 350-400 fpm on warm Carolina days. A Cleanex with a 3.0, 120 HP Corvair at 1250 lbs. gross will out climb a solo piloted VW powered version quite strikingly with well over a 750 fpm climb out rate. Excess power to climb is an excellent safety feature to have on an airplane. High density altitude, hot summer days, short strips, grass fields, climbing to get over mountains, etc., all become easier with more power that doesn’t over tax the engine, isn’t limited to a couple of minutes at WOT, or overheats the engine quickly requiring “step climbing.” Whenever recovering from a balked landing or a go around needs to be executed in a hurry it is easier with extra power on the nose of the airplane.
In 2009 two Corvair powered aircraft flew alongside a Jabiru 3300 powered one from Florida to Tennessee for the ASA gathering. Comparing notes upon arrival it was discovered that the fuel burn and speeds for the two different engines installed on these air frames were remarkably close to the same.
It has been suggested that a heavier Cleanex would suffer in take-off & climb performance. Take a moment to consider power loading numbers at gross for a few engines (realizing that the lower the number the better):
80 HP VW @ 1100 lbs. – 13.75
85 HP Jabiru 2200 @ 1100 lbs – 12.94
100 HP O-200 Continental @ 1250 – 12.5
100 HP VW Turbo @ 1150 – 11.5
120 HP Jabiru 3300 @ 1150 lbs. – 9.58
120 HP Corvair 3.0 @ 1250 lbs. – 10.41
110 HP Viking 110 @ 1250 – 11.36
Better numbers are available for some if using a lower gross. A 700 lbs empty weight, polished, Cleanex with a 3.0 and using 1150 lbs for gross would give a 450 lbs. useful load and the exact same numbers as the Jabiru 3300 for power loading. So when considering performance note that the 80 HP engine with the lower gross actually has the poorest power loading number while the 120 HP Corvair @ 1250 lbs. gross falls only behind the 120 HP Jabiru 3300 at 1150. That’s performance!
Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g
We talk about safety and that must be the number one factor in our approach to building. The key factor in safety is reliability. Regardless of money savings, visual appeal, ease of operation, no maintenance required, latest & greatest, or any other attraction … if it’s not reliable it’s not worth flying behind. One of my favorite safety reminders is a William Wynne quote; “There is no characteristic more important than reliability. Anything you could get in trade for reliability isn’t worth it.” Very close to this is consistency. A great trait for humans as well as flying machines is that they will continually do their work on a reliable, dependable, and consistent basis. Working within those parameters means that changes are a warning that something is wrong and requires an investigation. That’s why it’s important to me that my engine never stumbles on the take-off roll. If it does, something is wrong and we go back to the hangar and investigate.
Real performance! As we approach safety from a different view another ‘justification” is realized by the performance data of the Cleanex showing improved capability with the greater horsepower available from a 3.0 Corvair conversion. My earlier VW version of this air frame would climb solo at a rate of ~750 fpm, and at gross of 1100 lbs. at 350-400 fpm on warm Carolina days. A Cleanex with a 3.0, 120 HP Corvair at 1250 lbs. gross will out climb a solo piloted VW powered version quite strikingly with well over a 750 fpm climb out rate. Excess power to climb is an excellent safety feature to have on an airplane. High density altitude, hot summer days, short strips, grass fields, climbing to get over mountains, etc., all become easier with more power that doesn’t over tax the engine, isn’t limited to a couple of minutes at WOT, or overheats the engine quickly requiring “step climbing.” Whenever recovering from a balked landing or a go around needs to be executed in a hurry it is easier with extra power on the nose of the airplane.
In 2009 two Corvair powered aircraft flew alongside a Jabiru 3300 powered one from Florida to Tennessee for the ASA gathering. Comparing notes upon arrival it was discovered that the fuel burn and speeds for the two different engines installed on these air frames were remarkably close to the same.
It has been suggested that a heavier Cleanex would suffer in take-off & climb performance. Take a moment to consider power loading numbers at gross for a few engines (realizing that the lower the number the better):
80 HP VW @ 1100 lbs. – 13.75
85 HP Jabiru 2200 @ 1100 lbs – 12.94
100 HP O-200 Continental @ 1250 – 12.5
100 HP VW Turbo @ 1150 – 11.5
120 HP Jabiru 3300 @ 1150 lbs. – 9.58
120 HP Corvair 3.0 @ 1250 lbs. – 10.41
110 HP Viking 110 @ 1250 – 11.36
Better numbers are available for some if using a lower gross. A 700 lbs empty weight, polished, Cleanex with a 3.0 and using 1150 lbs for gross would give a 450 lbs. useful load and the exact same numbers as the Jabiru 3300 for power loading. So when considering performance note that the 80 HP engine with the lower gross actually has the poorest power loading number while the 120 HP Corvair @ 1250 lbs. gross falls only behind the 120 HP Jabiru 3300 at 1150. That’s performance!
Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g