Corvair Engines - The Justification Series

[rizzz]

Who says FWF weight was the limiting factor? When they test for ultimate load they turn the plane upside down and load the wing to 9x aerobatic gross. What does that have to do with hanging an extra 20 lbs on the nose? Did they put 9x200lbs on the engine mount and the structure failed at that point? Maybe a 200 lb artificial limit was placed to ensure the market did not have to be shared with the other auto conversion? Maybe not. I bet Pete Buck would know.

Indeed it would be good to know where the 200lbs limit actually comes from.

[dtwolcott]

Did anyone think of the fact that if you increase FWF weight that that might impart extra loads on other structural parts of the plan. i.e. elevator loads and subsequent tail cone loads in flight. There is more than structural g loads on the wings that must be taken into account when discuss max gross weight and where it is distributed through out the plane.

[kmacht]

If CG is maintained within limits and the gross weight is not exceeded the loads at the tail will be no different that what you are flying with today.

Keith
#554

[Rynoth]

If CG is maintained within limits and the gross weight is not exceeded the loads at the tail will be no different that what you are flying with today.

Keith
#554

True, but if FWF weight is exceeded the loads on, say, the fwd fuselage upper longerons, would be higher. Or, the upper/lower engine mount attach angles. Or something else that Sonex engineering keeps in reserve by saying “dont exceed this limit if using our plans”

[daleandee]

Quite an incredible response to my first posting. I want to thank all for the very civilized responses, great thoughts and information shared.
For sure there are some things I take a bit of a different view on but overall it seems that everyone is nearly on the same page.

I want to clarify that my opening questions were not intended as reasons or justifications for the Corvair install (although some of that data comes up later) but rather I seen these facts as things most builders of these airplanes might like to know but most likely did not. Under no circumstances would I suggest that anyone fly a Sonex over VNE (although Jeremy did that on the Turbo video) or over 1320 lbs.

So as an opening or preface let me put a few more thoughts on the list and see what others believe.

The Sonex line of aircraft exist today because a young man built an airplane he called the Monnett Mini, a.k.a the Mini Messashidt, which was a modification of the Parker Jeanies Teenie. Not only that young man but another builder in the mid-60's purchased a Stits Playboy and modified it by installing a larger engine. Later, he modified the aircraft by installing cantilevered aluminum wings with flaps, creating the RV-1 in 1965. Were these two men showing disregard or disrespect for the designers intent?

I would also ask if it could be said that the factory is showing "blatant disregard for the design limits" of the lowly VW engine by asking an engine designed originally to output 60 HP @ 4400 RPM to now deliver 25% more @ 3400 RPM ... and even further disregard the design by adding a turbo to seek 100 HP from this engine. I understand the upgraded racing parts used to build the engine but the case is basically the same and certainly the heads have less cooling area than before with heavier chamber walls and fins removed to add a second plug. Does this work? Appears it does. Reliably so? It appears that the answer to that is not quite as clear as some would like. I try to focus on safety (as I'm certain we all do) within the limits of my budget and abilities. I have to weigh my choices very carefully and determine, what for me is best.

I did consider that in my airplane I wanted the strongest air frame in my price range along with the most reliable power that I could find in an engine that would work on the air frame I choose. I nearly built a Zenith 601 ... but I digress. So here's some initial information:

1) Many Cleanex pilot fly aerobatics. I don’t.
2) Most flights are just me, fuel, and baggage and are well under 1100 lbs gross.
3) Flying smoothly at 1250 lbs. has proven to have no ill effects on aircraft handling and performance is quite good with 120 HP on the nose.
4) Va speed was reduced.

Here is the preface from the article (please note the disclaimer):

I’ve often been asked why I used a Corvair engine on my airplane and I’ve written many replies. Recently I put on the Builder’s list a set of twenty four (24) extremely compelling reasons why this engine should be considered if you are looking in the area this falls into for power & price. This engine is absolutely, by design, heads and shoulders above anything else in its price range. From crossflow heads to canted valves and the ability to cool itself extremely well, all while being smooth in operation and quite robust by design makes it an exceptional choice for an aircraft power plant.

But the question that was asked that needs to be answered wasn’t about why I put a Corvair engine on this airframe but rather the “justification” for doing so. Many guess at a few of the reasons I did this and some paint with a very broad brush. The purpose of this article is to show clearly that this was not done with any “blatant disrespect” nor was it done in an attempt to fit an engine to an “inappropriate air frame.” There is no intent to criticize or disparage the factory!

Here is the disclaimer: The information I will share in this series is my own opinions, speculations, calculations, and conclusions. I cannot and do not recommend that anyone do as I have done. Following my example could get you injured or killed for which I assume no responsibility. You have been warned. This information is not a license for you to believe that what has worked for me will work for you. I’m not aligned with anyone, or any company. No one has asked me to do this for their profit or their promotion. I’m sharing this so that the “justification” for my personal choice will be known.

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[kmacht]

If CG is maintained within limits and the gross weight is not exceeded the loads at the tail will be no different that what you are flying with today.

Keith
#554

True, but if FWF weight is exceeded the loads on, say, the fwd fuselage upper longerons, would be higher. Or, the upper/lower engine mount attach angles. Or something else that Sonex engineering keeps in reserve by saying “dont exceed this limit if using our plans”

I was specifically answering dtwolcotts question regarding changes in loads on the tail. As I said in a previous post I have done my own stress calculations on the mounts and associated parts and am comfortable with the margins. I also dont plan on increasing gross weight which would have a much greater impact on the airframe and not sometjing i tried to quantify. Each person will have to make their own decisions as to if they are comfortable enough deviating from the plans.

Keith
#554

[WaiexN143NM]

hi dale,
good discussion and postings. i am like larry, waiex 121yx, i always was a skeptic of the corvair. no more. its showing good reliability, on the 20 or so mounted on in the community.
at the panther booth i was impressed with the corvair kit.
phil davis plans on having his corvair sonex up from texas this year to osh18. any others?
maybe someone could hold a forum at oshkosh on this subject.

michael.

[daleandee]

phil davis plans on having his corvair sonex up from texas this year to osh18. any others?
maybe someone could hold a forum at oshkosh on this subject.

michael.

Hi Michael,

When you're at the Panther booth (SPA) William Wynne's booth (Fly Corvair) should be next to it. Last year Randy Bush flew his beautiful, recently finished, Cleanex up:



Complete article here:

https://flycorvair.net/2017/08/01/3000cc-cleanex-at-oshkosh-2017/

William has lots of info either doing forums or at his booth where other Corvair powered aircraft will be parked.

I work way too much to get to Osh-Kosh or Sun-N-Fun this year. Retirement hopefully comes soon and life will be different ...

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[daleandee]

In talking with a friend over the weekend concerning the ongoing discussion here he said, "like guns, Christianity, politics, etc. you should not be surprised if you don't change many minds." My answer is that I'm not here to change the thoughts and beliefs of anyone. This is the same man that made me understand that nobody can make me angry ... I have to allow it. Likewise I have no desire to change anyone thoughts as to what they should do. People have to persuade themselves by being willing to consider all that is presented. But my approach is not to suggest that anyone follow what I have done but simply to answer the question of why I did it for myself and how I came to the conclusion I did. So more from the article i.e. the introduction:


Introduction:

Having owned a nose roller version of this air frame with a VW conversion I learned some lessons about what I liked and didn’t like about the air frame and engine combination. I finished the build on this first one though it was mostly finished when I purchased it. The VW engine did require removal and disassembly to correct some assembly errors. I flew it for five years and 175 hours. The lessons I learned that I share here are only as they apply to me, my particular situation, and my expectations as to what I consider to be acceptable, safe, & reliable.

I adore the air frame. The elevator is lighter than the ailerons so the control harmony is not completely balanced but the controls are quite light and the airplane is a real pleasure to fly. Some have compared it to an RV series and some have labeled it “the poor man’s RV.” The rudder has gobs of authority and the airplane slips very well. Flaps are quite effective and the plane will fly rock steady to some pretty slow speeds. Stalls give ample warning. It is a sporty airplane that has to be flown most all the time unless you are using a wing leveler or auto pilot. Cruise speeds allow for cross country options.

I have concerns with the factory supplied engine and carb system. No reason to go into detail as to what I don’t care for about their system as it does work for some, but it just didn’t fit what I wanted or needed in a power plant.

The tail wheel version is my preference although the nose roller version was fun. The tail wheel tends to get more stares and respect at fly-ins and fuel stops. There was the challenge of learning to fly tail wheel that was intriguing also. Having flown in two tail wheel versions and getting a taste of what 120 horsepower would do when out on the nose of this airframe I knew what I wanted but I didn’t have Jabiru money. In retrospect I’m extremely glad the Corvair is on the nose.

The Corvair was an option that I could afford but it was not, is not, and will never be, factory supported. I read the warnings and the literature from the manufacturer and then began to dig into all the facts and data surrounding the install of a Corvair engine on this air frame that I could find. I've had some private & semi-private conversations with manufacturer personnel and other designers that will be kept confidential. I will share as much as I can. Most of the facts (given in question form) that were shared in my opening post are available by a thorough search of the available data from the company themselves. In doing this research I discovered multiple “justifications” for using this engine & air frame combination. These I would like to share, one at a time as I list them in the days to come and leave room for group discussions. My reason for giving these validations is to put forth a response to the question of what “justifications” I have for doing what I did. So to follow, in no particular order, are the answers.

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
171.9 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[Gordon]

Corvair Information Justification

Dale..........just to let you know there are some of us reading these posts that DO LIKE your opinions and experiences with the Corvair. More information and options are a good thing.

Since I have a Onex the Corvair is not in my future (a bit too heavy) and a 3300 Jabiru would be great but a bit too heavy in price.....I have the Hummel 2400 85 hp.

Don't let the naysayers discourage your "subject matter"......we should all be open to other options. Maybe someday some of us will take the same road as you have.........never say never.

Gordon.......Onex......Hummel 2400