601XL TD 3,100 Corvair Builder/pilot, MIT Aerospace engineering PhD and USAF T-38 instructor Andy Elliott wrote in with the following Comment about the Getting started Series:
“I really like your comments about allowable range specifications. This is something that is applicable to many parts of aviation, not only maintenance. Way back when I was a USAF T-38 instructor, the expression we used was “If it wasn’t good enough, it wouldn’t be the minimum. If it was too much, it wouldn’t be the maximum.” Most of the training maneuvers had performance specifications like “A loop can be entered between 400-500 knots, depending on power setting, and starts with a 4-5 G pull up.” One of the things pounded into the heads of instructors is that anything within those ranges is acceptable, as long as the student does not stall out at the top, overstress the airframe at the bottom, or bust any airspace limits.- Andy”
I typed out the footnotes in front of Andy’s name because it’s pretty safe to say he worked his ass off for many years in aviation to achieve the things he knows and has done. I tease him every chance I get, whenever he asks me a question I like to say “Jeeze Andy, every dumb grease monkey mechanic knows that, what did they teach you Phd’s at MIT anyway?” It hardly works, we both know that the size and scope of my expertise in aviation is about an acre and his is the size of Texas. The sole thing I have on him is that when we got started, none of my expertise acre was in his Texas. Over time Andy has gone after learning about Corvairs with the same thirst for information that he did with the rest of aviation he encountered. So far he has annexed about 1/3 of my acre into the boundaries of his Texas sized skill set. Thats OK, it was the goal all along, even if it erodes my ability to tease him.
The thing that Andy’s letter points out is that there is a lot of commonality to the logic of the disciplines within aviation. The individual tasks are not the same, but the logic and philosophy are. This is often missed by people who are just arriving in aviation. The fact that you will never see a big sign outside an airport that says:
“Warning: You have just left the regular world were score is not kept and it is always some one elses or societies fault. Score is kept here by the impartial judging panel of Gravity, Physics and Chemistry. Regardless of your good intention or state law, death penalty is in effect here, still considered cruel, but is not that unusual. Perfect protection and achievement is afforded by learning and exercising the Rules. You are on the property, the contest has already started, Get your “A” game on right now.”
You will not see that sign, but it is there. All of the things I write on philosophy is so builders just Getting Started can understand that there is a set of rules, and as a homebuilder working in your shop, you have plenty of time to learn them before your plane is done.
A guy with Andy’s background moving into building a Corvair is actually got a leg up on most people who have been a car mechanic for 20 years. Here is why: Andy knows the logic and philosophy of aviation very well, and just learning the parts that apply to Corvair flight engines does not require him to change his approach, perspective, values nor philosophy. He is just adding on. When he goes to the airport, he can see the warning sign as if it was in neon, the same sign that is invisible to new people yet to have a friend point it out.
There are people who arrive in aviation, who reject the very concept that there are ‘rules’ at all. A lot of these people achieved something outside of aviation, and they don’t like hearing that their previous work may be useful, but they crossed a philosophical border at the airport, and they have to start on some points beside novices they perceive to be beneath them. In the land of automotive conversions, I have seen a new crop of these people arrive every year. Their calling card is referring to certified engines as “Lycosaurs.” The mindset that you have nothing to learn from 100 years of existing aircraft powerplants is what is dangerous.
If being a great ASE auto mechanic of 20 years experience qualified your you work on aircraft engines, then it would be OK for these people to do annuals on certified planes, But the FAA does not allow it for good reason. In reality, a Lycoming 0-540 is a vastly simpler engine than any modern car motor. The FAA’s objection isn’t based on the concept that car mechanics are not capable of turning the wrenches. It is solely based on knowing that most car mechanics have little or no understanding of whats at stake in aviation, and therefore they don’t understand the value of the rules.
Think I am speaking theoretically? For several years a guy who promoted an alternative engine and gave forums on it, started every forum he gave by writing on the board “If Lycoming made car engines would you bother to drive one?” He promoted, and absolutely believed in contempt for existing certified engines. I spoke to him a number of times, and I would rate him as one of the most closed-minded people I ever met. He already knew and understood everything. He stood in my booth at Oshkosh and actually said to me that he had done some work with Corvairs 20 years before, knew all about them, and if I had questions I could call him. Where is he today? Well he had two crashes in planes with his modern car engine, both caused by fires. The second one killed him. Tragically it killed someone else also. To people who can’t see the sign outside of the airport, the mans end seems like something of a mystery. To people who can read the sign clearly, his death was a mathematical forgone conclusion. He was not killed by aviation, he was done in by his own willful decision not to respect the work of anyone who came before him. It’s that simple.
Keep in mind that the powers that be, who want to increase the numbers of people in aviation and membership organizations, have long sought to tear down the warning sign because they think it’s bad for marketing. They are joined by all the people who are in aviation to make a quick buck, and keep people in a ‘happy consumer’ mindset. These groups have often replaced the sign with one of their own that says: “Welcome! your safe, driving to the airport was more dangerous than flying here today, turn your mind off and open your wallet.” I personally think that message puts people on low alert and at risk, leads to tolerance of unsafe people and practices, leads to new guys getting a glimpse later that they have not been taught ‘the rules’ and then quitting, and it leads to a culture that elevates the man who has the expensive plane being regarded above the Aviator that possesses skill and knowledge. A big part of aviation has succumbed to this, but you don’t have to go there, hang out with it or absorb its corrosive message. You are a homebuilder, your better than that.-ww
To learn more about Andy’s adventures and perspectives follow this link:
Reviewing the options to this point, I want to bring the comparison up to the point where every engine has a 5th bearing on it. These 5 paths present proven options for builders to follow, Again, there are options for each of the five, but this is easier to keep track of with the numbering system. Right now, Phil Maxson has worked out a spread sheet and is keeping up with the series, but at this point I would still like to keep builders focused on the discussion here. We can resort to a spread sheet when we get a lot more information to juggle.
The Traditional terms we use to describe stages of completion are “Closed case”, where the 5 engines are to this point. “Short Block”, which is a closed case with pistons rods and cylinders installed, and “Long Block”, which is taking it one step further by putting the heads on. In the articles so far I have used the term “short block” because I intend to take each of the five through that stage of completion in the discussion. Our DVD series aligns with these stages. Engine build #1 is the case closed, #2 is the pistons and cylinders, #3 is getting the heads on.
Engine options with 5th bearings:
Allan Able = $2,062
Bob Baker = $2,516
Chas, Charlie = $2,770
Davie Dog = $4,270
Eddie Easy = $3,157
We are going to look at three piston and cylinder options and then apply each of them to each of the Closed Case systems above. That will give us 15 basic engine build paths.
Notice how the options expand geometrically as we get a little further along. 15 is actually something of a simplification, as I am not going to get into outdated displacements like 88mm, 90.5mm and 94mm bores. Don’t let the expanding possibilities overwhelm you. First and foremost, remember that it is the Corvair being adjustable to fit your exact needs. I am going to use the numbering system to make an easy to see, logical decision path, and I am going to highlight some common combinations like Allan Able building a .030″ over engine and Davie Dog opting for a 3,000cc displacement.
Yes, other engines come with options, The Rotax 912 comes in the 80hp 100hp and Fuel injected models. In Industry slang, these very expensive engines have nick names. 80hp = “Trust fund kid”, 100hp “Hedge fund Mgr.” and the Injected motor is “MMG” (more money than God). Obviously Rotax’s pricing isn’t really aimed at keeping homebuilding within reach of working Americans.
If you think their pricing is steep, you need to get a look at the typical cost of maintenance repair and overhaul to really understand why I refer to these things as ‘disposable appliances.’ There will be a Rotax ower who reads this, who will write in to tell me that I am all wrong about this, that he is very happy with his 912 engine on his $134,000 imported European S-LSA plane. To him and his budget, it is a great motor because all he wants out of it is that it is an acceptable appliance. He isn’t interested in learning anything about it nor working on it. It is a good match for his shallow needs, and he has the required bank roll. On the other hand, a typical homebuilder, a guy who wants to learn build and fly, a guy who got into homebuilding to get his hands dirty, will find the exact same 912 and the ‘support’ system for it aimed at pleasing wealthy appliance owners, a very frustrating proposition.-ww
Here is the number system for the next stage of engine building:
Builder ‘Eddie Easy’ is going to work with Roy of Roy’sgarage.com. Roy has his own 5th bearing design, and it is now flying on about a dozen aircraft. The bearing design requires builders to send their case and crank to Roy so that he can line bore his bearing to the case and he has to process the crank to install his 5th bearing journal on it.
Builders selecting Roy’s bearing design almost always have Roy assemble their bottom end for them. Also, Roy’s bearing design requires a special safety shaft and custom-made hybrid studs. (Dans 5th bearing uses parts straight from our catalog) For these reasons, an exact head to head price comparison isn’t possible, but we can come up with a reasonable comparison for builders. Since Roy’s set up utilizes a Moldex processed 8409 GM crank, It isn’t a fair match to compare it to ‘Davie Dog’s’ engine with a Billet crank. It is a better comparison with ‘Chas. Charlie’s’ short block. After we go through the numbers I will do some notes and comparisons at the end.
( CC stands for Clarks Corvair parts, SR stands for Summit Racing, ELS stands for Ebay Larry’s Corvair parts, and ECA stands for Ebay California Corvair parts.)
Crank group (1000)
1000- 8409 crank, no gear ($500 )
1001- Crank gear (new, $150, installed in crank processing)
1002- Crank gear key (Included in crank prep)
1003- Crank gear gasket (Included in crank prep)
1004- Rear keys -2-(CC-#5858, $1.50, $3)
1005- Fuel pump eccentric (used, from core engine)
1006- Spacer (used, from core engine)
1007- Bronze distributor drive gear (used, from core engine)
1008- Oil slinger (used, from core engine)
1009- Main bearings (From Roy, $120)
1010- Connecting rod bearings (ELS-$59)
Cam group (1100)
1100- Cam ( CC, part 8800, $235 )
1101- Thrust washer (new installed by Clarks, $12.60)
1104- Hydraulic lifter set -12 total- (Summitracing.com $2.99each, $36)
1105- Cam lubricant (comes with OT-10 cam)
1106- ZDDP oil additive (SR,$16)
Case Group (1200)
1200- Case -2 halves with studs- (used, from core engine)
1201- Main case bolts -8- (used, from core engine)
1202- Pipe plugs for oil galleries -2- (used, from core engine)
Special Items required in a Roy bearing closed case: The bearing itself; $1695, Hub modification $60, Difference in price for custom HS and SS; $30. Roy needs the case to be very clean, and he charges $120 for this service. It is not required, but Roy will assemble the lower end for the low price of $100. (during the bearing installation process he has to bolt the case together several times.)
The total of Eddie Easy’s engine parts on the chart above are $1252.10. To this must be added the bearing price, $1252.10 + $1695 = $2,947.10 . Add in the typical $120 case cleaning, and $90 for modified parts and the total comes out to $3,157.10. (Raise this to $3,257.10 and you get it back assembled.)
Chas. Charlie’s engine is identical, except it has a Dan Gen 2 bearing and it comes in at $2,770.10. $387 difference in the un-assembled form. There is some cost for shipping things back and forth, but it isn’t a deal breaker. For a builder who is looking for an assembled case, it isn’t the least expensive method, but it isn’t astronomically expensive either. There isn’t really a low-cost do it yourself option, nor a pay as you go approach that a guy like Allan Able can employ, but Roy’s product isn’t aimed at those builders.
Two things to frankly discuss: Roy has a very long waiting list, It has run over one year. Because of the hand done nature of the bearing, he can’t just phone up the CNC shop and order up another dozen bearings, and this leads to a long order time. Second, Roy has a background in working on things like Mercedes cars. To his perspective, applying the mercedes standard to the main bearing bores on a Corvair case means that 1/3 of cases are out of tolerance. This means you could need a whole new core case if he ‘rejects’ it.
To my perspective as an aircraft mechanic of 22 years, the GM tolerance is fine, and there is no need to arbitrarily cut it in half. Aluminum case opposed motors are traditional built a lot looser that Cast iron car blocks. Roy works with .0005″ as the limit of out of round on the bores. I have my doubts that all Corvairs passed this on the day they were made. The Gm new spec is .001″, twice as much. I have built many flight motors that were .0015″, They worked great.
For a reality check, Kevin and I once had about 20 140hp Corvair engines between us. These are Chevys high rpm/ high output engine. Inspecting many of these cases coming from 6,500 rpm engines which had 100,000 miles of beating on them, revealed that the main bores were often .0035, or seven times Roys tolerance. Yet none of these engines spun a main bearing. Thus I don’t agree that a Corvair between .001 and .0015 is in any danger of spinning a bearing or wearing out. You can ask any builder who has attended a number of colleges and seen 100 different engines that were torn down if he has ever seen one with a spun bearing, he hasn’t. In 20 years of working with Corvairs, I have seen two or three spun bearings, but they were all in engines that were literally run without oil.
At Embry-Riddle it was drilled into our heads that if the book said the allowable torque range determined by engineering was from 50 ft/lbs to 75 ft/lbs, then putting the item anywhere in that range made it air worthy. Mechanics that spent a lot of time trying to hit 62.5 ft/lbs were wasting effort and trying to prove something about their ego. If they would only be happy if it was between 55 and 70 because they were not sure about the torque wrench, then they were to get a new wrench. Guys who though they were making something ‘better’ by torquing it to 75 every time, were living under some illusion. In short, any mental justification that the mechanic used to put his own ‘custom’ touch on tolerance was to be frowned upon, because it probably indicated that the mechanic thought of himself as smarter than the engineer, or he did not trust the book. arbitrarily applying standards from one machine to another was really frowned upon. Less clearance isn’t always better, Closer fit in aircraft engine components isn’t always better, and neither is any arbitrarily set standard. The real issue with that kind of thinking is that you end up believing that you have a system that is ‘better’, and you stop looking at the field data that might suggest otherwise. No one gets smarter that way.-ww.
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