Ed Anderson
Joined: 10 Jan 2006
Posts: 475
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 Posted: Mon Nov 03, 2008 8:03 am Post subject: Alternative engines and vendors (Long) Was: Crossflow Subaru |
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An Alternative engine – your cup of tea???
An alternative engine project is certainly not for everyone – or even most, whose primary objective is to get an airplane in the air. But, for those who find it a challenge and are interested in something different – its kick- A_ _ fun. Just make certain you are aware of the risks and challenges – not to mention the frustration of chasing a solution.
Vendors
One thing that is a fact of life for any alternative engine project is at some point in the project you are probably going to have to purchase a critical item from a vendor. The problem is that some vendors (not all and not most), but some, do not fully understand how to design a subsystem, may not even understand the engineering/physics/chemistry basics or limitations behind it or may not understand some of the manufacturing limitations in implementing a design. Heck, they may not know even what performance data to collect or how to assess it. That’s not to say a successful product can not result when this situation exits – however, as you can imagine the likelihood of a good robust design that can handle all conditions decreases considerably.
We have all seen outrageous claims like 200 HP on 7 GPH, save 50% on fuel - convert H20 to fuel, etc. – those are easy to disregard – it’s the more complex and subtle ones, like electronic designs of an ignition or fuel injection CPU, etc. not readily or easily verified that can get you.
The problem, of course, is how to identify the vendors who have the right product for your conversion. That is a problem and one I don’t have a clear answer for. However, I would not buy from a vendor who was not flying that product in his own aircraft and had reasonable flight data to support its performance. I don’t care how well the design is though out, until it is flight proven it doesn’t belong in my aircraft and shouldn’t in yours - if it is a flight critical component.
But, how do you separate the reportedly “Proven” designs/products claims from reality – it can be tough to do. About the only two things I would rely on is 1. A long, proven history of quality engineed products from that vendor (may be hard to find a long term vendor serving alternative engine needs) and/or 2. The vendor can/will provide contact information on at least 10 individuals who have purchased the product.
Then it’s up to you to check with each and see if the claims are verifiable. Also, check and see if the vendor will admit to any problems encountered – rare that there are not some problems even in the best designs, but a good vendor will admit to them and tell you why they occurred and how they fixed them. A vendor who vemonly denies any problem always raises my suspicions a bit.
If you have not gathered by now, yes, I am one of those “Alternative Engine” crazies.
Last month was the 10th anniversary of the first flight of my rotary powered RV-6A. Any engine that can function in the intended operating regime with sufficient power and reliability has the potential to make an excellent aircraft power plant. Problems are generally not with the alternative power plant itself, but all the auxiliary systems (ignition, fuel, cooling, etc) which are of necessity a once-off design process done by individuals (of varying skills, experience and knowledge levels) rather than $$$ companies with engineering staffs.
I personally chose the rotary because, as an engineer, I could see that it was inherently more reliable than any piston engine primarily (but not solely) due to its much lower parts count. There is no camshaft, no rocker arms, no valves, no valve springs, no lifter rods, no connecting rods, no cylinder heads, etc. Those items which are frequently the source of failure in a reciprocating engine. Yes, like anything mechanical, the rotary engine can fail – but, it tends to do so somewhat gracefully. We have found that as long as fuel and spark is provided that the engine will generally continue to run (perhaps at reduced power but generally enough to get you to a safe landing) regardless of damage. The one thing it will succumb to is the lost of oil to the bearings. The most common cause of failure (with just about any engine) is failure of an auxiliary system – and not an engine block failure.
Then you also have the fact that there is no necessity to translate linear motion (of pistons and connecting rods) to circular motion (via a crankshaft journal) as the rotors are of course design for rotation. This reduces the inertia loads on parts considerably. The fact that the rotor is iron alloy and its housing is aluminum means the rotary does not seize when overheated – it does loose some compression as the aluminum housing expands faster/more than the iron rotor. In two cases, where all coolant was lost, the rotary got the aircraft back to a safe airport landing – true the engine was cooked and required a rebuild – but it got the pilot back. A brand-new, Renesis Rotary engine, Rx-8 crate engine from the manufacture or other sources can be purchased for between $4000 -$6000 depending on model and long or short bock. Of course, if you rebuild an older rotary on your own, you lower the price further.
I have over 500 hours time on a flying rotary engine – and I am not the high time rotary flier. One individual has over 1600 rotary flying hours in an RV-4.
There are other auto engines that have proven suitable for aircraft use, when used within reasonable operating limits and appropriate matched to the airframe power requirements – the Subaru and Corvair engines are two that come to mind, but there are obviously others as well. One of problems is that no two installations are exactly alike and when they are not identical and operated in identical regimes – then you have two different systems. I have frequently seen Joe copy Bill’s design and then discover his installation does not work as well as Bills – only to find that Joe made a few changes. If it’s not identical, it’s a different system and don’t be surprised if it reacts differently.
I am certainly not knocking the traditional aircraft engine – given the economies of their production run sizes and the enormous investment required to make a major redesign of the typical aircraft engine – has just made major changes a unattractive capital investment. Things are beginning to change for the better I believe – but we are still talking about basically 1930’s engine designs. Yes, a lot of improvements have been made – but there is a limit to how much incremental improvements can do for any basic engine design.
I repeat - an alternative engine project is certainly not for everyone – or even most, whose primary objective is to get an airplane in the air. But, for those who find it a challenge and are interested in something different – its kick- A_ _ fun. Just make certain you are aware of the risks and challenges – not to mention the frustration of chasing a solution and task of assessing the vendor you purchase products from. Word of mouth from customers is probably the best source – but, even there you need to separate real problem from a customer perceptions. Some customers will bad-mouth a vendor when the real problem is the customer’s lack of understanding or misunderstanding the true situation. But, if a major of a vendor’s customers are unhappy, there is likely a good reason for it.
Just my $0.02
Keep flying and keep it safe.
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson(at)carolina.rr.com
http://www.andersonee.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html
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Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com |
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