Two cycles, Boy some folks sure hate them

[martymayes]

That is OK but I came here to discuss two-cycle engines. If you are interested in a NASA style, project review of N19WT, let me know. I've already sent a note to the moderators asking where I should post it.

Bob Wilson

I'd definitely be interested in seeing such a review Bob. In particular, I'd like to see what kind of risk is incurred by flying at night in a homebuilt airplane with a converted auto powerplant or two-stoke engine.

[Enemy Ace]

An EAA Webinar recently discussed two-stroke failure rates. It seems that the lowest rate of engine failure was in slow, draggy aircraft such as powered parachutes. Next highest was ultralights, followed by slow light aircraft such as trikes and Kitfoxes. Highest of all were clean, fast airframes. Seems that two-strokes can have a kind of lean-mixture runaway when the prop unloads, which is more likely in a fast plane (like a Dragonfly). Here's a link to the Webinar on Youtube: http://www.youtube.com/watch?v=GaaLb-BzqT4
I'd like to put in a plug for HKS: I've spoken with pilots who fly behind HKS engines and love 'em. Many of them flew two-strokes previously.

Wayne

[bwilson4web]

Thanks!

An EAA Webinar recently discussed two-stroke failure rates. It seems that the lowest rate of engine failure was in slow, draggy aircraft such as powered parachutes. Next highest was ultralights, followed by slow light aircraft such as trikes and Kitfoxes. Highest of all were clean, fast airframes. Seems that two-strokes can have a kind of lean-mixture runaway when the prop unloads, which is more likely in a fast plane (like a Dragonfly). Here's a link to the Webinar on Youtube: http://www.youtube.com/watch?v=GaaLb-BzqT4
I'd like to put in a plug for HKS: I've spoken with pilots who fly behind HKS engines and love 'em. Many of them flew two-strokes previously. . . .

This is the type of facts and data that help everyone move forward. It is only by looking at two-cycle failures that we can see if there are ways to mitigate the risks. I'll take a peek at the Webinar and see if I can contact the author(s) with my mitigation plan. I'll share what I learn here, later.

The HKS is still in the running because it just meets the range requirement. Unfortunately it is rated at 60 hp for only for three minutes. That is enough for take off and to gain a little altitude so it is still in the running if the 3502 preliminary design hits a show stopper.

My engineering practices require a fairly detailed design, a preliminary design review (PDR) that defines everything necessary for an engineering solution. It includes the parts list and prices. This Preliminary Design is then presented and if no 'show stoppers' show up, the parts are ordered.

BTW, I'm also working on what is called a Mission review but I'm not yet ready to publish in part due to being pretty busy an translating from NASA system engineering terms to 'human'. But it is a good exercise because it sets of goals that the PDR needs to cover the requirements.

Thanks!
Bob Wilson

[ehawkins]

Thanks Ed, I'm also going with factory installed fuel injection to manage the mixture. But I have no illusions that any engine is 100% reliable plus I remember how I flew my ~320 hours.
Bob Wilson

Folks who think *any* engine is 100% reliable need to be grounded for ignorance. Due diligence MUST be exercised in maintaining and operating all systems of the a/c especially the engine if safe flight is to be accomplished. Education and training are the key. There is no excuse, in my opinion, for any pilot to attempt to fly an a/c without proper familiarization with the a/c and all of its operating characteristics.

Personal prejudice as to equipment choices are common, but education and familiarization with the available engine choices out there open up design possibilities not available to one-engine type mentalities. This is one of the reasons that the experimental market is the fastest growing segment of private aviation in the country today.

[Dana]

FWIW, and anecdotal evidence such as this means nothing, but I've had two complete engine failures with a certified Continental engine (one mechanical failure, one contaminated fuel, both resulting in forced landings) and two with my 2-stroke Cuyuna (both of which I believe to be carburetor icing, and in both cases I got it cleared up before having to land, though once it was on short final to a horse farm pasture) in roughly the same number of flight hours.

Certainly the 2-stroke takes more attention to maintenance to achieve that level of reliability, and the TBO is shorter, but it hasn't been onerous.

[bwilson4web]

Thanks Wayne,

. . . Seems that two-strokes can have a kind of lean-mixture runaway when the prop unloads, which is more likely in a fast plane (like a Dragonfly). Here's a link to the Webinar on Youtube: http://www.youtube.com/watch?v=GaaLb-BzqT4
. . .

I will contact them to learn more but I'm also well aware that motocross racing is (or has been) dominated by motorcycles with powerful, 2-stroke engines. Talk about 'off loading,' those folks regularly fly off the tops of bumps or humps and I find it difficult to believe that 'unloading' automatically leads to a lot of motocross engine failures. I'm not disputing the Webinar's observations as much as sharing that other 2-stroke engines seem to deal with 'off loading' without similar failures. It is a puzzle that needs understanding and insights.

Thanks again for the link. I have another data point.

Bob Wilson

[Dana]

There's a difference between a bike or kart unloading momentarily as it flies over a bump and an aircraft on a long unloaded descent...

[bwilson4web]

There's a difference between a bike or kart unloading momentarily as it flies over a bump and an aircraft on a long unloaded descent...

Agreed which suggests the failure is not quite as rapid as the Webinar suggested when it discussed transition to cruise leading to prop unloading. Also, I don't know if two-stroke, motorcycles are able to go down large hills and mountains. I have a friend who races them and I'll ask.

This is why I need to ask the webinar speaker a follow-up question. One of the reasons I'm looking at oil injection instead of pre-mix is the oil is engine rpm driven lubrication, not throttle driven. I'll ask if they've seen it with oil injection, 2-cycles. I just don't know.

Bob Wilson

[Dana]

A related issue I've been wondering about is aerobatics. I'm designing an aerobatic ultralight which will probably use a 447 or similar. I'd hate to have the engine seize coming out of a hammerhead or loop. The aerobatic Quicksilver Super used a 503 (with diaphragm carburetor) and I haven't heard of problems with it, though many 503's had oil injection.

[martymayes]

Agreed which suggests the failure is not quite as rapid as the Webinar suggested when it discussed transition to cruise leading to prop unloading. Also, I don't know if two-stroke, motorcycles are able to go down large hills and mountains. I have a friend who races them and I'll ask.

This is why I need to ask the webinar speaker a follow-up question. One of the reasons I'm looking at oil injection instead of pre-mix is the oil is engine rpm driven lubrication, not throttle driven. I'll ask if they've seen it with oil injection, 2-cycles. I just don't know.

Bob Wilson

Bob, I have ridden and raced two-stroke dirtbikes and fooled around with small (<50 hp) two-strokes for 40+ yrs. I'd say there is not much correlation between the motorcycle application and airplane application. For starters, a motorcycle has a gearbox where the rider continually changes gear ratios depending on load to keep his engine in the optimal power range. Also, the instantaneous unloading of a bike engine when airborne off a jump is easily controlled by throttle inputs. Airplanes are not flown in the same fashion. I'd be most concerned about putting a load on a two-stroke and not being able to keep the RPM in the proper range. I've trashed a lot of engines that way.