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Twin Auto Engine


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One of the enduring themes in the kit building arena is the certified vs auto engine debates.

Badly installed auto engine experimentals have the ability to paint the entire kit building fraternity with a not entirely respectable image. (this may not be a bad thing)

Given that auto engines are less reliable than certified engines. Why has there not been more emphasis on multiengined variants? With two power plants of suitable power output you go down the same path as hard disk manufacturers with RAID systems. Call it RAIE redundent array of inexpensive engines. Develop a standard mounts for a set of engines and the Certified vs Uncertified argument based around reliability dissappears.

Personally I would love to see a diesel engine twin based around some of the light diesels becoming available

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Well, auto engines are not necessarily less reliable than certificated aircraft engines...this is a point that is open to debate.

 

If you look at the reliability record of auto engine conversions, it's pretty dismal. However, if you look closely at the record, I think you'll find that most of the time it's not the engine that is at fault...it's the supporting systems. In effect all of the auto conversion installations out there are prototypes...and prototypes ALWAYS have issues.

 

So I think it would be fair to say that certificated engine installations as a whole are more reliable than auto engine installations, but I would not go so far as to say the engines themselves are more reliable.

 

Regarding twins...Twins raise all sorts of issues of their own. With the exception of centerline thrust twins and strange one-offs like the South American guy who has two engines driving a counterrotating prop in his Cozy, piston twins have real handling and performance problems when one engine goes out. In certain circumstances (low, slow and heavy) a twin can be more dangerous than a single when an engine quits.

 

Doubling the number of engines does not halve the chance of having a mechanical problem...it doubles it. There are twice as many points of failure. What the extra engine does for you is make that scenario more survivable most of the time (night, over water, mountainous terrain, etc.).

 

Then there's the engineering involved. Light twins are more complex structurally and aerodynamically than are singles.

======

Not started yet, maybe never will (currently having an affair with an RV project...shhh...don't tell my set of Cozy plans)....

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:) I have emailed Ruben Leon he is the owner of a Cozy that uses two motorcycle engines. I asked him "Have you ever try flying it on only one engine? If so, how dose the plane handle?" his reply was "The airplane holds altitude at 6000' with one engine, half fuel and two on board."

 

I was thinking that the VW Engine can produce 200+ph, and the weight is not allot. In fact it is light enough that one person can pick the engine off the ground.

 

:thumbsup: Two Suzuki 1600cc: http://www.infortel.com/cozy/

:thumbsup: VW Engines: http://www.cbperformance.com/company.asp

:cool: My Websight: http://www.geocities.com/deronjthomas/

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Each engine is actually a 4-cylinder auto engine from a Suzuki Swift.

And that was the best and cheapest solution at that time, almost ten years ago. Turbo-diesels, with their hugely improved power to weight ratio and their unchanged reliability and fuel efficiency, may be the better solution now.

I'd take a careful look at the Mercedes/Mitsubishi 1.5 liter 95 HP aluminum head and block, used in the Smart Forfour and the Mitsubishi Colt.

Kumaros

It's all Greek to me

It's all Greek to me

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Doubling the chances of engine failure is not a major concern if you have more than one engine. The impact of asymetric thrust depends how much of it you have. For example the starship design has the engines placed close to the centreline to reduce this impact in a simple manner. Your chances of complete power loss is n squared where n is the chance of failure.

From an engineering perpective are twins are significantly more complex than singles? Unless you are trying to cope with significant yaw issues relating to asymetric thrust. It is simply another engine, the engines are uncoupled. Of course I may be missing something.

Cozy designs have been modified to have two engines in the past without significant reengineering. Their performance may have suffered because the impact of hanging a couple of engines on the wings wasn't fully appreciated but apart from that they were simple cozy variations.

Is it possible to mount two engines on a cannard design in a manner where the yaw produced by a "low, slow and heavy" engine loss won't present significant risks? I suspect that it is possible.

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Doubling the chances of engine failure is not a major concern if you have more than one engine.

It certainly can be, as you yourself point out in the very next sentence....

The impact of asymetric thrust depends how much of it you have.

Right. There have been LOTS of Vmc rollovers in light twins. Many if not most designs are really marginal in this regard.

 

I point out that turboprop twins generally don't have a climb/stall/Vmc problem because there is ample power on one engine to avoid problems when low, slow and draggy...their single-engine climb speeds are well above Vmc.

 

Power loss in a piston twin is a really, REALLY big deal if there are controllability and/or climb issues in any part of the envelope with one engine out (most light piston twins fall into this category). The accident record speaks for itself. If having a second engine were a safety panacea, then piston twins would have a much lower accident rate than they do.

 

The Starship is a unique case. The configuration certainly does work to reduce asymmetrical thrust, but as noted above the real key is having enough power to get yourself out of the Vmc trap.

From an engineering perpective are twins are significantly more complex than singles? Unless you are trying to cope with significant yaw issues relating to asymetric thrust. It is simply another engine, the engines are uncoupled. Of course I may be missing something.

I'm no engineer, but it occurs to me that there are issues related to the structure of the aircraft in a typical light twin with engines on the wings, which is what I was referring to. You've got a lot of mass suspended well off the centerline, well forward of the spar, and far away from both the center of gravity and the center of lift. I'm sure a high speed film camera would show a twin wobbling and twisting in all sorts of interesting ways when it hits turbulence. Turn the whole thing backwards for a canard.

 

Aerodynamically, if you lose one engine the airplane will be flying in a slip, with thrust off the centerline. The design may or may not treat this situation well. There are rudder authority issues and roll control issues. It's not as simple as just hanging another engine on the airplane. With a typical canard that has an independent rudder system, is it sufficiently powerful and robust to counteract asymmetrical thrust? I don't know. Do you? How much power can you apply in a given design before asymmetric thrust overcomes rudder authority and rolls the airplane over? The Starship configuration makes this less of a concern, but the phenomenon still exists and must be dealt with.

Cozy designs have been modified to have two engines in the past without significant reengineering.

:yikes: :yikes:

 

Say what? You think that completely altering the aft end of the airplane to accommodate a second powerplant is not significant? Not even Rutan himself would say such a thing, IMHO. The airframe was designed to hang one engine in the middle. That's what the structure is capable of handling. If you put two engines in some other location, you HAVE to redesign the structure to accommodate the new loads. This is not trivial! As I said I'm no engineer, but this is obvious to me.

Is it possible to mount two engines on a cannard design in a manner where the yaw produced by a "low, slow and heavy" engine loss won't present significant risks? I suspect that it is possible.

I agree. At least one person has already done it...that twin Suzuki with counterrotating props. It's no small task, though.

 

I'd really like to find out what the actual performance of that airplane on one engine is. Can it climb at full gross on one engine? What if the landing brake is out? What's its single engine ceiling? If it meets the minimum requirements that all certificated light twins must adhere to, I'd be very impressed.

 

For that matter, it MUST be awfully tail-heavy. Two engines, two engine mounts, two reduction drives, two props, two cooling systems (they're auto engines).... Just what is the weight and balance like on that airplane? Most if not all Cozys already have to carry extra weight in the nose during single-pilot operations. How much ballast does that airplane need?

 

We already know that controllable pitch props are not used on canards as a rule because they represent a lot of weight well aft of the cg. How do you propose to handle that problem, doubled? Piston twins with non-feathering props have a great big drag problem in an engine-out scenario. It both kills climb AND increases asymmetric thrust.

 

This isn't simple.

 

My $0.02

======

Not started yet, maybe never will (currently having an affair with an RV project...shhh...don't tell my set of Cozy plans)....

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I agree. At least one person has already done it...that twin Suzuki with counterrotating props. It's no small task, though.

You guys are funny. See:

 

http://www.roughriver.org/2001_photos.html

 

about 1/2 way down. It's been done. It works. Mike removed the twin engines and is either in the process of putting a single engine back on his plane or has already done so.

 

IIRC, Ivan Shaw (of Europa fame) built a twin engine Norton Rotary version of a Long-EZ as well.

 

And there have been others.....

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IIRC, Ivan Shaw (of Europa fame) built a twin engine Norton Rotary version of a Long-EZ as well.

Googling "ivan twineze" brought me to this interesting quote, presumably from Ivan himself:

 

There are only two types of pilot who fly retractable gear aircraft. Those who have landed wheels up and those who have yet to!! I'll come clean straight away and admit to being in the former class. In mitigation, it was whilst dead sticking my TwinEze to a landing after a double engine failure.

 

I did pump the main gear down but got distracted and forgot about the nose gear. 99% of all the LongEze, VariEze pilots I know have at some time forgotten to put the nose gear down and had a rather embarrassing arrival. Experience appears to have nothing to do with it as several are airline pilots in regular practice and used to complex retractable aircraft. Even warning devices seem of limited value. A close friend was so convinced that he had put the nose gear down on his LongEze, a mind set, that even when the warning light flashed and bell sounded, he said "Ah shut up" pressed the warning defeat button and landed wheel up!

I don't know why the double-engine failure happened, but playing with statistics, this amounts to "25-33% of all homebuilt twin-engine canards have had an all-out engine failure."

 

A benefit of the canard design, compared to a 'conventinal' aircraft, is that ALL wing surfaces contribute lift, resulting in better glide ratios. In the case of an engine failure, this amounts to more time to find an emergency landing area. I suspect that a double-engine failure for a twin canard would result in a glide ratio that might even be less than that of a 'conventional' aircraft design (ie. a Cessna). That tells me to put the extra energy into making just 1 engine work perfectly.

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

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Oh, I *know* it's been done (I said so earlier in the thread). I didn't mean to imply that it's impossible or even a bad idea. For all I know it's the greatest thing since the invention of the flight attendant.

 

My point is that it's not a trivial endeavor, nor does it *automatically* mean the airplane is safer. Conventional light twins are safer than singles under some circumstances, but less safe under others. You can't have a Vmc rollover in a single.

 

Every design change involves tradeoffs. Turning a single into a twin is no different.

 

Great. We've got a TwinEZ (I actually knew that...don't recall where I've seen it before, though).

 

Can it climb at gross with one engine out?

What is its single engine service ceiling?

What are its flight characteristics at low speed, with a full load and everything hanging out?

Does it have to carry a ton of extra ballast to balance all that weight aft of the cg?

What engineering was done on the structure to ensure that the new loads are carried safely? Was due diligence carried out, or was it "eyeball" engineered? Marc, as an engineer yourself you know full well how important this stuff can be.

What flight testing has been done?

======

Not started yet, maybe never will (currently having an affair with an RV project...shhh...don't tell my set of Cozy plans)....

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So I guess that trick is to have 2 engine that take up the same space, and roughly the same weight. As well as cranking in optiset directions. Wile having enough power that you could take off and land on only one engine.

 

:confused: Dose any one know how much the recommended engine weighs in at. When it has all assembled? :confused:

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A benefit of the canard design, compared to a 'conventinal' aircraft, is that ALL wing surfaces contribute lift, resulting in better glide ratios.

As an aeronautical engineer, I can tell you that the fact that both wings are lifting in the "up" direction has almost nothing to do with the glide ratio of the aircraft as a whole. Ask a Vari-Viggen pilot what his glide ratio is :-).

 

Low drag and wing aspect ratio are far more important factors.

 

....Marc, as an engineer yourself you know full well how important this stuff can be. What flight testing has been done?

Not a clue. However, since Ivan Shaw is an aircraft designer, I would THINK that he'd covered those bases. I was told that Mike Bowden's installation was VERY nice and very well thought out, but that he never got the performance out of the Jabiru's that he had expected.

 

As far as your specific questions, you'd have to ask Ivan and/or Mike.

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Ask a Vari-Viggen pilot what his glide ratio is

Does the word Bowling Ball sound familiar.

 

I have about 50 hours in VariViggen, They fly like a fully loaded cement truck.

 

Waiter

F16 performance on a Piper Cub budget

LongEZ, 160hp, MT CS Prop, Downdraft cooling, Full retract

visit: www.iflyez.com

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As an aeronautical engineer, I can tell you that the fact that both wings are lifting in the "up" direction has almost nothing to do with the glide ratio of the aircraft as a whole. Ask a Vari-Viggen pilot what his glide ratio is :-).

True, of course, but the context of my statement was limited to current canards (Long-EZ and Cozy types) and their derivatives (excluding the Wright Flier, etc.).

 

Still, your point is well taken and leaves me wanting to see the data, but back to my original point -- I'd rather be 6,000 feet up in a single-engine Long-EZ/Cozy than I would in a Cessna (under any conditions).

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

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True, of course, but the context of my statement was limited to current canards (Long-EZ and Cozy types) and their derivatives (excluding the Wright Flier, etc.).

We're getting far away from the topic, but my point was that the wing configuration of the aircraft is NOT the dominant factor in determining it's glide ratio.

 

Still, your point is well taken and leaves me wanting to see the data, but back to my original point -- I'd rather be 6,000 feet up in a single-engine Long-EZ/Cozy than I would in a Cessna (under any conditions).

Well, sure, but there are any number of standard configuration aircraft that have glide ratios as good as LE/COZY.

 

Look at glider design if what you're interested in is maximum L/D ratios. Rutan designed the Solitaire, but while it flew OK, it was a dud from the standpoint of glider performance. The "stall resistant" design point of the canard configuration does not lend itself to optimizing the drag bucket synchronization of the two lifting surfaces, and a canard configuration aircraft will almost always have a slightly lower L/D max than a similar performance conventional aircraft. There are NO canard configuration competition gliders (at least not any that win :-) ).

 

You win some, you lose some :-).

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Is it possible to mount two engines on a cannard design in a manner where the yaw produced by a "low, slow and heavy" engine loss won't present significant risks? I suspect that it is possible.

Way you have directional stability is to 1) not have asymmetric thrust such as a Rutan Defiant... or 2) have enough airflow over vertical stabilizers and rudders to provide enough control effectiveness.

 

The minimum indicated airspeed at which this control effectiveness with asymmetric thrust is called Vmc, and when you obtain your multiengine rating in certified planes, you demonstrate flight approaching Vmc as part of your training. This control effectiveness is reliant on a minimum velocity over the vertical stabs.. One way to augment that is to have twin tails in the propellor slipstream like the Beech 18.. the other is simply to go fast(er). Using a pusher, without a tail surface mounted behind the engine, the answer is brute airspeed.

 

When flying a light twin, your best rate and angle of climb speeds are usually WELL below the Vmc (indicated by a red radial or "red line" on the ASI). For the safest operation, you rotate, clear any obstacles and then lower the nose and accelerate past Vmc/Red Line, then to Vyse (Single Engine Best Rate of Climb/Blue Line). Doing this in a canard twin with the potential for asymmetric thrust simply takes time and distance. Dont plan on short fields with lots of obstacles.

 

A twin, by the way, will likely double to triple your operating costs. Twice as many engines burning fuel... prudence would dictate a propellor system that is featherable to make an engine out a workable event.. and those arent cheap...to buy nor maintain. You are adding a level of complexity that may not be called for. If you want dependability, go with a turbine or turboprop installation.. by the time you get two engines, ECU's, propellors, and everything put together, you can get better reliability from an adapted turboprop app. for not much more cost.

 

Dave

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A twin, by the way, will likely double to triple your operating costs.

And don't forget, twice the risk of failures.

 

Waiter

F16 performance on a Piper Cub budget

LongEZ, 160hp, MT CS Prop, Downdraft cooling, Full retract

visit: www.iflyez.com

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Well, sure, but there are any number of standard configuration aircraft that have glide ratios as good as LE/COZY.

 

Look at glider design if what you're interested in is maximum L/D ratios.

Okay, I agree -- a glider (as well as some other "standard configuration" aircraft) will out-soar a Long-EZ or Cozy.

 

Back on topic, here's a quote from an article that talks about the Defiant's glide ratio:

 

Back in the pattern, the Defiant exhibits some characteristics that are atypical of other twins. If you’ve been flying a Long-EZ or VariEze, you’ll be prepared for the Defiant’s glide ratio. Otherwise, it may come as something of a shock. The airplane loves to fly, and even power off it gives up speed and altitude grudgingly. Melvill suggested that I hold 90 knots in the pattern. My lack of recent experience with extremely slick Rutan designs almost forced a go-around on the first attempt. Until you’re used to the airplane’s power-off response, you’ll tend to consistently overshoot the touchdown spot.

I tried to get some data on the topic, but it's all over the map (due to weight, altitude, and airspeed). Still here are some quick numbers as found on the 'net:

 

Rutan Solitaire: 32

Berkut: 18

Cozy: 14.25 (CAFE) / 10.8 (another Web site)

Long-EZ: 11 / 20+ (N3R)

Wright I Flyer (1903): 8.3

Sparrow: 4

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

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...we got way off topic.

A little, but we're allowed to stray in the 'Coffee House' (this sub-forum). The next topic on the tip of my tongue was about to be a discussion on the airspeed of an unladen swallow, but I wouldn't do that.

 

Dose any one know how much the recommended engine weighs in at. When it has all assembled?

A Lycoming 360 series engine is ~270lbs dry / ~350 lbs wet/installed (I think).

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

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The next topic on the tip of my tongue was about to be a discussion on the airspeed of an unladen swallow, but I wouldn't do that.

African or European? This stuff is IMPORTANT, man! Get with the program!

:banana::banana::banana::banana::banana:

======

Not started yet, maybe never will (currently having an affair with an RV project...shhh...don't tell my set of Cozy plans)....

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And don't forget, twice the risk of failures.

 

Waiter

I disagree, in that the above statement "can" be correct but it is misleading in that vein.

 

If you want to play with statistics, lets play with statistics. The risk is not additive, as you suggest. The risk of any one engine failing is independent of the risk of another engine failing (barring some freak mishap that causes the simultaneous failure of both engines - such as fuel exhaustion, volcanic ash ingestion or parts of one engine impacting the second).

 

Yes, there are now two sets of "points" that can fail as compared to a single engine aircraft, but barring obvious sources of double failure (which would sideline a single engine plane too), you are actually less likely to have a total power loss.

 

The risk of a double failure due to non-coincident circumstances is the product of the two risks multiplied against each other..and since both are already fractions/decimals already, the product equates to a smaller risk of "total engine failure" than a single engine product of the same type. A 1% risk of failure in each engines results in a 0.01% chance of simultaneous failure (excluding common causes, again)

 

Much of the "trouble" with certified light twins is that they are usually not well-powered enough to operate suitably on a single engine after failure. The reason is that the Feds (FAA) didn't/doesn't require it for the light twins to be certified. That unfortunately results in a certified light twin having just enough power to take you to the scene of a crash :scared:

 

Compare this to transport category twin engine aircraft.. They have a "good" single engine rate of climb compared to light twins. The Learjet I used to do medical stuff in the back of, could climb at 1000 fpm with one engine out... and over 5,000 fpm with both turning, and the nose yanked up.. I'd gladly have a twin engined plane if it was affordable for me... but it would have to be a safe design as well.. and some of the things that would make it safe make it unaffordable for me.

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Here's an interesting point to consider whether a twin-engine approach is worth the effort... the FAA has recently formalized requirements for twin-engine experimental aircraft: http://www.canardzone.com/forum/showthread.php?t=1282

Jon Matcho :busy:
Builder & Canard Zone Admin
Now:  Rebuilding Quickie Tri-Q200 N479E
Next:  Resume building a Cozy Mark IV

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If I have two engines, the risk of an engine failure is exactly two times greater than if I have one engine. This isn't statistical, its math.

 

Right on, I agree 100 % with everything you said.

 

Whats the joke about twins; "Everything doubles except your airspeed". :(

As an interesting side note, one of the major reasons airlines are pushing for two engine aircraft, vs three / four engine aircraft, is the equipment availabilty percentages. It seems the three and four engine aircraft have a lower availability record than the two engine models.

 

It'll be interesting to see how the two engine Boeing 7X7 fairs against the 4 engine Airbus (380?).

 

 

Waiter

F16 performance on a Piper Cub budget

LongEZ, 160hp, MT CS Prop, Downdraft cooling, Full retract

visit: www.iflyez.com

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