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Traveling with a twin engine 2 stroke airplane?

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Wanttaja

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'nother thought I had was overlapping the props so the thrust centerlines are closer to the centerline of the aircraft. I was looking at a Beech Starship when I thought of that. Extend one of the prop shafts and the distance between the prop centerlines can be reduced about 40%.
Well, there are the various Wagner twins, of course.
1606679092601.png
You can just make out the spacer on the left engine that gets the prop a bit further forward than the one on the right.

Haven't heard any sort of aeronautical analysis of this system, but suspect the overlap area has some horrid effects.

Wagner also just strapped two fuselages together, too....
1606679150841.png
Ron Wanttaja
 

mwflyer

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This is true, but let's not forget that 93 years ago piston engines in general were EXTREMELY unreliable. Lindbergh knew that his engine would work only for a limited amount of hours, pretty much irrespective of how much fuel he had or how carefully he managed it.
One of the things that contributed to Lindberg's decision was that the Wright Whirlwind was the first aero engine with a published TBO. About 500 hours IIRC.
 

blane.c

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That is about the reliability I would expect from most of the better options under 50hp that people seem to be considering, and most people not trying to do a stunt (like crossing the Atlantic solo) would be better off with multi engine options considering there engine options. In my opinion.
 

Dana

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Ironically, I've got a 1984 Nissan pickup truck with dual ignition. Two spark plugs per cylinder, two coils, but a single distributor.
We had one of those. I presume it was for emissions or fuel economy, not any reliability considerations... though its last ride, when I drove it to a junkyard with a thrown rod, was epic!
 

rv7charlie

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The thread title is *traveling* with 2 strokes. I confess to just doing a very quick scan of all the posts, but didn't see the unavoidable reason to avoid the idea, even if 'reliability' wasn't an issue. It's fuel consumption. 'Traveling' implies, well, traveling. We're always wishing for more fuel in our 4 stroke traveling a/c like RVs, etc; can you imagine the reduction in 'travel-ability' with 2 2strokes instead of one 4 stroke? The closest real world comparison would probably be a pair of Rotax 503s vs a 912. Roughly the same HP; roughly twice the fuel burn with the 503s.

Unless you're talking about a 2 stroke turbo-diesel optimized for aviation, fuel burn alone is a show stopper.

Charlie
 

blane.c

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The thread title is *traveling* with 2 strokes. I confess to just doing a very quick scan of all the posts, but didn't see the unavoidable reason to avoid the idea, even if 'reliability' wasn't an issue. It's fuel consumption. 'Traveling' implies, well, traveling. We're always wishing for more fuel in our 4 stroke traveling a/c like RVs, etc; can you imagine the reduction in 'travel-ability' with 2 2strokes instead of one 4 stroke? The closest real world comparison would probably be a pair of Rotax 503s vs a 912. Roughly the same HP; roughly twice the fuel burn with the 503s.

Unless you're talking about a 2 stroke turbo-diesel optimized for aviation, fuel burn alone is a show stopper.

Charlie
Not necessarily.

While personally not a avid two stroke fan they can be reasonable in fuel consumption when the throttle is backed off a tad like in cruise, also they are considerably lighter than four strokes of the same hp in the smaller engines so you could offset the weight reduction with fuel and if that is within your goal of time/distance they couldn't be ruled out for the fuel consumption reason.
 

blane.c

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Well, there are the various Wagner twins, of course.
View attachment 104736
You can just make out the spacer on the left engine that gets the prop a bit further forward than the one on the right.

Haven't heard any sort of aeronautical analysis of this system, but suspect the overlap area has some horrid effects.

Wagner also just strapped two fuselages together, too....
View attachment 104737
Ron Wanttaja
A more modern adaptation;
1606748547902.png
 

blane.c

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Site for article and more pictures.

 

blane.c

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Voyager was a stunt, applications of things used in a stunt are not necessarily advisable for everyday use, like for instance a planned engine shutdown. The problem then is something goes wrong with the engine that is supposed to be running and now you have two problems, shutting down and/or "babying" the supposed to be used engine and starting up and bringing on line the supposed to be auxiliary engine which may be cold soaked and in need of a period of time to warm-up before being fully brought on line.

I would term it "engine mumblypeg".

 

BBerson

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Total engine failure shouldn't be an issue after climbing to cruise altitude in most developed rural farm areas. Leave both engines running when crossing the strait or forest or city. I wouldn't restart in flight. The boost engine is like jato assist on first climb only.
 

EzyBuildWing

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New Rotax 582 2-strokes now come with improved spark-plugs ...they're the same plugs as they supply in their 4-strokes.
Maybe having 4 spark-plugs per cylinder and 4 separate ignition-systems to fire them would make the 582 more reliable?
De-rate it to say 14cc per HP ( 42HP ) so all the mechanicals are under-stressed and loafing, and the only potential problem-area remaining is fuel.
The mechanical simplicity of the 2-stroke is beautiful.

 

BBerson

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Running a 582 direct drive is the same as derating. I estimate about 40hp at around 4500-5000 with correct prop.
Direct drive is simpler for something low drag and faster than an ultralight.
 

Wanttaja

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New Rotax 582 2-strokes now come with improved spark-plugs ...they're the same plugs as they supply in their 4-strokes.
Maybe having 4 spark-plugs per cylinder and 4 separate ignition-systems to fire them would make the 582 more reliable?
Quick look seems to indicate that ignition systems aren't the problem. Out of 116 engine-failure accidents involving Rotax two-stroke engines (1998-2018), only six were related to ignition. In comparison, there were 27 involving internal mechanical issues (seizing, broken crankshafts, etc.).

Ron Wanttaja
 

ragflyer

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Quick look seems to indicate that ignition systems aren't the problem. Out of 116 engine-failure accidents involving Rotax two-stroke engines (1998-2018), only six were related to ignition. In comparison, there were 27 involving internal mechanical issues (seizing, broken crankshafts, etc.).

Ron Wanttaja
Hi Ron! Are you able to tell how many failures where related to 582? Perhaps even what percentage of accidents that involved 582 where engine related. I suspect its somewhere between 4 stoke (18%) and generic 2 stroke (36%) rate that you derived, though the data set may be very small.
 

EzyBuildWing

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582 mechanic diagnoses a 582 engine failure....vid below.
Maybe filtering gasoline through a Chamois filter is worthwhile.....
Chamois was historically used as a gasoline filter.[13] When soaked with clean gasoline, chamois will not allow water to pass through its surface fibers.
This property is used to filter fuel that has been stored in drums prone to ingress of water, or from any other doubtful source. The technique is to provide a large-mouthed funnel with a wide outlet surface that supports a woven wire base, or metal plate with a grid of holes. The lower part of the funnel is tapered to fit the receptacle or tank-filler aperture.[14]

A suitably sized chamois skin is soaked in clean fuel and placed over the grid in the funnel and brought up the sides, forming a bowl, to prevent any leakage past the skin. Fuel can then be pumped into the top of the funnel by the fuel dispenser and watched for signs of water accumulation. The process can be stopped to lift out the assembly from the tank and the trapped water removed so that the job can be continued. Chamois leather is used thus as a fuel filter by boaters,[15] auto detailers, and aircraft refuellers, particularly of a past age when aircraft were flown into very remote areas.

Anyone heard of a direct-drive 582?
Would be an interesting concept!
Gyros with "72 HP" McCulloch 2-strokes typically spin 50" x 28" props and get 260lbs static-thrust at 3500 RPM

 

Wanttaja

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Hi Ron! Are you able to tell how many failures where related to 582? Perhaps even what percentage of accidents that involved 582 where engine related. I suspect its somewhere between 4 stoke (18%) and generic 2 stroke (36%) rate that you derived, though the data set may be very small.
Got 67 power-loss accidents with Rotax 582s. The Rotax 582 does come out a bit better than the overall two-stroke results; about 32% of 582-powered aircraft accidents are engine related. Here's the breakdown as to causes:
Cause​
Count​
Undetermined​
28​
Engine Internal​
19​
Fuel - Engine​
3​
Fuel - System​
5​
Ignition​
2​
Reduction Drive​
4​
Oil Delivery​
0​
Carb Mechanical​
3​
Cooling​
3​
Three out of the four "Reduction Drive" cases were for belt reduction drives, not the Rotax gearbox. The fourth was due to corrosion in the "Power Takeoff Bearing" which may actually be on the engine itself.

"Fuel - Engine" is problems with the fuel system inside the engine compartment, while Fuel - Systems is for fuel delivery problems within the airframe. I do lump those in with the engine-related cases.

Ron Wanttaja
 

aeromomentum

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I have always be amazed at the high failure rate and short life of 2 strokes in aircraft (and snowmobiles). While 2 stroke outboards seem to have a higher failure rate than 4 stroke outboards, they seem to be an order of magnitude more reliable and longer lived than 2 stroke aircraft engines.

Running an engine direct drive may be a usable solution but it is not the same as derating. In fact it can actually increase stress on the engine if the BMEP is higher at that RPM. Plus faster turning props are less efficient and smaller diameter props are less efficient.
 

Wanttaja

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Do you like the 582?
"Like." Hmmmm.

When I put my data analyst hat on, I see that the 582, like other two-strokes, has a higher rate of engine failure than traditional engines, as well as higher than new-technology four-stroke aircraft engines like the Rotax 912. This I do not like.

When I put my EAA hat on, I recognize that the power-to-weight ratio provided by two-stroke engines has led to the development of some very good light aircraft. I like that. We wouldn't have the Kitfox, for instance, without two-stroke engines, nor most of the ultralights nor the ULs that have morphed into Light Sport Aircraft. These are also slow, light aircraft that have a better chance for a successful forced landing after an engine failure.

When I put my Fly Baby hat on (I own a ****-load of hats), I feel that the 582 is not suitable; it's TOO light and the CG issues, while not insurmountable, are a lot more problems than putting a 70-year-old Continental on the nose. That I do not like.

Earlier this year, I got asked about putting a 582 in a Fly Baby. Here's part of my response:

"There are guys who successfully and safely operate two-stroke engines, and do so for years. But while they might be expensive to maintain, and PIA to hand-prop, the little Continentals don't seem to be as "delicate." The average Joe seems to be able to keep them running, more than they can the two-stroke engines.

"So if you do it, you REALLY have to pay attention to the engine."
1606927659224.png
Ron Wanttaja
 
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