Gweduck Amphibion Flight VIDEO

[Dave Krall CFII]

It's been a long haul for these guys, Congrats to them:

http://www.youtube.com/watch?v=NakXEfQcibc&feature=channel_page

 

[flyingcheesehead]

It's been a long haul for these guys, Congrats to them:

http://www.youtube.com/watch?v=NakXEfQcibc&feature=channel_page

Can't wait to see it at OSH. I'm a big fan of flying boats.

 

[wanttaja]

Stillshot:

We have our EAA Chapter officer's meeting at the hangar where they've been doing the Gweduck, so we've had a neat time watching it develop....

Ron Wanttaja

 

[docmirror]

Nice. I'm going to go out on a limb her and speculate about a design feature I see, or think I see.

It looks like the sponsons are designed to eventually retract outward to the tip of the wing and become a tip tank kind of feature. maybe with or without fuel, who knows.

 

[flyingcheesehead]

It looks like the sponsons are designed to eventually retract outward to the tip of the wing and become a tip tank kind of feature. maybe with or without fuel, who knows.

Yup. I don't know if they'll hold fuel, but they will retract to the wingtip.

That's also a feature that was available as an STC to the Grumman Goose at least, and maybe some of the others. (The Gweduck is patterned on the Widgeon.) The company that's trying to bring the Goose back is adding that as a standard feature as well.

 

[Dave Krall CFII]

BTW, Ron, Thanks for posting the original article & PIX in the EAA Chapter 26 Newsletter.

Stillshot:

We have our EAA Chapter officer's meeting at the hangar where they've been doing the Gweduck, so we've had a neat time watching it develop....

Ron Wanttaja

 

[Cap'n Jack]

Looks like it has contra-rotating props (in the stills posted in the thread). Looks like fun!

 

[flyingcheesehead]

Looks like it has contra-rotating props (in the stills posted in the thread). Looks like fun!

Looks counter-rotating to me... (Both rotating inwards).

I've heard two definitions of contra-rotating: Both engines rotating outward (so both engines are critical), or two props on a single engine rotating in opposite directions. As far as which is correct (or both?)

I've also heard that counter-rotating props hurt performance (but they do, of course, eliminate the critical engine so are good for safety) but that contra-rotating props increase it. For the life of me, I have no idea why that would be.

 

[Capt. Geoffrey Thorpe]

Nice. I'm going to go out on a limb her and speculate about a design feature I see, or think I see.

It looks like the sponsons are designed to eventually retract outward to the tip of the wing and become a tip tank kind of feature. maybe with or without fuel, who knows.

If you watch the video, the starbord float is still retracted when it rolls down the ramp into the water - results in a bit of wing drop.

 

[Cap'n Jack]

Looks counter-rotating to me... (Both rotating inwards).

I've heard two definitions of contra-rotating: Both engines rotating outward (so both engines are critical), or two props on a single engine rotating in opposite directions. As far as which is correct (or both?)

I've also heard that counter-rotating props hurt performance (but they do, of course, eliminate the critical engine so are good for safety) but that contra-rotating props increase it. For the life of me, I have no idea why that would be.

Being multi-rated I'm sure you know more than I about counter vs. contra- rotating...

My observation was merely that the propellors appeared to rotate in opposite directions.

 

[Dave Krall CFII]

Looks counter-rotating to me... (Both rotating inwards).

I've heard two definitions of contra-rotating: Both engines rotating outward (so both engines are critical), or two props on a single engine rotating in opposite directions. As far as which is correct (or both?)

I've also heard that counter-rotating props hurt performance (but they do, of course, eliminate the critical engine so are good for safety) but that contra-rotating props increase it. For the life of me, I have no idea why that would be.

The energy used in the reverse gearing of one engine eats some thrust performance from that engine as compared to the "clean" engine but that would be true in either configuration. I wonder if the contra rotation gets more air away from the fuselage drag and over the wings?

 

[flyingcheesehead]

Being multi-rated I'm sure you know more than I about counter vs. contra- rotating...

But not much, as you can tell from my own questions.

Counter-rotating is what it's called when both props rotate inward. As you know, in a climb the descending blade has a higher angle of attack, leading to the left-turning tendency. A twin with both props rotating the same direction has the same left-turning tendency.

However, counter-rotating props do two things: First, they eliminate the left-turning tendency because the two descending blades are the same distance from the longitudinal axis. (Viewed from the perspective of each individual engine, the "normal" left engine has a left-turning tendency, while the opposite-rotation right engine has a right-turning tendency, and they cancel out.)

Second, since the descending, higher-angle-of-attack blade is always closer to the center of the airplane, the turning tendencies are minimized during an engine failure no matter which engine fails. On a "normal" twin like an Aztec, both props rotate the same direction as they would on a single. Since both individual engines have a left-turning tendency, losing thrust on the right engine means that the left engine, while it's inducing a large yaw moment to the right no longer being counteracted by the right engine, also has that left-turning tendency to somewhat counteract the lack of thrust on the other side. If the left engine fails, however, you have both the thrust differential and the left-turning tendency to counteract with rudder. So a failure of the right engine will require less rudder than a failure of the right engine. (The other way to look at this is the distance of the descending blade from the longitudinal axis.) That is why the left engine is the critical engine on most twins.

On a counter-rotating plane like the Seneca (or the Wright Flyer for that matter), both descending blades are close to the fuselage and each prop's individual turning tendency will be towards the outside, so there is no critical engine.

I've heard that (due to this performance issue which makes no sense to me) some planes have props that both rotate outward, making BOTH engines critical. Highly uncommon, for obvious reasons.

 

[flyingcheesehead]

The energy used in the reverse gearing of one engine eats some thrust performance from that engine as compared to the "clean" engine but that would be true in either configuration.

I didn't think they were geared at all - It's simply a different engine (different crank) that goes the opposite direction, isn't it? For example, on a Seneca I you'd have an IO-360 on one side and an LIO-360 on the other side. I don't think the LIO-360 is geared. Ted? Bruce?

I wonder if the contra rotation gets more air away from the fuselage drag and over the wings?

I dunno. Wouldn't air going up next to the fuselage have the same amount of drag as air going down? Maybe there's a little extra wing surface on the inboard side of the propwash than the outboard, so having upwash gives it just a hair of "free" lift?

 

[flyingcheesehead]

Hell, as long as we're talking engines, props, and amphibs...

Do any of the multi-engine amphibs have reversible props for easier maneuvering on the water? Does any normal-category piston-engined airplane have reversible props?

 

[Capt. Geoffrey Thorpe]

I didn't think they were geared at all - It's simply a different engine (different crank) that goes the opposite direction, isn't it?

Camshaft.

The crank may be different because they may drill the oil passages in different places.

Starter / mags will have to be different. And the prop.

Auto company story:
Years ago, in the building I used to work in, you would just put parts out in the hall with a note that said "scrap" to get rid of stuff no longer needed. Of course, anything shiny was likely to get picked up by a passerby before the maintenance people got to it and properly disposed of it.

A guy I worked with had a prototype right hand (reverse) rotation marine cam for a 302 that he was done with. And, he had an idea. He labeled the cam "302 H.O." (high output) and set it out. 10 minutes later it was gone.

A week or so later, someone in the department gets a call. A guy had just put this new high output cam in his 302 Mustang. It wouldn't start. He wanted to know if anyone had an idea what what might be wrong.

"What are the symptoms"

"It won't fire - it just seems to go 'puh puh puh' out the carburetor."

"What's the part number on the cam?"

The guy rattles off the prototype part number for the right hand cam.

"Oh, where did you get one of those?"

"Uh... never mind. Thanks anyhow, bye."

We nearly died laughing.

 

[Ghery]

On a counter-rotating plane like the Seneca (or the Wright Flyer for that matter), both descending blades are close to the fuselage and each prop's individual turning tendency will be towards the outside, so there is no critical engine.

I've heard that (due to this performance issue which makes no sense to me) some planes have props that both rotate outward, making BOTH engines critical. Highly uncommon, for obvious reasons.

For some reason I seem to recall that the early P-38s had that problem, and that somewhere along the line they swapped the rotation direction of the props to solve that very problem. Urban legend?

 

[Cap'n Jack]

But not much, as you can tell from my own questions.

Counter-rotating is what it's called when both props rotate inward. As you know, in a climb the descending blade has a higher angle of attack, leading to the left-turning tendency. A twin with both props rotating the same direction has the same left-turning tendency.

<SNIP>

To confuse matters even more, some Wiki author claims contra-rotating props share the same axis:

http://en.wikipedia.org/wiki/Counter-rotating_propellers

 

[Cap'n Jack]

For some reason I seem to recall that the early P-38s had that problem, and that somewhere along the line they swapped the rotation direction of the props to solve that very problem. Urban legend?

A wiki author (http://en.wikipedia.org/wiki/P-38 ) claims this was done to improve gunnery- they made both engines critical!

Now why should that make a difference in shooting the guns?

 

[Dave Krall CFII]

Hell, as long as we're talking engines, props, and amphibs...

Do any of the multi-engine amphibs have reversible props for easier maneuvering on the water? Does any normal-category piston-engined airplane have reversible props?

Some SeaBees have reversible props and it's an option on various seaplanes.

 

[flyingcheesehead]

For some reason I seem to recall that the early P-38s had that problem, and that somewhere along the line they swapped the rotation direction of the props to solve that very problem. Urban legend?

The P-38 is one of the few that had two critical engines. They did rotate the "wrong" direction, I'm not sure if they ever "fixed" them. Especially if the performance differences are true, I would think not.

To confuse matters even more, some Wiki author claims contra-rotating props share the same axis:

http://en.wikipedia.org/wiki/Counter-rotating_propellers

That is one of the two definitions of contra-rotating that I've seen. I do not think it is incorrect. In fact, I think that the "outward-counter-rotating" may not actually be correctly called contra-rotating but I don't know.