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Hmmm..do you like low flying aircraft?....then here ya go!

cannonfoddertfc

cannonfoddertfc

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Another Ahab said:
What's the story on the counter-rotating prop:

- All about increased thrust/ speed?
Click to expand...
The purpose of a counter rotating prop is to allow a more powerful engine. If an engine is too powerful for the aircraft, the rotational force of the prop could twist/flip the plane. Look up the Sopwith Camel (sp?) and I don't mean the doghouse snoopy was flying. The pilots had to feather the engines up very carefully to prevent flipping the a/c over on the runway. With a counter rotating prop, you get rotational force in both directions hence negating each other (laymen's version). There are a few helicopters in existence that have counter rotating rotors (coaxial) and no tail rotor. The Ka-50 Kamov and the Ka-52, both of which are a products of the Russian military.
 
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steelypip

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Another Ahab said:
steelypip, you always know your stuff:

- Had an episode with "ground effect" years ago (or at least I think that was the term used at the time, if I remember right)

- If you don't mind, can you give a (brief) "Dumb-and-Dumber" explanation of it for a non-flyer?
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Ground effect is really simple: In level flight at altitude, the airplane maintains altitude because the wing displaces a mass of air downward at the same rate that the airplane is trying to fall. The air is pushed down and away from the airplane's path until friction damps the motion. As a matter of practice, the height of this downwash is 2-3 wingspans most of the time.

Now imagine level flight when the downwash can't go down because the wing is parallel to the ground and within three wingspans of it. Where does the air go? It can't go down, so it just stays there under the wing in a zone of elevated pressure that results in the wing having more lift than it would in free air. Sort of like a skirtless hovercraft. Low-wing airplanes like the Mustang obviously have more of this sort of fun because the wing is closer to the ground when the airplane is landing.

Now if you think this quirk could be a feature, you're right. Meet the Ekranoplan (100% low flying MV content!).

https://www.youtube.com/watch?v=V8Nu94khHoo
 
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Another Ahab

Another Ahab

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steelypip said:
Ground effect is really simple:

Now imagine level flight when the downwash can't go down because the wing is parallel to the ground and within three wingspans of it. Where does the air go? It can't go down, so it just stays there under the wing in a zone of elevated pressure that results in the wing having more lift than it would in free air. Sort of like a skirtless hovercraft. Low-wing airplanes like the Mustang obviously have more of this sort of fun because the wing is closer to the ground when the airplane is landing.
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I get it; very cool!

The episode I encountered was in a C-130 that lost power in one of the (4) engines, and the pilot feathered that prop and then took us all down just off the deck over the Atlantic, around the Carolinas. Flew like that all the way to Puerto Rico. We were probably a good 100 feet or more above the water (I'm not sure exactly), but when you looked out those portholes it seemed a whole LOT closer than that to the drink. And as long as the Loadmaster didn't get excited I figured we were all OK. But I watched him close for the first half-hour or so of it all.

And now I understand what it was all about (Loadmaster told us all, it would save us fuel and make it easier to fly on the (3) good engines we had: I get it now, thanks!)
 
M813rc

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To go back just a moment, the late model Spitfires/Seafires (Griffon engined) had contra-props to absorb the power. There were a LOT of handling issues with the ones fitted with the Griffon/5-blade setup, they were not nice to less experienced pilots (and embarrassed experienced ones on occasion!).

So, everything Cannonfodder said above, plus-

The torque from a powerful engine/prop can be more than the rudder can handle at lower speeds and it will actually pull the aircraft off to the side when you apply power to take off. You have the actual engine torque to deal with, and also asymmetric slipstream along the fuselage. Basically, all that propwash is pushing one side of the aircraft (the ground effect prevents it going all the way around). Too much power and you literally cannot go straight ahead.

In addition, the contra-rotating prop allows more blade area for a given diameter, which in the case of the short landing gear Spitfire was important. The F-4U Corsair had those long legs and bent wings mainly to allow a big prop that wouldn't hit the ground (there were also some aerodynamic benefits from fitting a wing at 90* to the fuselage).

Also, shorter blades keep the tip speeds down. Having your blade tips getting into the trans-sonic region causes unpleasant issues, and if they go supersonic, you are in for some real excitement!
Basically, think of the prop as making two arcs, one at the blade bases, one at the tips. The entire blade turns about the center point at the same speed, but the hub arc is small in comparison to the tip arc. This means that the tips have a much higher relative speed than the hubs, since they have to cover more distance with each rotation. The shorter the blade, the slower the tip arc will be.

I tried to keep it simple, so is all that clear as mud? :)

Cheers
 
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Another Ahab

Another Ahab

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M813rc said:
So, everything Cannonfodder said above, plus-

Also, shorter blades keep the tip speeds down. Having your blade tips getting into the trans-sonic region causes unpleasant issues, and if they go supersonic, you are in for some real excitement!


I tried to keep it simple, so is all that clear as mud?

Cheers
Click to expand...
The whole tip speed thing is like being the last ice skater in line playing crack-th-whip: the longer the line of skaters the rougher the position is to be in.

Totally clear, M813rc. I get all of it (that, and the other items) completely; thanks a million!


teacher-appreciation-week.jpg
 
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m1010plowboy

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Another Ahab

Another Ahab

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A good number of these videos are borderline irresponsible (and close to homicidal/ suicidal):

- and that part bothers me some (I mean in sone cases inches from tragedy/ disaster).

BUT still (an accomplice to the crime), I'm checking them all out!
 
jedawson1

jedawson1

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I shall resist the urge to prevent another from being reckless with his own life. But when he is reckless with an unwilling other, it is then I must act.

How would that apply to someone else's aircraft?
 
M813rc

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That has always been one of my favourites!

The Vulcan video above reminded me of watching the real things flying around in my youth. Sometimes age has its advantages, we got to see a lot of cool stuff over the years. :)

Cheers
 
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