another e plane upstart

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What a great name for a company involved in electric aircraft, "Eviation"! I saw this on one of the flying forums I'm on, and I at first had a hard time finding the means of propulsion as the picture was small. OK, pusher prop in the tail, nothing new there.....but two additional props out at the wingtips? That's never been done, mostly I believe because of an engine out causing huge yawing issues. In fact most twins have the pwoerplants as inboard as possible just for that reason. More thinking outside the traditional aviation box, thanks to the e evolution. I'd suspect the concept, the tip props, was NOT dreamed up by an old school aero guy, but maybe by a design team member taking a fresh look at things. The wing itself is smooth and uncluttered, clean as hell. https://www.eviation.co/

I've mentioned before here I think, that I happen to know a guy who is known as "Mr. Winglet" in the aviation world, his company has their winglets on all Boeing aircraft and many others. A big time aero genius heading a multi million dollar high tech company, he has a ranch in my state where he goes to unwind, with an airstrip and I fly in there in my lowly homebuilt from time to time. I want to mention this plane to him, and ask him how the props out at the tips would effect the span wise flow/wing tip vortices, and then stand back as his head explodes. :twisted:
 
Continuous and max power ratings being what they are I wouldn't be too surprised if they are planning on a "emergency power" feature so the thing can climb with just the rear motor for a short period if there's trouble on takeoff, or maintain altitude for a while if there's a problem in flight.

I'll check it out in x-plane and see how it flies.
 
The Dornier Do-335 "Pfeil" (Arrow), had a tail propeller, and they added vertical fin under the tail to prevent accidental ground-strikes (during takeoff/landing). Much cheaper to replace a fin-tip than a bent propeller...just a thought...
 
craneplaneguy said:
What a great name for a company involved in electric aircraft, "Eviation"!
I note that in one of the pictures, they have two Tesla Smart modules wired up on a table. Gotta start somewhere.
I saw this on one of the flying forums I'm on, and I at first had a hard time finding the means of propulsion as the picture was small. OK, pusher prop in the tail, nothing new there.....but two additional props out at the wingtips? That's never been done, mostly I believe because of an engine out causing huge yawing issues.
That's true in conventional aircraft, but with the level of control you get with electric you could throttle back the other engine instantaneously if yaw exceeds (for example) 20 degrees. Thus you don't see a huge yaw excursion, and you get the power back as soon as you add rudder.
 
The broader engine pattern might be to circumvent the pfactor of the pusher motor. Trimotors have a problem, especially when the lone opposing spin motor stops.

A broader wingspan is like a long handled wrench, it gives greater power to control surfaces. So I might theorize two low power motors opposing the high pwer pusher.

images
 
Dauntless said:
The broader engine pattern might be to circumvent the pfactor of the pusher motor. Trimotors have a problem, especially when the lone opposing spin motor stops.
This would have the same problem. If all the props are rotating in the same direction, they all contribute to P-factor turning; putting the props far out on the wing doesn't help. In any case, P-factor is just one of the four effects that cause turning in conventional propeller aircraft, and is only an effect at high angles of attack. It is not unique to pushers, and in any case is less of an issue for tricycle gear aircraft (which this has to be due to the pusher prop.)
A broader wingspan is like a long handled wrench, it gives greater power to control surfaces.
Nope, not unless the prop is directly ahead of said control surface. However, putting the engines further out on the wing _is_ like a long handled wrench, and will tend to increase the authority of any asymmetric thrust, and decrease the (relative) authority of the rudder to counteract it. In fact, by moving the props far from the rudder, you also reduce the authority of the rudder by reducing airflow over it. That's why many World War II aircraft (with large engines, and thus large propellers, for the time) went to twin tail designs - to move the rudders, and vertical stabilizers, back into the prop's airflow. That way the huge amount of adverse yaw during an engine out could be handled with opposite rudder on the vertical stabilizer behind the remaining engine.
So I might theorize two low power motors opposing the high pwer pusher.
They would not oppose the turning tendency of the high power pusher unless they were rotating in the opposite direction. There are, of course, other advantages.
 
billvon said:
craneplaneguy said:
What a great name for a company involved in electric aircraft, "Eviation"!
I note that in one of the pictures, they have two Tesla Smart modules wired up on a table. Gotta start somewhere.
I saw this on one of the flying forums I'm on, and I at first had a hard time finding the means of propulsion as the picture was small. OK, pusher prop in the tail, nothing new there.....but two additional props out at the wingtips? That's never been done, mostly I believe because of an engine out causing huge yawing issues.
That's true in conventional aircraft, but with the level of control you get with electric you could throttle back the other engine instantaneously if yaw exceeds (for example) 20 degrees. Thus you don't see a huge yaw excursion, and you get the power back as soon as you add rudder.

Yes indeed, I was thinking the same, and why they thought they could use that design, could "get away with it!". That type of "new" thinking possible with electric powerplants, combined with old school aero thinking, is what I find so interesting as e planes are fine tuned. I love the concept of "distributed thrust", not really a viable concept when designing around conventional ICE powerplants. I can even see some kind of aux cross wind control, perhaps computer controlled, using those two tip motors, nothing new about that, but they would open new ways to use that capability perhaps. Single engine pilot here, mounted right in the center, so just guesswork!
 
Dauntless, I don't remember the Caproni Ca-5, thank you for that. The Ford "Tri-Motor" became famous during a certain era, but the benefits of a Caproni Ca-5 would have appealed to me...
 
Two considerations I can think of with the tip mounted motors:
-reduced intersection drag.
-you can use the prop tip vortices to counter the wingtip vortices, potentially.

Otherwise it would be horrible under asymmetrical power and the tail prop doesn't seem brilliant either. Taxiing it would be extremely stressful with those props out there.
 
billvon said:
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Nope, not unless the prop is directly ahead of said control surface.

Did you even read what I wrote before you responded? Why would you say opposing are rotating in the same direction?

I'll repeat one thing you really got wrong. The longer the wingspan, the greater the inertial moment. No motor necessary. Gliders, etc.

But I'm sure the guy designing it can give a much better explanation than some troll. 50-50 chance, but we got the wrong one.
 
Dauntless said:
I'll repeat one thing you really got wrong. The longer the wingspan, the greater the inertial moment.
Of course - which is the opposite of what you said. A greater inertial moment makes it harder, not easier, for ailerons to cause a certain roll rate, due to the larger inertial moment. (Which is why aircraft designed for aerobatics tend to have short wings.) The other control surfaces are not affected.
 
craneplaneguy said:
Yes indeed, I was thinking the same, and why they thought they could use that design, could "get away with it!". That type of "new" thinking possible with electric powerplants, combined with old school aero thinking, is what I find so interesting as e planes are fine tuned. I love the concept of "distributed thrust", not really a viable concept when designing around conventional ICE powerplants. I can even see some kind of aux cross wind control, perhaps computer controlled, using those two tip motors
Indeed. After the DC-10 Sioux City crash, several people proposed a secondary control system that used differential thrust to control an aircraft that had lost all control surfaces.

https://www.nasa.gov/centers/dryden/pdf/88414main_H-2048.pdf
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000025333.pdf

It would be very cool to see what could be done with today's computing power.
Single engine pilot here, mounted right in the center, so just guesswork!
I have just enough twin time (~25 hours) to be dangerous. The first time we did an engine-out drill in a Twin Otter, the force on the rudder needed to keep the thing flying straight was startling. Suddenly I understood the "dead foot, dead engine" rule a lot better.
 
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