FLYING WINGS / Tractor VS pusher / Marko's vision

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nestofdragons

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Jun 8, 2016
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305
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Near Antwerp, Belgium
Hello,

i just want to share why i once changed my own project from Pusher to Tractor. The reason was this reasoning of Marko Stamenovic, a rising star in flying wing world in my point of view (just ask Albion Bowers to say i am right)


Moving engine to tractor position ->Engine mass is at front, no need to put pilot in front of CG in order to balance aircraft. No need for ballast. ->Easier to accommodate pilots of different mass since pilot can be closer to CG ->Due to moving pilot to CG, fuselage can be moved to the back also, easier to design it to contribute to directional stability, lower interference drag with wing due to better aligning of pressure gradients, Sleeker look since rear part isn't cut off ->No engine at back means that fuselage can be narrowed in clean manner. It can end like vertical tail compensating yaw instability of tractor configuration without drawbacks. No need for spoilers. This structure can be quite light and with lower drag.
->Propeller works in better airflow giving around 15% more efficiency ->Better propeller efficiency leads to less fuel needed (12- 15% less). Airplane is lighter and wing area can be probably reduced a few %. ->Slight possibility to use bigger propeller, giving a little bit better performance. No chance of propeller hitting the ground on take off and landing. ->Prop can be placed closer to vertical position of CG, meaning less pitching moment with throttle change.
->Engine cooling produces less drag and provides better cooling at taxi, it is simpler to make and would be lighter. For pusher you need to design more complex cooling system which satisfy taxi and climb requirements. Motor mount is smaller. ->Central flap is possible giving higher Cl (6-7%) which can reduce wing size. With pusher and cooling system being at the bottom (the best place) it is not possible to position central flap there. ->Central flap would be blown by propeller increasing lift while flaps in front of pusher prop reduce efficiency.
->Mass is better balanced around main frame (connecting forward spars) in the fuselage, there is engine at the front and pilot at the back. With pusher everything is at the back. Balanced position gives more compact and probably lighter structure. ->No need for strong structure behind the pilot to support motor mount which would be connected to the strongest part of the aircraft - main frame in the fuselage.
->Nose landing gear can be made a little bit shorter depending on desired angle at the ground and prop size. ->Rear landing gears can be made considerably smaller since they don't need to provide ground clearance for propeller. they can be moved even further to the back and made even shorter if airplane is set at take off angle. Lighter and more compact solution.
->Ballistic parachute can be placed in the more rearward position with improves opening and there is no risk of parachute catching propeller.
->There is no need for special handling on the ground since engine is at the front and airplane won't tip over to the back when pilot is not in the cockpit.


Conclusion: By changing rear part of the fuselage yaw stability is provided to compensate instability added by tractor engine. Spoilers are not needed any more since rudder can be installed on fuselage. This is done without any drawbacks, on the contrary: drag is reduced considerably and prop efficiency increased, mass is the same or lower due to fuselage change. this leads to less fuel needed, size of the airplane can be probably reduced or less fuel can be used for the same range. Structure is more efficient, landing gear is smaller, possible better flaps. Safer parachute operation. Cooling is better and gives less drag. Safer ground handling.

this concept works for smaller flying wings where central fuselage must be provided to accommodate pilot. If airplane is bit enough to have aerodynamically integrated cockpit pusher is probably better option.

DRAWBACKS: Pilot is more to the back leads to slightly worse downwards visibility, solvable with bottom windows, no worse than on Verhees Delta. Unconventional solution for flying wings.
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I am curious how this forum will comment on Marko's point of view.
This model shows a bit what Marko has in mind. The 3D next to it was the project as we first thought it would be. It looks hot, sexy, but ... i really love the advantages of the tractor even more.

IMG_8078.JPGIMG_8081.JPG
 

Hot Wings

Grumpy Cynic
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Lots of valid (and some semi-valid) points. For some of us the superior view of the pusher means that we will put up with the disadvantages. We fly for the fun, not the efficiency. For a point A to point B plane or one used in some form of competition then the tractor may be the better compromise.

Just my opinion...........
 

Sockmonkey

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Apr 24, 2014
Messages
1,880
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Flint, Mi, USA
Lots of valid (and some semi-valid) points. For some of us the superior view of the pusher means that we will put up with the disadvantages. We fly for the fun, not the efficiency. For a point A to point B plane or one used in some form of competition then the tractor may be the better compromise.

Just my opinion...........
Quite a few designs have an opaque nosecone that blocks almost as much of the forward view as the engine would.
 

Riggerrob

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Sep 9, 2014
Messages
1,448
Location
Canada
Tractor allows tiny tail wheels (see Verhees Delta). This allows designer to set ground angle (at rest) at the same angle as optimum take-off angle. One Dyke Delta pilot reports that he just advances the throttle and the Delta takes-off by itself. That angle is pretty much the same as the best angle for landing.
Fixed angle of attack also limits pilot from getting too deep into the drag bucket, because when delta wings get to steep, their massive leading edge vortexes generate massive amounts of drag. Even the Concorde SST did not have enough thrust to "power" its way out of the low speed, high A0A, low altitude corner of the envelope.
There are two ways to improve visibility - in a tractor delta. First, install clear panels in the cockpit floor (see Verhees Delta and Pitts Special.) Secondly, hanging the pilot under the wing allows great visibility downwards but negligible visibility upwards ... like most Cessnas. The real question is whether a high-wing delta will allow the pilot to keep the runway in sight while doing that last turn onto final approach (my pet peeve about Cessnas).
 

nestofdragons

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Jun 8, 2016
Messages
305
Location
Near Antwerp, Belgium
I experimented a bit with bad forward view in flying wings and ... the system of Lindberg still works. Periscope! You only have a small bubble at the underside of wing. And it gives you the impression as if you look right through the spar. If interested i will post the youtube of this test.
 

berridos

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Joined
Oct 10, 2009
Messages
928
Location
madrid
Those deployable wingtips should work only at low aoa. I guess at hight angles where eddies are intense, they should be blanketed by the le. Would be interesting to test them under more aggresive conditions than a glider.
Their function is to suck the eddies and stretch them along the le?
 
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