topspeed

Recent FLIGHTmagazine and pusher pusher story by Peter Garrison made me think if a pusher is a "dead end" after all.

I have been very keenly developing a pusher design during last 8 years and last 5 months actively.

I got the impression tractor is more efficient if you have fuselage dia more than 50% of the prop dia.

Did anyone read the story ?

Pushpull Cessna is know to be 33% more efficient ( climb rate ) when running with pusher prop alone than in tractor mode.

The drag and turbulence and several other factors were mentioned but seems that real comprehensive data is vague. Is pusher technology still like a new frontier in aviation ?

Also the Piaggio Avanti P-180 loud noise was mentioned.

Sport_Pilot

Pusher is more efficient, but tractor has more elevator and rudder authority at low speeds.

rmh

Push me pull you is an old issue

It all boils down to trying to get a clean exit of the accelerated air
Pusher wins THAT round but unfortunately looses a number of other battles.
Once upon time I tried cmpetition pattern designs made as pushers
and dual boom and rudders
It al worked very well BUT look ed awful in flight during rolls
also maneuvers designed ar ound tractor dsigns di not work very well -
The rudder needed to be in the accelerated airstream.
very stable -no torque reaction as th prop was ON the cg. (swept wings with proplocated at the root. which was also CG)
a very interesting project at the time
Pylon mounted engines are also amongst those setups used for tractor /pusher setups
Pylon setups are lousy at best because structuraly they weigh more and thrust lines really suck
But sometimes the overall compromise is worth it -in full scale.

rmh

PS I found old pix of this stuf if anyone really cares.

combatpigg

My Feedback: (3)

I've given it a try for 1/2A speed. I run the engines on high pressure bladders, so tank position is a non-issue. Otherwise, the average sport flyer with a pusher set up has a condition where every time the model tries to climb, the fuel tank is above the engine and causes it to go rich. Exactly the opposite of what you want. To make matters worse, in a dive, the tank is below the engine and now the engine is trying to run itself into fuel starvation.
YS owners with medium pressure fuel injection need not chime in with dissenting views, you make up 5% of the general population.
Lack of prop selection makes trying a pusher set up more "trying" if you have any aspirations of finding optimal speed. Consider yourself a "propellor R&D Man" if you choose to go this route. In the speed game, nothing exists "off the shelf".
Besides speed, pusher set ups really don't have any "mission" in the model world.

da Rock

One detail that's seldom mentioned about pushers.............

When the fan is close to the wing's trailing edge, there will be an unsolvable problem.  The size of the problem depends on lots of things, but it's one reason there aren't a lot of commercially viable pushers.   The air the fan see's over the top of the wing versus the bottom is different.   Different pressure, turbulence, lots of differences.   Depending on all that stuff, and it's impact, it's often less efficient.   Sometimes it causes additional problems, like odd vibrations. 

rmh

That was not aproblem on my  pattern setup   maybe I will pull out the old pics and copy digitally
   I had very low wing loading soa very low  difference in pressures.
 The pure mechanics tho of pusher is  typically a bag of  compromise after compromise. The  Rutan stuff  was  darn good 
BUT if you flat spun those setups be preparred  to  use  the parachute.
 
 Like the  old Ercoupe 
 "you can't spin em " However if you happen to  spin one - get out.

larrysogla

Gentlemen,
With all the research done and being done on very high tech military and commercial propeller driven aircraft, it is the overwhelming predominance that the choice by a huge majority is the "TRACTOR" propeller configuration. This alone says something about "EFFICIENCY" of the tractor configuration since military and commercial aircraft are always focusing on efficiency for speed and range. It is must be the "clean" air encountered by the tractor prop versus the "dirty" air (airframe induced turbulence) encountered by the pusher prop. The prop is a very high speed airfoil and it thrives on clean air hitting the prop blades for maximum efficiency. The monstrous B-36 bomber and the UAV Predator are the notable pusher military designs that went into full production for the military. Everything else are tractor props including the fastest propeller driven WWII fighter which is the XP-47J with a top speed of 505 mph. Tractor props dominate in both military and commercial designs due to inherent efficiency and ease of airframe accomodating the forward mounted engine.
Thanks
larry

HighPlains

My Feedback: (1)

The pros and cons on this subject have been debated for years.

Pros for the pusher
- the fuselage is working in clean air, so it is easier to have laminar flow for low drag.
- the high speed air from a prop (about 10% faster than the airspeed of the airframe) is not going down the fuselage for lower drag too.

Cons for pusher
- prop working in dirty air, with uneven pressures so efficiency goes down
- need really long heavy landing gear or you can not get down to stall speed for landing.

Pros for the tractor
- best performance from prop
- turns out that the air from the prop tends to go laminar between mini wakes of turbulance from the prop.

All the really fast prop airplanes have always been tractor designs.  Nothing likely to change.

topspeed

If you study history of aviation really carefully this is not quite true. But I agree that the "absolutely" fastest is not likely to be a pusher (for various reasons ), but most economical it could be.

1. New Avanti Piaggio goes 740 km/h (name a faster turbo prop passenger craft )
2. Learfan 2100 was more economical and faster than Citation I Bizjet
3. Mixmaster did the same as B-17 but with 2 engines and was 100 mph faster
4. Edson Fessenden Gallaudet flew 130 mph in 1912 with a pusher.

I could also mention that Lars Giertz whose VMax Probe was demolished in testflite mentioned his plane could go(calculated estimate )240 mph at 50 hp and was after 300 mph at 80 hp.

I do appreciate your input..there is lotsa variables to consider. Also the Molt Taylor dream of a really economical pusher Micro Imp never realised it became 240 kilo plane. Jerry Holcomb was able make a one (Perigee )at 166 kg.

I think to accelerate the flow at fuse and reduce drag the fuse would have to be really clean and the turbulent air to the prop would have to come somehow projected evenly pressurewise...you know what I mean ? This is why I have the wing throwing the "turbulence" middle of the prop arch in my MAX III. The fan/prop would then have to deal with this wash as efficiently as possible. new ellipse prop for instance could have an answer.

I think the biggest obstacle in pusher systems so far is the cooling and maintenance of the engine. (Second is the CG management..they tend to be tail heavy ).

More about my pusher here: http://max3fan.blogspot.com

topspeed

I think you have a point, but also a pusher has the suction caused power steering option..not many realize that!

canardlover

Topspeed wrote....but also a pusher has the suction caused power steering option..not many realize that!

That sounds interetsting but please elaborate a bit on the subject, I am not sure I get the point.....thank you....Cheers/Harald

andrew66

I honestly think that the reason that pushers got sidelined was safety.  I read a magazine that was stating that the first planes (mostly pushers) had a tendancy of killing pilots cause when the plane crashed, the engine would break loose and crush the pilot.  Once the engines were mounted up front, that problem went away.  Since then, most all planes have been built around the tractor prop.  I personally think that if that original problem didnt exist, we would see alot more aircraft with pushers. 

Lnewqban

You really love those canards, Canardlover!!!

It seems natural for canards to have pusher power plants, just for a logical distribution of weight in order to achieve balance.

Don't you have cooling problems with those engines out of the propeller's blast?

Villa

Hi lnewqban
I have been flying my SPAD Pusher Canard for over five years with an OS46FX engine. The engine will overheat on the ground, but not in the air. To tune the engine I replace the pusher prop with a tractor prop of the same diameter, pitch, and make. Once the engine is tuned, I replace the prop with the pusher prop. I always get the plane into the air within 1 minute of engine start to prevent overheat. Same engine over 5 years. You can see my plans in the SPAD section below.

Avaiojet

I owned a Lake LA4-200T for years. Put 377 hours in it. Before that a Piper 180. The Lake out performed or was just as airworthy as the 180.

See if I can dig up a photo.

Charles

HighPlains

My Feedback: (1)

Comparing apples and oranges make it impossible to decide which configuration is best. What is needed is a set of design parameters that a design must use in order to decide what works. If the same engine, wing area and weight were part of the design requirement then which is faster?

Well, there is an event that has been santioned for over 60 years. Formula One or Goodyear as it was known in the early years. While there have been several pushers racing at different times, tractors have always dominated the event. If pushers were best, then that is what the racers would run. While the Pushy Cat did win Reno one year at 237, the Nemesis clearly out ran the design on the race course. Off the pylon course, the Nemesis held one record of 290 mph.

wellss

One of the main differences is the effect on pitch stability. Tractors are destabilizing, and require greater stabilizer surface with less control power. The opposite for pushers.

Thrust decreases with speed and so in theory, a pusher should be able to operate at greater efficiency if the air entering the propeller is slowed down, albeit smoothly, rather than turbulent.

TFF

http://www.sikorsky.com/vgn-ext-temp...extfmt=default

We have at the airport 2 Cirrus VK30s one with the prop knocked off; its a total. It has a tubine the other has a liquid cooled Voyager. Not the plane for the average pilot; over rotation and no prop. I also know that the PT6 exhaust kills the Piaggio props. Vari-Easy like planes are a little better because the moment of the engine is closer to the cg so the prop has better ground clearance when rotation is taken into account.
I have always liked pusher planes but they have to be perfect in plane and pilot to get out the performance. A tractor plane is easer to get good performance without being good.

Piaggio stayed in business by making the Vespa scooter; their engineers are a little crazy.

da Rock

It's hard for a pusher to match a tractor simply because of one thing. The pusher prop is almost always going to have a fair amount of the air that's presented to it affected significantly by some structure or another. Put the prop directly behind the wing and the better part of the fan area right through the hub is going to be really messed up, turbulated/slowed/etc. Draw a rectangle right through the middle of the prop's available area and that's going to basically be screwed up air. And the area above that rectangle is going to have whatever it gets from above the wing. The area below will see something different from below the wing. Hang that pusher out on a nacelle on a stalk and you can reduce that disturbed air, but it'll never be like a tractor sees.

Doc.316

I have to say that it depends on the installation. A pusher instalation has problems cooling. (Look at the big scoop on the 337). So it will have more cooling drag. The pusher has less drag on the airframe since the local airflow behind the prop is speeded up and then blows over the airframe on a tractor. I believe that a pusher will be more efficient IF the instalation is good. This is very hard to do. I believe there have been a couple of airplanes that have really tried to come up with a nice installation. The xmc was one the prescott pusher was another.

Oh, BTW I am not saying that it is practical in real life. If you look at most of the commercial airplanes (FAR 25) that have tried the pusher installation they have all had problems with certification and were commercially impractical. A few examples are the lear fan and the beech starship, come to mind. The piaggaio while it is a cool airplane probably fits in there also (am not sure if they have made money on them or not) Far 23 powered planes haven't faired well either really. The 337 is a cool airplane but it had many cooling problems, people taking off with the rear engine not running etc.

Steve

topspeed

Right..but this would have to be considered and not just built "a strange tractor plane with prop in the rear pushing". You see/know what I am after ?
Like golf swing..gotta consider all variables to execute a perfect stroke and make a double eagle.

da Rock

And example of your problem:
This chosen example includes a quite disruptive variable that has nothing to do with comparing pusher vs tractor. It really doesn't take into consideration the presence of the non-working prop in each case and it's effect. They are variables that affect the outcome. It's just as probable that the rear prop being feathered creates significantly more drag than the front being out. Drag is just as important as lift as important as thrust as important........

You don't make a double eagle with just your drive, or your approach, or your putt.
But are you after a lower score or a longer drive. The Cessna achieved a lower score with two engines on the same line. It isn't faster (drives the golf ball farther) with just one engine is it? If you wish to consider all things, then consider that the pusher receives disturbed air no matter what. The Cessna example actually does suggest something to that idea. Very disturbed air to the pusher really screws up the efficiency of the climb and evidently operating the front alone isn't as efficient as the rear alone IN A CLIMB. Disturbed air increasing drag appears to be a significant problem with a pusher. And that can cause problems. Be prepared.

It would be interesting to see where you are in your years of development. Any pictures? And experimental results?

Sport_Pilot

Don't you mean effectiveness? Were we comparing fuel usage between front and rear engines? Unless we do we do not know which is more efficient. The front engine could be using much less fuel and thus more efficient even if the climb rate is worse. IMO many here confuse the heck out of me when they say something is more efficient when they should say effective.

da Rock

OK effectiveness.

But efficiency is perfectly accurate. A more efficient aerodynamic package usually does whatever the pilot is asking better. For example, a cleaner trimmed airplane will have less drag and usually more speed. So the pilot backs off his power or allows the extra speed. If he backs off the power he'll probably get better economy (the term for efficiency in fuel use), but not always.

An airplane that climbs more efficiently (less drag) usually climbs faster. If it climbs faster with one engine out, that out engine's added drag is causing far less drag than whatever is hurting the climb rate when the other engine is the out engine. Is it efficiency or effectiveness? You're right, I should have used both words in spite of wishing to point primarily to the drag problem.

A wing that creates the required lift with less drag is more efficient. The P51 carried more weight faster than (pick another airplane) because it was more efficiently creating lift/drag. An airframe configuration (trim settings) that creates less drag and more speed or climb is more efficient but not always more economical.

BTW, running one engine versus two might be more economical as well. But economy isn't the issue.