Tractor vs. Pusher?

Discussion in 'Firewall Forward / Props / Fuel system' started by BDD, Apr 24, 2005.

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  1. Apr 24, 2005 #1

    BDD

    BDD

    BDD

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    What are people's opinions of tractor drive engine/ prop installations vs. a pusher configuration?

    One thing that's always bothered me about the pusher config. is what could happen and where would the engine go in a crash landing?

    Still, that is sometimes the cleanest configuration for drag, etc.
     
  2. Apr 24, 2005 #2
  3. Apr 24, 2005 #3

    Waiter

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    Good read on the above links. With one minor difference of opinion. Looks do matter. If it didn't, we would all be driving the same make and model car

    I'd like to think of most of these as "Peculiarities". HOWEVER, There is one that I would definitely consider as an advantage/disadvantage, because it would be a decision factor to fulfill a mission requirement. That would be the pushers performance on soft/unimproved fields. If I was doing a lot of this sort of flying, the Tractor would be a better choice.

    I'm not considering planes like "Breezy" or "Lake Amphibian" in the comparison.

    My experience with pushers is limited to Canard, EZ's and a Cessna 337.

    I also throw in a couple Canard Specific. (These wouldn't apply to conventional winged aircraft that are pushers)

    PUSHER ADVANTAGE

    Quieter - MUCH quieter.

    P factor = ZERO. No prop wash pushing against the side of the rudder.

    Cooler passenger compartment, no heat from engine (warm outside)

    Cleaner aerodynamic lines.

    Improved visibility over the nose.

    No prop standing still at night time with strobes.

    Engine fire less likely to penetrate passenger compartment.

    Engine leaks, i.e. oil, exhaust, less likely to enter passenger compartment.

    More "Jet" looking. YES LOOKS DO COUNT.

    (CANARD ONLY) STALL PROOF - Cannot be stalled, cannot be spun.

    (CANARD ONLY) Roomier cabin - No Wing spar going through middle of Passenger compartment.

    (CANARD ONLY) Smoother ride - Rides turbulence significantly better than conventional.

    PUSHER DISADVANTAGE

    You can't "Cheat" the airfoils into thinking their at flying speed. In a tractor, you usually have full elevator / Rudder authority just by applying full power, This is known as "prop wash". "Prop Suck" from a pusher doesn't achieve the same result. (Sounds like I just invented a new aviation term to be used by pushers)

    Anything that comes off the aircraft, nuts, bolts, rocks, stones, goes through the prop. (My personal favorite is an "exhaust valve", BTDT).

    If something is leaking from engine. You must rely totally on instruments for the fault indication, as there is no visual indication.

    Cooler passenger compartment, no heat from engine (cold outside)

    (CANARD ONLY) STALL PROOF - Cannot be stalled, cannot be spun. Cannot perform these types of maneuvers (I like acrobatics)

    OK, This is my list, and its by no means complete.

    Waiter
     
    Last edited: Apr 24, 2005
  4. Apr 24, 2005 #4

    Waiter

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    One thing that's always bothered me about the pusher config. is what could happen and where would the engine go in a crash landing?

    Without going through and researching actual accident reports. I would venture to make an educated guess:

    If you can find comfort in this statement; In a 100 Kt crash, you'll be dead from major trauma (sudden stoppage) well before the engine hits you in the back (60 milliseconds later).

    Look to the automotive industry for crash survivability information. I think their numbers suggest anything above 30 - 50 mph is usually the limit on survivability, and thats with vehicles that are specifically designed to maximize survivability, i.e. air bags, crumple zones, roll cages, door reinforcements, etc. and thier initial impacts are almost always horizontal (MAJOR FACTOR in aircraft survivability).

    I would guess that in the majority of accidents, it doesn't make a difference. However, I also bet that in those rare few where it could have made a difference, the tractor would be "marginally" safer than the pusher.

    Your mileage may vary.

    Waiter
     
    Last edited: Apr 24, 2005
  5. Apr 24, 2005 #5

    BDD

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    I'm thinking of a slower but serious forced landing were many things could happen. If the engine came loose it would be a serious problem for the pilot one millisecond later. With a tractor airplane if that happened it wouldn't necessarily be heading in your direction. Engines have also come loose when a prop blade breaks and the vibration shakes a motor mount loose.

    In a car, having the engine in front of you is an advantage. It (and the crumpling of the sheet metal up front) absorbs much of the inertia of the impact. The inertia of a moving engine, the heaviest object in the plane, would help absorb much of the kinetic energy of an impact if it hit anything first.

    In model airplanes I think that it helps in a crash to have the wing pop off. It can many times just flutter to a stop undamaged. If it stayed on it would have been broken in the crash. This is a similar kinetic energy/ inertia thing. The model breaks into components and is made lighter and survives the crash.
     
  6. Apr 24, 2005 #6

    Midniteoyl

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    Here's a thought or three:

    Planes in a dive tend to hit the ground nose first. If this happens at any speed, you dead no mater what plane you have

    In a situation where one is forced to land in a field, planes tend to land less than 'flat' or slightly nose down then 'flip'. In a tractor, the ground would tend to 'push' the engine in your lap - firewall or no. As long as the firewall in a pusher could withstand the initial impact the only place for the engine to go would be away from the plane.

    In a 'hard' landing wherre the nose gear collapse, the first to hit in a tractor are the blades, bending them at least, snapping them at worse. Both cases tend to bring the blades closer to your head/nads. In a pusher, the nose hits cuasing the engine/blades to be farther from the ground. Even if they did hit, the effect would be the blades bending/flying away and to the rear of your head/nads.
     
  7. Apr 24, 2005 #7

    Waiter

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    I would speculate that the crash forces required to cause an airframe / engine separation, are more than lethal for its occupants. I base this partially on my observations while assisting with crash investigations. The occupants will be dead long before the engine separates.

    There are two major sources of mass in a single engine aircraft, the engine, and the pilot. If the pilot is going to survive, the deceleration forces must be low, and spread out over time. (This is where the 30 to 50 mph comes in). An aircraft engine mount will accommodate significantly higher deceleration forces.

    Generally speaking, if the engine on a single engine aircraft departs the airframe in flight, the CG is so screwed up, the aircraft will no longer be capable of controlled flight. ( I'm sure there are single engine aircraft that the engine is at or near the CG, These would be the exception)

    If the engine comes loose in flight, we have a problem that was initiated by poor design or poor maintenance. Fix these problems. If the aircraft is going to crash, I refer back to my statement regarding deceleration forces.

    Keep in mind that a pusher is designed to PUSH. The airframe was designed to be pushed from the back, and it has a structural advantage over its tractor cousin when involved in a crash. The Tractor was designed to PULL, these forces are reversed during deceleration.

    In the event of a prop strike on landing, the tips will usually curl. If the blades do separate, the safest place to be, is inside the airplane. The worst place to be is anywhere outside the plane. The blades will be flung away because of centrifugal force.

    Good luck with your decision

    Waiter
     
  8. May 25, 2013 #8

    zebra100

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    So these assumptions that pusher are safer than tractors in crash landing? Unfortunately these are wrong. Read the accidents reports in the first place why the Air Force banned the pushers in the early years. You can use wiki to search 'pusher".
     
  9. May 25, 2013 #9

    autoreply

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    You do realize you're responding to an EIGHT year old topic?

    Unlike you write, pushers have never been found to be considerably riskier. A bit of common sense would tell you the same; if you can restrain a 250 lbs pilot, that sturdy engine mount won't have much of a problem with a 250 lbs engine...
     
    delta likes this.

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