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Most of the tricycle gear planes have a level or mostly level posture when on the ground. Why weren't coonvention gear planes designed like this? It would give pilots better visibility and give passengers a more comfortable seating position when on the ground.

A few hypotheses I have gathered are:

Prop clearance, i.e., designers can fit larger propellers on an engine if it was farther away from the ground. However since planes pitch downward slightly when accelerating for takeoff I don't think this could have been a consideration.

Center of gravity. Early engines were heavy and when you mount one on the nose you would want to tilt the plane upwards so it doesn't flip forward due to the weight of the engine. I'm not sure to what extent this is true. And if it were, couldn't they just shift more weight from other parts backwards?

Being able to pitch up for take off. If the plane with a long tail wheel strut tried to pitch up, the tailwheel would be pressed into the ground. In this case couldn't they design some kind of suspension for the tailwheel?

Sorry if this is a silly question. I have absolutely zero knowledge in aircraft design and this just occurred to me as odd.

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Tricycle gear airplanes typically "rotate" for takeoff-- the nosewheel is lifted off the ground to place the aircraft in a nose-high pitch attitude, to increase the angle-of-attack of the wing.

If a tailwheel gear airplane were set up to have the fuselage basically horizontal on the ground, it too would need some way to "rotate"-- to lift the nose-- to increase the angle-of-attack of the wing for takeoff.1 But the tailwheel (touching the ground) would prevent this.

Being able to pitch up for take off. If the plane with a long tail wheel strut tried to pitch up, the tailwheel would be pressed into the ground. In this case couldn't they design some kind of suspension for the tailwheel?

Yes that's basically it. You seem to be imagining some kind of elaborate suspension that would keep the fuselage level most of the time but would allow the pilot to still push the tail down for takeoff? That seems like a lot of weight to add to the tail of an airplane. CG issues can always be dealt with by lengthening the nose, but the increased pitch rotational inertia would likely be objectionable. Plus the added weight and complexity simply wouldn't be worth it.

Actually we could introduce a further nuance by asking "given that tailwheel airplanes typically lift the tail to take off, why not make the tailwheel long enough to support the aircraft in the usual take-off attitude, even if the fuselage is still somewhat nose-high rather than fully horizontal?"

The answer is that 1) there would be some extra weight and drag, and 2) it's advantageous to be able to land the aircraft in a pitch attitude and angle-of-attack where the wing is nearly completely stalled, which is a higher pitch attitude and angle-of-attack than would be safe for a normal takeoff.

Footnotes--

  1. Unless of course the wings were attached to the fuselage at an unusually high "angle of incidence", so that they would be in a good position to create lift for takeoff even with the fuselage horizontal. This would have other disadvantages-- the fuselage would be flying in a nose-down attitude when the wings were flying at the relatively low angle-of-attack typically used for cruising flight. Of course there are exceptions to every rule, and there are some aircraft designed to be able to lift off the ground without "rotating" at all, so all the wheels lift off at the same time. Most (but not all) of these aircraft sit in a rather nose-high attitude on the ground. Others have minimal fuselages so fuselage drag is low regardless of pitch attitude. To the best of my knowledge none of these aircraft have either "tricycle" or "tailwheel" landing gear, though many aircraft with "tailwheel" landing gear can be safely "3-pointed" (a take off with all three wheels lifting the ground at the same time) in smooth conditions. Examples of aircraft designed to normally take off with all wheels lifting at the same time -- B-47, B-52, Aerianne Swift ultralight sailplane.
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  • $\begingroup$ I imagine some sort of sturdy spring on the tail wheel could keep a aircraft level as well as allow the pilot to pull up no? especially since a majority of the weight is on the main gears anyway. perhaps early designers could be excused for not having adequate technology, but surely we have strong lightweight suspension systems these days? I can see the hindrance to landing at a high angle of attack though. that might necessitate some mechanism to adjust the tailwheel $\endgroup$
    – AirCanada
    Commented May 8, 2022 at 5:12
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Principally conventional landing gear was used in the past for simplicity, lighter weight and propeller clearance. It still remains a popular configuration for aerobatic aircraft, ultralights, and bush aircraft where propeller clearance from rocks and other kinds of debris is needed. It’s also less prone to digging into soft or waterlogged fields than tricycle landing gear is. The tail wheel design also prevents tail strikes from over rotation during takeoff and landing.

The downside to conventional landing gear is that it’s dynamically unstable, and proned to ground looping if disturbed. It is also more difficult to control and steer an airplane with conventional landing gear than a tricycle gear configuration.

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  • $\begingroup$ If it is the nose up attitude that helps with prop clearance, wouldn't that be nullified when accelerating for take off since the plane pitches down to a more level attitude? $\endgroup$
    – AirCanada
    Commented May 8, 2022 at 16:31
  • $\begingroup$ @AirCanada. Not necessarily. A pilot can perform a three point takeoff if they feel prop clearance is imperative during the takeoff roll. $\endgroup$ Commented May 8, 2022 at 17:48
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Note that it is possible to design the AoA of a wing on a tricycle-gear plane in such a way that when you hit the right airspeed, the plane lifts off and flies itself off the ground, after which it proceeds to climb in a more-or-less "flat" attitude. This means the airplane designer has the flexibility to either have the plane break ground without rotation, or stay stuck to the ground until the pilot hits the rotation speed and then pulls back to increase the AoA- after which the plane climbs out.

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