Lower vs. upper wing....

[DeltaTango]

A friend asked me yesterday about the differences between planes with lower wings vs. planes with upper wings(I'm not sure I'm using the correct term). anyway besides the fact that upper wings give more stability and that they have a great advantage in cross wind landings I could'nt really think of anything else, though I'm sure there are other differences...?!?!?

Any ideas????

Thanx
DT

[mad_jock]

Biggest difference to the pilot is that your relatively blind on the inside while turning in a high wing.

Low wing you get a much better view of the circuit when your going round it.

Highwing gives a better view looking straight down which some people say makes nav easier.

Personally it dosn't bother me either way if its a high wing or low wing configuration.

Must be a bit crap in a bi-plane you get the worst of both worlds.

MJ

[QNIM]

MJ
I would have to disagree with you regards vis in a biplane, you can see far more in a tiger, stearman or similar types than any others I have flown.
Cheers Q

[mad_jock]

I will bow to your knowledge.

Unfortunatley nae buggar has let me had a shot yet so...

Talking through my arse again.

MJ

[slim_slag]

Problem with some biplanes is you can see sod all in front which can make it interesting on final. All part of the fun.

[flyingfemme]

Rough ground.
Aircraft made for rough, grass or unmade strips generally have a high wing; it's further from things that might damage it.

[DeltaTango]

Well, geeeeeeez, dude
That was A real constructive input
thank u very clutch

[chicken6]

Dude, high wing is more stable - it's called the pendulum effect.

Imagine your a/c is disturbed in roll (gust of wind under the wing for example). The resulting sideslip causes some air to bunch up under the fuselage-wing joint (in it's armpit) on the downhill side. This gives the lower wing a bigger pressure difference betweeen bottom (now higher) and top (same as before). This moves the centre of lift from the centre of the wing span to some position slightly downhill from the centre, thereby tending to rotate the a/c around it's longitudinal axis i.e. roll back towards whence it came i.e. it is stable.

You can't make this scenario work with low wing. Therefore high wing aircraft are inherently stable just because their arms come out their shoulders not their hips.

As for scraping wings - what the hell are you doing with the wings that far over? I've never (in only seven years flying mind you) heard of an aeroplane that has enough rudder control to beat the ailerons in a classic XW technique at landing speed. I've only ever run out of rudder, not aileron. IMHO the wings would never get close on any (light) type because you'd run out of rudder first in the classic crosswind technique. Except in a Moth, and then you're just out of options! (Good thing they raised that bottom wing).

And DT - high wing is better for scenics, but low wing is better for travelling pax because it gives them the feeling they're sitting on something rather than hanging from something.

Most passenger planes have the engines underneath the wings in order to keep the air smooth over the top, but in a high wing that puts them in the way of the view for the pax! All they can see is down down down.

Last one I can think of - if you build a wing section and plonk an aircraft on top it will sit there coz the wings push up and gravity pulls the fuselage down, but if you hang the fuselage underneath it still wants to go down but the wings are still trying to go up.

It may sound like I'm all in favour of low wing, but they don't keep you dry if it rains when you're getting out, and I'd still rather have the back seat of a Tiger Moth anyway. :ok:

c6

[machonepointone]

Chicken6,

I feel I must take you to task on some of your comments. "A high wing aeroplane is more stable." Stable than what? I assume you mean more stable than a low wing aeroplane. You then go on to give an inaccurate description of how a high wing aeroplane gets its lateral stability and then make the statement that a low wing aeroplane cannot do the same. Have you never heard of dihedral? Sweepback? The effect of a T tail on lateral stability?

Your theory that the lateral centre of lift moves "downhill" is wrong. The reason that a high wing provides lateral stability is due to the fact that, when the aircraft is sideslipping towards the lower wing, some of the airflow moves so as to go across the top of the fuselage. This upwards movement increases the angle of attack on the lower wing compared to the other one, thereby increasing the lift of the lower wing. The rolling moment so produced provides the lateral stability. The pendulum effect is not really aerodynamic, it is as its name suggests, like moving a pendulum from the vertical - gravity will make it try to return to its previous position.

As to why some aircraft have high wings and some have low wings, I think the only people who can answer that question are the manufacturers. Having flown and instructed on both types, the only advantage I can think of for a high wing aircraft (apart from keeping dry in the rain if that is what is important to you), is the downwards view. This is more than negated by the appalling and potentially dangerous lack of visibility into the inside of a turn. And yes, it may be nice to stay dry when it rains, but unless you are at least seven or more feet tall, you will have to climb up to check the fuel contents and the conditon of the upper surfaces of the wing. Another major disadvantage I have found with a high wing aeroplane is the lack of pre-stall buffet due to the turbulent airflow from the wings at high angles of attack passing clear over the elevators. I am not criticising that stalling characteristics of the aircraft, merely the almost total lack of aerodynamic warning of an impending stall.

There are advantages to high wings for a transport aircraft, and there are numerous examples flying today - C5, C17, C130, C141, An 124 etc. the advantage being ease of loading/unloading, but I suspect these aircraft were not in the mind of the person who originated this forum.