physics flaw in AH?

[Westy]

"The tail provides lift. (Why does the tail come off the ground during the takeoff roll on a taildragger type aircraft?)"

 True.  I was going to be a wise guy and say you must have auto-takeoff enabled.

  Conversely however, when landing in AH why does the tail remain up in the in the air even while I've slowed down to a crawl and it only comes down to rest on the runway after I've come to a complete stop - or just a split second prior?

[GScholz]

Originally posted by Westy
Conversely however, when landing in AH why does the tail remain up in the in the air even while I've slowed down to a crawl and it only comes down to rest on the runway after I've come to a complete stop - or just a split second prior?

Because you're applying the wheel brakes, and they provide a torque moment around the wheels axis. Just like a car noses down (lifting the rear end) when you brake hard.

I was gonna be a wiseguy and say you must take the bus.

[GScholz]

Originally posted by bloom25
The tail provides lift.  

(Why does the tail come off the ground during the takeoff roll on a taildragger type aircraft?)

Because the main gear of a taildragger is naturally mounted forward of its CG (otherwise it would nose over on the ground), a taildragger is not balanced on its main wheels. And because the aircraft is not levelled into the wind. In level flight the horizontal stabilizer does not generate positive (upward) lift.

On the fist example on this webpage;

http://142.26.194.131/aerodynamics1/Stability/Page6.html

... click on "Show positive gust". This will show how and why the tail rises on a taildragger during take-off. Note that once the plane is heading into the wind the tail provides no lift.

[dBeav]

Originally posted by bloom25
The tail provides lift.  

(Why does the tail come off the ground during the takeoff roll on a taildragger type aircraft?)

Wouldn't the AOA have something to do with that? I mean my hand doesnt provide much lift but if I stick it out a car window at 80mph and tilt it, it's sure as hell gonna go up or down.

PS:I don't mean to downplay the importance of my hand providing a lift when I need it.

[Westy]

"I was gonna be a wiseguy and say you must take the bus."

Not the short one


"Because you're applying the wheel brakes...."

True. But in AH they are modelled a bit "odd"  These are the same breaks that keep my tail up off the ground until I come to a complete stop but can't stop me for all my standing on them when I land dead stick?

[Ozark]

Wouldn't the AOA have something to do with that? I mean my hand doesnt provide much lift but if I stick it out a car window at 80mph and tilt it, it's sure as hell gonna go up or down.

Are you creating lift or just deflecting air?

[GScholz]

Originally posted by Westy
"Because you're applying the wheel brakes...."

True. But in AH they are modelled a bit "odd"  These are the same breaks that keep my tail up off the ground until I come to a complete stop but can't stop me for all my standing on them when I land dead stick?

In AH the effect of brakes are limited to the point where you nose over and crash. If you apply too much brake in RL you're going to plough the airfield with your prop spinner. If you're deadstick I assume you have turned the rpm down so the prop does not "windmill" so much, and therefore the prop is creating less drag. Normally this drag would counteract the braking torque movement allowing you to apply more brakes without nosing over. Since brakes in AH are of the on/off type HTC has limited the effect (kind of like the stall limiter) so us poor slugs won't bend our prop every time we land.

[GScholz]

Originally posted by Ozark
Are you creating lift or just deflecting air?

Both. In fact the deflection of air accounts for about 25% of a wings lift. The horizontal stabilizer is a wing, and therefore must produce lift if the AoA is positive. In level flight however the CG being forward of the CL/AC the horstab must produce a negative lift to hold the nose up. The plane is balanced with more weight in front of the wing then behind it. Of course this is all based on the premise that the CG is indeed forward of CL/AC.

[Ozark]

Both. In fact the deflection of air accounts for about 25% of a wings lift.

The Skipping Stone Theory

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong2.html

[GScholz]

Originally posted by funkedup
What I meant was, "Tell me how what happens in AH is different from real life."

Another thing that AH does not model correctly is compression. In AH no plane truly compresses, the stick forces just become excessively heavy. Every plane in AH can trim out of a compression dive, this is wrong, only those planes that had a trim system like the 109 (there was a few) could do this, and even most of them didn't make it and lawndarted. If you went into compression in a P38 the plane would nose over into a death dive (another indication that once the horstab/elevator lose effect the nose will drop). There was NO WAY the P38 could pull out of this dive until they fitted dive flaps that would reduce speed so the P38's horstab no longer was compressed, and therefore able to push the tail down bringing the nose up. When a plane is compressed the controls does not become heavy. You can move the controls easily, they just don't have any effect because the normal airflow over the control surfaces are disrupted by localized supersonic airflow, so normal trimming would have NO effect.

The 109's trim system moved the whole horstab not just the elevators, so the 109 could trim out of compression. Historically this was very difficult however, and even if death was not guaranteed like in other planes, it was most probable.

[GScholz]

Originally posted by Ozark
The Skipping Stone Theory

http://www.grc.nasa.gov/WWW/K-12/airplane/wrong2.html

Yes, but it only accounts for about 25% of the lift produced by an airfoil. The remaining 75% is created by the Bernoulli effect, as the air is flowing at a higher velocity over the curved upper wing surface than under the flat underside produce less pressure, i.e. more pressure on the underside lifting the wing up.

EDIT: "Surfing on air" would be a better description IMHO.

[funkedup]

Gscholz thanks for the replies.  I answered here:  http://www.hitechcreations.com/forums/showthread.php?s=&postid=956394#post956394

[funkedup]

I'm not sure about the compressibility stuff.  I think the basic problem is that (according to HT, IIRC), AH doesn't actually calculate the hinge moment caused by the trim tab.  When you move trim it just changes the offset between your current stick position and the position of the control surface.  It's as if you were lengthening or shortening the control cable.
If your elevator had no effectiveness at really high speeds, then the trim tab would probably be ineffective too.

I don't know of any sim that actually simulates trim tab hinge moments.  Maybe HTC can be the first?  

[Ozark]

The remaining 75% is created by the Bernoulli effect, as the air is flowing at a higher velocity over the curved upper wing surface than under the flat underside produce less pressure, i.e. more pressure on the underside lifting the wing up.

"Longer Path" theory
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

[GScholz]

Ok let's continue there. More appropriate anyway.