Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: Citabria on August 28, 2003, 04:35:58 PM
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it would seem ah has a flaw in the cg of its airplanes, when one looses its tail its engine heavy nose goes up and its nonexistant tailpoints downward.
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could this also explain low speed and stall inaccuracies too?
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This has been coverd more then a few times.
Do a search. Folks even provided pretty pictures and stuff.
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Or maybe it's because the propeller on the plane is still pulling you? ;)
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The wings are still creating lift;)
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Thats actually the correct physics if I understand flight dynamics of wing loading....especially with prop turning.
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Citabria, CG is usually aft of the wing's center of lift. Otherwise you wouldn't need a tail. So when you lose the tail's lift, the nose goes up.
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cg shifts to rear as pilot deposits a hefty load in his britches :)
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CG is cheeting
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Originally posted by funkedup
Citabria, CG is usually aft of the wing's center of lift. Otherwise you wouldn't need a tail. So when you lose the tail's lift, the nose goes up.
That's at least partially wrong. Tails provide NO lift in a stable a-c.
Mullah:cool:
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but its a function of CG a tail heavy aircraft will go nose up perhaps
but a plane with no tail NO TAIL and therefor a forward cg on the remaining aircraft should fall nose down
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Drag from the prop perhaps?
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That's at least partially wrong. Tails provide NO lift in a stable a-c.
That tells me one thing, Mr. Hooper- That you college boys don't have the education enough to admit when your wrong.
Unless the horizontal stabilizer is just a flat piece of wood or inverted airfoil, it is going to provide some lift.
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Ever heard of a "full flying tail"?
Check those Horz stabs out sometime, most of the WWII ones havea lift produceing airfoil much like the wing. ie they DO provide lift along with stablisation.
Even if they don't they provide control. Without it there is nothing to keep the wing's angle of attack stable.
No surpise it try's to go nose up.
I'd say its more PROOF that AH is correctly modeled than proof that its not.
Nice try :)
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Sorry Ghosth ;)
The stabilizers' job is to provide stability for the aircraft, to keep it in controllable flight. The rudder and elevator is used to deflect the tail and the ability to move on the vertical and lateral axis. Lift from the horizontal stabilizer would make the aircraft unstable.
The full flying (all-moving) tail means the full movement of the horizontal stabilizer and/or vertical stabilizer.
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I always thought the stabilizers on the tail provided DOWN pressure to counteract the UP pressure (um..ok, lift) from the wing. Without a tail a plane would continuously loop.......however if the tail suddenly disappears while in level flight then the massive amount of lift being generated by the wing suddenly has nothing to counteract it and so the plane noses up sharply into an immediate stall.
However, why the nose STAYS skyward after the stall is at it's most pronounced and the plane falls tail first is beyond my knowledge. I mean, after the stall has happened the wing is no longer generating any lift.......one would think that the plane would simply tumble and eventually stabilize nose down. Although if it did then the wing would begin to generate lift again and force the nose higher. Hmmm.
(http://image1ex.villagephotos.com/extern/640697.jpg)
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Swoop,
By this time, the nose being initially pointed upward and the engine usually being in full throttle position, your aircraft has undergone an amazing transformation... it is now trying to be a helicopter! :) I guess the test would probably be to immediately cut throttle and see if what's left of the plane flops back over. Hmmm... next time I get my bellybutton end shot off, I gotta remember to try this. On second thought, I think I'll remain pointing up under full throttle and try and take out a few of the idiotic "assist grabbers" who invariably dive on a totally crippled, flaming, non-combatant aircraft that is plummeting to the earth, just to get a quick fraction of a point. :D
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Now think about the shape of the propeller. (Airfoil)
If that don’t work… think of the airfoil of a helicopter.
Lift one way… auto-rotation (drag) the other way.
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Skorpyon
Beat to to it. ;)
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There are some fishy elements in AH's FM. There may have been some aircraft where the tailplane provided positive lift, large aircraft most likely, but on small planes it most certainly provided negative lift. The strange part is that AH does model this. As your plane slows down you need more up trim to stay in level flight, i.e. your CG is forward of your CL, however when you lower flaps CL should move aft, dropping your nose down rather than lifting it up like in AH. If a plane like a WWII fighter loses its tail the nose should drop quickly and the plane should pancake into the wind inverted, and then flip-flop down.
EDIT: Actually I remember in the BoB movie they blew the tail section off of an RC 109 model during one of the dogfights, and as expected it nosed over and flip-flopped while burning.
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EDIT: Actually I remember in the BoB movie they blew the tail section off of an RC 109 model during one of the dogfights, and as expected it nosed over and flip-flopped while burning.
Now you added a new and fun parameter to the mix… Momentum!
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This small plane went into a nose dive after losing its tail.
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At this point, another climber, Craig "Crash" Bennett came forward, to thank Dawson for the flight. There was a bang and the plane went into a nose-dive. It was Moline and his canopy hitting the left horizontal stabiliser on the tail assembly.
"I didn't see it, but I heard it, and I felt it," says Dawson, "and I just knew that someone was over the tail. I didn't know it was Simon. I was just hoping they could get off, and trying to bring the aircraft up and level and from going down. We were still buffeting around."
Dawson shouted for everybody to get out.
Meanwhile, cameraman Chaberka was falling, with his eyes turned upward and locked on to Moline and the plane's tail. Chaberka saw the parachute canopy go past him and over the tail. He was a little below Moline as Moline was dragged from Boyle's and Drinkwater's hands by the chute. "I saw Simon's canopy get wrapped around the tail and then the tail twisting, 45 degrees to the right, before it snapped off. Simon was still hanging off the tail."
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http://www.theage.com.au/articles/2002/04/27/1019441314240.html
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Originally posted by RDSaustinTX
That's at least partially wrong. Tails provide NO lift in a stable a-c.
Mullah:cool:
Sorry that's just wrong.
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Guys who are contradicting me, get a flight mechanics textbook, read and learn the section on longitudinal stability, then get back to me.
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Originally posted by Citabria
but its a function of CG a tail heavy aircraft will go nose up perhaps
but a plane with no tail NO TAIL and therefor a forward cg on the remaining aircraft should fall nose down
Good point. Losing the mass of the tail could move the CG forward. I wonder if that loss of mass is in the model?
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But would it really matter Funked? As long as the the engine is running and the prop is turning its thrust will over come the tendancy for the nose to drop.
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Originally posted by funkedup
Guys who are contradicting me, get a flight mechanics textbook, read and learn the section on longitudinal stability, then get back to me.
Stop looking at the picture and read the text. :p
You want equilibrium. Airflow that creates equal forces up and down.
If the horizontal stabilizer created lift, then you would need trim the nose up to force the horizontal stabilizer into equilibrium.
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This small plane went into a nose dive after losing its tail.
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http://www.theage.com.au/articles/2002/04/27/1019441314240.html
As I stated before, Now you added a new and fun parameter to the mix… Momentum!
Entanglement of the horizontal stabilizer pitched the aircraft on a downward attitude and momentum completed the process. The scenario in the report is not like getting your tail shot off.
“During the investigation it was calculated that on opening after entanglement, the reserve parachute would have applied a load of approximately 1.6 tonnes to the horizontal stabiliser. That load exceeded the aircraft design limits.”
Full accident report link follows:
http://www.atsb.gov.au/aviation/occurs/occurs_detail.cfm?ID=389#factual
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Hey Guys!
Thanks for the fun. This thread kept me awake during my (un)scheduled night shift at the airport. Time to look busy before folks start arriving.
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Originally posted by funkedup
Guys who are contradicting me, get a flight mechanics textbook, read and learn the section on longitudinal stability, then get back to me.
I have.
"The movie below shows a main wing and stabilizer in equilibrium. Equilibrium means that the nose down moment created by the wing is exactly balanced by an equal nose up moment created by the stabilizer. As a result the pitching moment is zero. It is important to remember that the pitching moment must be zero at almost all times during flight. A positive or negative pitching moment is only required for a short moment to start the aircraft pitching, or stop it from pitching."
http://142.26.194.131/aerodynamics1/Stability/Page9.html
Btw. this is an excellent site for leaning the basics.
Interesting to read their conclusions in this chapter: Velocity changes do not produce pitch changes directly. In AH they do.
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This page also is very informative conserning what makes a stable wing.
http://142.26.194.131/aerodynamics1/Stability/Page7.html
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Originally posted by Eagler
cg shifts to rear as pilot deposits a hefty load in his britches :)
-Sik
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The physics are correct.
And we do not loose mass when loosing the tail.
HiTech
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Will the plane lose mass as parts fall off in 2.0?
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Originally posted by GScholz
Interesting to read their conclusions in this chapter: Velocity changes do not produce pitch changes directly. In AH they do.
Please elaborate, on how velocity changes in AH directly produce pitch changes, and how this is different from real life.
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watch hitech refuse to answer, as he never follows up after droppin in
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Gscholz, do you realize that the CM vs CL charts on the link you posted show the exact situation in AH, i.e. they support Hitech's conclusion?
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Originally posted by Rutilant
watch hitech refuse to answer, as he never follows up after droppin in
Yeah you gave him a whole 4 minutes to answer.
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LOL, i didnt mean it as a response to him not answering within 4 minutes - just tellin it like it always is
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Originally posted by funkedup
Please elaborate, on how velocity changes in AH directly produce pitch changes, and how this is different from real life.
If your plane is trimmed for level flight, no change in velocity would affect pitch. Change in thrust however will. If you turn off the engine and turn the rpm down and trim the plane; no change in velocity would affect pitch. I.e. if you nose the plane down in a shallow dive the plane should not start to level out as speed increases, but rather stay in the dive.
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What I meant was, "Tell me how what happens in AH is different from real life."
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Originally posted by funkedup
Gscholz, do you realize that the CM vs CL charts on the link you posted show the exact situation in AH, i.e. they support Hitech's conclusion?
When you see the flash display at the bottom of the following webpage it is clear that the horizontal stabilizer creates a downward force to counteract the upward force of the wing. If the plane looses this downward force on the tail the nose should drop.
http://142.26.194.131/aerodynamics1/Stability/Page9.html
CG is forward of the wing on dynamically stable planes. I have not heard of a WWII fighter that was dynamically unstable.
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Check this out Fester (http://www.hitechcreations.com/forums/showthread.php?s=&postid=956233#post956233)
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Originally posted by funkedup
What I meant was, "Tell me how what happens in AH is different from real life."
1. Loose tail and the nose goes up. R/L nose goes down because the horizontal stabilizer provides a down force that is in fact "holding your nose up".
2. Deploy flaps nose goes up. R/L nose pitches down because the CL of the wing moves back, further away from the CG.
3. Changes in airspeed requires drastic trimming changes. R/L not so, in fact the Fw190 didn't even have movable trim because it was so stable at all speeds, only small fixed trim tabs were needed. One example how dynamically stable aircraft are just that; stable at all speeds, because speed does not change the balance of forces acting on the pitch axis.
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The tail provides lift.
(Why does the tail come off the ground during the takeoff roll on a taildragger type aircraft?)
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"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?
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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. ;)
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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.
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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.
:)
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"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?
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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?
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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. :)
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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.
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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
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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.
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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.
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Gscholz thanks for the replies. I answered here: http://www.hitechcreations.com/forums/showthread.php?s=&postid=956394#post956394
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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? :)
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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
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Ok let's continue there. More appropriate anyway. :)
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My brain hurts. :)
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(Why does the tail come off the ground during the takeoff roll on a taildragger type aircraft?)
I got an idea. Lets discuss the forces of ground effect, prop wash and deflection on the horizontal stabilizer during take-off and landing.
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GScholz: You havn't a clue how compression effect are done in AH.
Almost every time I see you make an attempt at a factual statement of what or how AH models somthing, your statement is incorect. Please stop making statments about AH that are just simply incorect, and that you have no knowledge of.
HiTech
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Originally posted by hitech
GScholz: You havn't a clue how compression effect are done in AH.
True, I have no clue how your FM models compression. I do know however that a plane which is compressed cannot trim itself out of the compression. In AH they can, and this is wrong.
Please do not take offence from me debating airplane physics and AH. I mean no offence, and I'm sorry if you have taken it as such.
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If Bernoulli is right how does a plane fly upside down????
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GScholz:
it's just statments like this.
In AH no plane truly compresses
That are over the top. Debating physics questions is fine.
HiTech
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True. I should have added AFAIK to that statement. I apologize.
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When I saw the title I expected a discussion about the N1K-UFO.
I like the helicopter theory, always assumed that to be somewhat true.
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well it was just discussed in another thread provided by frenchy that I missed. seems the tail gone behavior is accurate :D
wtg HTC :)
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well it was just discussed in another thread provided by frenchy that I missed. seems the tail gone behavior is accurate :D wtg HTC :)
Darn you! I was forced to use my brain too!
Maybe I should check Frenchy's link. ;)
Hey Frenchy, Would FIT be proud?
;)
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The tail comes off the gound only if you move the stick forward during the take off roll.
The tail does not provide positive lift, it produces a downward force. If a tail comes off, as happened to me, 1968 VietNam, from Triple AAA (L19 Birddog, 1900ft AGL) the aircraft noses up, way up.
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WOW!
IcKid
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ickid how did you escape? parachute out the side door?
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Originally posted by Citabria
it would seem ah has a flaw in the cg of its airplanes, when one looses its tail its engine heavy nose goes up and its nonexistant tailpoints downward.
Hi Citabria,
I think I posted this explanation in another thread, but I'll post it again here to save folk searching for it.
The behaviour you have described appears to be perfectly correct to me, and is exactly what I would expect from the excellent flight model in AcesHigh. I think the confusion in this discussion has been caused by some misunderstanding of the system of forces known to exist during flight, and in the way they are used in trying to explain what happens when the tail has gone away.
Just bear with me while I build an image of what happens… There you are flying along, minding your own business, in level flight at some constant speed. At this point the stability diagram you find in most text books is doing us proud! All the forces on your aircraft are balanced. The prop’ thrust is balanced with drag, the lift with weight and so on. All the moments are balanced too, the pitching yawing and rolling moments are all in equilibrium. The nose down pitching moment caused by the weight and lift couple is balanced at the tail, and so on.
Now, since the question only concerns what direction the nose points when the tail goes away, let’s just think about those pitching moments. Most folk think like this… During flight the weight and lift couple was trying to rotate the nose downwards, and the tail was preventing this from happening. So, if we remove the tail, there will be nothing to prevent that rotation, and the nose will drop… Not so fast! That’s not what happens, you might not see this right away, so bear with me, I’m going to go slowly… But first, the flaw in that reasoning is that it overlooks the fact that the nose down pitching moment that existed during controlled flight, also goes away with the tail. You see, the tail wasn’t only responsible for the balancing moment, it was also indirectly responsible for the lift that was produced the nose down pitching moment in the first place. Once the tail has gone, the couple rotating the nose down, no longer exists… So what does happen?
Firstly, the wings are only producing lift when they are forced to do so by the control surfaces at the tail. Those surfaces (using a small force but long lever arm) rotate the wings against the airflow, forcing the wings to fly at an angle to the free air stream, thereby rotating the airstream, causing downwash, and thus lift. When the elevators go away with the tail, the wings will begin to move upwards, due to the lift already there, but they won’t go far because as they move the lift decays rapidly until the wings weather vane, and no longer produce any lift. That all happens in just a few degrees, so when the tail goes away, the nose might move down slightly, but only momentarily, because now that only leaves an engine, with the wings and forward/mid fuselage acting as little more than dead weight that simply wants to fall downwards, with a propeller attached to it that is still producing thrust.
Now, all you really need to consider at this point is how a heavy lump of metal with a propeller attached to it would fall. I think most people can see intuitively, that the heavy lump would fall first, dragging the propeller behind it. An admittedly weak analogy would be the stable condition that arises with a man hanging beneath a parachute. The aircraft falls, dragging the prop behind it, and falls more slowly because the prop is producing thrust and slowing it down.
That's exactly what happens in AcesHigh... Kudos HT!
Hope that helps.
Badboy
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Originally posted by ICKID
The tail comes off the gound only if you move the stick forward during the take off roll.
The tail does not provide positive lift, it produces a downward force. If a tail comes off, as happened to me, 1968 VietNam, from Triple AAA (L19 Birddog, 1900ft AGL) the aircraft noses up, way up.
Now that's a story that I would love to hear!
Would you be interested in putting something together for publication on the http://www.simhq.com website?
Badboy
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But what happens after it noses up?
Does it hover and land on the tail like a helicopter like in AH? Or does it nose up and then tumble around?
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This is a good question. would the plane do the same thing every time it loses its tail. It seems to me, after the tail is gone, the plane would yaw and lift for sure, since the rudders and elevators are the only things controling these movements anyway. The pilot may be able to roll for a cupple of seconds, but intuitively, i think HTC has got this one pretty close.
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Originally posted by GScholz
This small plane went into a nose dive after losing its tail.
http://www.theage.com.au/articles/2002/04/27/1019441314240.html
You failed reading comprehension 101 GS.
This small plane went into a nose dive THEN lost its tail:
As the tail snapped off, the plane whaled on to its back and Crash (Craig Bennett) got pushed up against the windscreen
Sounds to me like the plane was diving, the tail seperated, then the plane flicked into a nose up position while falling and spinng...
Losing his new boot, Dawson hauled himself along the floor as if he was trying to climb a wall while glued to it, using the harness seatbelts as a hand grip. The plane was tilting about 45 degrees, then it would go vertical, then flatten out, then tilt again.
I think you proved yourself wrong ;)
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Wouldn't be the first time ;)