Back of the drag curve
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58 and doing an assignment on flight on the backside of a drag curve? Contemplating the possible reporting for a fake user... Think about it, the backside of the drag curve means that you need more power the higher your angle of attack to maintain the current altitude, ie. the transition between flight and hover in a fixed wing aircraft where the thrust vector is keeping the plane up instead of lift.
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How about you do your homework and then tell us what you think it means? Then we can discuss it.
Look....
Get on the web site and look up some good tourist sites... and if you go there you will see the sights, from that site. Ex cit ing!
Meanwhile at the back of the drag curve... the F-18 with a high angle of attack needs to pour on the power to arrest its rate of descent. Pulling the nose up to stay on the CLS creates more drag, requires more power.. and if eventually there's none left.... into the spud locker for you..!
What a sight !
Meanwhile at the back of the drag curve... the F-18 with a high angle of attack needs to pour on the power to arrest its rate of descent. Pulling the nose up to stay on the CLS creates more drag, requires more power.. and if eventually there's none left.... into the spud locker for you..!
What a sight !
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What happens to the a/c on the backside of the power curve?
I've been told that control reversal takes place. Is that true?
When does an a/c end up at the backside of the power curve?
I've been told that control reversal takes place. Is that true?
When does an a/c end up at the backside of the power curve?
Superfly, are you referring to the power curve or as per the op, the drag curve?
If referring to the drag curve, an aircraft is on the "wrong" side of the drag curve when it is operating below its minimum drag speed.
When operating above minimum drag speed, if the aircraft is upset (say a gust) such that the speed increases, so too does the drag. Without touching power, the increase in drag will then slow the aircraft back to its original speed. Likewise, if the gust results in a reduction of speed, the drag reduces which then allows the aircraft to accelerate back to its original speed without touching the power. This is a "stable" condition, i.e. an upset results in a return to the original state.
When below minimum drag speed, if the gust results in a reduction of speed, the drag increases (increased angle of attack to stay level) which slows the aircraft even more, resulting in more drag, which slows it even more... etc. At some point, an aircraft may subsequently run out of power to be able to accelerate the aircraft back to a suitable speed.
Looking at the Concorde crash, seeing it struggling along at a high angle of attack and knowing that its on the wrong side of the drag curve, with no more thrust available to accelerate, and no altitude to use to accelerate, you know that there can only be one result...(systems failures aside).
An application of the drag curve is the holding speed for a jet. Maximum endurance normally occurs at the minimum drag speed. If a jet was in the holding pattern at exactly minimum drag speed, when it rolls into the reversal turn where the drag increases, without touching power the aircraft would slow to below minimum drag speed where it becomes speed unstable. Consequently, jets tend to hold at a speed just above minimum drag speed so when the drag increase in the turn slows them down, they are still above minimum drag speed when they roll out and increase speed back to their original holding speed without needing to touch the power.
There is not normally any control reversal associated with being on the wrong side of the drag curve.
Hope this helps.
If referring to the drag curve, an aircraft is on the "wrong" side of the drag curve when it is operating below its minimum drag speed.
When operating above minimum drag speed, if the aircraft is upset (say a gust) such that the speed increases, so too does the drag. Without touching power, the increase in drag will then slow the aircraft back to its original speed. Likewise, if the gust results in a reduction of speed, the drag reduces which then allows the aircraft to accelerate back to its original speed without touching the power. This is a "stable" condition, i.e. an upset results in a return to the original state.
When below minimum drag speed, if the gust results in a reduction of speed, the drag increases (increased angle of attack to stay level) which slows the aircraft even more, resulting in more drag, which slows it even more... etc. At some point, an aircraft may subsequently run out of power to be able to accelerate the aircraft back to a suitable speed.
Looking at the Concorde crash, seeing it struggling along at a high angle of attack and knowing that its on the wrong side of the drag curve, with no more thrust available to accelerate, and no altitude to use to accelerate, you know that there can only be one result...(systems failures aside).
An application of the drag curve is the holding speed for a jet. Maximum endurance normally occurs at the minimum drag speed. If a jet was in the holding pattern at exactly minimum drag speed, when it rolls into the reversal turn where the drag increases, without touching power the aircraft would slow to below minimum drag speed where it becomes speed unstable. Consequently, jets tend to hold at a speed just above minimum drag speed so when the drag increase in the turn slows them down, they are still above minimum drag speed when they roll out and increase speed back to their original holding speed without needing to touch the power.
There is not normally any control reversal associated with being on the wrong side of the drag curve.
Hope this helps.
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@Amiri01 ,Thanks for pointing out the effects of being above or below VIMD. So, I take it that - below the min. drag speed decrease in speed leads to an increase in drag which in turn leads to a further decrease in speed?
Also, with regard to power curve. I was told by a friend that reversal of control occurs on the backside of the power curve. He didn't know what it was either but had read about it. Any idea what exactly happens on the backside of the power curve ?
I've understood that it is in relation with power required to power available.
Also, with regard to power curve. I was told by a friend that reversal of control occurs on the backside of the power curve. He didn't know what it was either but had read about it. Any idea what exactly happens on the backside of the power curve ?
I've understood that it is in relation with power required to power available.
Last edited by SuperflyTNT; 31st Mar 2013 at 15:21.
Originally Posted by Aroa
Pulling the nose up to stay on the CLS creates more drag, requires more power.. and if eventually there's none left.... into the spud locker for you..!
Into the Spud Locker? You forgot the A/B.
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I was told by a friend that reversal of control occurs on the backside of the power curve.
Example: stick/yoke to the right means left aileron down, right aileron up. In normal flight this pushes the left wing up and the right wing down, banking the aeroplane to the right (which is what you want). The same thing very close to stalling angle of attack could make the left wing stall and drop (because of the downward movement of the left aileron, increasing the angle of attack of that wing), making the aeroplane bank very sharply and suddenly to the left.
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@armchairflyer
Ok but that's what would happen on the backside of the drag curve right?
What about the power curve? Aren't the drag curve and power curve two different things?
When I was told that control reversal would occur I thought, adding thrust to the engine would reduce the airspeed (if that's even possible) or reversal of controls to the ailerons or elevators like you mentioned.
I'm a bit confused here so sorry about that.
Ok but that's what would happen on the backside of the drag curve right?
What about the power curve? Aren't the drag curve and power curve two different things?
When I was told that control reversal would occur I thought, adding thrust to the engine would reduce the airspeed (if that's even possible) or reversal of controls to the ailerons or elevators like you mentioned.
I'm a bit confused here so sorry about that.
Your friend mis-read, or misunderstood, about reversal. It's not that there is a control reversal, but the back side of the power curve is referred to as the 'region of reversed command', not 'reversed control(s)'. This is what I think you & your friend have misunderstood
This refers to the inability of the aircraft to return to a previous state if disturbed from that state ie is unstable in one parameter or other. Others have described the speed instability that occurs in this area.
Normally ie on the 'front' side of the power curve, an aircraft is speed stable. This happens because on the front side of the curve total drag increases as speed increases, and reduces as speed reduces. If the aircraft experiences as speed increase then drag increases. The increasing drag 'self corrects' the speed increase until the speed is back to original. If speed reduces then drag reduces. Less drag allows the aircraft to accelerate until it is once again at the original speed. The pilot doesn't have to do anything to correct a speed change thanks to it being self correcting.
In the region of reversed command this doesn't happen. Drag increases as speed reduces, and decreases as speed is increased (until on the front side of the curve again). If the aircraft experiences a speed reduction the increased drag results in increases drag and a continuing speed reduction. The reverse for a speed increase. Now the pilot has to actively make control inputs (power &/or pitch) to keep the speed constant.
This refers to the inability of the aircraft to return to a previous state if disturbed from that state ie is unstable in one parameter or other. Others have described the speed instability that occurs in this area.
Normally ie on the 'front' side of the power curve, an aircraft is speed stable. This happens because on the front side of the curve total drag increases as speed increases, and reduces as speed reduces. If the aircraft experiences as speed increase then drag increases. The increasing drag 'self corrects' the speed increase until the speed is back to original. If speed reduces then drag reduces. Less drag allows the aircraft to accelerate until it is once again at the original speed. The pilot doesn't have to do anything to correct a speed change thanks to it being self correcting.
In the region of reversed command this doesn't happen. Drag increases as speed reduces, and decreases as speed is increased (until on the front side of the curve again). If the aircraft experiences a speed reduction the increased drag results in increases drag and a continuing speed reduction. The reverse for a speed increase. Now the pilot has to actively make control inputs (power &/or pitch) to keep the speed constant.
Last edited by Tinstaafl; 31st Mar 2013 at 16:29.
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What about the power curve? Aren't the drag curve and power curve two different things?
As the airplane slows down, parasitic drag decreases but induced drag increases. At a certain point (which corresponds to glide speed for maximum range IIRC), slowing down even more would increase total drag, so if you get slower than that you would have to increase power just to maintain airspeed (I haven't heard of or read about slowing the plane down by adding power, though), as also explained in the previous post.
This thread from another forum may be your friend, as may Google, if you are still confused
.
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Thank you guys (@Armchairflyer and @Tinstaafl).
So, in short - the backside of the power curve would result in reversal of command - instability to the a/c.
Seems a lot more clearer now. Appreciate the help
So, in short - the backside of the power curve would result in reversal of command - instability to the a/c.
Seems a lot more clearer now. Appreciate the help
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Not necessarily instability in the sense that you have to struggle for stable flight (unless very close to stalling), but instability in the sense that the airplane might slow even further although (not because!) you add power (if the added power is insufficient to bring you back to the "front side of the power curve").
The "power" curve (or, more correctly, the thrust horsepower required vs EAS curve) is derived directly from the thrust required vs EAS curve (which is identical to the Total drag curve), so they are indeed related.
Cap'n Bloggs..
CLS Carrier landing system ( Carrier ILS )
The spud locker...below the round down of the rear carrier deck...veggies and spuds kept in cool rooms either side of an alley way that leads...at least on some levels into the hangar deck.
There is a famous story of some F18 dude getting 'behind the drag curve' and impacting the back of the ship..only the cockpit and the surviving pilot ending up down the alley past/thru the spud lockers.
When he could stand?..promptly went upstairs and handed in his wings.
That was my last carrier "landing". Accepted. You have no further luck available for carrier flying.
Having spent many "interesting" hours flying sim CLS approaches...and if yr angle of attack/drag is not correct for yr power setting and yr airspeed drops off, eventually you cannot get the nose up..increase in angle of attack =more drag=more descent rate with any available power to make the deck.
So...the spud locker or the drink !!
Those Naval aviators who do all weather carrier approaches and landings on dark and stormy nights have got to be the VERY BEST.
Or the very dead.
Definitely a job for adrenilan junkies.
I dips me lid.!
The spud locker...below the round down of the rear carrier deck...veggies and spuds kept in cool rooms either side of an alley way that leads...at least on some levels into the hangar deck.
There is a famous story of some F18 dude getting 'behind the drag curve' and impacting the back of the ship..only the cockpit and the surviving pilot ending up down the alley past/thru the spud lockers.
When he could stand?..promptly went upstairs and handed in his wings.
That was my last carrier "landing". Accepted. You have no further luck available for carrier flying.
Having spent many "interesting" hours flying sim CLS approaches...and if yr angle of attack/drag is not correct for yr power setting and yr airspeed drops off, eventually you cannot get the nose up..increase in angle of attack =more drag=more descent rate with any available power to make the deck.
So...the spud locker or the drink !!
Those Naval aviators who do all weather carrier approaches and landings on dark and stormy nights have got to be the VERY BEST.
Or the very dead.
Definitely a job for adrenilan junkies.
I dips me lid.!
