View Full Version : Playing around with the pitch phugoid
You've blundered into the white room. You have primitive gyro guidance in the form of a turn rate indicator and so you are keeping the wings level, sort of. You are trimmed for 55 and the airspeed has just risen (alarmingly rapidly) to 85 and then temporaily plateaued there, staying constant for a couple of seconds. Answer quick: what do you do with the stick?
S
Sean Fidler
July 6th 15, 04:26 PM
Trim slightly forward. Nothing to stick.
Push aggressively to hold the airspeed; left to its own devices the airspeed will soon decrease rapidly. The glider is in roughly a normal glide attitude (or a bit more nose-down from that) but way above trim speed, so this is not a steady-state situation in any way, shape, or form. Left alone, the nose will rise dramatically as the flight path curves upward, and the airspeed will bleed away to far below trim speed-- you may even get a stall break.
S
On Tuesday, July 7, 2015 at 3:31:25 PM UTC-5, wrote:
> Push aggressively to hold the airspeed
And then slowly relax forward pressure to let the stick come back to trim
S
On Tuesday, July 7, 2015 at 4:31:25 PM UTC-4, wrote:
> Push aggressively to hold the airspeed; left to its own devices the airspeed will soon decrease rapidly. The glider is in roughly a normal glide attitude (or a bit more nose-down from that) but way above trim speed, so this is not a steady-state situation in any way, shape, or form. Left alone, the nose will rise dramatically as the flight path curves upward, and the airspeed will bleed away to far below trim speed-- you may even get a stall break.
>
> S
I don't think the question can be answered with any degree of confidence if you don't know how the glider will respond hands off. If the CG is aft, it may well diverge and have a bigger change the next cycle due to less stability. If the CG is forward, it may well be damped and be better off left alone.
A very good reason to know the glider well.
Simply saying push seems to mean the writer is more worried about a stall than over speed.
UH
Last post-- you raise some good points. It is certainly true that the phugoid may either diverge into increasing highs and lows, or damp out into decreasing highs and lows, depending on the glider and the CG position. I'm a light guy and so my CG is usually well aft, making the dynamics on the lively side. Even if the CG is well forward, I think that some mild forward pressure on the stick at this particular point in the oscillation would help the situation.
Thanks for chiming in.
S
I guess my mindset is that if that if you can apply whatever forward stick pressure is needed to freeze the airspeed, and then slowly ease the airspeed back to trim, that is always better then simply riding along with the oscillation, regardless of whether the oscillation is going to get more severe, or damp out. Obviously the latter situation is much more user-friendly than the former...
S
So....you are still in the White Room.
What about bank?
On Sunday, July 5, 2015 at 11:50:39 PM UTC-6, wrote:
> You've blundered into the white room. You have primitive gyro guidance in the form of a turn rate indicator and so you are keeping the wings level, sort of. You are trimmed for 55 and the airspeed has just risen (alarmingly rapidly) to 85 and then temporaily plateaued there, staying constant for a couple of seconds. Answer quick: what do you do with the stick?
>
> S
Open the spoilers (add drag) and leave the stick alone. A phugoid is damped by drag.
Don't believe it? Put your glider into a stick-free phugoid pitch/airspeed oscillation (roughly 17 seconds peak-to-peak) and then open the spoilers and watch it go away - or at least be significantly reduced.
Mike I Green
July 8th 15, 01:39 AM
On 7/7/2015 1:57 PM, wrote:
> On Tuesday, July 7, 2015 at 4:31:25 PM UTC-4, wrote:
>> Push aggressively to hold the airspeed; left to its own devices the airspeed will soon decrease rapidly. The glider is in roughly a normal glide attitude (or a bit more nose-down from that) but way above trim speed, so this is not a steady-state situation in any way, shape, or form. Left alone, the nose will rise dramatically as the flight path curves upward, and the airspeed will bleed away to far below trim speed-- you may even get a stall break.
>>
>> S
>
> I don't think the question can be answered with any degree of confidence if you don't know how the glider will respond hands off. If the CG is aft, it may well diverge and have a bigger change the next cycle due to less stability. If the CG is forward, it may well be damped and be better off left alone.
> A very good reason to know the glider well.
> Simply saying push seems to mean the writer is more worried about a stall than over speed.
>
> UH
>
The first thing I used to do is contact the manufacturer and some pilots
I knew and respected and ask ask what is the recommended CG position.
When I was racing our Duo Discus, I would be changing the water in the
tail daily. It made flying a delight rather than fighting the stick
every flight.
MG
--
Mike I Green
Bob Kuykendall
July 8th 15, 05:11 PM
On Sunday, July 5, 2015 at 10:50:39 PM UTC-7, wrote:
> You've blundered into the white room. You have primitive gyro guidance in the form of a turn rate indicator and so you are keeping the wings level, sort of. You are trimmed for 55 and the airspeed has just risen (alarmingly rapidly) to 85 and then temporaily plateaued there, staying constant for a couple of seconds. Answer quick: what do you do with the stick?
>
> S
Flaps 90, pitch to hold 55 kts. Expect a 45-degree deck angle on emergence.
kirk.stant
July 8th 15, 08:42 PM
> On Sunday, July 5, 2015 at 10:50:39 PM UTC-7, wrote:
> > You've blundered into the white room. You have primitive gyro guidance in the form of a turn rate indicator and so you are keeping the wings level, sort of. You are trimmed for 55 and the airspeed has just risen (alarmingly rapidly) to 85 and then temporaily plateaued there, staying constant for a couple of seconds. Answer quick: what do you do with the stick?
Wait, WTF are you trying to ask?
If you are planning to "blunder" into a cloud, you better know how to maintain attitude and airspeed via needle-ball and airspeed, if that is all you have in the cockpit.
Oh, and unless you are on an instrument flight plan (and trained and equipped) you are busting the FARs big time, so might as well declare an emergency and get ATC to give you a lot of room to screw up.
Then, fly the damn glider! Nothing primitive about needle & ball & airspeed, gliders do it all the time in other countries. If you can't control the airspeed, you should never have put yourself in the situation of being in a cloud!
It sounds like you are really worried about getting stuck IMC during a wave flight. If so, get a good T&B or even an attitude indicator, and some instruction under the hood in a power plane until you can safely fly on instruments.
Remember, the guy who lost it over Reno had tons of time IMC in fighter jets - and trust me they are not forgiving on the gauges - and he lost it when he went IMC....
Then you suggest to "push aggresively and hold the airspeed"! Really? That is a recipe for a quick trip past VNE! No **** "the airspeed will soon decrease rapidly" - when you impact the ground!
All this talk about benign spirals and phugoids are really BS - you HAVE TO FLY THE EFFING GLIDER, UNLESS YOU HAVE TERMINAL VELOCITY LIMITING DIVE BRAKES. PERIOD, DOT.
Arrrgggghh!!!
Kirk
Charlie M. (UH & 002 owner/pilot)
July 8th 15, 09:06 PM
On Wednesday, July 8, 2015 at 3:42:46 PM UTC-4, kirk.stant wrote:
> > On Sunday, July 5, 2015 at 10:50:39 PM UTC-7, wrote:
> > > You've blundered into the white room. You have primitive gyro guidance in the form of a turn rate indicator and so you are keeping the wings level, sort of. You are trimmed for 55 and the airspeed has just risen (alarmingly rapidly) to 85 and then temporaily plateaued there, staying constant for a couple of seconds. Answer quick: what do you do with the stick?
>
> Wait, WTF are you trying to ask?
>
> If you are planning to "blunder" into a cloud, you better know how to maintain attitude and airspeed via needle-ball and airspeed, if that is all you have in the cockpit.
>
> Oh, and unless you are on an instrument flight plan (and trained and equipped) you are busting the FARs big time, so might as well declare an emergency and get ATC to give you a lot of room to screw up.
>
> Then, fly the damn glider! Nothing primitive about needle & ball & airspeed, gliders do it all the time in other countries. If you can't control the airspeed, you should never have put yourself in the situation of being in a cloud!
>
> It sounds like you are really worried about getting stuck IMC during a wave flight. If so, get a good T&B or even an attitude indicator, and some instruction under the hood in a power plane until you can safely fly on instruments.
>
> Remember, the guy who lost it over Reno had tons of time IMC in fighter jets - and trust me they are not forgiving on the gauges - and he lost it when he went IMC....
>
> Then you suggest to "push aggresively and hold the airspeed"! Really? That is a recipe for a quick trip past VNE! No **** "the airspeed will soon decrease rapidly" - when you impact the ground!
>
> All this talk about benign spirals and phugoids are really BS - you HAVE TO FLY THE EFFING GLIDER, UNLESS YOU HAVE TERMINAL VELOCITY LIMITING DIVE BRAKES. PERIOD, DOT.
>
> Arrrgggghh!!!
>
> Kirk
Ummmm...... chill a bit. Quite a few, "What if I went IFR in a sailplane" questions being bandied about recently.
1-A good pilot attempts to AVOID the "what if".
2-It won't be the first, or last, "issue" that "happens".
3-If it happens and the pilot is not equipped and trained, it's likely yet another front page issue.
I will admit "scud running" in a SEL many years ago. I knew the terrain and good landmarks so the issue of hitting a "granite cloud" were limited, still didn't mean I wasn't worried (got stuck between cloud layers over northern NJ coming from the south heading to my home airport in lower NYS).
Just because I did it does NOT mean I want to repeat it or condone it.
While I hate to see stupidity, nature has a way of dealing with it.......
Some say "Darwin", others say "God"..... either way, the end result is the same..... someone is DEAD....... "There is no such thing as gravity, the Earth sucks!".
I can understand the VERY LIMITED discussion for the, "Major WTF, it just happened" conversation, I feel for the most part it's someone trying to justify a "stupid frame of mind", nature/God will deal with it down the road.
BTW, when my step father had access to a, "pilot assessment questionnaire", he gave it to me. The results were, "You would make a GREAT fighter pilot, if I didn't know you better, I would NOT let you fly my planes......!".
I still fly his stuff, no, I have yet to break anything..... hope to continue the trend......
This discussion just keeps coming back..over and over and over...
Buy an electronic artificial horizon, full 3 dimensional like those offered with LX Varios (S80, etc.)
THEN
get some training in how to use it.
Trying to hand fly out of the "white room" is just plain nuts.
Trying to fly IFR with a compass and airspeed is just plain nuts.
I believe in "social darwinism."
ENOUGH with this dangerous line of discussion.
kirk.stant
July 9th 15, 12:45 PM
On Wednesday, July 8, 2015 at 3:06:51 PM UTC-5, Charlie M. (UH & 002
> Ummmm...... chill a bit. Quite a few, "What if I went IFR in a sailplane" questions being bandied about recently.
> 1-A good pilot attempts to AVOID the "what if".
> 2-It won't be the first, or last, "issue" that "happens".
> 3-If it happens and the pilot is not equipped and trained, it's likely yet another front page issue.
<snip>
Ok, deep breath, fresh cup of coffee...
My frustration is with the OP's refusal to accept what has been proven over and over again in blood and bent metal: there is NO way to safely exit a fully developed IMC situation without either gyro instruments (and the skills to use them) or resorting to terminal dive brakes (rare these days) or maybe the retro method of a spin (in planes that will hold a stable spin long enough - also rare these days).
The benign spiral approach is fine in theory (anybody have any personal stories of using it for real to exit a cloud?) but is highly glider-specific and requires a stable starting condition - OK perhaps if you are trapped above or see that you are about to get trapped - but you better have practiced it A LOT before trying it for real - and it will do you no good once you have lost visual references and the airspeed and bank angle start to run away.
Sure, it's great to "what if" various scenarios. And I've done the same, and done my share of marginal flying in various aircraft in marginal conditions - and what I take from it is getting stuck unprepared in a cloud is about as bad as getting stuck in heavy sink in an unlandable box canyon - some things must be avoided at all costs!
Finally, what really got me was the OP's comment about pushing aggressively on the stick to control the airspeed. Maybe it's semantics, but to me that implies a forceful forward motion of the stick - which in my glider at cruise speed would bring the dead cats out of the bottom of the cockpit and result in a RAPID increase in airspeed to potentially dangerous levels. I wonder how often the OP has done speed sweeps in his glider, seeing how long it takes to accelerate from cruise to redline, and how little forward stick it take to do it?
Kirk
66
Interesting replies, thanks for chiming in.
I certainly agree that the phugoid is HUGELY damped by adding drag.
I would suggest that even some pilots who consider themselves well trained in "partial panel" flying, may not be really be familiar with the best way to end a pronounced pitch phugoid. And also may not appreciate the fact that in some sailplanes at some loadings, in the absence of pilot inputs, the pitch phugoid can tend to slowly get larger and larger, to the point where there is a stall break at the point of minimum airspeed. Even in a glider that seems quite well-behaved in normal visual flying.
If you disagree with my suggested inputs, I'd invite you to explore the phugoid a bit yourself. Accelerate or decelerate to 20 mph/ knots above or below the trimmed speed, let go the stick, and watch what happens.
I'd suggest that during a well-developed phugoid, if the airspeed is increasing (or is momentarily frozen and about to increase), the pilot ought be applying aft pressure on the stick, and if the airspeed is decreasing (or is momentarily frozen at a peak value and about to decrease), the pilot ought be applying forward pressure on the stick. I'd suggest that the very best opportunity for decisively breaking the phugoid is the moment where the airspeed peaks and as about to start decreasing. The glider is in a nearly level attitude at the "bottom" of an oscillation cycle at this instant. I'd suggest that if the airspeed is well above the trimmed airspeed at this moment, it will indeed take quite an "aggressive" push on the stick to freeze the airspeed at this moment. Then the glider can be slowly eased back to trim speed.
If this seems wrong to you, I'd invite you to explore the phugoid a bit yourself the next time you fly-- you might find the suggestion makes more sense after some hands-on explorations.
Or you may find that your glider is so dynamically stable at your loading, that the pitch phugoid is a non-issue.
S
PS "aggressive" is a relative turn. Whatever it takes to freeze the airspeed. Not enough to raise the dead cats to the canopy, but it's still a much larger input than you might at first think would be appropriate in a blind flying situation. The point is that at the point of maximum airspeed in a well-developed pitch phugoid, the glider is flying much faster than trimmed speed, and really wants to slow down by pulling up, and your job is to prevent that and then to slowly ease it down to a slower airspeed. Play around with it a bit and the ideas I posted may make a bit more sense. You have to see if first-hand in your own glider to really appreciate it.
S
kirk.stant
July 9th 15, 06:33 PM
Why are you playing with the pitch phugoid in a cloud? If you are flying the airplane, it won't get into a pitch phugoid in the first place. And if you are in a cloud, why would you let go of the stick?
It's simple (given you have a gyro turn indicator). Stop the turns. Control speed with pitch (drag helps). If you do get into a spiral and manage to roll out, expect a strong pitch up if over trim speed when you roll wings level.
This whole thread is absurd at best, dangerous at worst (people get ideas...)
Kirk
66
I must sheepishly admit that some years ago I allowed myself to become accidentally enveloped while flying the wave at Minden in a G103. I did indeed use the benign spiral to exit the cloud safely, after I considered other options to be exhausted. This involved a descent of over 1500 feet. It worked perfectly, and I consider that it saved my life -- I stupidly had no parachute with me on that flight. Even still, I can't recommend the procedure without reservation because it doesn't seem to work in all gliders, or even in that glider every time. But I can tell you that it worked once, even in turbulent conditions.
Lynn Alley
"2KA"
Dan Marotta
July 10th 15, 03:39 AM
This sounds very interesting for a pilot testing a new design or getting
to know his new glider. It certainly doesn't seem to me to have any
relationship with day to day soaring. Or is this simply a mind experiment?
On 7/9/2015 8:51 AM, wrote:
> Interesting replies, thanks for chiming in.
>
> I certainly agree that the phugoid is HUGELY damped by adding drag.
>
> I would suggest that even some pilots who consider themselves well trained in "partial panel" flying, may not be really be familiar with the best way to end a pronounced pitch phugoid. And also may not appreciate the fact that in some sailplanes at some loadings, in the absence of pilot inputs, the pitch phugoid can tend to slowly get larger and larger, to the point where there is a stall break at the point of minimum airspeed. Even in a glider that seems quite well-behaved in normal visual flying.
>
> If you disagree with my suggested inputs, I'd invite you to explore the phugoid a bit yourself. Accelerate or decelerate to 20 mph/ knots above or below the trimmed speed, let go the stick, and watch what happens.
>
> I'd suggest that during a well-developed phugoid, if the airspeed is increasing (or is momentarily frozen and about to increase), the pilot ought be applying aft pressure on the stick, and if the airspeed is decreasing (or is momentarily frozen at a peak value and about to decrease), the pilot ought be applying forward pressure on the stick. I'd suggest that the very best opportunity for decisively breaking the phugoid is the moment where the airspeed peaks and as about to start decreasing. The glider is in a nearly level attitude at the "bottom" of an oscillation cycle at this instant. I'd suggest that if the airspeed is well above the trimmed airspeed at this moment, it will indeed take quite an "aggressive" push on the stick to freeze the airspeed at this moment. Then the glider can be slowly eased back to trim speed.
>
> If this seems wrong to you, I'd invite you to explore the phugoid a bit yourself the next time you fly-- you might find the suggestion makes more sense after some hands-on explorations.
>
> Or you may find that your glider is so dynamically stable at your loading, that the pitch phugoid is a non-issue.
>
> S
--
Dan Marotta
Re what is the point of this thread?
I just find it fascinating that cloud flying without an artificial horizon IS routinely done in sailplanes by some pilots in some nations (see previous posts withing last 6 months to RAS), yet very little information is out there on how to stop the pitch phugoid.
My experience is that some sailplanes are dynamically unstable in pitch even when flown within the published CG limits. Of course I can't rule out an error in weighing or computations, but that's my experience.
This idea of "if your flying it right, a phugoid will never develop" doesn't hold water with me.
The idea of moving the stick forward when the airspeed is high, seems bizarre at first glance. Yet it works. See earlier posts for more. When the airspeed is high but no longer increasing, the glider is in a nearly level pitch attitude, and the excess airspeed will soon make the flight path curve upward strongly. The pilot needs to prevent that. By moving the stick forward.
After what I've seen firsthand in clear skies, I shudder to imagine any pilot ever venturing into clouds without an intimate knowledge of the dynamics of the pitch phugoid, and how to stop it. So you have an artificial horizon display. Do you want to bet your life that it will not fail? Then you are down to partial panel, and then what?
Besides, what's the point in just droning around the sky without understanding what is going on? Any pilot should be interested in these topics even if he never intends to come within ten miles of a cloud.
Those in the "I manipulate the stick to make the sailplane do what I want it to do so why do I need to understand anything about anything" camp need not engage in this topic...
S
On Thursday, July 30, 2015 at 9:07:20 AM UTC-5, wrote:
> Re what is the point of this thread?
>
> I just find it fascinating that cloud flying without an artificial horizon IS routinely done in sailplanes by some pilots in some nations (see previous posts withing last 6 months to RAS), yet very little information is out there on how to stop the pitch phugoid.
>
> My experience is that some sailplanes are dynamically unstable in pitch even when flown within the published CG limits. Of course I can't rule out an error in weighing or computations, but that's my experience.
>
> This idea of "if your flying it right, a phugoid will never develop" doesn't hold water with me.
>
> The idea of moving the stick forward when the airspeed is high, seems bizarre at first glance. Yet it works. See earlier posts for more. When the airspeed is high but no longer increasing, the glider is in a nearly level pitch attitude, and the excess airspeed will soon make the flight path curve upward strongly. The pilot needs to prevent that. By moving the stick forward.
>
> After what I've seen firsthand in clear skies, I shudder to imagine any pilot ever venturing into clouds without an intimate knowledge of the dynamics of the pitch phugoid, and how to stop it. So you have an artificial horizon display. Do you want to bet your life that it will not fail? Then you are down to partial panel, and then what?
>
> Besides, what's the point in just droning around the sky without understanding what is going on? Any pilot should be interested in these topics even if he never intends to come within ten miles of a cloud.
>
> Those in the "I manipulate the stick to make the sailplane do what I want it to do so why do I need to understand anything about anything" camp need not engage in this topic...
>
> S
Platyp, if you have a couple hundred hours in a glider and still need to consciously avoid a phugoid - then something is seriously wrong with you or your glider. Your entire postings are not related to anything I have experienced in 35 years of flying. Let it go, nobody else is interested in your musings, you are just scaring the kids, please stop.
kirk.stant
July 30th 15, 03:29 PM
On Thursday, July 30, 2015 at 9:07:20 AM UTC-5, wrote:
> Re what is the point of this thread?
>
> I just find it fascinating that cloud flying without an artificial horizon IS routinely done in sailplanes by some pilots in some nations (see previous posts withing last 6 months to RAS), yet very little information is out there on how to stop the pitch phugoid.
>
> My experience is that some sailplanes are dynamically unstable in pitch even when flown within the published CG limits. Of course I can't rule out an error in weighing or computations, but that's my experience.
>
> This idea of "if your flying it right, a phugoid will never develop" doesn't hold water with me.
>
> The idea of moving the stick forward when the airspeed is high, seems bizarre at first glance. Yet it works. See earlier posts for more. When the airspeed is high but no longer increasing, the glider is in a nearly level pitch attitude, and the excess airspeed will soon make the flight path curve upward strongly. The pilot needs to prevent that. By moving the stick forward.
>
> After what I've seen firsthand in clear skies, I shudder to imagine any pilot ever venturing into clouds without an intimate knowledge of the dynamics of the pitch phugoid, and how to stop it. So you have an artificial horizon display. Do you want to bet your life that it will not fail? Then you are down to partial panel, and then what?
>
> Besides, what's the point in just droning around the sky without understanding what is going on? Any pilot should be interested in these topics even if he never intends to come within ten miles of a cloud.
>
> Those in the "I manipulate the stick to make the sailplane do what I want it to do so why do I need to understand anything about anything" camp need not engage in this topic...
>
> S
Funny, people have been flying IMC using only a turn and bank and airspeed for a long time - without worrying about the pitch phugoid. As I said before - if you are actively flying the plane (actively controlling the speed via angle of attack, and the bank angle by controlling the turn rate by reference to the needle (while keeping the ball centered), your pitch phugoid is not a factor.
If you so mishandle the controls that you lose airspeed control (which is basically what you are describing) then you are probably going to end up in a spiral dive - a whole different ball game!
Are you saying you run into problems with a pitch phugoid "in clear skies"? How? You letting go of the controls? WHY?
And sure an AI makes IMC flight easier - and sure it can fail (which is why plane certified for IMC fligh have to have redundant gyros), but again that has little to do with the pitch phugoid! If you lose your AI (or T & B), you will most likely end up in a spiral dive.
Again: If you are flying it right - A PITCH PHUGOID WILL NEVER DEVELOP. If you let go of the controls, it probably will - but then by definition you are no longer flying the plane, are you?
IMHO, you are making a big mountain out of a small molehill...
Just fly the damn plane, for christ's sake!
Kirk
I find the best response to the pitch phugoid to be--
When the airspeed is decreasing, or when the airspeed has plateaued at the peak airspeed and is about to decrease, move the stick forward. In short, move the stick opposite to the direction that the airspeed is changing, or is about to change. Try to freeze the airspeed, and then ease the stick aft a bit to ease the airspeed slowly back toward trim.
When the airspeed is decreasing and has dropped below the trim speed or the midpoint of the oscillation, relax your inputs, in anticipation of giving a new input as soon as the airspeed plateaus at the minimum airspeed.
When the airspeed is increasing, or when the airspeed has plateaued at the minimum airspeed and is about to increase, move the stick aft. Try to reduce the rate of increase in airspeed. In short, move the stick opposite to the direction that the airspeed is changing, or is about to change. Go easy on it so you don't invite a stall-- don't be so aggressive as to try to completely "freeze" the airspeed at this point in the oscillation. But don't be afraid to give a little aft pressure on the stick even when the airspeed is quite low-- the dynamics are such that gentle aft pressure at this point in the oscillation will have a helpful effect, and won't stall the wing.
When the airspeed is increasing and has risen above the trim speed or the midpoint of the oscillation, relax your inputs, in anticipation of giving a new input as soon as the airspeed plateaus at the maximum airspeed.
Recurring theme: "Move the stick opposite to the direction that the airspeed is changing, or is about to change."
Recurring theme: relax your input at the midpoint of the airspeed oscillation, or upon passing through trim speed, in anticipation of the next input.
Recurring theme: the peak airspeed is a good time to break the oscillation, by moving the stick forward as needed to freeze the airspeed-- to prevent a rapid decrease in airspeed-- and then easing the stick slowly aft to ease on down to trim speed.
S
Tango Whisky
July 30th 15, 04:45 PM
As some posters already stated:
If you fly the sailplane with your hand on the stick, there won't be any significant phugoid (I've flown about 3 dozend different gliders in 35 years, from 10m span to 29m span - never seen a phugoid while flying the glider).
If you take your hand off the stick, most sailplanes will start a phugoid.
Best way to end it: grab the stick and fly the glider.
Are you sure that you have actually flown a glider?
Bert
Ventus cM TW
Bruce Hoult
August 8th 15, 06:27 PM
On Thursday, July 30, 2015 at 6:45:39 PM UTC+3, Tango Whisky wrote:
> As some posters already stated:
> If you fly the sailplane with your hand on the stick, there won't be any significant phugoid (I've flown about 3 dozend different gliders in 35 years, from 10m span to 29m span - never seen a phugoid while flying the glider).
>
> If you take your hand off the stick, most sailplanes will start a phugoid..
> Best way to end it: grab the stick and fly the glider.
>
> Are you sure that you have actually flown a glider?
Does that work if you close your eyes at the same time?
Certainly I've never had a problem with unwanted pitch phugoid, but then I've never flown a glider with absolutely no outside pitch reference, even if only showing me changes in pitch, not absolute pitch. e.g. I'm fine in a mountain valley I have my doubts about deep inside a cloud.
Andy Blackburn[_3_]
August 8th 15, 08:40 PM
I find this an odd discussion since this is in reference to a dynamic mode that is related to the interaction between speed and pitching moment - it requires you not to make control inputs for many tens of seconds and the pitch, airspeed and altitude excursions that result are considerable. I don't know of any pilot or any airplane where this would happen without a deliberate effort to NOT fly the airplane - or if your elevator became disabled.
No one needs to think about controlling the phugoid - it is subordinated to simple pitch and airspeed control that happen on a far, far shorter timescale. The dominant dynamic mode there is short-period, but even that's not a big factor from a pilot control perspective.
9B
This discussion is such a mish-mash.
The phugoid came up in the discussion of the so-called benign spiral mode of exiting a cloud.
I once owned a flew a Grob 104 Speed Astir. It had a benign spiral configuration for exiting a cloud. It was full flaps, trim full aft, spoilers out, and hands and feet off of the controls. I experienced that situation and can tell you that the aircraft still had a phugoid behavior but it stayed within reasonable limits.
I now have an LS8. I practiced the benign spiral situation a couple of times and the phugoid got worse and worse until it was full stall to Vne. However, I neglected to pull the spoilers.
Last week I tried it again but pulled full spoilers. No phugoid! However, there would still be no way to control roll without proper instruments.
Now I have a full time, solid state, artificial horizon in an LX S80. No worries.
Andy Blackburn[_3_]
August 9th 15, 01:55 AM
On Saturday, August 8, 2015 at 5:40:44 PM UTC-7, wrote:
> This discussion is such a mish-mash.
> The phugoid came up in the discussion of the so-called benign spiral mode of exiting a cloud.
> I once owned a flew a Grob 104 Speed Astir. It had a benign spiral configuration for exiting a cloud. It was full flaps, trim full aft, spoilers out, and hands and feet off of the controls. I experienced that situation and can tell you that the aircraft still had a phugoid behavior but it stayed within reasonable limits.
> I now have an LS8. I practiced the benign spiral situation a couple of times and the phugoid got worse and worse until it was full stall to Vne. However, I neglected to pull the spoilers.
> Last week I tried it again but pulled full spoilers. No phugoid! However, there would still be no way to control roll without proper instruments.
> Now I have a full time, solid state, artificial horizon in an LX S80. No worries.
Yes - good point. One way to damp the phugoid (If you don't want to touch the elevator - either because it's jammed or because you are trying a benign spiral) is to open the speed brakes at the bottom of the oscillation. I can attest that it works on a G103.
9B
Bruce Hoult
August 9th 15, 02:43 AM
On Saturday, August 8, 2015 at 10:40:35 PM UTC+3, Andy Blackburn wrote:
> I find this an odd discussion since this is in reference to a dynamic mode that is related to the interaction between speed and pitching moment - it requires you not to make control inputs for many tens of seconds and the pitch, airspeed and altitude excursions that result are considerable. I don't know of any pilot or any airplane where this would happen without a deliberate effort to NOT fly the airplane - or if your elevator became disabled.
>
> No one needs to think about controlling the phugoid - it is subordinated to simple pitch and airspeed control that happen on a far, far shorter timescale. The dominant dynamic mode there is short-period, but even that's not a big factor from a pilot control perspective.
Yes OF COURSE if you are controlling the pitch and therefore the speed then you will never see a phugoid. OF COURSE. But how do you control the pitch if you can't see the pitch or even changes in the pitch? What control input should you make? Normally you don't even think about this because it's so obvious and subconscious. But it DOES rely on outside visual references, and isn't going to work when you're in a cloud and don't have any.
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