technical questions
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tecnical questions
Could please someone help me....
How is ranged increased in a headwind?
What is transport wander for an uncorrected gyro?
what is the realtionship between Vmcg and V1?
Tell me about ETOPS?
What is higher Vmcg or Vmca on a 747 -400 why?
What happens to stall speed at hiogh altitudes?
I know I don't ask a lot but I am stuck on these it is for a good cause believe me!
How is ranged increased in a headwind?
What is transport wander for an uncorrected gyro?
what is the realtionship between Vmcg and V1?
Tell me about ETOPS?
What is higher Vmcg or Vmca on a 747 -400 why?
What happens to stall speed at hiogh altitudes?
I know I don't ask a lot but I am stuck on these it is for a good cause believe me!
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Afraid I don't have the background to answer all your questions, but here goes for those I can:
According to FAR 25.107a(1)and(2), V1 may not be less than Vmcg plus a margin to account for pilot recognition time. So, crudely, Vmcg sets a min value for V1.
But V1 may also be set by other criteria - V2min, for example. So the relationship between V1 and Vmcg may be very tenuous for some aircraft. Typically V1 may be Vmcg dependent at light weights, but unlikely to be so at heavy weights for the same aircraft.
At higher altitudes the Mach number at the stall increases, which generally acts to cause a lower stall angle-of-attack, and so increase the stall speed. This is most pronounced for wings with 'hard' leading edges - no slats. Although there are often altitude restrictions on slat extension anyway.
ummm - it isn't?
what is the realtionship between Vmcg and V1?
But V1 may also be set by other criteria - V2min, for example. So the relationship between V1 and Vmcg may be very tenuous for some aircraft. Typically V1 may be Vmcg dependent at light weights, but unlikely to be so at heavy weights for the same aircraft.
What happens to stall speed at hiogh altitudes?
How is ranged increased in a headwind?
Why do it if it's not fun?
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I'll see if I can add any answers to Mad Scientists:
Range can be very slightly increased by flying at a higher speed, therefore reducing the amount of time you're flying for, and reducing the amount time the headwind can affect you.
Can't figure out how to explain this without lots of diagrams and things. Basically, as you move a gyro across the earth, it continues to point the same way in space, but the way it points relative to North will change.
I haven't got to this chapter yet, so I don't know the details. But the idea is that, without ETOPS, you're not allowed to be more than a certain distance from a diversion airfield in a twin-engined aircraft. So flight across the Atlantic, for example, would have to be in an aircraft with 3 or more engines (or take a long route). ETOPS enables an operator to operate twin engined aircraft on these routes, once the authority is happy that the operator's procedures are sufficiently safe.
FFF
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How is ranged increased in a headwind?
What is transport wander for an uncorrected gyro?
Tell me about ETOPS?
FFF
-------------
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dynamite dean,
see if you can find the book "Ace the technical pilot interview" by gary v. bristow, mcgraw hill isbn 0-07-139609-8
all those questions and more are answered.
btw...those questions look like they came straight out of the cx reviewer!
goodluck!
see if you can find the book "Ace the technical pilot interview" by gary v. bristow, mcgraw hill isbn 0-07-139609-8
all those questions and more are answered.
btw...those questions look like they came straight out of the cx reviewer!
goodluck!
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Dynamite D:
Most of our fellow ppruners have answered your questions. If I may I would like to add...
How is range increased in a headwind ?
Take the worst case, one in which the headwind is equal to cruise speed. The only way to increase range would be to increase speed. Therefore, flying at an increased speed in a headwind improves range.
Which is higher Vmcg or Vmca on a B747 ?
Vmca is always higher that Vmcg and this fact is not airplane related. Actually the only factor which affects Vmca and Vmcg is Air Density and no other variable. Example: In High Air Density the engine produces higher thrust therefore the loss of a critical engine causes more asymmetry requiring higher speeds to maintain control. Therefore both speeds are lower in Low Density Air and vice versa.
What happens to stall speed at high altitudes?
If you have had the chance to see any jet QRH performance page indicating Vref speeds for different flap settings, you will notice that no correction is provided for altitude. Vref is determined from 1.3 Vso and the absence of any altitude correction implies that INDICATED stall speed is not affected by altitude. For every AOA there is a corresponding IAS. In addition, the coefficient of Lift does not vary with altitude for the same IAS. Since we as pilots have only the IAS Indicator, Stick Shaker and maybe the AOA sensor, the calculation of TAS Stall speed is not critical. However, you should know that TAS Stall speed will vary with altitude.
If these questions are in prep for an interview good luck.
Chryse
Most of our fellow ppruners have answered your questions. If I may I would like to add...
How is range increased in a headwind ?
Take the worst case, one in which the headwind is equal to cruise speed. The only way to increase range would be to increase speed. Therefore, flying at an increased speed in a headwind improves range.
Which is higher Vmcg or Vmca on a B747 ?
Vmca is always higher that Vmcg and this fact is not airplane related. Actually the only factor which affects Vmca and Vmcg is Air Density and no other variable. Example: In High Air Density the engine produces higher thrust therefore the loss of a critical engine causes more asymmetry requiring higher speeds to maintain control. Therefore both speeds are lower in Low Density Air and vice versa.
What happens to stall speed at high altitudes?
If you have had the chance to see any jet QRH performance page indicating Vref speeds for different flap settings, you will notice that no correction is provided for altitude. Vref is determined from 1.3 Vso and the absence of any altitude correction implies that INDICATED stall speed is not affected by altitude. For every AOA there is a corresponding IAS. In addition, the coefficient of Lift does not vary with altitude for the same IAS. Since we as pilots have only the IAS Indicator, Stick Shaker and maybe the AOA sensor, the calculation of TAS Stall speed is not critical. However, you should know that TAS Stall speed will vary with altitude.
If these questions are in prep for an interview good luck.
Chryse
Why do it if it's not fun?
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Chryse,
You said:
Why is this? I would assume it's to do with the stabilising effect of the friction from the gear? Makes sense, it's just that I've never heard this before.
Also, if this is the case, would it not be true that tail-draggers would have a lower Vmca than Vmcg, since the friction from the main wheels will de-stabilise the aircraft on the ground? Not very relevant to modern aviation, since there aren't too many tail-dragger twins still flying - I'm just curious.
Cheers,
FFF
-------------
You said:
Vmca is always higher that Vmcg
Also, if this is the case, would it not be true that tail-draggers would have a lower Vmca than Vmcg, since the friction from the main wheels will de-stabilise the aircraft on the ground? Not very relevant to modern aviation, since there aren't too many tail-dragger twins still flying - I'm just curious.
Cheers,
FFF
-------------
Moderator
Chryse,
Leaving the headwind thing to one side .... for the benefit of all, could we get you to substantiate some of your comments, please ? A few authoritative references would be nice ...
Leaving the headwind thing to one side .... for the benefit of all, could we get you to substantiate some of your comments, please ? A few authoritative references would be nice ...
Vmca vs Vmcg
On the B747 series, Vmcg is higher than Vmca by about 5 or 6 knots.
It's a certification thing. Remember "3 to 5 to the live" when you did your first twin rating???
The advantage gained by the bank angle/sideslip ought to mean that most aircraft Vmca figures are less than their Vmcg.
It's a certification thing. Remember "3 to 5 to the live" when you did your first twin rating???
The advantage gained by the bank angle/sideslip ought to mean that most aircraft Vmca figures are less than their Vmcg.
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[QUOTE] If you have had the chance to see any jet
QRH performance page indicating Vref speeds for
different flap settings, you will notice that no
correction is provided for altitude. Vref is
determined from 1.3 Vso and the absence of any
altitude correction implies that INDICATED
stall speed is not affected by altitude. For every AOA there is a corresponding IAS. In
addition, the coefficient of Lift does not vary with altitude for the same IAS. Since we as
pilots have only the IAS Indicator, Stick Shaker and maybe the AOA sensor, the calculation
of TAS Stall speed is not critical. However, you should know that TAS Stall speed will vary
with altitude. [\quote]
Sorry, but you cannot derive information about the
aerodynamic behaviour of an aircraft from the
QRH. The aerodynamics determines what goes in the
QRH, but you can't go backwards, and you
certainly should not generalise from a QRH to the
underlying theory.
Stall speed is quite definitely affected by
altitude - whether IAS, CAS, EAS or TAS. The Mach
number effect is real, and is presented in the
stall speed charts of our aircraft (we quote
stall speeds for SL and 15,000ft)
If a single Vref has been chosen this is because
the plane is likely only certificated for
landings at low altitudes, and the variation in
stall speed is small. The Vref will have been
then defined by the highest stall speed in the
altitude band. It *could* have been defined as a
function of altitude, but it was probably only a
knot or so variation so the manufacturer decide
to swallow the effect in the interest of
simplifying the charts.
QRH performance page indicating Vref speeds for
different flap settings, you will notice that no
correction is provided for altitude. Vref is
determined from 1.3 Vso and the absence of any
altitude correction implies that INDICATED
stall speed is not affected by altitude. For every AOA there is a corresponding IAS. In
addition, the coefficient of Lift does not vary with altitude for the same IAS. Since we as
pilots have only the IAS Indicator, Stick Shaker and maybe the AOA sensor, the calculation
of TAS Stall speed is not critical. However, you should know that TAS Stall speed will vary
with altitude. [\quote]
Sorry, but you cannot derive information about the
aerodynamic behaviour of an aircraft from the
QRH. The aerodynamics determines what goes in the
QRH, but you can't go backwards, and you
certainly should not generalise from a QRH to the
underlying theory.
Stall speed is quite definitely affected by
altitude - whether IAS, CAS, EAS or TAS. The Mach
number effect is real, and is presented in the
stall speed charts of our aircraft (we quote
stall speeds for SL and 15,000ft)
If a single Vref has been chosen this is because
the plane is likely only certificated for
landings at low altitudes, and the variation in
stall speed is small. The Vref will have been
then defined by the highest stall speed in the
altitude band. It *could* have been defined as a
function of altitude, but it was probably only a
knot or so variation so the manufacturer decide
to swallow the effect in the interest of
simplifying the charts.
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John T. and other fellow ppruners,
Did not mean to cause ripples here, after all I thought it was a discussion forum. Anyways heres some supporting documentation and Authoritative References....
Regarding Range and Headwind - refer to Aerodynamics for Naval Aviators by H.H. Hurt Jr. (ISBN 1-56027-140-X) page 170 second para from the top left.
Regarding Vmca and Vmcg: I agree that I could be wrong about Vmca and Vmcg on a B747. I was writing in reference to an airplane performance graph depicting the various speeds in a timeline. In the graph (generic airplane) Vmcg was depicted before Vmca. Vmca, from my basic performance classes, is the threshold speed for getting airborne, so should follow Vmcg, which is the threshold speed for continuation of takeoff. If Ive stated something wrong please let me know why? The rest of the info on Vmca and Vmcg I provided is listed in Aircraft Performance Theory for Pilots by P.J. Swatton 2000 (ISBN 0632-05569-3) pg 138 third para from the top.
Regarding Stall Speed at high altitude: The formula for stall speed is given by Vs (ktas) = Sqrt (295 L/qSClmax) where q is the density ratio. However since the speed is given in Vs (ktas), this part of the formula can be rewritten as Vs(ktas) = (SMOE)*(EAS) where SMOE = 1/sqrt(density ratio). When both equations are simplified the density ratios at altitude cancel out leaving only EAS. Position error also cancel each other. Refer to Classnotes for Basic Aerodynamics by Norbert R. Kluga 1991 page 124 from Embry-Riddle Aeronautical University and Flight Technique Analysis for Professional Pilots by Les Kumpula page 30 also from Embry-Riddle Aeronautical University.
Cheers
Did not mean to cause ripples here, after all I thought it was a discussion forum. Anyways heres some supporting documentation and Authoritative References....
Regarding Range and Headwind - refer to Aerodynamics for Naval Aviators by H.H. Hurt Jr. (ISBN 1-56027-140-X) page 170 second para from the top left.
Regarding Vmca and Vmcg: I agree that I could be wrong about Vmca and Vmcg on a B747. I was writing in reference to an airplane performance graph depicting the various speeds in a timeline. In the graph (generic airplane) Vmcg was depicted before Vmca. Vmca, from my basic performance classes, is the threshold speed for getting airborne, so should follow Vmcg, which is the threshold speed for continuation of takeoff. If Ive stated something wrong please let me know why? The rest of the info on Vmca and Vmcg I provided is listed in Aircraft Performance Theory for Pilots by P.J. Swatton 2000 (ISBN 0632-05569-3) pg 138 third para from the top.
Regarding Stall Speed at high altitude: The formula for stall speed is given by Vs (ktas) = Sqrt (295 L/qSClmax) where q is the density ratio. However since the speed is given in Vs (ktas), this part of the formula can be rewritten as Vs(ktas) = (SMOE)*(EAS) where SMOE = 1/sqrt(density ratio). When both equations are simplified the density ratios at altitude cancel out leaving only EAS. Position error also cancel each other. Refer to Classnotes for Basic Aerodynamics by Norbert R. Kluga 1991 page 124 from Embry-Riddle Aeronautical University and Flight Technique Analysis for Professional Pilots by Les Kumpula page 30 also from Embry-Riddle Aeronautical University.
Cheers
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How is range increased in a headwind ?
Take the worst case, one in which the headwind is equal to cruise speed. The only way to increase range would be to increase speed.
Take the worst case, one in which the headwind is equal to cruise speed. The only way to increase range would be to increase speed.
Don't know about threshold speeds???
Vmca - Minimum Control Speed in the Air
Vmcg - Minimum Control Speed on the Ground.
Hence Vmcg is the minimum speed from which the pilot will be able to maintain directional control to continue the take off, all other performance factors being satisfied. Quite obviously below Vmcg you must stop or go off the runway.
There are, of course, various configurations defined for the testing. JT and Mutt can, I'm sure, expand on this.
Vmca - Minimum Control Speed in the Air
Vmcg - Minimum Control Speed on the Ground.
Hence Vmcg is the minimum speed from which the pilot will be able to maintain directional control to continue the take off, all other performance factors being satisfied. Quite obviously below Vmcg you must stop or go off the runway.
There are, of course, various configurations defined for the testing. JT and Mutt can, I'm sure, expand on this.
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mustafagander,
Vmcg is defined as the minimum CAS at which when the critical engine is suddenly made inoperative during the take-off run it is possible to maintain control of the airplane using primary aerodynamic controls alone (no tiller control - nosewheel steering) to enable the takeoff to be safely continued using normal piloting skills. This includes:
a. the use of primary aerodynamic controls only (rudder only) since on the ground
b. Rudder pedal force not exceeding 150 f/lbs
c. assuming 7 knts of crosswind from the inop engine side
d. without reducing thrust on the live engine, and
e. landing gear remaining extended.
In addition, the path of the aeroplane at which engine failure occurs to the point at which recovery to a direction parallel to the centre-line of the runway is attained may not deviate by more than 30 ft laterally from the centre-line at any point. JAR25.149(E).
Vmca is the minimum CAS at which when the critical engine is suddenly made inop, it is possible to maintain directional control of the aircraft with:
a. Rudder pedal force not exceeding 150 f/lbs
b. Bank not exceeding 5 degrees
c. Directional Change not exceeding 20 degrees
d. Without reducing thrust on the live engine
e. A/c airborne with little or no ground effect. It may not exceed 1.2Vs JAR 25.149(B) and (D).
Since V1 can never be less than Vmcg, and Vr cannot be less than V1 or 105%Vmca (among other things) it is possible to have Vmcg higher than Vmca in theory, but it should not be more than by a few knots. If anyone knows of such cases and why/ how, I am always eager to learn.
Cheers
Vmcg is defined as the minimum CAS at which when the critical engine is suddenly made inoperative during the take-off run it is possible to maintain control of the airplane using primary aerodynamic controls alone (no tiller control - nosewheel steering) to enable the takeoff to be safely continued using normal piloting skills. This includes:
a. the use of primary aerodynamic controls only (rudder only) since on the ground
b. Rudder pedal force not exceeding 150 f/lbs
c. assuming 7 knts of crosswind from the inop engine side
d. without reducing thrust on the live engine, and
e. landing gear remaining extended.
In addition, the path of the aeroplane at which engine failure occurs to the point at which recovery to a direction parallel to the centre-line of the runway is attained may not deviate by more than 30 ft laterally from the centre-line at any point. JAR25.149(E).
Vmca is the minimum CAS at which when the critical engine is suddenly made inop, it is possible to maintain directional control of the aircraft with:
a. Rudder pedal force not exceeding 150 f/lbs
b. Bank not exceeding 5 degrees
c. Directional Change not exceeding 20 degrees
d. Without reducing thrust on the live engine
e. A/c airborne with little or no ground effect. It may not exceed 1.2Vs JAR 25.149(B) and (D).
Since V1 can never be less than Vmcg, and Vr cannot be less than V1 or 105%Vmca (among other things) it is possible to have Vmcg higher than Vmca in theory, but it should not be more than by a few knots. If anyone knows of such cases and why/ how, I am always eager to learn.
Cheers
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Stall Speed at Altitude
Chryse
Your equations are valid only if you assume that CLmax does not vary.
In practice what happens is that CLmax is a function of Mach number, and so altitude for a given speed. This results in a lower CLmax at higher altitudes and hence higher stall speeds. I'm afraid you are not accounting for all the factors with those equations.
Regarding Stall Speed at high altitude: The formula for stall speed is given by Vs (ktas) = Sqrt (295 L/qSClmax) where q is the density ratio. However since the speed is given in Vs (ktas), this part of the formula can be rewritten as Vs(ktas) = (SMOE)*(EAS) where SMOE = 1/sqrt(density ratio). When both equations are simplified the density ratios at altitude cancel out leaving only EAS. Position error also cancel each other. Refer to Classnotes for Basic Aerodynamics by Norbert R. Kluga 1991 page 124 from Embry-Riddle Aeronautical University and Flight Technique Analysis for Professional Pilots by Les Kumpula page 30 also from Embry-Riddle Aeronautical University.
In practice what happens is that CLmax is a function of Mach number, and so altitude for a given speed. This results in a lower CLmax at higher altitudes and hence higher stall speeds. I'm afraid you are not accounting for all the factors with those equations.
Moderator
Chryse,
No problem with your basic explanations.
However, it is endemic in most areas of study, not only flying, that different explanations are pitched at different target audiences and, in consequence, varying levels of simplification/approximation/assumption are used appropriate to the reasonable needs of the target audience. So, for instance, a new PPL student needs a story rather different to that which would be appropriate to a post-graduate level. You will notice that several of the posts make reference to the Mach No. variations (which appear in numerous texts), but not the Reynolds No. variations (which tend to hide in aerodynamics texts), when discussing indicated speed at the stall .. same sort of thing.
One needs to be a little wary when quoting design standards (Part 25 and the like) as the "real" words of interpretation are in the explanatory documentation used by certification practictioners. One ought to be very wary of consulting design standards in respect of a particular aircraft unless the relevant (ie not the current) standard is obtained. These animals are an evolving thing and the differences in requirements over time vary quite significantly.
Vmcg/Vmca
There is no necessarily hard and fast relationship between the Vmcg and Vmca numbers of which I am aware... the point I was trying to make is along the lines that I can't see any reason why one need be higher than the other. Just trying to highlight the dangers in making definitive statements and/or drawing a general conclusion from an inadequate range of specific examples. Perhaps some of our experienced FT brethren might be able to add comment ?
Far more important is your suggestion that the values are only dependent on density... while the certification figures are very tightly controlled it is necessary that the pilot-in-the-wild be aware of a variety of factors which, most definitely, do affect the real values which are going to bite the pilot on the day. Consider
(a) CG
(b) crosswind for Vmcg (as an aside, the 7 kt derives from ancient UK practice .. be aware that US practice is to determine Vmcg for nil wind .. and the actual limitation on the day is VERY wind dependent. Also, depending on the vintage of design standard being used, the centreline deviation may relate to different limits)
(c) bank angle for Vmca (very dependent)
...etc
Indicated Stall Speed
Putting to one side the argument that stall is driven by incidence, not speed, indicated stall speed will vary with altitude. What you have missed, I suspect, is the often/usually ignored variation in CLmax due to variations in other parameters such as Mach and Reynolds Nos. which, themselves, vary with level. CLmax reduces at higher values of Hp and the KIAS increases slightly. Reference to any standard aerodynamics text will bring you up to speed on this matter. It is, however, generally not addressed to any extent, if at all, in pilot texts.
No problem with your basic explanations.
However, it is endemic in most areas of study, not only flying, that different explanations are pitched at different target audiences and, in consequence, varying levels of simplification/approximation/assumption are used appropriate to the reasonable needs of the target audience. So, for instance, a new PPL student needs a story rather different to that which would be appropriate to a post-graduate level. You will notice that several of the posts make reference to the Mach No. variations (which appear in numerous texts), but not the Reynolds No. variations (which tend to hide in aerodynamics texts), when discussing indicated speed at the stall .. same sort of thing.
One needs to be a little wary when quoting design standards (Part 25 and the like) as the "real" words of interpretation are in the explanatory documentation used by certification practictioners. One ought to be very wary of consulting design standards in respect of a particular aircraft unless the relevant (ie not the current) standard is obtained. These animals are an evolving thing and the differences in requirements over time vary quite significantly.
Vmcg/Vmca
There is no necessarily hard and fast relationship between the Vmcg and Vmca numbers of which I am aware... the point I was trying to make is along the lines that I can't see any reason why one need be higher than the other. Just trying to highlight the dangers in making definitive statements and/or drawing a general conclusion from an inadequate range of specific examples. Perhaps some of our experienced FT brethren might be able to add comment ?
Far more important is your suggestion that the values are only dependent on density... while the certification figures are very tightly controlled it is necessary that the pilot-in-the-wild be aware of a variety of factors which, most definitely, do affect the real values which are going to bite the pilot on the day. Consider
(a) CG
(b) crosswind for Vmcg (as an aside, the 7 kt derives from ancient UK practice .. be aware that US practice is to determine Vmcg for nil wind .. and the actual limitation on the day is VERY wind dependent. Also, depending on the vintage of design standard being used, the centreline deviation may relate to different limits)
(c) bank angle for Vmca (very dependent)
...etc
Indicated Stall Speed
Putting to one side the argument that stall is driven by incidence, not speed, indicated stall speed will vary with altitude. What you have missed, I suspect, is the often/usually ignored variation in CLmax due to variations in other parameters such as Mach and Reynolds Nos. which, themselves, vary with level. CLmax reduces at higher values of Hp and the KIAS increases slightly. Reference to any standard aerodynamics text will bring you up to speed on this matter. It is, however, generally not addressed to any extent, if at all, in pilot texts.
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John T. and Mad F. S.,
You both are correct regarding the Reynold no./Mach effect on Clmax. An oversight on my part.
Thanks for the info and a pot of ale for you sir.
Cheers
Chryse
You both are correct regarding the Reynold no./Mach effect on Clmax. An oversight on my part.
Thanks for the info and a pot of ale for you sir.
Cheers
Chryse
Why do it if it's not fun?
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CPB,
Correct me if I'm wrong, but I don't believe that gliding range varies with weight, so long as you fly the best glide speed for that weight.
As weight goes up, best glide speed goes up. Rate of descent also goes up by the same percentage, resulting in a glide of exactly the same distance, but taking less time.
However, manufacturers generally only quote best glide speed for maximum all-up weight. So, if you fly the speed in the manual, then you are correct - the heavier you are, the closer the quoted best glide speed is to the actual best glide speed, and so you'll be able to glide further if you fly the book numbers.
At least, that's how I understand it.....
That aside, as with powered flight, you'll get better range by increasing your speed slightly in a headwind, and decreasing it slightly in a tailwind, to maximise or minimise the effect of the wind, but this effect is negligable.
FFF
---------------
Correct me if I'm wrong, but I don't believe that gliding range varies with weight, so long as you fly the best glide speed for that weight.
As weight goes up, best glide speed goes up. Rate of descent also goes up by the same percentage, resulting in a glide of exactly the same distance, but taking less time.
However, manufacturers generally only quote best glide speed for maximum all-up weight. So, if you fly the speed in the manual, then you are correct - the heavier you are, the closer the quoted best glide speed is to the actual best glide speed, and so you'll be able to glide further if you fly the book numbers.
At least, that's how I understand it.....
That aside, as with powered flight, you'll get better range by increasing your speed slightly in a headwind, and decreasing it slightly in a tailwind, to maximise or minimise the effect of the wind, but this effect is negligable.
FFF
---------------
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Flying for fun,
I was referring to the effect that you mention in your final paragraph. Whether its a negligable effect or not is obviously a function of proportions. In any event negligable effects are often the nub of many an exam question....
CPB
I was referring to the effect that you mention in your final paragraph. Whether its a negligable effect or not is obviously a function of proportions. In any event negligable effects are often the nub of many an exam question....
CPB