Pof F/ power curve question
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So if a plane always flies in still air, how come I have still got the bruises on my shoulders from the straps on my shoulders fron a recnt flight across France where my head was hitting the canopy.
Or did I just imagine it?
Or did I just imagine it?
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World of difference between the horizontal component of airflow (i.e. the wind) and the local vertical component (bumps). I have been beaten around the sky on a calm day (very hot so lots of vertical airflow but in a high pressure system so little horizontal) and had a ride smooth as glass with 80 knots on the nose at FL100.
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That was due to turbulence, which is a different thing. Turbulence can be caused by air flowing over terrain below. Here is a nice picture. This is not related to whether the airflow is a tailwind or a headwind relative to the aircraft.
A lot of pilots think that a plane flies somehow "sideways" when there is a crosswind, for example. One pilot swore blindly his plane vibrated more if flying in a crosswind. It's a favourite old topic - always raises a little smile. I have even met an instructor who believed this.
A lot of pilots think that a plane flies somehow "sideways" when there is a crosswind, for example. One pilot swore blindly his plane vibrated more if flying in a crosswind. It's a favourite old topic - always raises a little smile. I have even met an instructor who believed this.
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But the whole point is that you are more likely to encounter turbulance on a windy day.
Plus when the wind componant is 30% of the cruise speed the effect is much more noticeable.
I have always found it more comfortable flying into wind on a turbulent day, rather than tailwind. Hard to define but the plane just feels "happier" .
Plus when the wind componant is 30% of the cruise speed the effect is much more noticeable.
I have always found it more comfortable flying into wind on a turbulent day, rather than tailwind. Hard to define but the plane just feels "happier" .
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Plus when the wind componant is 30% of the cruise speed the effect is much more noticeable.
I have always found it more comfortable flying into wind on a turbulent day, rather than tailwind. Hard to define but the plane just feels "happier" .
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It may be pure conjecture but if the plane is going to pitch up, it always appears to pitch up tail first(ie nose down) as if the turbulence is coming from the rear.
As I say, it may just be me, but I know I am much happier in a headwind if its turbulent.
I take your point about the " hardness" of the bumps.
Coming over the channel on the day mentioned above, I was well throttled back to stay well clear of the yellow arc but we were still covering the ground at over 200mph on what would normally almost be decent power!
As I say, it may just be me, but I know I am much happier in a headwind if its turbulent.
I take your point about the " hardness" of the bumps.
Coming over the channel on the day mentioned above, I was well throttled back to stay well clear of the yellow arc but we were still covering the ground at over 200mph on what would normally almost be decent power!
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In general if the windspeed is 30% of cruise, I would expect more turbulance down low than at 20% (i.e. 50 knots rather than 30 knots). However, I have never noticed that bumps on a 30 kt day are worse when I slow down. The physics say the particularly hard bumps should be softer at a slow speed (because the wings stall a bit and you can't get as high a G load).
However, in my flying, I am most likely to be slow at less than 1500 ft (fitting into circuit traffic) and fast at altitude, which means it is typically rougher when I am slow than fast - but this is down to altitude not speed.
None of this has anything to do with the practicality of flying at best range speed and how this changes with head/tail wind.
your preference for headwind may be that it gives more time to think and therefore you have less pressure. With 60knots of wind I find it easier (other than the frustration) to have it on the nose as everything that relates to the ground happens at half speed relative to the wind from behind.
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A further thought, the main cause of turbulence will be a change in local vertical airflow - and this will happen over a certain distance. The faster you are going over the ground the higher the frequency of these reversal (you should have more g reversals per second). this may be perceived as less comfortable or being more beaten up (head bashes per minute goes up but the total number of head bashes remains constant)
However, in my flying, I am most likely to be slow at less than 1500 ft (fitting into circuit traffic) and fast at altitude, which means it is typically rougher when I am slow than fast - but this is down to altitude not speed.
None of this has anything to do with the practicality of flying at best range speed and how this changes with head/tail wind.
your preference for headwind may be that it gives more time to think and therefore you have less pressure. With 60knots of wind I find it easier (other than the frustration) to have it on the nose as everything that relates to the ground happens at half speed relative to the wind from behind.
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A further thought, the main cause of turbulence will be a change in local vertical airflow - and this will happen over a certain distance. The faster you are going over the ground the higher the frequency of these reversal (you should have more g reversals per second). this may be perceived as less comfortable or being more beaten up (head bashes per minute goes up but the total number of head bashes remains constant)
Last edited by mm_flynn; 27th Aug 2009 at 12:14. Reason: further thought
IO540, if you're going to make it that complicated, then you'll need to specify whether its FP or CSU, since you can maintain quasi-constant BSFC with a CSU, but it will degrade more rapidly when reducing power with a FP propellor.
edit: actually, I don't think it will make any difference to my badly drawn graph, since the only thing that will change is the shape of the drag power curve (OK, you'll need to re-label that as SHP to be strictly correct). I think the curve will only change subtlely - not enough to make my diagram any more inaccurate.
The main point is to demonstrate the effect of a tailwind (in this case), where GS > TAS
edit: actually, I don't think it will make any difference to my badly drawn graph, since the only thing that will change is the shape of the drag power curve (OK, you'll need to re-label that as SHP to be strictly correct). I think the curve will only change subtlely - not enough to make my diagram any more inaccurate.
The main point is to demonstrate the effect of a tailwind (in this case), where GS > TAS
Avoid imitations
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Aircraft have inertia.
If a "headwind with updraught" gust hits the aircraft, it will momentarily give an increase in IAS and in lift, which will tend to amplify the updraught effect because the wings will generate an addition to the upwards "bump".
If the same aircraft is travelling downwind, the same gust will be "tailwind with updraught". The reduction in IAS will decrease the lift, which will offset the "updraught" and give a lesser "bump" effect.
Obviously, this is one case where our oft mentioned "aircraft on a conveyor belt" might be an easier ride....until it takes off, of course.
If a "headwind with updraught" gust hits the aircraft, it will momentarily give an increase in IAS and in lift, which will tend to amplify the updraught effect because the wings will generate an addition to the upwards "bump".
If the same aircraft is travelling downwind, the same gust will be "tailwind with updraught". The reduction in IAS will decrease the lift, which will offset the "updraught" and give a lesser "bump" effect.
Obviously, this is one case where our oft mentioned "aircraft on a conveyor belt" might be an easier ride....until it takes off, of course.
Avoid imitations
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I've never heard otherwise - surely on finals the horizontal variations in IAS are known as "windshear" - larger aircraft being more affected by it due to their larger inertia.
As moving air, like other gases, likes to form a vortex, an aircraft passing through one is likely to experience both horizontal and vertical components.
As moving air, like other gases, likes to form a vortex, an aircraft passing through one is likely to experience both horizontal and vertical components.
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Wind shear is not turbulence. WS is just the natural variation of wind speed with height, and yes a plane with more inertia (or a longer engine spool up time) will be more affected because it won't be able to maintain a constant IAS.
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I think our opinions will continue to differ in that respect.
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OK, there are umpteen types of turbulence but I was thinking of the kind referred to higher up, which was caused by wind passing over terrain, and causing a bumpy ride for a plane flying at say 1000-2000ft AGL.
It would suprise me if there was a significant small-scale horizontal airflow speed variation in the above case. But plenty of vertical movement.
It would suprise me if there was a significant small-scale horizontal airflow speed variation in the above case. But plenty of vertical movement.
