Somebody who know this?
Thread Starter
Join Date: Sep 2008
Location: under the sky
Posts: 60
Likes: 0
Received 0 Likes
on
0 Posts
Somebody who know this?
Hello all
I have 2 questions I would like to figure out so I hope there are some smart brains out there.
What effect does headwind have on max angle of climb (Vx) speed ?
I found out there is an increase in the climb angle but what about the speed?
What gives the worst icing condition:
Largewater droplets with temp. below 0
or
small water droplets with temp. below 0?
Cheers
I have 2 questions I would like to figure out so I hope there are some smart brains out there.
What effect does headwind have on max angle of climb (Vx) speed ?
I found out there is an increase in the climb angle but what about the speed?
What gives the worst icing condition:
Largewater droplets with temp. below 0
or
small water droplets with temp. below 0?
Cheers
Join Date: Aug 2005
Location: fl
Posts: 2,525
Likes: 0
Received 0 Likes
on
0 Posts
I was flying a J3 cub playing in a 40+ knot wind and if you can slow it down to the wind speed you can climb with no forward movement so guess on that day slowing down the climb speed increased Vx to 90 degrees.
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by flyhigh85
What effect does headwind have on max angle of climb (Vx) speed ?
I don't think that the question about small or large supercooled water droplets can be answered in general. It depends primarily on the water content and on the type of de/anti-ice protection of the airplane (e.g. rubber boots versus thermal). Larger droplets due to their inertia tend to be less deflected by the airflow than smaller droplets, which affects the catchment-efficiency and the extent of the area of impingement on the airplane.
Regards,
HN39
Last edited by HazelNuts39; 7th Mar 2011 at 20:51. Reason: words in italics added for clarity
Join Date: Mar 2000
Location: Arizona USA
Posts: 8,571
Likes: 0
Received 0 Likes
on
0 Posts
The speed for max angle of climb reduces with headwind and increases with tailwind. By how much depends on how thrust and drag change with airspeed.
Groundspeed, on the other hand, is a different kettle of fish.
Don't make the mistake of confusing the two.
Guest
Posts: n/a
hi Hazel
just imagine you are flying the glider with only 4 instruments
altimeter, ASI, VSI and compass
so you are "connected" to air and have no clue of wind or groundspeed
so how will
???
when you do not know the wind ?
Besides gliders NEVER climb.
They constantly descend even in a an updraft. Right ?
just imagine you are flying the glider with only 4 instruments
altimeter, ASI, VSI and compass
so you are "connected" to air and have no clue of wind or groundspeed
so how will
The speed for max angle of climb reduce with headwind
when you do not know the wind ?
Besides gliders NEVER climb.
They constantly descend even in a an updraft. Right ?
Originally Posted by bubbers44
slowing down the climb speed increased Vx to 90 degrees.
Wiki:
Climbing at Vx allows pilots to maximize the altitude gain per unit ground distance. That is, Vx allows pilots to maximize their climb while sacrificing the least amount of ground distance. This occurs at the speed for which the difference between thrust and drag is the greatest (maximum excess thrust).
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
Green Guard;
I wasn't referring to gliders, just to glider pilots, because they should be familiar with optimizing their airspeed for vertical and horizontal air movement.
I suggest you make a plot of rate-of-climb on the vertical or y-axis versus airspeed on the horizontal or x-axis for whatever airplane you are interested in. You'll get a curve shaped somewhat similar to one of the curves shown here. Then draw a straight line from the origin and tangent to your curve. The angle of that tangent to the x-axis represents the angle of climb, and the point it shares with your curve is your speed for max angle of climb in still air. Now draw another tangent to your curve from a point at 10 kt on the x-axis. The point where the second tangent touches your curve is the airspeed for max angle of climb in a 10 kt headwind.
Regards,
HN39
I wasn't referring to gliders, just to glider pilots, because they should be familiar with optimizing their airspeed for vertical and horizontal air movement.
I suggest you make a plot of rate-of-climb on the vertical or y-axis versus airspeed on the horizontal or x-axis for whatever airplane you are interested in. You'll get a curve shaped somewhat similar to one of the curves shown here. Then draw a straight line from the origin and tangent to your curve. The angle of that tangent to the x-axis represents the angle of climb, and the point it shares with your curve is your speed for max angle of climb in still air. Now draw another tangent to your curve from a point at 10 kt on the x-axis. The point where the second tangent touches your curve is the airspeed for max angle of climb in a 10 kt headwind.
Regards,
HN39
Last edited by HazelNuts39; 8th Mar 2011 at 10:54. Reason: graph
Join Date: Mar 2000
Location: Arizona USA
Posts: 8,571
Likes: 0
Received 0 Likes
on
0 Posts
Sorry, it sure does (airspeed), and any glider pilot can explain it to you.
Originally Posted by Hazelnuts
The point where the second tangent touches your curve is the airspeed for max angle of climb in a 10 kt headwind.
Are you suggesting that if you slow down twenty knots (IAS), the gradient will increase?
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes
on
0 Posts
Join Date: Jun 2010
Location: On the ground too often
Age: 49
Posts: 127
Likes: 0
Received 0 Likes
on
0 Posts
I am struggling to get my head around this a little bit. I came up with the following thought experiment. Imagine an aircraft that has a Vx of 60kts. The aircraft is flying in a 50kt headwind. So the aircraft has a ground speed of 10kts, and one could imagine that it is climbing farily steeply (relative to the ground). If the pilot were to now slow down to an airspeed of 50 kts, thus reducing the groundspeed to 0, provided the aircraft can climb at 50 knots - it will now have a climb angle of 90 degrees.
Does this make sense?
Golf-Sierra
Hazelnuts,
Sorry, but no it doesn't. All that graph shows is that, as the thrust-to-weight ratio increases, the vertical speed increases (as we would expect), and that there is only one airspeed for each T to W that will provide maximum climb performance ie top of each curve. The curve clearly shows that if you change the airspeed then the ROC will reduce.
The 20m/s headwind speed bar merely shows the groundspeed, not the new airspeed as you claim, in that wind; all the groundspeeds are simply 20m/s less than the airspeed. What is does show is that in a headwind, you will get a higher gradient when at the best IAS for the ROC, but only because same ROC is being achieved at a slower groundspeed, not a lower IAS.
So I maintain that a headwind has no effect on the Vx speed. It affects the resulting gradient but not the speed itself.
Correct. See Bubbers post above. Tigers used to do it. A vertical circuit. Takeoff, Up, fly "backwards", down, touch and go, up...
Reducing your speed from Vx of 60KIAS to 50 would problably reduce your climb performance somewhat (as per Hazelnut's graph), but any climb would in effect be vertical.
Sorry, but no it doesn't. All that graph shows is that, as the thrust-to-weight ratio increases, the vertical speed increases (as we would expect), and that there is only one airspeed for each T to W that will provide maximum climb performance ie top of each curve. The curve clearly shows that if you change the airspeed then the ROC will reduce.
The 20m/s headwind speed bar merely shows the groundspeed, not the new airspeed as you claim, in that wind; all the groundspeeds are simply 20m/s less than the airspeed. What is does show is that in a headwind, you will get a higher gradient when at the best IAS for the ROC, but only because same ROC is being achieved at a slower groundspeed, not a lower IAS.
So I maintain that a headwind has no effect on the Vx speed. It affects the resulting gradient but not the speed itself.
Originally Posted by Golf-Sierra
Imagine an aircraft that has a Vx of 60kts. The aircraft is flying in a 50kt headwind. So the aircraft has a ground speed of 10kts, and one could imagine that it is climbing farily steeply (relative to the ground). If the pilot were to now slow down to an airspeed of 50 kts, thus reducing the groundspeed to 0, provided the aircraft can climb at 50 knots - it will now have a climb angle of 90 degrees.
Reducing your speed from Vx of 60KIAS to 50 would problably reduce your climb performance somewhat (as per Hazelnut's graph), but any climb would in effect be vertical.
Thanks for producing another of your superb graphics, HN39. Prior to that, trying to get my head around your written description was only partially successful, and cost me several minutes sleep at bedtime!
The mists are now slowly lifting, although you haven't drawn us a sample tangential line. Do I infer correctly that at a thrust/weight ratio of, for example, 0.2, a H/W of more than 30m/s (60kts) does not further improve my chances of missing the top of the mountain? But what if headwind equals TAS (see Cpn Bloggs et al)?
Don't worry, you'll get us there in the end.
The mists are now slowly lifting, although you haven't drawn us a sample tangential line. Do I infer correctly that at a thrust/weight ratio of, for example, 0.2, a H/W of more than 30m/s (60kts) does not further improve my chances of missing the top of the mountain? But what if headwind equals TAS (see Cpn Bloggs et al)?
Don't worry, you'll get us there in the end.
Last edited by Chris Scott; 8th Mar 2011 at 14:58. Reason: Additions (in red font)
Originally Posted by Gary Scott
Do I infer correctly that at a thrust/weight ratio of, for example, 0.2, a H/W of more than 30m/s (60kts) does not further improve my chances of missing the top of the mountain?
Thread Starter
Join Date: Sep 2008
Location: under the sky
Posts: 60
Likes: 0
Received 0 Likes
on
0 Posts
Great answers guys
, AIR speed will be unchanged but groundspeed will decrease makes perfectly sense. About the water droplets I guess there is just to litle information in the question to make a general conclussion.
, AIR speed will be unchanged but groundspeed will decrease makes perfectly sense. About the water droplets I guess there is just to litle information in the question to make a general conclussion.
Let's suppose that we are climbing at 100 kts airspeed, producing our best angle of climb in still air.
If we meet a 90 knot headwind and reduce our airspeed to 90 knots will be in a vertical climb. So going slower in a headwind increased our climb angle.
If the headwind then increases to 110 knots we will need to increase our airspeed to 110 knots to restore our vertical climb. So going faster in a headwind increased our climb angle.
Curiouser and curiouser!!
So depending on the relationship between our airspeed and our headwind, we may need to increase or decrease our airspeed to maximise our climb angle.
If we meet a 90 knot headwind and reduce our airspeed to 90 knots will be in a vertical climb. So going slower in a headwind increased our climb angle.
If the headwind then increases to 110 knots we will need to increase our airspeed to 110 knots to restore our vertical climb. So going faster in a headwind increased our climb angle.
Curiouser and curiouser!!
So depending on the relationship between our airspeed and our headwind, we may need to increase or decrease our airspeed to maximise our climb angle.
Capt Bloggs and 411a,
Sorry, you are both incorrect.
Bloggs- think about the senerio above- the aircraft that has a STILL AIR Vx of 60 kts will climb MORE STEEPLY wrt the ground at 50 kts in a 50 kt headwind.
Vx is max excess thrust- IN STILL AIR.
reference:-
Performance of light aircraft - Google Books
Sorry, you are both incorrect.
Bloggs- think about the senerio above- the aircraft that has a STILL AIR Vx of 60 kts will climb MORE STEEPLY wrt the ground at 50 kts in a 50 kt headwind.
Vx is max excess thrust- IN STILL AIR.
reference:-
Performance of light aircraft - Google Books
Join Date: Oct 2006
Location: Europe
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Nonsens
You guys are cutting a hair in two. If you want to do that then you have to be logical and include the vertical component of the wind as well. The only way to resolve this problem is to take into account the change of drag with speed and the change of thrust with speed, and if you want to be precise, also the change of TAS with altitude at constant IAS. Having said so even the ADC change the IAS as a function of AOA. Some ADC take this into account and some don't. Is there a solution to your question? Yes there is. If all relationships between the variables are known you can solve the equation. So what I want to say is: don't worry be happy and keep it simple or you are going to stall. Now what are you going to do if ATC asks you max angle of climb while climbing in a increasing headwind while at the same time they give you a radar vector that swings you 180° around?