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

No change to Vx since that is referenced to the still air distance covered during the climb afaik...

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.

The air-speed for max angle of climb reduces with headwind and increases with tailwind. By how much depends on how thrust and drag change with air-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

Sorry, it does not, with regard to airspeed.
Groundspeed, on the other hand, is a different kettle of fish.
Don't make the mistake of confusing the two.:ugh:

411A;

Sorry, it sure does (airspeed), and any glider pilot can explain it to you.

Regards,
HN39

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 ? :hmm:

Talk about confusing the poor guy. Vx is not an angle, it's a speed. :cool:

Wiki:
So Vx remains constant regardless of wind. It is purely aerodynamic in nature, being the speed where excess thrust/power is greatest, and is not affected by the wind. The actual angle achieved will vary: more headwind, the steeper the climb. This is because while the rate of climb eg 500ft/min is constant, the groundspeed has reduced (because of the wind. Over say 1nm, the aircraft will spend longer to get there, therefore allowing more climbing time. Higher after 1nm means a steeper angle/gradient achieved. The pilot would still only see the "normal" rate of climb on the VSI though.

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

Gliders are generally not used in airline operations...as the paying passengers would undoubtedly be slightly less amused at the thought.:}

I have been thinking about this all day and still do not understand. If you change the airspeed axis to groundspeed (ie applying wind to the IAS), I agree you may be showing the achieved gradient but that must be still at the same groundspeed.

Are you suggesting that if you slow down twenty knots (IAS), the gradient will increase?

Capn Bloggs;

Does this graph answer your questions?

Regards,
HN39

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.

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. ;)

IMO, the gradient will increase as the windspeed increases until the windspeed reaches 142-ish m/s. At that point, you'd be going vertical (in the climb attitude, of course, with 142m/s showing on your ASI). Your groundspeed would be zero.

Great answers guys:ok:, 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.

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

Nonsens