B52 Crash Video's

Hey D.H., he was NOT speaking of you.

Reply to
Six_O'Clock_High
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Mr. McLaren,

You stated the following:

-There is another reason.

As you get close to the ground, the wind speed generally drops, all th way to almost zero a few inches off the ground. So if you're landin into the wind, your airspeed will drop as you go down even if you ground speed stays the same. This helps the plane stall onto the groun in those last few inches in what is usually considered a perfect landing.

However, if you land downwind, this reduction in wind speed as you g down will actually increase your air speed, causing your plane to tak much longer to land, even longer than you'd expect it to after takin into account the wind speed. I've seen people take up the entire runwa landing downwind and smacking into the fence at the end because the didn't take this into account. (The only way around it is to us controls to burn up airspeed -- spoilers, crow, slip, etc., or to do

180 degree turn and land upwind (can be dangerous if you have no power or to land the plane rather hard (and very fast) and not go for smooth landing.)-

Excuse me for saying so, but this is soooooo wrong it's not even funny In fact, it's about 180º from right, it's so wrong. You aren't eve in the same city as the ballpark, this is so wrong.

  1. Wind speed does not necessarily diminish the closer it gets to th ground. Wind speed will be the same at 1' or 100'. There may b buildings, trees, or other obstacles that make it appear that the win is calmer, but in an open field, like an airport, the wind speed is th same. This precludes things like microbursts. I'm talking a norma day.

  1. Landing into the wind will reduce your ground speed, not you airspeed. This is a basic tenant of aviation that a student pilo learns before they solo. Your ground speed is always affected by th wind. If you fly into a 15 knot headwind, your ground speed will be 1 knots slower than your airspeed. If you fly with a 15 knot tailwind your ground speed will be 15 knots faster than your Indicate Airspeed. The reason you land -into- the wind is to lower your groundspeed, so a to use a little runway as possible. The same for take off. You shoul always take off and land into the wind. The landing reduces you ground speed, but the take off will add extra lift to the wings. take off into a 15 knot headwind at a ground speed of 60 knots give you 75 knots over the wing, and increases lift. Conversely, a take of downwind, with a 15 knot wind at a ground speed of 60 knots will onl give you 45 knots of wind over the wing!

  2. The stall, for those people who make full stall landings ha

-nothing, repeat Nothing- to do with ground speed or whether you are o are not flying into the wind. A stall occurs at any altitude or an speed where the angle of attack exceeds the point where the wing ca produce lift. In a landing situation, the pilot of the airplan reduces the airspeed, NOT groundspeed, of the aircraft, as shown on th airspeed indicator (IAS, or Indicated Airspeed) by reducing throttle o adding drag (flaps, landing gear, spoilers, or a slip) until the poin where he flares the aircraft over the runway, the wing, in that angl of attack, is no longer able to produce enough lift to keep th airplane flying. However, I will conceed that reducing airspeed doe reduce the ground speed a like amount, all else being equal. However that wasn't the point I was trying to make. It's the Airspeed over th wing, and not the ground speed that controls when the wing stalls.

  1. As for your downwind explanation, you have no idea what you ar talking about. If the air is moving at 15 knots, then your groundspee has increased by 15 knots. If your planned touchdown speed is 70 knot (not unrealistic in two and four place trainer aircraft today) the with a 15 knot tailwind, you will be doing 85 knots flying down th runway. Your airspeed will still read 70 knots, but your groundspeed which is important because you're going to be ON the ground in moment, is still at 85 knots. Hence, you will take up a lot longer t land. Landing -into- that 15 knot headwind will continue to help you to slow down all throughout the landing, but landing -with- the tailwind will continue to push you along, greatly extending your landing run.

Your statement of using controls to offset the effect of a tailwind on landing will cause you to decrease the AIRSPEED of the airplane, which will lead to a stall, and a recreation of the accident this whole thread is about. Stall, Spin, Crash and Burn!! As to landing fast and hard, be my guest. You -will- be landing fast.

Just to make sure, you aren't a FAA licensed pilot, are you? If you are, please, I highly suggest that you find an instructor and take a biennial flight review as soon as possible, because you are going to severly dangerous in an airplane.

Gary

Reply to
GaryMC1

"Six_O'Clock_High" wrote

I do that a lot, Jim. In fact, it is my favorite way to fly. I'm a fun fly plane type of junky.

I follow my previously mentioned practice when I'm flying standard sport or scale models. It is real easy to become accustomed to having tons of power and grossly authoritative control surfaces. So much so that one can easily find themselves in an untennable situation before they realize that they are flying a brick with no power and no control authority. I don't like surprises like that. 8>)

Ed Cregger

Reply to
Ed Cregger

Yup, elevator's one of those clues. If I find I'm having to add more and more up elevator to keep the plane level I know it's time to bump up the throttle a bit.

Reply to
C G

That is true enough. It never ceases to amaze me how many fail to put the nose down when the prop stops. . . . It is dramatically worse on biplanes with their big drag bucket.

Reply to
Six_O'Clock_High

Or how many think the elevator controls altitude... Dr.1 Driver "There's a Hun in the sun!"

Reply to
Dr1Driver

it does doenst it? Under power that is...:0)

Dr1Driver wrote:

Reply to
jim breeyear

I never said it waz!

Roger that!. It is the difference between precision turns (making cycloids) and turns about a point. Try making figure 8ates when the air mass is moving without correcting for drift. bye bye.

Reply to
jim breeyear

Reply to
jim breeyear

Huh? Did you actually read Doug's message? What you said in your message doesn't in any way contradict what he said, which makes your "soooooo wrong it's not even funny" comments to look rather strange. You said basically the same thing, with the only difference between your point of view and his in what you said under 1: the difference between the wind speed close to the ground and at higher altitude. You attempts to emphasize the difference between ground speed and airspeed are completely uncalled for. I don't see anything in Doug's message that would suggest that he mistakes one for another.

First thing that should be said here is that the wind speed close to the ground is indeed always lower than than that at some altitude. This is not discussable. This is a basic fact from physics of gases (or fluids, for that matter). In fact, the speed of that very thin layer of air that actually _contacts_ the ground is always _zero_, regardless of the current wind speed. As you get further from the surface, the wind speed increases until it becomes equal to the current wind speed (say, S). The only question that exists here is what is the hight (say, H) of that transitional area where wind speed raises from 0 to S as we get further from the ground. In most circumstances, the value of H will be to small to have any effect of full-scale aircraft (and your final comments about "FAA licensing" and such are more than irrelevant), but it can have certain effect on model aircraft for obvious reasons (exactly how Doug described). The actual value H depends on many factors. It can depend significantly on the ground temperature, type of surface (pavement, gravel, grass) and many other factors. There's no way to give a definitive answer without taking these factors into the account.

Reply to
Andrey Tarasevich

Wow, where did this stuff come from? The reason people smack into the fence on downwind landings is because the plane is travelling double the windspeed faster (relative to ground speed). For illustrative purposes, if your landing approach is 25mph TAS and you are landing into a 10mph wind, your ground speed will be 15mph. Turn that around to a down wind landing and your ground speed is now 35mph. The difference between these is 20mph!

The difference in wind speed closer to the ground is insignificant and the plane will adjust to the change in wind speed fairly quickly. Just as when you chop the throttle in level flight the plane doesn't take the length of the runway to slow down unless it is a very heavy, slick airframe.

Reply to
Paul McIntosh

No. Under ENOUGH power, maybe. Elevator only controls attitude in pitch. Ask anyone who's stalled a plane while holding full "up" elevator. I plane with less than or equal to a 1:1 thrust to weight/drag ratio will eventually stall at some AOA and degree of elevator deflection. If the power ain't there, it ain't going "up". Dr.1 Driver "There's a Hun in the sun!"

Reply to
Dr1Driver

| Excuse me for saying so, but this is soooooo wrong it's not even funny. | In fact, it's about 180º from right, it's so wrong. You aren't even | in the same city as the ballpark, this is so wrong.

No, it's not. It's right.

| 1. Wind speed does not necessarily diminish the closer it gets to the | ground. Wind speed will be the same at 1' or 100'.

No, it will not. This is completely and utterly wrong.

Due to drag from the ground, the wind closer to the ground will generally be slower than it is up higher. And right at the ground (I'm talking a mm or so), it will basically be zero.

| There may be buildings, trees, or other obstacles that make it | appear that the wind is calmer

If the wind appears calmer, it is calmer. And yes, buildings, trees and even the ground will make the wind `calmer'. (They'll also create turbulence, but that's not what we're talking about here.)

| but in an open field, like an airport, the wind speed is the same. | This precludes things like microbursts. I'm talking a normal day.

And we're talking about models. Model strips are often surrounded by trees, which make the effect much larger, but trees are not needed for the effect to manifest at all. Perfectly flat ground will create a wind gradient as well, just to a smaller degree.

| 2. Landing into the wind will reduce your ground speed, not your | airspeed.

OK, you're preaching to the choir here. I offered this diminishment of the wind as you get close to the ground as an additional reason why you land upwind, not the only reason. If you feel that I was suggesting something else, you need to work on your reading comprehension.

| 3. The stall, for those people who make full stall landings has | -nothing, repeat Nothing- to do with ground speed or whether you are or | are not flying into the wind.

Incorrect.

As you get closer to the ground, wind generally decreases in velocity. This is due to the drag caused by the Earth and things on it. Right at the ground, the wind is zero. (In fact, in anything that flows through the air, there is a region right around it where wind speed is practically zero. This is why ceiling fan blades collect dust rather than blowing it off -- the dust gets caught in this zero-wind region.)

So, if you're coming down right at stall speed, as you get closer to the ground the wind decreases. If you're landing upwind, the decreasing wind will mean your airspeed will decrease, and unless you compensate for this, you will stall and probably crash.

Full scale instructors generally teach you that it's not smart to be close to the ground right at stall speed. But with a R/C model, it's not always obvious how close you are to stall speed and how you're getting closer as you come down.

| 4. As for your downwind explanation, you have no idea what you are | talking about. If the air is moving at 15 knots, then your groundspeed | has increased by 15 knots. If your planned touchdown speed is 70 knots | (not unrealistic in two and four place trainer aircraft today)

We are talking about models here, not full scale planes. This is rec.models.rc.air, after all. Most models land much slower than that.

If your model lands at 30 mph, and you've got a 20 mph tail wind, that gives you an ground speed of 50 mph. However, as you come closer to the ground, the wind generally drops off. So, if you drop far enough where the wind speed is only 10 mph, your plane still has the same velocity (with respect to the ground -- it's the wind that's changing quickly, not your plane's velocity) and so it now has an air speed of

40 mph. Generally this extra air speed will cause your plane to balloon up until you bleed it off, unless you put the nose down. Which works fine, but as you get even lower, the effect becomes even larger, and if you never slow the plane down, you'll end up landing with almost 50 mph of air speed (and 50 mph of ground speed too, of course.) When people try to bring the air speed down, that's when you end up taking the entire runway.

The effect is larger for a model than a large plane. This is because a full sized plane's wing may be 5 feet off the ground -- but a model's plane may be only 5" off the ground. The wind speed will definitely be higher at 5 feet than at 5 inches.

| Your statement of using controls to offset the effect of a tailwind on | landing will cause you to decrease the AIRSPEED of the airplane, which | will lead to a stall, and a recreation of the accident this whole | thread is about.

Did you see the video? He was fairly high up when things started going wrong. He was not really landing or taking off anymore. I don't see where simply making a downwind landing could possibly lead to an accurate recreation of the B52 model accident.

| Stall, Spin, Crash and Burn!! As to landing fast and | hard, be my guest. You -will- be landing fast.

Yes, a downwind landing is generally a fast landing. Thank you, Captain Obvious.

| Just to make sure, you aren't a FAA licensed pilot, are you?

Are you?

It's nice that you want to correct me. However, it would be nice if you could at least make sure that you're right before you do so. Also, in the future it would be best if you could try to be not so arrogant about it -- it helps save face when you end up being completely wrong, as you have in this case.

Fortunately, if you are a licensed pilot, the advice given to you by your instructor is still correct -- 1) land and take off upwind whenever possible and 2) don't fly near the ground right at stall speed, and if you are at stall speed, get some more speed before you do anything (like leave the ground effect in a take off.) This effect (the wind gradient) just reinforces these pieces of advice -- it's not the only reason for them.

If you need more information on this,

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covers the dangers of a downwind takeoff (which is relatively analogous to the dangers of a downwind landing) from the perspective of an ultralight. It's not exactly what I'd like to show you, but it's online so you can see it right now, and the pictures do graphically show the wind gradient nicely.

The book `Model Aircraft Aerodynamics' by Martin Simons covers it very well on page 40 (in the 4th Edition.) If you're going to correct people online about things like this, I suggest you buy a copy and read up -- it's a great book. $24, or $13 used. WELL worth it. You can find it on Amazon.com by searching for 1854861905.

Let me quote a passage from the book (page 40) --

Landing downwind is also dangerous. The effect is the opposite of landing into the wind. The aircraft now descends into air which is moving more slowly over the land. Ground speed decreases deceptively, but the model is in effect entering a head-on gust which strengthens as it gets lower. The aircraft has it's own flying speed and also the speed of the wind at higher levels. As it gets into the lowest layers of the gradient the airspeed accordingly increases just when the pilot is anticipating a landing. There is more, not less, left than before, the model still has flying speed. If it does touch down it immediately bounces off again and flies on a long distance, possibly running out of out of landing space.

[There's a good diagram too, but it's hard to type out diagrams.]

This is *exactly* what I was referring to, and I've seen it happen more than once. It's not essential that you understand all these things to be a good pilot, either R/C or full scale, but it doesn't hurt, and it can help save you from embarrassing yourself online.

And if you feel that I was suggesting that you *should* land downwind (I'm not sure if you were or weren't), then you really need to work on your reading comprehension skills.

Reply to
Doug McLaren

Yeah, similar problems arise here and there more often than not. I remember arguing with some folks who couldn't understand how an airplane can take off from a moving conveyor belt (i.e. a conveyor belt that moves against the take off direction) because they didn't seem to understand the difference in the ways automobiles and airplanes propel themselves. At certain abstract level these misperceptions have a lot in common. Probably, that's just the way an unprepared human brain works.

Reply to
Andrey Tarasevich

The ability to comprehend mechanical concepts is not something everyone has. Just like some of us can't figure out what color tie should go with a particular shirt. I admire those who can coordinate colors, but for the life of me I can't understand how they do it. :-)

Reply to
C G

I'm not taking specifically about why "people smack into the fence on downwind landings". There could be more than one factor at play here. We are taking about the existence (or non-existence) of the effect the difference of wind speed at different altitudes makes on the model airplane. This effect does exist. Whether it plays significant role in the aforementioned "smacking" depend on too many factors. For example, flying gliders I notice that in certain cases combination of lift, ground effect and wind can lead to upwind landings that take up much more space than downwind ones.

Reply to
Andrey Tarasevich

You obviously didn't read exactly what I said or misunderstood. Taking off and landing into wind means a lower ground speed.

All aircraft have a minimum airspeed at which they can fly. This has absolutely no relation to ground speed except in totally still air conditions when airspeed can equal ground speed.

Try to fly a plane of any size more slowly than that airspeed at which the wing will support the plane's weight will result in a stall.

With sufficient height, the situation can be rectified. With not enough a crash is the only outcome.

I still maintain that a plane, flying more slowly with respect to the ground, will suffer less damage than one travelling at a higher ground speed.

Malcolm

Malcolm

Reply to
Malcolm Fisher

| Wow, where did this stuff come from? The reason people smack into | the fence on downwind landings is because the plane is travelling | double the windspeed faster (relative to ground speed).

Yes, but we can pick nicer numbers than yours.

Suppose your plane flies at 30 mph airspeed. Assume 15 mph wind at altitude.

Landing upwind, your ground speed will be 15 mph. Landing downwind, your ground speed will be 45 mph.

Ignoring the wind gradient, you'd think the downwind landing would take three times as much space, which would be generally accurate, except that the wind gradient makes the difference even larger.

Landing upwind, the wind gradient makes your plane come down faster (by eating up airspeed), so you need less space. Landing downwind, it makes your plane come down slower (by adding airspeed), so you need even more space.

It's not an insigifigant effect by any account.

| The difference in wind speed closer to the ground is insignificant | and the plane will adjust to the change in wind speed fairly | quickly.

Ok, suppose the plane adjusts to the change in wind speed (let's assume the gradient goes from 15 mph to 5 mph right near the ground, so the plane gains 10 mph in airspeed) in one second (which would be a de-accelleration of approximately 0.45 g -- the exact time will depend on your plane, but this would be a pretty draggy plane) so that's one more second of flight time spent bleeding off energy, and when your ground speed is 45 mph, that's 66 more feet of landing space you need.

And landing upwind, the opposite happens -- you lose the same amount of airspeed, so that would presumably be 1 second less time spent bleeding off airspeed and altitude. 15 mph at one second = 22 feet

*less* space needed to land. So the total difference here is 88 feet, just due to the wind gradient.

| Just as when you chop the throttle in level flight the plane doesn't | take the length of the runway to slow down unless it is a very | heavy, slick airframe.

Yes, it's usually not a huge effect. But it's certainly noticable.

Not that it has anything to do with how the B-52 model crashed ...

Reply to
Doug McLaren

Well, thankfully I do understand aerodynamics, and relationships wit

the wind, airspeed, and ground speed.

Doug, you asked "| Just to make sure, you aren't a FAA licensed pilot are you? Are you?"

In fact, I am. I have several hundred hours flying real airplanes, an have only stopped due to medical reasons. I've taken up flying R/C t keep my hand in, and what applies to a real airplane applies to R/C.

Furthermore, I won't go into a further discussion on this.

Gar

-- GaryMC

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jim breeyear

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