Wind & Aircraft

[PatMc]

Posted by MarkyMarc on 18/01/2011 17:43:49:

Hope we haven't put Stewart off!

 

Conspiracy theory - maybe he's a ringer?

 I wondered if he might be a "she" trolling in a different persona.

[Erfolg]

Martin

 

If the plane you are travelling on changes direction (an acceleration), or the car you are traveling on stops,  and you feel no effect, you are remarkably light.

 

Of course if Newton had not lived things may be different.. 

 

 

Edited By Erfolg on 18/01/2011 17:52:45

[Martin Harris - Moderator]

No - it's me changing direction in a medium moving a lot faster than the wind does!  It's what our models do but more extreme.  Perhaps I should have taken a metaphorical Minium up in a 747!

[Peter Miller]

Anyone noticed that the Troll, Sorry first poster, has not said a word since.

 

I suspect that he has chucked a large lump of something nasty  into the fan and has now ducked and run. Either that or is waiting to refresh the stirring of the thick and smelly.

 

 

Edited By Peter Miller on 18/01/2011 18:53:40

[Eck]

To be fair to the OP, Peter, after one post, any arguments that have come about - we've done it ourselves - with no further incitement.

[Peter Miller]

Oh I agree. He didn't need to.

 

And I am not arguing at all, just having a laugh as I suspect many of the others are.

 

As someone mentioned the other person who started a similar thread. I also said that that was a total waste of time, effort and space.

Edited By Peter Miller on 18/01/2011 19:21:55

[Erfolg]

Peter and Biggles are obviously correct.

 

 

[Peter Beeney]

 
   Maybe this discussion has been going on for a long time. I wonder what they were talking about in Kill Devil Hills, near Kitty Hawk, back in 1903? Do you think it might have got a mention?
   There was another article in a mag many, many years ago, which was also fairly pointed and insistent that the wind didn’t affect my model. At the time I was mildly surprised, because up to that time I hadn’t really given it a lot of thought anyway. There were the technical explanations as to why this was so, which I’m sure I didn’t understand; and still don’t! I think! But I was quite pleased to note that nobody had told me this when as a complete starter I had first lobbed my sloper off the Hills, back then I feel all my crashes were due to my lack of affecting the model, rather than the wind not affecting my model.
   However, when the author then earnestly advised that the way to prove this was to fly my model whilst standing on top of a hot air balloon, presumably at a few thousand feet, so that I could fly in a block of still air, this did give rise to some cause for concern. For a start, I was somewhat unsure about taking off and landing, especially dead-stick landing, (walking out to the edge to retrieve the model seemed a trifle foolhardy, the canopy might become unbalanced), and I had some qualms about the pointed pole for the windsock… …but silly me, of course I don’t need this, there’s no wind!

   Seriously, though, why would I need to do this if the wind does not affect my model? Why not just simply fly in a wind to prove it? It seemed to almost imply that the opposite is true.
   If the wind does not increase or decrease airflow, lift and control response, then why do folks put parts of aeroplanes into long containers of fast moving air, in what seems like an effort to prove otherwise; and so why are they then indeed called wind tunnels?

   Looks like a nice day tomorrow, I’ll not say a word about this at the strip, and then despite the fact there might not be any wind with luck we should get our usual little incident prone flying display.
   I wouldn’t want to spoil anyone’s fun!

   PB   

             

[stewart grant]

Nice that a few pilots care. Those who ridicule the theoryare likely to betaking alot of bin bags full of wreckage home because they cant work out why its happened again!

And by the way the stall is dictated by angle of attack NOT airspeed.

An aircraft can stall at ANY speed.

Those of us who increase power when turning do so to overcome the increase in lift induced drag when bankingand loading the aircraft and therefore maintain a constant airspeed.

This technique is also used to increase airspeed in order to travel upwindsmartly to keep the aircraft positioned correctly relative to the field.

[Peter Beeney]

Stewart,
In your OP you stated, with some emphasis, that wind does not affect the airspeed of an aircraft.
I’m afraid I cannot aspire to being an expert, or probably even a novice on this, I’ve never really studied it at all so I’m afraid I’m having a spot of difficulty here. To me, it seems as though to begin to understand it I first have to define what I mean by airspeed.
If I stand in a wind blowing at 15 mph I would recognise that as a wind but I might also be able to say it is an airspeed of 15 mph, because the air is passing me by at 15 mph. So in relation to me and the air there is a moving component of 15 mph. If there is no wind and I run forward at 15 mph then my airspeed must surely again be 15 mph? For the same reason? If I am again now stationary and facing into the 15 mph wind and then start to run forward at 15 mph then my airspeed jumps to 30 mph? This may well be wrong but it seems fairly logical to me.

My model plane generates lift by virtue of the fact that the air passes over the wing, in the form of a wind, if you like. I suspect that there is a relationship between the speed of the air and the amount of lift, the faster the airspeed, the greater the lift. I can accept that it has to be moving forward in the first instance to obtain lift. So assuming my model is moving forward into still air at 15 mph then the wing will generate 1n amount of lift. If it now flys into a headwind of 15 mph the airspeed is now 30 mph and the wing will generate 2n amount of lift. So how does the wind not affect airspeed, and indeed the whole flying configuration? I’m sure in practise the drag also increases and the plane tends to slow but even if it came to a standstill in relation to the ground there would still be 1y amount of lift generated.

With regard to your second post, and the stall related to the AoA, I don’t think I’d have many problems with that; or the fact that the model can stall at any speed. What I would be interested in though, is, how do you get it to stall at any speed, to order? For instance, if I’m flying a standard sports model straight and level, fairly fast, what control inputs would I need to cause it to stall? And, indeed, if I’m flying it fairly fast in any sort of manoeuvre, (I say fairly fast, to conform to the ‘any speed’ instruction), how do I get it to stall? To be clear on this, I’m assuming ‘any speed’ is anything other than slow, as in a standard stall procedure.
I only ask this because I can’t say that I’ve particularly noticed this a great deal, but then with my flying it’s perhaps only one more mistake in all the others anyway.

What I can say, though, is that the only crash that I’ve had, for probably some years, was recently when a popular brand of 2.4 radio decided to go on strike; and rather unfortunately it was a nearly new model and it wasn’t mine!

So I’ve either been very lucky, or I’ve been doing something right.

PB

[Tony Smith 7]

The "stall at any speed" needs a little qualification. As speed increases the aircraft may not have enough control authority to reach stalling AoA, or the flying surfaces may deflect to shed lift (or break of course).

[Martin Harris - Moderator]

Posted by Peter Beeney on 22/01/2011 15:25:55:

If I stand in a wind blowing at 15 mph I would recognise that as a wind but I might also be able to say it is an airspeed of 15 mph, because the air is passing me by at 15 mph. So in relation to me and the air there is a moving component of 15 mph. If there is no wind and I run forward at 15 mph then my airspeed must surely again be 15 mph? For the same reason? If I am again now stationary and facing into the 15 mph wind and then start to run forward at 15 mph then my airspeed jumps to 30 mph? This may well be wrong but it seems fairly logical to me.

My model plane generates lift by virtue of the fact that the air passes over the wing, in the form of a wind, if you like. I suspect that there is a relationship between the speed of the air and the amount of lift, the faster the airspeed, the greater the lift. I can accept that it has to be moving forward in the first instance to obtain lift. So assuming my model is moving forward into still air at 15 mph then the wing will generate 1n amount of lift. If it now flys into a headwind of 15 mph the airspeed is now 30 mph and the wing will generate 2n amount of lift. So how does the wind not affect airspeed, and indeed the whole flying configuration? I’m sure in practise the drag also increases and the plane tends to slow but even if it came to a standstill in relation to the ground there would still be 1y amount of lift generated.

 

 

All this is largely the case...while you're firmly attached to Mother Earth...but your 30 mph model will continue flying at an airspeed of 30mph unless you interfere with the angle of attack.

 

Assuming an into wind take off, let's imagine a turn through 180 degrees. If you make a gentle turn, the model will continue (roughly speaking) to fly at the same AoA and airspeed.

 

The groundspeed will vary constantly during the turn until you stop turning and establish the reciprocal heading . At 90 degrees to your original heading, your airspeed will be 30 mph and you will be doing 30mph away from you - but the model will be drifting downwind at 15 mph so if you maintained that heading, the track would be diagonal from your perspective. This is why we need to crab in order to fly a square circuit.

 

The model's pilot will not have a 15 mph breeze in the same ear that you're feeling it in at the time from your position on the flight line - or at any other part of the turn!

 

In other words, the model does not notice the wind in flight.

Edited By Martin Harris on 22/01/2011 20:49:10

[stewart grant]

The wind is only relative to the ground. If its 15mph, thats because you are on the ground. If you threw a feather in the air it would be doing 15mph over the ground downwind. BUT it would have no airspeed. If you could power it into wind with a motor at 15 mph airspeed it would be stationary relative to the ground but have an airspeed of 15mph.

Stalling at any speed? One has to assume control force / structure available but angle of attack ( angle of local air flow relative to wing aerofoil ) can normally be increased, particularly in models, rapidly enough to create a sudden stall from high speed flight.In aerobatics aflick roll actually takes advantage of this phenomina.

My interest in the this subject is largely safety related. Iknowmodel instructors and examinerswhodon't understand this theory. The way they teach and test is ultimately flawed because of it and pilotsstruggle with accidents and poorprogress as a result.

[Peter Beeney]

Martin,
I’m afraid I didn’t mention turning the plane, and I don’t think Stewart did in his original post, either, he just simply stated that wind doesn’t affect the airspeed and I’m trying to figure out why. He then said that when flying down wind the ground speed increases, which I’m sure is perfectly true.
So are we now saying that once the plane is in the air and continuing to fly straight forward at a steady 15 mph in still air, if a 15 mph wind appeared coming toward it the airspeed would remain at 15 mph? If this is the case then obviously I have to agree that the wind will not affect the airspeed. However, if the airspeed does speed up to 30 mph then I would have to consider that the wind will affect the airspeed.
Incidentally, would this be the indicated airspeed, calibrated airspeed, true airspeed, equivalent airspeed or density airspeed? From reading about all this, all these might have a different value for the same condition.
I guess the model’s pilot would not have the 15 mph breeze in the same ear because he is always facing the direction the plane is going, whereas I’m just observing the model from the side, more or less always facing the same direction, and also he is travelling at the same speed as the model, whereas I’m stationary on the ground. Our conditions of this same activity are different.
Maybe the plane doesn’t notice the wind in flight but I seem to. If I get out of control and make uncoordinated control movements the model very quickly gets carried downwind by the wind. So with that in mind I shall continue to observe which way the wind is blowing and take off and land into the wind. With the view that the model is going to notice the wind. It seems safest to me.

I’ve also noticed that my post formatting on the forum seems to have changed?

PB

[Peter Beeney]

Stewart,
I feel that I’m happy with the airspeed query now, or as least as far as I’m wanting to be concerned.

With regard to the stalling it did occur to me about the flick roll etc. I quite like to indulge in these type of manoeuvres, the faster and harder the better, and including every which way spinning and so on. I have noticed though, with the simultaneous application of all control surfaces, with plenty of throw, it all slows down very quickly. So here the stall may again be happening at a much lower speed.

PB

[Martin Harris - Moderator]

Peter,

 

Are you using IE9 Beta by any chance - things do seem to happen a little differently with it - like line spacings and word spaces disappearing even in compatibility mode.

 

This wind speed instantaneous changing thing which many people use to argue with...I don't think it's physically possible for it to happen (we're not talking about turbulence which is a vertical component or wind shadow e.g. as used in dynamic soaring). Air is a fluid with mass and you can't suddenly accellerate it by pushing some more (compressable) air in its general direction and as there is no change in the AoA there's no change in the model's airspeed - just a reduction in groundspeed as the model flies into windspeed of increasing velocity.

 

I don't think there's any need to define the type of airspeed as most of the ones you quote are adjustments to relate the indicated airspeed to true airspeed under different conditions.

 

There's certainly no argument from me that taking off into wind is a good thing. Less time on the ground, better directional control, less wear and tear on the undercarriage, earlier take off and better angle of climb amongst its benefits as I'm sure you're aware along with similar benefits on landings.

 

The golden rule to avoid problems in turbulence is to have a reserve of airspeed in order to deal with its effects but this is not really the subject raised by the OP

Edited By Martin Harris on 22/01/2011 23:54:38

[Ian Jones]

Doesn't this box of air induce any drag?

How big is the box of air that my aeroplane is in? Where are the corners? I don't want to catch it on anything!

Edited By Ian Jones on 23/01/2011 00:13:13

[Tony Smith 7]

Posted by Peter Beeney on 22/01/2011 23:20:00:

So are we now saying that once the plane is in the air and continuing to fly straight forward at a steady 15 mph in still air, if a 15 mph wind appeared coming toward it the airspeed would remain at 15 mph? If this is the case then obviously I have to agree that the wind will not affect the airspeed. However, if the airspeed does speed up to 30 mph then I would have to consider that the wind will affect the airspeed.

You're speaking about changes in wind, and I'm sure we've all experienced the effect either on models or full size. Whether instantaneous, rapid or gradual, a change in wind speed presents the aircraft with a change in airspeed which needs to be accommodated. For a slow change in wind speed this may be unnoticeable, a more rapid change like a gust requires some control input.

[Former Member]

[This posting has been removed]

[Former Member]

[This posting has been removed]

[Rob]

I thought it was willpower that got an airframe into the air...As the speed increases and the plane is galloping down the runway everybody onboard is willing it to fly.