Ballooning Into The Wind

[Christopher Wolfe]

Ballooning into the wind.

 

I recently read this description being used in another thread and for a radio controlled model this is just not true if piloted correctly.

 

I suspect that this is a result of pilots attempting a turn (Not forgetting the dreaded downwind turn) while forgetting that their feet are firmly planted on terra firma and unconsciously trying to correct the turn by juggling the observed airspeed.

 

One only has to observe a Free Flight model as it drifts downwind as the model has no idea about wind and so does not balloon as it turns.

 

OTOH, a Control Line model actually can balloon into wind as it's reference point is actually fixed to the Earth (by the pilot's feet).

 

So time to put this term to bed people as apart from wind shear when flying very low (maybe on approach on a windy day) Ballooning In The Wind is just a myth.

 

* Chris *

Edited August 11 by Christopher Wolfe

[Nigel Sharp]

If it was my thread. Then

 

It had nothing to with speed  nothing to with control overcorrection. Nor being fixed to the ground. But the aircraft surged upward if that is more in keeping with your terminology. And did a series of porpoise type oscillating.

 

What was causing it?

 

I know it's solved.

[Mike Blandford]

An aeroplane travelling downwind has a certain amount of kinetic energy, which is related to ground speed.

On turning into wind the ground speed becomes reduced, so the kinetic energy is also reduced. The "lost" kinetic energy needs to go somewhere and gets turned into potential energy, appearing as an increase in height.

 

Mike

[Nigel Sharp]

Agreed.

[john stones 1 - Moderator]

3 hours ago, Christopher Wolfe said:

Ballooning into the wind.

 

I recently read this description being used in another thread and for a radio controlled model this is just not true if piloted correctly.

 

I suspect that this is a result of pilots attempting a turn (Not forgetting the dreaded downwind turn) while forgetting that their feet are firmly planted on terra firma and unconsciously trying to correct the turn by juggling the observed airspeed.

 

One only has to observe a Free Flight model as it drifts downwind as the model has no idea about wind and so does not balloon as it turns.

 

OTOH, a Control Line model actually can balloon into wind as it's reference point is actually fixed to the Earth (by the pilot's feet).

 

So time to put this term to bed people as apart from wind shear when flying very low (maybe on approach on a windy day) Ballooning In The Wind is just a myth.

 

* Chris *

 

Well I have to ask, what's the logic behind your opinion that the pilot is juggling the observed airspeed ? Sounds an odd take to me.

[Martin Harris - Moderator]

Not agreed. 

 

If that were so, in indoor model flown in a Lockheed Galaxy would have an immense amount of kinetic energy flying forward through the cargo hold and have to dissipate it as it starts flying “backwards” at several hundred knots as it starts its return to the tail end. 
 

Our models are flying in a moving air mass, similar to the hold of the Galaxy…

 

What is happening is that during the turn into wind, the model is drifting downwind, the pilot observes the lack of progress and tightens the turn by increasing bank.  As we all know, we need to add elevator (and ideally power) to balance the loss of lift and increased G loading.  When the inexperienced pilot comes out of the turn, he is slow to reduce the elevator (and if he’s added power, throttle) so the model balloons. Nothing to do with kinetic energy, which cancels out in the relevant equations, which I can probably dig out if required. 

[Mike Blandford]

Sorry but the inside of the Galaxy is a somewhat different problem. The kinetic energy of the model is based on the velocity. The model velocity is the sum of the velocity of the Galaxy and the velocity of the model relative to the Galaxy. The relative velocity is positive when the model is flying towards the nose and negative when flying towards the tail. As it turns the model's kinetic energy will reduce. The question is where does the "lost" kinetic energy go?

 

Mike

[Martin Harris - Moderator]

We all know that energy doesn’t just disappear - it converts to another form.
 

This can be demonstrated by flying a model into a tree at 29 knots airspeed in a 30 knot wind.  
 

Upwind, there may be some scuffing to the spinner and dirt from the branches left on the leading edges. 
 

Downwind, there may be one or two larger pieces of debris to pick up. 
 

Kinetic energy effects can be discounted from any discussion of upwind/downwind flying until motion relative to a fixed object is introduced to the equation. 
 

An aircraft doesn’t stall or balloon due to kinetic energy or airspeed. It does so due to changes in the angle of attack. 

 

If you accept that it is perfectly simple to fly a model successfully in the air moving over the ground at 300 knots inside a large aircraft, how does this differ from doing so in a mass of air travelling at 20 knots?

[john stones 1 - Moderator]

Way over my head.

Can the increased windspeed change the models angle of attack, assuming the pilots inputs are neutral ?

[Martin Harris - Moderator]

No. 

[john stones 1 - Moderator]

I struggle with No as an answer, does not the angle the wing sits at, and the airfoil play no part, if not an explanation would be welcomed.

[PatMc]

In the past, when it was ic powered, I've set up my Jnr60 in light wind conditions to a steady circular flight path using a smidgeon of elevator & rudder trim, carefully adjusted the throttle so that it's maintaining the same altitude (as near as the throttle accuracy would allow), then let the model drift downwind for several minutes. I returned the model to it aproximate start point & repeated this 3 or 4 times. Each time the model gained a little altitude due to the throttle setting but at no time did it "zoom" or "balloon".    

[Nigel Sharp]

In my example in t'other thread then John Stones is very close to my problem...

[Geoff S]

I first came across this issue when sailing in a current (analogous to wind when flying). There used to be the myth of lee bowing the current when going to windward upcurrent but if all boats are experiencing the same current in a race then it's as if they're on a moving tablecloth, so the current affects all boats equally (admittedly, at sea it's an unlikely scenario and getting in the right current is important).  An aircraft does not notice a constant wind - just changes in strength or direction.  In our case, we're piloting from a fixed point and unconsciously attempt to correct for wind, which is the cause of both ballooning and the hazards of the notorious downwind turn.

 

In practice, a strong wind is more likely to be affected by natural obstructions (trees/ buildings/banks) so will vary in its effects, particularly at the low altitudes LoS piloted models fly and make landing tricky, but that's a different matter.  I think if you flew a model from a hot-air balloon (which drifts at wind speed) you could fly it in circles round the balloon without any problems - recovery might be tricky though 🙂

[Martin Harris - Moderator]

John, I have spent literally hundreds of hours circling in gliders while thermalling.  During these continuous 360 degree turns in winds varying from non existent to well above the gliders’ stall speeds, no wind related effects could be felt. 
 

The only times that wind “effects” were noticeable was while “scratching” at low altitudes.  These were purely due to the visual effects of slowing and speeding up relative to the ground, where it was imperative to maintain a constant attitude while monitoring airspeed - again, no ballooning turning into wind etc.  This is a direct analogy to the situation where an observer on a fixed point on the ground is attempting to control an aircraft flying in a moving air mass. 
 

If anyone doubts this, try Pat’s test. 

[Mike Blandford]

OK, simple question:

An aircraft is flying straight and level at a constant speed and angle of attack.

With no other changes, the airspeed is increased, what happens?

 

Mike

[Martin Harris - Moderator]

Why would it increase?

[Geoff S]

5 minutes ago, Martin Harris - Moderator said:

Why would it increase?

Or even how would it increase?  The only way would be to increase power, in which case it would likely climb or, alternatively, you could apply down elevator and increase the speed but it would dive.   Or the wind-speed might increase in which case it might also climb but it would no longer be a constant environment and, as I said earlier, aircraft respond to changes in wind-speed but not to changes of aircraft direction in a steady wind.

[Christopher Wolfe]

6 hours ago, john stones 1 - Moderator said:

 

Well I have to ask, what's the logic behind your opinion that the pilot is juggling the observed airspeed ? Sounds an odd take to me.

I suspect that from the pilot's fixed reference point a model flying downwind has a perceived higher airspeed than when flown on a calm day and the opposite is true when flying into the wind. It could be an instinctive reaction to adjust the throttle in an unconscious attempt to counter this.

 

4 hours ago, Martin Harris - Moderator said:

We all know that energy doesn’t just disappear - it converts to another form.
 

This can be demonstrated by flying a model into a tree at 29 knots airspeed in a 30 knot wind.  
 

Upwind, there may be some scuffing to the spinner and dirt from the branches left on the leading edges. 
 

Downwind, there may be one or two larger pieces of debris to pick up. 
 

Kinetic energy effects can be discounted from any discussion of upwind/downwind flying until motion relative to a fixed object is introduced to the equation.

 

Exactly Martin. Thank you for that practical observation.

As for kinetic energy, I have flown models (typically sailplanes) that have struggled to return to the landing spot in a decent breeze and can actually drift backwards. So does the model now have negative kinetic energy? I think not.

 

3 hours ago, PatMc said:

In the past, when it was ic powered, I've set up my Jnr60 in light wind conditions to a steady circular flight path using a smidgeon of elevator & rudder trim, carefully adjusted the throttle so that it's maintaining the same altitude (as near as the throttle accuracy would allow), then let the model drift downwind for several minutes. I returned the model to it aproximate start point & repeated this 3 or 4 times. Each time the model gained a little altitude due to the throttle setting but at no time did it "zoom" or "balloon".    

 

This mirrors my own observations exactly Pat.

 

One could maybe assign a fixed rate safe turn and throttle setting to a switch on a modern tx and at a safe altitude operate the switch and observe.

 

* Chris *

[Brian Cooper]

Ballooning when coming into wind: 

Yes they do, but some are more affected than others. Slow models seem to be more affected by it. 

It depends on the amount of wind, the model, the speed of the model, the rate of turn and the degree of altitude gained to label it as  "ballooning".

 

Most of the time, it isn't really a problem. . . It is more of an observation.  

 

At the end of the day, keeping an aeroplane on an even keel comes down to the pilot. 

[Mike Blandford]

I don't believe you may discount kinetic energy changes when turning. When flying downwind and aeroplane does have more kinetic energy than when flying into wind (even if the airspeed is less than the wind speed. You cannot have negative kinetic energy as the expression for it involves a velocity squared term.

 

The answer to my simple question above is as the airspeed is increased the lift generated increases so the aircraft increases in height.

 

Mike

[Nigel Sharp]

Or rubber bands give. Changing incidence.

 

Leading to weird things at the sticks.

 

Balloon was/is a simple one word description.

[Steve Dunne]

Just an observation, having had this discussion over several decades...

At the altitudes we fly los, the wind is very unlikely to be straight and at constant altitude, it is usually rolling after passing trees or other obstacles, or "dragging" due to ground effect.

This means that a circling aircraft is changing its angle of attack due to the flow angle of the airmass it is flying in, and this can give the illusion of ballooning.

To observe this, just release a balloon or even just a piece of paper at your flying site, and observe the path it takes...

 

Steve.

[John Lee]

7 minutes ago, Steve Dunne said:

Just an observation, having had this discussion over several decades...

 

 

Yep, Here's one from 2011 & the same arguments are regularly regurgitated over the decades. I had hoped that Pete Russell's discourses in the 70's in his 'Straight & Level' column in the RCM&E had put it to bed but I expect it will run for ever......

 

 

[Robin Colbourne]

The two most common reasons for 'ballooning' are:
 

1. The excess airspeed to maintain a banked turn is converted into height as the wings are levelled.  A stab of down as the wings are levelled will counteract this.
2. When turning into wind, the model's climb rate appears greater to the pilot on the ground as its position relative to him changes more noticeably in the vertical sense than the horizontal sense.  Imagine being in a department store walking alongside the escalator.  If someone steps onto the escalator at the moment you pass them, then if you keep walking, they go up relative to you, but horizontally maintain position.
   
   One thing that doesn't get mention as much as it should in model flying is wind gradient.  Full-size glider pilots have this drummed into them all the time as it is a killer.  Friction with the ground reduces wind speed as one descends; so one loses energy when descending into slower moving air if flying into wind.  If you do an approach dead on stall speed in a strong wind, the aircraft will lose airspeed and stall unless you have a margin in hand. 
   
   Likewise, if you have to do a dead stick turn close to the ground, You will lose less height completing the turn quickly by flying faster and banking more, than to stretch it round with minimal banking angle and airspeed.
    

Edited August 12 by Robin Colbourne