I am a newcomer to RC powered fixed wing but have a military fixed wing and rotary flying background. I would appreciate feedback on how a model reacts to flight both in to wind and downwind. To put it into context in a full size machine if I execute a 360 deg turn at a constant angle of bank - say 20 degs - I do not have to change the attitude or power of the aircraft to compensate for wind and my indicated airspeed does not vary. I know that to an observer on the ground my flight path is biased downwind and that my groundspeed changes relative to the wind. Flying a model I make far more power and pitch attitude adjustments to maintain level flight than I can explain. I would appreciate some insight in to this phenonima. Happy to receive answers based on the experience of fliers in addition to those which contain fundamental Principles of Flight.

In full-scale, unless you're doing say turns around a point on the ground, you will as you've experienced be able to do 360s at constant attitudes.. etc in a wind.
A model in flight IS referenced to the ground. Namely you!
The legendary "downwind turn" situation is a direct result of having to consider the wind effect relative to placing the plane in the air as seen from the fixed point on the ground.
Left to its own, as a free flight would be, a model is as free of wind influenced manuvers as a full-scale.

Bryan......Point of reference has alot to do with flying a model plane ...but little to do with the aerodynamic forces at work.....Being a pilot as well just by having some feedback( say altitude-airspeed -vertical speed) from a model in flt would make flying the much easier from the standpoint of what a pilot knows already.........flying a model is more focused towards depth perception, reference to the ground(no horizon to use) and that sort of stuff......basic aerodynamics apply the same for models as they do for full scale planes( Helis).........there are some differences for scaling down in Reynolds numbers/boundary layer airflow which someone like Bruce ,Bill, Ben or B-T-B are more knowledgable than I am.......for example the Aerobatic flyers (IMAC and the like) fly all the same manuevers(and then some) just like their full scale counterparts and have to maintain manuevers in the "BOX" with any number of wind conditions......but just like full scale ....theres a learning curve to figuring out how all the pieces of the aerodynamic/perception puzzle fit together........have fun and good luck.....Bill....

It is basically simple, the wind has no effect on either models or full size.

Now for some details. Look at the two cases of smooth wind and wind with gusts.

Note that the flight path of an airplane can be determined by 6-degree-of-freedom equations which include everything, control inputs, lift forces, masses, inertias, etc. For instance control inputs produce forces which produce accelerations which end up producing positions relative to the ground. The same logic can be applied to any particular part of the inputs including the wind. Leaving out all the barfy middle stuff it becomes...

position with respect to ground = ( wind + control inputs + motor thrust ) + barfy middle stuff and a lot of constants

For no wind conditions with our models there is a tendency to make the maneuvers with respect to us on the ground. To make a circle with respect to the ground takes constant airplane angular velocities and accelerations. With no wind this is an airplane with constant throttle and control surface deflections which lead to the forces that make the accelerations and angular velocities which make the circle.

With a smooth wind if the flight path relative to us on the ground is to be a circle then accelerations on the airplane and the resultant velocities must be the same as the no wind case. But since the wind's input to the equations is a linear velocity the there must be some input from somewhere else to balance the equations to maintain the angular velocities and accelerations. The only input can come from the throttle settings and airplane controls. The higher the wind the more airplane control force that is necessary.

When considering gusty winds the exact same thing applies but with a difference in observations. In full size flying we can feel the gusts of the wind in our butts fairly easily as accelerations. There are rates of change of gusts that we can't feel and consequently we can't feel a smooth wind when flying. For the same gusty winds the big airplanes are slower to respond. Full size airplanes have higher speeds than models and the percentage change in accelerations due to the gusts are smaller.

But, because the model airplanes have low inertials they do bounce around a lot in a gusty wind relative to the ground both in angles and directions. We are fixed to the ground and have pretty good senses and those bounces are easily detected. But to look smooth and impress our flying buddies (at least I do) I try to smooth out the bounces. So we add throttle or control inputs. We are in that respect acting like an autopilot.

So with any wind or wind with gusts when flying relative to the ground to balance the big equations in the sky control inputs needed to balance the wind are the ones we input.

My theory on possible modifying factors. There is a variation of wind with respect to alititude close to the ground, a boundary layer type of thing.

Another extreme is the thing that happens with dynamic soaring. Using wind velocity variatons because of flow around hills, etc. to accelerate a slope plane to extreme speeds. Some form of this may happen even with a smooth wind and a flat ground.

There may be standing waves of a small sort caused by tree lines, cars, etc. that cause variations in velocity beyond what might be expected.

All these things can muddy the water when trying to figure out how a model is reacting in the wind.

Thanks chaps for your informative and helpful replies. I'm off to the field to do soe serious circuit bashing.

Cheers,

Bryan