I wrote this up in the beginners forum in response to a question about plane size vs wind. The origional thread is here:

http://www.rcuniverse.com/forum/Do_l...1121129/tm.htm

This particualr post, I was talking about two planes of the same size but different weights, and if the heavier plane would fly better in the wind.

So, what do you guys think? Did I miss something? There's some other comments in the thread about larger size planes in the wind. Comments?

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You know, I'm not at all sure that is true. I've never heard a solid, aerodyanmics-based explaination of why a heavier plane would "handle" wind better.

We all know it's usually easier for us to fly a heavier plane in the wind, but I think that is because of where we are standing, outside the plane, than anything else.

A heavier wingloading will result in a faster glide, but the actual glide angle will be the same, since the glide angle is the L/D ratio, which doesn't change directly with weight. (It does change a little, since at a higher weight, you have to operate at a higher AOA, which means a different L/D for most airfoils, but that effect is generally minimal).

Anyway, a lighter plane and a heavier plane will glide though the airmass exactly the same, following the same path. However, a ligher plane will do so at a lower airspeed. So, if the wind is high compared to the airspeed, a lighter plane will fly very slowly against the wind, and will show a larger apparent change in speed when it turns from downwind to upwind or vice versa.

So, a heavier plane will be faster flying, which will make a given wind speed a smaller percentage of the ground speed, which will make the airplane appear to fly at a more constant speed (airspeed remaining constant, but ground speed varying due to wind), and the higher speed will make covering ground against the wind easier.

However, all the above is mostly talking about planes with out engines, where the airspeed is set totally by the rate of descent and the L/D. Put an engine in there, and the situation changes.

Your airspeed is no longer controled mostly by weight, a lightly loaded plane can fly at the same airspeed (or usually faster) than a heavily loaded plane. So wind penetration with an engine is less of an issue. A lighter powered plane can throttle up to get better wind penetration and match the heavier plane.

On landing, and intersting thing happens. A pilot flying a lighter plane is going to be used to slowing the plane way down, and using that light wingloading for a nice slow glideslope. However, a pilot of a heavier plane is going to be used to a faster descent. In effect, a landing approach turns a powered plane in to a glider as above. So the pilot of the lighter plane will, out of habit, slow down farther, causing the ground speed to drop way down, and making the landing seem "harder". The pilot of the heavier plane is not going to see the plane slow down nearly as much (as a percentage), so the plane will look and feel closer to "normal" in a high wind.

If the pilot of the lightly loaded plane simply holds more power all the way to the ground, and uses the engine to establish an approach with a higher airspeed and a "normal" ground speed, they will find the lightly loaded plane lands just fine in the wind.

The above is all assuming a steady wind.

In turbulance, lightly loaded planes seem to bounce around more, but part of that is because of the lower airspeed. If you power up and fly the same airspeed as a heavier plane, the bouncing reduces quite a bit. I haven't flown side-by-side comparisons to see if the bouncing around becomes equal at equal airspeeds or not, but again, I can't see any aerodynamic reason why a lighter loaded plane would bounce more.

I can see one reason, and that would be inertia. I'd be willing to believe that a heavier plane (even with a lighter wingloading) would bounce less in the same turbulance, since the turbulant air acts as a force trying to accelerate the airplane in a direction. A heavier plane will take more force than a lighter one. But that's mass, not wingloading that matters.

Anyone see where I got something wrong in this? It does match the experiences I do have flying lightly loaded and small planes in high winds compared to flying larger, heavier planes in the same wind.

This matches my experience too.

I always agree that lighter is better, although I admit that having a little more weight/higher loading can make those dive-to-swoop passes a little more fun.

Typical example in small sport planes is the old Great Planes "Ultra Sport" series, which were a little heavy, compared to the newer and much lighter planes they're making today. Overall, the lighter ones fly better, and I'm all for it, but the older ones would dive faster thanks to their weight/loading. (with "all things being equal" - shapes (drag) similar, etc.)

A steady wind makes no difference in how the airplane flies when viewed from the airplane reference system. It does seem to make a difference when the airplane is viewed from a different reference system, say standing on the ground, but this is not an aerodynamics change but a reference point change. The aerodynamics do not change with the wing loading of the airplane.

Lower wing loading usually implies a lower mass. For a given wing size the one with the lower wing loading (lower mass) will respond with higher accelerations if both are subjected to the same force due to aero.

Real flying referenced to me while I am standing on the ground in a gusty wind will show the airplane with the lighter wing loading being bounced around more than one with a heavier wing loading because of the mass-acceleration effects of the aero forces. Bigger airplanes usually have larger masses which will allow less acceleration (bounce) in the gusty wind.

I believe there is also a favorable Reynold's number effect that occurs with larger airplanes that makes them handle better.

It's been my experience that a lighter model will handle gusty winds just fine IF it's clean aerodynamically and has it's balance point to the rear of the acceptable range.

By clean aerodynamically I mean a low camber or symetrical airfoil that's not too thick on a model that doesn't have gobs of frontal area and fat wheels and such.

A couple of my most memorable days were dynamic soaring an old aileron 2 meter glider on a couple of blustery days. It was a thermal glider with no added ballast and it handled great even if it DID need lots of my attention. Some extra down trim kept the speed up and the light weight of the model ensured that the control response was crisp.

I've also flown heavy models that did not have that nice crisp response and even tended to overshoot on some planes of motion thanks, I assume, to the weight. No thanks, not for me.

The responses so far are good but one factor hasn't been mentioned. A more stable aircraft will respond to gusts more than a less stable one. For instance with a more rearward cg the pitching moment due to a momentary change in airspeed (in response to a gust) will be less than with the cg more forward. Likewise, an airplane with high lateral stability (dihedral effect) will respond to a momentary upset with a more positive motion than one with a flat wing. Inertia effects are there but within the range of sizes of R/C models, they are not very large.

To sumarize, to be least effected by gusty wind conditions, a model should have:

1. Lower overall stability (more rearward cg and less dihedral)
2. Higher wing loading
3. Low drag (clean aerodynamic lines)

While size may have a small effect, it is not the major factor. I have a little "Perky" with a Norvel .061 that meets the above criteria and it handles winds that many larger models have trouble with.

Lou, you pretty much said what I did but I will take exception to the higher wing loading.

A higher wing loading means a higher stall speed and that stall speed can catch you unawares in gusty situations or when dropping down through the very strong ground shear effects that come with stormy days.

A heavier airplane with a higher wing loading only masks the effects by making the response to gusts seem less but a heavier or higher loaded model also takes longer to react to throttle or control inputs.

I had the experience of flying thru turbulence in a 200 ton airplane, and then an hour later a 2 ton airplane. The larger airplane exhibited NO turbulence response. The smaller was bounced all over the place.
While sloping, I've observed any number of serious upsets when one side is in one "bundle" or air and the other in air going a different direction. Much more severe than you will see flying at a typical airfield on the flats..
The larger the sloper also, the less response to these transients.
Watching the wind coming up the slope (the grass motions) it's fairly obvious the wind comes in packets, which at one site are about a standard wingspan wide. Get one wing in one of these while the other isn't, and a 90° uncommanded roll happens instantly!
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"Bigger" airplanes, 25%-45% have more resistance to upsets, either commanded or transient due to their inertias, and consequently feel better when they're flying.

I base my inclusion of wing loading on several thousand hours flying full scale aircraft. There is no doubt at all that within the same general size, an airplane with a higher wing loading handles gusts better than a similar one with a lighter wing loading. In neither full scale nor model aircraft should you operate close to the stall in turbulent conditions, however in a normal flight regime, the higher wing loading has the advantage. In the typical light aircraft, the maneuvering speed (a structural limit) is lower for the same airplane carrying a lighter load because flight loads in turbulance are greater for the lighter wing loading.

Doesn't anyone remember their High School Physics class when they talked about inertia and centrifugal and centripital forces?
The higher the mass of an airplane, the more resistant it will be to forces trying to change its attitude or direction but once it is changed the farther it will go from its' stable state.

It takes more force to move a heavier airplane than a light one, simply put, hence the better it handles wind. All these formulas and stuff are great for theoretical discussions but the factor that most effects airplane stability is its weight.
Now before you all go off on me, read that carefully. That statement works in both directions.

Well, pedantically, it's weight AND wing span.
Short-span planes don't respond to gusts as much as longer span planes do.
The C-130s and PB-4Y water bombers that collapsed in mid-air are examples of this.
Not even designed for the environment they were being used in.
The BAC Jaguar with its short wings is intended to fly in turbulence.
F-104.
etc.
For our toys however, it's getting the darn things down that wingloading is most important.
(takeoff are optional... failure to take off is a safety feature in many instances.. but landings ar mandatory!)
High loadings land FAST!

Back to high school physics. Jim is right. A heavier mass is accelerated less by the same force than a lighter mass. However as he stated, the reverse is also true. The same weight airplane with a larger wing (lighter wing loading) is accelerated more by the same gust since the larger wing produces a larger force. As the overall size goes up, the weight goes up but so does the force acting on that weight.

In summary, I stand by my original points, and for the same reasons. To handle gusty wind, an airplane should have:

1. A little less stability
2. Higher wing loading
3. Low drag

Obviously my full size Cherokee can handle wind better than a R/C model and a B-747 can handle more wind than my Cherokee, because there are scale effects involved. However within the size range of our models, overall size is not nearly as important a factor as these three.