CrateCruncher,

Yes, the comparison was not great, but it makes my point about how nature solves the same problem of improving penetration without adding weight.

Thank you; now that I have read your mathematical explanation, I get it: heavier models have a bigger range of AOA and less pitch sensibility.

Then, there is inertia for resisting lateral gusts and drag reduction for achieving high speeds.

Gotta interject some reality into the "theory"
1. How many 8 ounce electrics (they ARE the fastest `1/2 lb models) can hit 40 mph?
2. pitch change of one (1) degree?
ouch!! I'll say 1/2 degree has adramatic effect!
That is a loop on most of that stuff
one degree is 1/4 " in one foot.
Our pattern planes typically never trimmed out with a pitch change of more than a tiny percentage of ONE degree.
anyway 8 ounces in 40 mph is unmaneuverable as is 40 POUNDS in 40 mph
contests are called at 20 mph
Slope gliders -an entirely different approch to flight -can tolerate speeds up to -likely 300 mph but there is no maneuvering done - Numberss are nice but why not use some realistic ones ??

I'm with Dick on this one. From having flown some light weight "racy" high speed models as well as light slow speed model in all sorts of conditions I never had any issue with them. Of all the planes I've flown by far the easiest to fly in the worst conditions was a small lightweight 1/2A racing model. It flew so good I actually built two of them. The speed allowed them to slice right through turbulence with no noticable effect other than slight displacements in roll or a sort of flat sideways or up and down kick here and there. They never suffered from the sort of pitch related disturbances your math is indicating. Or at least not enough to notice. And this wasn't some small wing design with a high wing loading. It was a 14 oz 36 inch span wing that flew slow enough in the glide that I once managed to extend my post engine shutoff glide by a few minutes by riding out a passing strong thermal.

Even my free flight models, for the most part, have dealt with bad turbulence easily other than some that got caught in bad rotors near the ground that did not leave enough height for the model to recover from the disturbance. But once up over 30 to 40 feet they ride out and stabilize themselves easily in some really harsh turbulence that is often found in connection with very strong thermals. I just had to run a lot further to get them back....

So I'd have to suggest that you've got some nice numbers there that indicate that a lighter model will get kicked around more. But I have not noticed the sort of pitch related issue that your math predicts. I suspect you're missing one or more aspects of the real world conditions. Or perhaps the magnitude of this effect isn't that big a deal when taken in combination with the rest of the factors the models are being subjected to at the same time. Or perhaps it's less of an issue with models that have stability margins that are close to nuetral. Certainly the airplanes that are more like trainers with generous pitch stability were more work to fly in bad turbulence. But I always attributed the issue to the softer control response of a trainer not being able to counter the disturbance as easily.

Well first off thanks for actually reading the post everyone. I figured I'd only hear crickets after posting it. Second, I admit I have very little hands-on experience with park flyers. I used a cute little lightweight advertised in a recent Tower flyer as a guinea pig. Third, the disparity in Re# for models vs. published AOA data becomes even more of a problem when we start getting into these tiny planes. Fourth, a 20 mph wind seems reasonable to me. I fly in 20mph winds all the time around here. The electrics pack up at 10! Lastly, I picked a slender symmetrical I had data on (naca 0006) because I felt a cambered airfoil would confuse the data with negative AOA's contributing positive lift.

Dick since you have the most heartburn with the conditions how about suggesting some better ones. I'll redo the numbers and see what happens.

Looks like I am a little late to the discussion, but I understand this as inertia and drag ultimately no?

On an ultralight airplane, power down and stick has to go forward. They are comparatively very light, but also very high drag.

Its kind of like throwing a golf ball and a cotton ball. When I look at it like this, its obvious which will go further.

Am I basically in the right space on this?

Well, it's hardly fair to compare golf and cotton balls to this issue. I'd suggest go back and read the parts about how light models can penetrate just fine if they are engine powered. The only time your analogy sort of applies is in the case of lighter and slower gliders with higher than normal amounts of drag. Like the Goldberg Gentle Lady. The design is such that they do not like to fly fast without generating a lot of drag even when ballasted.

Anyhow, there's more to it than just pure weight and momentum such as with the ball throwing analogy. It's about model design, pitch stability trim and maximum flying speed. A slow model can be clean and light so at first it seems like it would not penetrate well. But if it's clean and has extra power that power can go into producing a higher flying speed. So when you look past the golf/cotton analogy a bit further the cotton ball equivalent can do just fine or do even better than the golf ball provided the other features are there to carry the day.

After thinking about this for a while I'm not as enthusiastic as I once was about adding mass to powered planes for penetration. Gliders are a different story. In an uplift, the airstream (and by definition, drag) has a small vertical component that can be countered with increased weight. Without a propeller any small increase in forward acceleration is important. Looking at it graphically using force vectors it's apparent how adding mass improves "penetration" by offsetting the drag.

When we apply down elevator to add forward speed it's the same thing. We are pointing some of the weight vector in a direction opposite the drag.

Incorrect. It will drop out of the sky (at a rate relative to the percentage of weight gained) trading potential energy for kinetic energy until it gains enough speed to maintain altitude. If the power doesn't change at all, then it will slowly descend until altitude=0. That is, of course, assuming that ALL things remain the same and that the plane was not accelerating in straight-and-level flight..

Guys,

The thing you have to realise is that while talk about "Wind Penetration" etc is from your point of view on the ground, and aircraft in flight has no idea as to whether there is any wind blowing or not. All it reacts to is the air passing ove it, usually termed relative wind or relative airflow.

The aircraft that will fly fastest into the wind is the same one that flys fastest in nil-wind or down-wind. Thus a light model that can fly fast will fly upwind just as well as a heavy model that can fly fast.

In powered models there is the advantage that a heavier model will be less effected by gusts.

In Gliders there IS an advantage in using ballast. The distance a glider will travel relatve to the air (and thus, in nil wind, relative to the ground) for a given loss of altitude at a particular angle of attack is it's glide ratio and is also equal to it's lift/drag (l/d) ratio. This is independent of wieght. Two gliders identical except for weight will glide the same distance if flown at the same AofA, but the hgeavier one will do so faster both vertically and horizontally. Thus if you ballast a glider it WILL have a higher maximum griound distance (assuming no assistence by external lift) into the wind, as it will experience the headwind for a shorter time. It will also have LESS potential distance down-wind.

Cross-country gliders carry ballast if there is going to be good lift available, as the slower climb in thermals is made up for by the higher speeds available in between them. In light conditions they will fly without ballast, and dump it on route if the lift weakens or isn't as good as predicted.

A slope-racer will achieve it's best speed when ballated such that it's sink rate at its best l/d speed is equal to the available slope lift- any heavier or lighter and it will hve to fly at a different, and thus less efficient, angle of attack to fly level.