Low speed and windy day flying

[flying-llama]

I have a small flying area (about 30x60 feet), so I tend to fly small and slow,
and I am not that good with harriering or other 3D yet.
Also, often I need to deal with some wind.

For very low speeds (about harrier speed), I have been told that
pizza box flyers
(tailess, square or low aspect ratio rectangular flat or KFwing) are
simple and good, better than
swept wings and deltas (tendency to tip stall from spanwise flow).
But as the speed increases, pizza box flyers are not so good because they
get real 'pitchy'.

For wind, I have been told that swept wings and deltas are good,
with mentions of deltas being hard to stall (vortex lift).
I am guessing that these are deemed good for the wind because
they are easier to fly with varying airspeeds, such as when going from
headwind to tailwind, etc.

I am looking for both comments on this and also
wing shapes that are both
good at low speeds and can handle some wind.

Thanks.

[JetPlaneFlyer]

Llama,
First of all lets dismiss the idea of airspeed varying due to 'headwind' and 'tailwind'.. To a model in flight there is no such thing as headwind or tailwind. Providing throttle end elevator settings are the same then airspeed remains constant regardless of which way you fly relative to the prevailing wind, only ground speed changes. What can and does affect the models airspeed is gusts, wind-sheer and turbulence.

Regarding model wing 'shapes'... Some shapes do have different flying characteristics than others (regardless of wind) but I don’t think any shapes that are intrinsically better for wind than others. A wing shape that handles well in calm conditions should handle well in the wind also.
The biggest factor in wind is wing loading. A heavier loaded model tends to get blown about less in wind than a light one but all other flying characteristics of the heavy model will be worse.

As for what handles best.. a 'conventional' tractor prop monoplane of 'normal' proportions, little or no wing taper with a standard tail assembly takes some beating for overall handling properties. Check this site: http://www.uoguelph.ca/~antoon/hobby/pmdesign.htm
It will end up looking like 90% of every model out there but there is good reason why many models look similar..

Steve

[flying-llama]

Llama,
First of all lets dismiss the idea of airspeed varying due to 'headwind' and 'tailwind'.. To a model in flight there is no such thing as headwind or tailwind. Providing throttle end elevator settings are the same then airspeed remains constant regardless of which way you fly relative to the prevailing wind, only ground speed changes. What can and does affect the models airspeed is gusts, wind-sheer and turbulence.
...
Yes, I forgot to mention 2 items:
-Since I am making tight turns which are relatively fast, to the plane,
the turn itself may feel like a gust.
-The throttle and elevator settings probably will not stay the same, as I will
tend to want to reduce variations in ground speed as the plane flies around
(need to increase airspeed to go forward relative to the ground with a headwind,
need to decrease airspeed in a tailwind so that ground speed is not too fast
for me trying to fly in a small area).

Thanks.

[BMatthews]

Unless you're jamming the throttle on during those turns the airplane will not see a turn, no matter how tight, as a gust or anything like it. If it seems to over rotate during very tight turns then chances are you are noticing the transit time delay of the servos. You may let the stick snap back to center but it still takes a 1/10 second for the servo to travel from full deflection to center. On a very responsive model this will show up.

The pizza box wings only get "pitchy" for one of two reasons. First is that the owners tend to set the CG at the 25% or even slightly further back point. This means they are inherently unstable and need constant inputs when flying "normally" with the wing not actually stalled or near the stall. Setting the CG at 23 to 25% will get rid of most or all of the issue. Second is the often flexible and flimsy material that the PBF's are typically made from. A wing with some rigidity will not have that issue. For example there was one fellow that made a PBF design but used a proper airfoil with spars and regular covering. It flew just fine, would do all the PBF type oddball flight stunts but was able to level out and fly fast without becoming unstable. The only thing it wouldn't do was to crash with minimal damage.

I've also seen guys flying the smaller flat foamie 3D models in very tight spots. You may want to look into some of those that are in the 24 to 30 inch span range and use the smaller motors and gear.

[MCarlton]

(need to increase airspeed to go forward relative to the ground with a headwind,
need to decrease airspeed in a tailwind so that ground speed is not too fast
for me trying to fly in a small area).

Not really, you airspeed should remain the same whatever your groundspeed.

Think of it like this;

15mph wind
15mph stall speed

Ok, if you follow your logic, to maintain a 20mph groundspeed, heading into wind, your airspeed will be 35mph, which is fine and plenty above the stall speed.

To maintain a 20mph ground speed doing downwind, you would need to have an airspeed of 5mph.

Instead, you need to maintain airspeed and just deal with the difference in ground speed.

As for models, I concur with BMatthews, a shocky or similar would be a good option.

This might be perfect;

http://www.budgetrc.com/PDFs/BRC%20Hornet.pdf

[flying-llama]

To BMatthews: Thanks for that explanation of PBFs.
I will probably need to adjust for minimizing crash damage as I am still learning
and flying in a small area.

Not really, you airspeed should remain the same whatever your groundspeed.

Think of it like this;

15mph wind
15mph stall speed

Ok, if you follow your logic, to maintain a 20mph groundspeed, heading into wind, your airspeed will be 35mph, which is fine and plenty above the stall speed.

To maintain a 20mph ground speed doing downwind, you would need to have an airspeed of 5mph.

Instead, you need to maintain airspeed and just deal with the difference in ground speed.
...
Yes, I cannot really maintain a constant groundspeed,
but until I get better, I do need to lower the groundspeed when I can
to give me a breather when trying to fly in a small area.

With your scenario, this might mean
fly at 20mph airspeed (5mph ground speed) into the wind,
and a little over the minimum 15mph airspeed (30mph ground speed) downwind.
Thanks.

[JetPlaneFlyer]

With your scenario, this might mean
fly at 20mph airspeed (5mph ground speed) into the wind,
and a little over the minimum 15mph airspeed (30mph ground speed) downwind.
Thanks.

Flying deliberatly slower downwind is a recipe for disaster.. A model has no air speed indication so attempting to slow to near the stall speed in gusty conditions when visual airspeed 'clues' are distorted by wind will result in one thing... a stall.. and proberly a crash if you are flying low at the time.

Let the model fly at it's natural trimmed airspeed. This will mean that in the downwind leg you will proberly have to be turning all the time to prevent the model drifting downwind, but thats ok.... just dont attempt to pull it round too tight to compensate, otherwise a stall is again likely.

[BMatthews]

JPF is right as are the others trying to tell you that you can't do things this way. If the wind comes up to such a degree then it's time to pack it in and wait for calmer moments or just learn to make your downwind portions of your flying really short and basically an extended circle that brings it back into the wind.

Wind flying can be fun and challenging but at some point you just can't fly "normally". Instead you need to adjust your flight paths to minimize your time spent in the less desireable attitudes.

[vintage1]

Be careful. You will run into an intractable physical problem - or several.

Off the top of my head here as some points to ponder.

Safe airspeed is stall speed plus maximum gust over average windspeed. Slower than that and a guts will stall you downwind, or a lull will stall you upwind.

I had loads of fun with a Peter Rake Sperry Monoplne - IPS engine, but marginal on power. In wind, I remember flying it clear across the garden at the in-laws house, downwind, full throttle and nose up and gaining no height whatsoever in the gust that came after it..until the gust passed and it ballooned up 20 feet. Conversely landing it required almost full throttle to beat upwind, and naturally at that airspeed, it dint want to come do9wn!"

So you cant fly upwind in wind that exceeds the models top speed AT ALL, and its very dangerous to fly in gusts that exceed the stall speed of the model. You WILL stall it one day.

So plenty of speed and plenty of power is one thing you need for wind.

Now look at turbulence. A small lightweight model gets tossed around like a leaf. A jumbo jet does not. Well the ones that do are at the bottom of the atlantic..

So there is a scale of turbulence size to model size to consider. Ive taken small parkflyers up in breezy conditions, and yes, I can fly them and usually land them safely. But I don't. Its simply no fun fighting a model that wants to flip around the whole time.

OTOH, you can land a light slow model in a 30x50 meter garden. I've done it. In calm air.

With wind, you can go higher in airspeed, because ground speed is less upwind. But weight helps - inertia is your friend. The model will punch through turbulence and not flip upside down. So go heavier on your wind models, and put more power in.

Another absolute disaster for small patch flying is the 'floater'. In wind, you need the speed, and in wind with the speed, the model has to be flown into the ground, you cant just glide land it, because the glide angle is too shallow to clear your trees and hedges, and still touch down.

I had one model which I flew in the field next door - its roughly 180 meters sqaure with trees on two sides, my house on the third, and some electricity pylons on teh fourth side. To land a gafst model I had there was a nightmare..no flaps, cut the engine and go low, hope I was THIS side of the trees turning hard pulling Gs quite near a high speed stall, then line up and bring it in..to find that the safe turn speed was well over straight 1g stall and safe landing, and there simply wasn't enough space to slow down in :)

I snapped several props simply dumping it into the ground because it was too near the field boundary to turn, and too fast to land properly.
.

[Tom Harper]

An enlightened presentation - but, years ago, you convinced me that an airplane flies at equilibrium, oblivious of the motion of the supporting air mass.

"Safe airspeed is stall speed plus maximum gust over average windspeed. Slower than that and a guts will stall you downwind, or a lull will stall you upwind."

I couldn't agree more!

[vintage1]

An enlightened presentation - but, years ago, you convinced me that an airplane flies at equilibrium, oblivious of the motion of the supporting air mass.


Oblivious of the steady state speed of the air yes, bot not oblivious to changes in that.

By definition, if its flat calm, there are no gusts and no turbulence.

In idealised steady wind conditions, apart from pilot perception the only issue is whether you can make headway upwind at ALL. Because of top speed limits. This was terribly important when I used to fly single channel years ago. Sure you could keep the model heading into wind, but they were trimmed for a natural climb..and it was a choice between losing it downwind or at altitude! You had to hope you could get far enough upwind to risk a spiral dive to lose altitude, or hope the thing ran out of fuel more or less overhead..in which case something akin to a vertical descent was possible.

That or a long walk..


Once you get into gusts and turbulence, which is a very common thing on a fine afternoon surrounded by trees, its an entirely different matter. Wind shear and rolling turbulence makes a mockery of anything that's small and light., and makes every landing a chancy business. There simply is no safe way to fly, as the old pilot's adage - safety equals airspeed or altitude - is hard to maintain when landing.

[flying-llama]

JPF is right as are the others trying to tell you that you can't do things this way. If the wind comes up to such a degree then it's time to pack it in and wait for calmer moments or just learn to make your downwind portions of your flying really short and basically an extended circle that brings it back into the wind.

Wind flying can be fun and challenging but at some point you just can't fly "normally". Instead you need to adjust your flight paths to minimize your time spent in the less desireable attitudes.
Yes, as the winds get higher, at some point, it will be time for me to pack it in.
For me, this point is currently fairly low (below 10mph).
I am trying to increase the wind speed at which this point is reached
and do this for small areas (as a point of calibration,
30x50 meters is for me a fairly large area).
And for my mistakes in judgement on when to quit,
I fly with a plane and in a place and manner so that crashes
do not cause much damage to anything or body:
I get frequent reminders of how much damage a crash can do :)

[BMatthews]

Vintage raises the issue of turbulence. In tight confines with lots of trees and buildings around this is easily more important than the wind speed itself.

To fly a highly responsive model inside what amounts to a washing machine once all that turbulence comes up will test anyone's skills. At that point the design of the planform isn't as important as the responsiveness of the model to deal with the sudden shifts.

One option may be to look at using thin sheets of EPS foam curled around some EPS or depron ribs to form a symetrical airfoil shaped PDF or slightly swept delta'ish model. Such a design should "bounce well" with minimal damage.

Hey, you're testing yourself and there's no doubt that you're learning a lot about flying in turbulence. If you can live with the inevitable crashes then keep on with it. You'll soon be better at this than many, many other flyers that pack up and stay grounded at the first sign of "roughness" in the air.