Real Windy Day Slowflyer Design??

[Butch777]

I've posted this a couple of times and got no real answers. I have several fast planes, jets and wings to fly on real windy days. I want something to fly in front of my house on real windy days, when I don't have time to pack everything up and go to the flying site. I fly my modified E-starter in winds backwards at times. I removed the dihederal, put larger ailerons w/differential, larger elevator and narrowed the fuselage about 40%. It weighs 11oz with a gws 350 and lipos. It tracks real well and climbs at about 45 degrees. I also recently picked up a PAF, by Potensky. A 30" slow flyer EPP wing. It weighs 5.9oz and has a 250 geared motor and huge elevons. I fly it in front of my house in over 10 mph winds. It does ok but not as stable as some of my planes. My idea for a windy day slowflyer are;
High wing
Swept wing, no dihederal
excess power, geared
large control surfaces
epp and carbonfiber, for crashability
pusher prop, for when your thumb is not as fast as the wind sheer
A tail, for better weather-vaneing

My questions;
Would a gull wing be more stable? like a bird
How much sweep? And tapered, stright or delta like?
What about wing tips? Drooped, swept back, like on some sailplanes
or swept up? I think they call it poly-something
Airfoil? Undercambered balloons, symmeterical is not as efficent, so semi?

I just need to get the best ideas I can to start this project. Any Ideas would be greatly appreciated, Butch

[BMatthews]

The design requirements for slow flight models in calm air versus a windy weather slow flyer are completely different.

For windy weather flying, especially in the undoubtedly very turbulent air in front of your house, you really do not want a stable model of the type that will return to level flight. Such designs have a mind of their own that is easily confused by the rapidly changing airspeed and direction due to gusting and turbulence found on windy days. Stability IS still important but you want the sort of stability found in a 3d fun fly type model where the aircraft is close to neutraly stable.

A small electric fun fly depron profile model would easily do well in higher winds. The light weight will let you fly slowly. The effective controls will let you control the model quickly to restore the model's attitude when it is disturbed by the turbulence. The flat symetrical airfoil will let you change speed without having the model's flight attitude change apreciably. In otherwords it won't want to suddenly balloon up as the airspeed changes due to gusts or moving the controls.

Looking at your own ideas so far....

Make it swept wing if you like but you won't gain anything other than looks if that's what you want. Models do not weathervane, they fly in a river of air that affects the whole model the same all at once. I have not done many flying wing designs but from what I've seen the Zagi style models do quite well in wind as well as calm. Don't bother with the polyhedral (a type of dihedral), You're using ailerons so dihedral is not needed and in fact dihedral will just work with the wind gusts to make the model flit about against your wishes.

[HELModels]

Dihedral isnt the problem in wind. Wingloading and airfoil to a lesser degree is important for wind penetration. Dihedral in any form, poly or simple, can only help stability in windy conditions. If you have aileraons you want less dihedral because the roll initiation comes form the ailerons and not dihedral. You do want an airfoil that can penetrate. Medium thickness and small camber will produce a slope like airfoil. Slowstick stock wing has no thickness but lots of camber, so it is slow from high lift high drag. Find an airfoil that is already used on genuine slope planes of about the same wing area as the stick. I'd keep the basic dimensions of the wing the same and only change the airfoil and AUW. The UIUC database has lots of airfoils with typical application indicated i.e., Low reynolds, slope, sailplane, etc. Even a HLG arfoil will provide better penetration than the stick wing and HLG foil is pretty easy to duplicate. Take a piece of balsa, round the leading edge, sand till the high point is 30% and sand from there to a sharp trailing edge. That is almost what the Drela arfoils are and is where they came from back in the olden days.

At low reynolds, increasing wingloading does not really hurt the glide, but boosts wind penetration. At full scale reynolds the relationship between increased wingloading and best glide is 1:1. Increase the wingloading by 10% and you decrease the glide by 10%, but that is not true for small models. It takes a huge increase in weight to really dog the model.

[Butch777]

Flying my dihederal wing planes in strong wind, they seem to flip over real easy, so I thought that some sweep would give some stability like a dihederal effect and help it to penetrate the wind. And what about droop tips? Would that help?
When I watch the seagulls hovering motionless, I thought of copying there design. There gull wing seems to sweep back as the winds get stronger. They just really caught my eye and thought it would be nice to fly like that on a real windy day. Butch

[HELModels]

I've seen vultures do that too. They kind of curl the last 1/4 span down and the root curls up. Maybe what they are doing is reducing the effective wing area and thus increasing wing loading to get better penetration. Curving the wings is also like polyhedral.

[Butch777]

That would make sense, in that when a gust hit them, they could reduce there wing area to keep from rising from the gusts.
Has anyone ever seen a model that pulled in the outboard wing section maybe in conjunction with the elevator for going up and down? That might make a interesting project! But as usual, too many ideas and not enough time and money. Butch

[Ollie]

"That would make sense, in that when a gust hit them, they could reduce there wing area to keep from rising from the gusts."

Not true.

For the truth see:
http://www.wfu.edu/albatross/atwork/dynamic_soaring.htm
http://members.tripod.com/douglasturner/id27.htm
http://www.sloperacing.com/results/ds-speeds.htm

[HELModels]

Which part is not true? If the wing is effectively reduced in area, the wingloading goes up? higher wingloading means higher airspeed?

Those links are real nice explanation of DS, but soaring birds dont always DS.

I've seen vultures kind of reel in their wings like I described on real windy days and when going downwind. It looks like a half-hearted flap.

[Ollie]

"I've seen vultures kind of reel in their wings like I described on real windy days and when going downwind. It looks like a half-hearted flap."

That makes the vulture avoiding a stall from a gust because the gust makes the vulture airspeed too low.

[DaveGherardini]

"That makes the vulture avoiding a stall from a gust because the gust makes the vulture airspeed too low."

Thats right because the vulture under no circumstance wants to die. They are setup to try to maximize every change in there enviroment for survival and that means trade offs are made because there enviroments change all the time. It dosent mean that their setup for that condition is the most efficeint.

[BMatthews]

That would make sense, in that when a gust hit them, they could reduce there wing area to keep from rising from the gusts.
Has anyone ever seen a model that pulled in the outboard wing section maybe in conjunction with the elevator for going up and down? That might make a interesting project! But as usual, too many ideas and not enough time and money. Butch

There was a full sized glider that used telescoping wings but not for the issue you're trying to deal with in this case.

The real key to flying in strong winds is a model that is stable but only just barely. A model that is close to neutraly stable is not only going to require you to fly it with more attention but it will be upset by external influences as well. Trying to produce a variable area wing as you suggested is just way too much effort for any advantage that it may bring you.

You keep mentioning dihedral. Are you flying aileron equipped designs? You need to realize that if you're flying rudder-elevator models that you MUST have dihedral for the yaw from the rudder to induce a bank. Adding droop at the tips or some other "trick" will counter your yaw to roll couple and reduce the ability to control the model. Far better to move over to ailerons and learn to fly with them.

One of my more memorable days of flying was with an aileron equipped 2 meter glider on a day that became VERY stormy. But with the high winds came a lot of turbulence, ground shear and intense gusting. I was able to fly for just over 20 minutes by sliding back and forth across the oncoming wind and turning into and pulling up as each gust tried to roll the model downwind. The altitude varied from second to second by as much as 40 feet. The model never went above the high start launch altitude and at times was less than 20 feet up and a second later would be at 100. It was like riding a crazy roller coaster and much like the seagulls you mention. But it was also a crazy workload on the pilot and left me totally wrung out. Truly exciting though.

But of course this sort of stuff is as far from a typical calm weather slowfly design as you can get. This is why I suggested the 3D fun flier type model. It's light enough to react to sudden wind gusts and drops without stalling, can be set up for close to neutral stability so the gusts do not upset it as much, flies slow enough to "back it up" in the wind yet with power will punch into the wind enough to get back to the pilot if you get downwind a bit. A glider equivalent would be one of the hotter DLG types or a 60 inch slope racer set up with larger control surface areas to deal with the sudden and big control inputs that are often needed to react to the gusts.

But equally as important as the model choice and design is the change in judgement the pilot must adopt for windy flying. You will need to learn a whole new set of practices, judgement calls and reactions to deal with stormy weather flying. It's well worth it though as it's not only a ton of giggles but it'll make you a better model pilot as well. It's these flying skills and techniques that you need, not some overly complex model that still can't deal with all the variables like a quick mind and thumb can.

[Butch777]

I live 30 miles east of San Francisco, where there are 90,000 wind mills here in the hills because its windy here most of the time. I normally fly at a site in the hills that the slope flyers use on the week ends. I go on week days. Winds average 15 mph and on windy days its 20mph gusting to 30mph. I fly E-starters to microjets up there almost always in the wind. I even modified a pico Tigermoth with a 250 and large ailerons to fly better in the wind, but undercambered wings don't quite cut it. I fly a 4.2oz Butterfly and a 5.9oz PAF in front of my house that goes backwards if I get too high. So almost all my flight time is windy time. I have over 70 planes with about 20 flying and several helicopters. I have planes flying in real windy conditions that just drop 20 ft out of the sky, because the wind gusts or shifts so quickly.
I'm just trying to find the best of the best, windy day designs, Wing shape, airfoil etc.
I asked about droop tips because the Robertson stol conversion uses them on real slow flight aircraft, like the Maule or bush type Cessnas. I've owned a Cessna Aerobat and it had droop tips. I've flown many real planes, military jet, helicopters and gyrocopters. I just don't know a lot about the aerodynamics of slow controlable model planes. That why I'm asking. Butch

[Butch777]

BMatthews,
I really don't understand why you say planes don't weathervane. I have a couple of light weight, slow flyers that have large vertical tails and I can see them shift there tail from left to right when the wind changes dirrection. I can also feel the wind shift on my face. If not weathervaneing, what would you call it?
I asked about dihederal because it seems to flip the planes over when the wind changes direction and from what I understand, sweep adds a dihederal effect. I have several wings and they all have sweep and fly good in fast wind just not so good at slow speed. So I was thinking a wing with a little sweep and a conventional tail might be more stable in fast winds. But I think your idea about the 3D models is worth a try. I have 3 or 4 of them around here some where, maybe I'll put one of those together and see what it does. Thanks, Butch

[Arthur P.]

Haven't tried it myself yet, but in theory flaperons and high thrust + prop speed? Could help get the right balance between really slow flying on calm days and fast flying on windy days. I don't think that on a windy day you'd want to stick it out low between trees and houses. Probably would want to go vertical to a bit of safe altitude, so the flaperons could help get up quickly and come down 'elevator-like', while in their up position you should be able to have sufficient penetration to get up against the wind. And a flat wing may help have a bit less buffeting accross wind?

[Ollie]

It's been done. See:
http://www.polecataero.com/
The Red Wing

[Ollie]

There is more.
Assume the plane can have a low air speed at 10 MPH (14.6 feet per second) and a high air speed at 20 MPH. Assume the wind speed at 10 MPH and plane at air speed 20 MPH pointed down wind. The ground speed is 30 MPH. A surprised gust appears. A normal person has about half a second lag for control. The plane control is about 20 feet lagging position.

How big is your yard? How big for maneuvers plus the 20 feet gust buffer plus the surprise maneuver after the gust?

[BMatthews]

....I asked about droop tips because the Robertson stol conversion uses them on real slow flight aircraft, like the Maule or bush type Cessnas.....

Oh, THAT sort of drooped tips. You were talking about dihedral and then suddenly mentioned drooped tips and I was thinking you were considering anhedral like gull wings or similar.

Those sorts of wingtips are to try and reduce or contain the tip vortices. Modelers often shortuct to a flat tip plate and from all I've read and tried I would say they work but not by much and can have other odd side effects. Others say the effect on aileron response is quite noticable. Probably because they are closeing the open end of the aileron and that sharpens up the response. The best way is to make up a model and then try tack glueing on various shapes and see what happens. Lots to learn in that area and undoubtedly some fun to be had.

Models don't weathervane unless you spike them onto a pole on top of the house.....:D However gust response of models, and in particular slow light ones, can often have a weathervaning like appearance to the pilot depending on the model's design and weight. Having flow a lot of free flight I can assure you that if any model was going to weathervane it would be those ones. And if such models show signs of weathervaning it's only becuase they don't have any rudder trim properley in place.

Our models fly in a "river of air" and float downwind with that wind. Only localized gusts that result in quick wind velocity change will affect the models in any sort of dynamic way. Once it's again flying happily within the steady current it won't weathervane or do anything else odd until you tell it too. Make sense?

[Tom Harper]

Hmmm....windy , slow flyer....I'd try a modest aspect ratio (5:1) thin curved section. Something like an SS only built up. No flaps - too much drag. Short aileron - one side only.

Thin sections are difficult to build. Carbon spars might help but I'd use egg crate construction with no spars at all:

[Butch777]

Thanks Tom,
So a stright thin wing, slightly undercambered. With no sweep or taper. What about wing tips? I work with fiberglass and carbonfiber by trade, so I could come up with a thin wing no problem. Thanks, Butch