Prawnik

Can anyone give me the appropriate equations or other advice for building a set of winglets similar to those found on the BTE Flying King, aka "STOL wingtips"? I am getting ready to build a Goldberg Falcon III, and it seems that STOL tips would be a welcome addition to an excellent design.

Would STOL tips be effective in an airplane of that size? Would adding STOL tips cause unwanted effects such as yaw control problems, poor roll control, or excessive drag? How much area should STOL wingtips encompass for maximum increase in low-speed lift with a minimum unwanted side effects? What is the best angle w/r/t the wings themselves for the winglets to take maximum effect?

scalebldr

My Feedback: (7)

you may want to ask this in the aerodynamics forum but after flying the original falcon 56 for 4 years and still have it today .i really do not see what you will be gaining with the addition of the wingletsbut this is a hobby so if you want them go ahead ,just wondering what type of performane you are expectinf to improve.when i built my falcon back in the fall of 1970 it was covered with silk and dope weighed 5 1/4 pounds had no steerable nose gear and used a os 35 with muffler and a 10/4 prop and it was flown first sat in january 1971 with a kraft series 70 radio using kps 11 servoes.soloed easter weekend of the same year and added steerable nose gear that summer and installed a new os h40 p engine and removed 8 ounces of weight under the fuel tank.now could do aerobatics using an 11/6 prop

Tall Paul

In the full-scale world, winglets are designed for a single speed, usually to reduce drag at cruise, where most fuel is used.
For a model, this is seldom of importance.
About all you could do is try some, varying the sizes and angles, and comparing the way each feels in flight.
There's no real quantitative way to check the effect on a model, it will be up to you to decide what you like.
There won't be any serious bad effects in any event.

BWooster

I read once in an aerodynamic textbook that the effect of winglets is over-stated, and that much the same reduction in drag and increase in lift can be gained by increasing aspect ratio. Whether that's true, or over-simplified, I don't know.

Prawnik

Interesting stuff.

Meditating on the issue further, it seems that, even if winglets were to give an appreciable increase in low-speed lift, this could well be gained at the expense of roll-rate. Since the Falcon has good low-speed flying characteristics as it is, and (unlike most full-sized GA aircraft) I want to retain aerobatic capability, the whole STOL winglets idea may not be such a good one.

Tall Paul

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That's winglets in a nutshell... as span is usually restricted by structural considerations once the plane is made, adding the aspect ratio by going vertical makes it less of a structural problem.... less of an added bending load on the wing.

Ed_Moorman

My Feedback: (1)

If you want to experiment with wing tips, make the end of your wing flat with a ply or thick balsa rib. Then you can bolt or screw on end plates of various types.

I have done this numerous times and have published it and have had readers of my column duplicate the experiment. End plates for a Falcon 56 sized plane need to be about a 1/2-3/4" extension all around the wing.

Plates will increase the roll rate, lower the stall speed, lower the landing speed, tighten up your loops and maneuvers and also make good skids if you tip over.

Lower only end plates act like anhedral and will reduce or eleminate the roll due to rudder in high wing planes. I have done this experiment before, but am doing it again, hopefully, this weekend or the next, for my column. You make a lower plate that extends down about 1 1/2 inches. Fly and put in rudder and check for roll. The plane should roll backwards, right rudder-left roll. This indicates plates extending too far down. Trim off in 1/4" increments until you kill the roll due to rudder. This one is really easy to do with a SPAD (Coroplast) plane. You just carry some utility shears to the field, fly & trim.

For STOL, you need to use flaps or flaperons. With big plates-try an inch and a half all the way around-and flaperons, you are trapping a bunch of air under the wing when you go full power. I like to hold full up, giving full down flaperons, and hit full power. A light plane can literally levitate into the air. You might also need to add another inch or so to the flap (inboard) section of your ailerons.

britbrat

Actually, there can be very serious effects if you don't get them "square" to the slip stream, or slightly "toed-in". If you somehow have one (or both) of the tip-plates slightly toed out you will have a violent roll response.

Tall Paul

True, but the correct angle is only correct for one flight condition, and inefficient at others.
For a plane with a limited speed range it probably could be a worthwhile addition, but for both slow and fast flight, probably not a good idea.

Prawnik

Ed: Care to comment? For that matter, what are the disadvantages of plates - or to put it another way, why doesn't everyone design them in?

Bob101

In full size airplanes you really on see them on planes that are designed to cruise at high speed. Such as the corporate jets that are hitting .89 or more mach...

My understanding (no engineer at all ) is that true winglets are there to reduce/stop some of the airflow from going spanwise across the wing. At some point in speed/drag the airflow finds it easier to go along the wing and off the wingtip than to go over the wing.

Now endplates and etc.. are another matter...

Bob101

Double post.

scalebldr

My Feedback: (7)

what you are talking about above are wing tip vorticies.they are i believe designed to reduce the turbulent airflow at the wingtip but from the boeing site winglets arefor the 737 line:
Benefits
Depending on the airplane, its cargo, the airline's routes and other factors, winglets have the potential to give:
IMPROVED TAKEOFF PERFORMANCE

By allowing a steeper climb, winglets pay off in better takeoff performance, especially from obstacle-limited, high, hot, weight-limited, and/or noise-restricted airports. Performance Improved climb gradients increase 737-800 allowable takeoff weight (TOW).

Some examples include:

Chicago-Midway: ~1,600 lb additional TOW
Lanzarote (Canary Islands): ~3,500 lb additional TOW
Albuquerque, Denver, and Salt Lake City: ~4,400 lb additional TOW
REDUCED ENGINE MAINTENANCE COSTS

Better climb performance also allows lower thrust settings, thus extending engine life and reducing maintenance costs. Lower Required Thrust Levels Extend On-Wing Life.

Takeoff - Winglets allow up to 3% incremental derate.

Cruise - Cruise thrust levels are reduced by up to 4%.

FUEL SAVINGS

Winglets lower drag and improve aerodynamic efficiency, thus reducing fuel burn. Depending on the missions you fly, blended winglets can improve cruise fuel mileage up to 6 percent, especially important during a time of rising fuel prices.

INCREASED PAYLOAD RANGE

The addition of Aviation Partners Blended Winglets to the 737 Next Generation has demonstrated drag reduction in the 5 to 7% range that measurably increases range and fuel efficiency . In addition, the Blended Winglets allow the 737-NG to take off from higher, hotter airports with increased payload.

Series Range (nm) Normal Range (nm) With Winglets
-700 3250 3634
-800 2930 3060
-900 2670 2725



ENVIRONMENTALLY FRIENDLY

With winglets, you can be a good neighbour in the community you serve. They enhance performance at noise-restricted airports and cut the affected area by 6.5 percent, saving you money on airport noise quotas or fines. By reducing fuel consumption, winglets help lower NOx emissions by 5%.

IMPROVED OPERATIONAL FLEXIBILITY

By increasing Payload Range and Overall Performance, Blended Winglets add flexibility to fleet operations and route selection. Air Berlin notes, "Previously, we'd step-climb from 35,000 to 41,000 feet. With Blended Winglets, we can now climb direct to 41,000 feet where traffic congestion is much less and we can take advantage of direct routings and shortcuts which we could not otherwise consider."

MODERN DRAMATIC APPEARANCE

Blended Winglets bring a modern look and feel to aircraft, and improve customers' perceptions of the reliability and modernity of the Airline.



Dimensions
Each winglet is 8 feet long and 4 feet in width at the base, narrowing to approximately two feet at the tip.

Added wingspan
Winglets add approximately 5 feet to the airplane's total wingspan - from 112 feet 7 inches to 117 feet 2 inches. (All Next-Generation 737 models have the same wingspan

TheParrot

Here's some good info on winglets
http://www.mandhsoaring.com/winglets.html

Villa

Last year I built a pusher/puller plane w/ 48" wingspan and two 28 Magnum engines. I had a tough time getting off the ground and as a result ended up putting on winglets, as shown on the attached photo. I later found that my poor takeoff performance was due to improper engine tuning. A change in props also helped. I ended up liking the appearance of the winglets and decided to keep them anyway. I sometimes take off on one engine. Some days it is very difficult. I literally "jack" the plane off the ground with rapid movements of the elevator. It appears fully stalled at takeoff and then it is time to start a turn. It wallows a little but has never "snapped rolled" into the ground. It may be the winglets that make it so steady, but I'm not going to take them off to find out. They even serve a little as out riggers during poor landings or fast ground turns. The winglets are about 1-1/2 inch larger than the wing, top and bottom. I followed Ed Moorman's suggestions, as I recall. Thanks, Ed.