Author Topic: Wing Tips:  (Read 6904 times)

Doug Johnson

Wing Tips:
« on: April 02, 2011, 11:24:33 PM »
I've read repetively about how useless the wing tip mod on the 7-800's was has anyone experimented with the wing tips. I put Met-Co-Aire Hoerner tips on my old C-172B and they seemed to make difference and I liked their looks. I always intended to put a Hoerner tip on my Helio and see if it made any difference but as things went I never got them done. I only got as far as making the plugs for the molds before I sold my helio.

Here is the stuff I found on that particular wing tip also Met-Co-Aires sales pitch.

I also considered the information on the Flint and Hoerton wing tip tanks extensions. They seem to give no weight penalty to the 172. because of the extra wing surface and now the Xtips are here.  With tip tanks you had 24 exta gallons (2 hr's fuel) and you didn't have to fill them. Also look at the turbine mods, you need all the fuel you can get. With the 120 gallon wings you're already transfering fuel so whats a couple more tanks. Also look at the Stallion with its Tuna Tips if these tanks were made to slide into the end of the wing replacing the end rib they would be about 75 Gallon tanks. Of course if you did that it would get into structural Engineering flight testing on and on. Back to the original question. Below are the Helio wing tip exdtensions.

Hoerner Wing tips
by David Sakrison
 
This is the story of an accomplished wartime aerodynamicist from Germany, a former Douglas Aircraft aeronautical engineer and self-professed "character" from California, an invisible corkscrew, and a revolutionary wing tip.

As an aerodynamicist for Germany's Fiesler Corporation, Dr. Sighard Hoerner, Ph.D., worked on the Fiesler Storch (Stork), a short takeoff and landing (STOL) reconnaissance and liaison aircraft. During the Second World War, Hoerner worked as head of design aerodynamics for Junkers and later for Messerschmitt. After the war, he was invited to come to the United States to work on aerodynamic research at Wright Field, in Dayton, Ohio. There, while working on new concepts for high performance for Navy fighters, Hoerner designed the wing tip that bears his name. He was one of the first aerodynamicists to acknowledge the existence of the wingtip vortex, the corkscrew-shaped wake that forms on a wing's outboard edge, and the Hoerner wing tip was specifically designed to minimize the effects of wingtip vortices on lift, drag, stability, and control.

In 1953, Tom Hebert quit work as an aeronautical engineer for Douglas and started his own company at Fullerton Municipal Airport, in California. Friends described Hebert as "a genius." He described himself as "a character." His new company, Met-Co-Aire, seems to have reflected both portrayals. His company was the first to offer "metalizing" of Stinson and Cessna wings, stripping off the fabric covering and replacing it with aluminum. Hebert's tricycle gear conversion for the Cessna 170 was copied by Cessna and gave birth to the Cessna 172. And Hebert was the first to hang 180-hp Lycomings on the popular but underpowered Piper Apache.

The design of the Met-Co-Tips comes directly from the research of Dr. Sighard Hoerner, Ph.D., a prominent aeronautical engineer involved in designing a high performance wing tip for use on Navy fighter planes. His technical data and conclusions were compiled at Wright-Paterson Field and published in USAF Technical Report #5752. Met-Co-Aire applied his work to civilian aircraft.

The primary reasons for this design are as follows: A square wing tip gives the greatest wing area for the least span. A smoothly finished, thin, leading edge provides for the best possible airflow over the tip. The convex underside accelerates the speed of the air passing under the tip to a velocity more equal to that of the air flowing over the top of the tip, thereby creating streamline flow. This flow reduces turbulence, which markedly decreases the size and intensity of tip vortices. By having a deep, straight trailing edge we are moving the point at which the vortex begins away from and behind the main surface of the wing, which means less drag and better control. By keeping the outermost point of the wing in a level plane with the wing top surface, we effectively increase wing dihedral angles. (Gain lateral stability.)

The design of the Met-Co-Tips comes directly from the research of Dr. Sighard Hoerner, Ph.D., a prominent aeronautical engineer involved in designing a high performance wing tip for use on Navy fighter planes. His technical data and conclusions were compiled at Wright-Paterson Field and published in USAF Technical Report #5752. Met-Co-Aire applied his work to civilian aircraft.

Dr. Hoerner showed that the efficiency of a wing tip depends on six critical areas. His findings were:

1. The tip must be as thin as possible but still maintain a round leading edge.

2. A blending of wing top and bottom surfaces along a straight line.

3. The edge formed at this blend to be as thin as possible.

4. Obtain a sharp trailing edge leading to a corner, this corner to be in a straight a line as possible with the entire wing trailing edge.

5. The top of the tip to remain in a level plane with the top of the wing.

6. The bottom plane to be brought up in a convex curve.

The primary reasons for this design are as follows: A square wing tip gives the greatest wing area for the least span. A smoothly finished, thin, leading edge provides for the best possible airflow over the tip. The convex underside accelerates the speed of the air passing under the tip to a velocity more equal to that of the air flowing over the top of the tip, thereby creating streamline flow. This flow reduces turbulence, which markedly decreases the size and intensity of tip vortices. By having a deep, straight trailing edge we are moving the point at which the vortex begins away from and behind the main surface of the wing, which means less drag and better control. By keeping the outermost point of the wing in a level plane with the wing top surface, we effectively increase wing dihedral angles. (Gain lateral stability.)

What's all this mean?

Quite simply, your wing has a finite length, that is, it has ends (tips). The air flowing under the wing will seek the region of low pressure above the wing by "spilling over" these ends. This spillage creates vortices or regions of turbulence which roll inboard and backward at the tips. The vortices absorb energy and increase drag, also since they roll directly over the ailerons they hamper stability and handling. From elementary physics we know if we can reduce the magnitude of these vortices, the plane will have more energy available to pull itself through the air. Also, if we redirect the position of the vortices away from the ailerons we will gain stability and control.

Met-Co-Aire claims are.

• Increase range 1-2% at no additional fuel cost!
• Increase rate of climb by 60 feet per minute!
• Increase cruising speed by 3-5 mph!
• Reduce distance required for take off, resulting in a 10-20% quicker take off!
• 4-5 mph lower stall speed with more positive aileron control!
• Increase the overall stability of the aircraft!
• Improved appearance with a more aerodynamic profile!

The Hoerner design, agreed to be the best wing tip design available.

My desire was to have a set of tips that fit my airfoil perfectly. Since I was going to have to make the tips from scratch, I decided to research the different types of tips and choose the most efficient.

As I began researching the topic of wingtips and was surprised to find that there is little information available. One of the few sources of information I found was a paper written by Chris Heinz aeronautical engineer and designer of the Zenith aircraft, entitled “Anatomy of a STOL Aircraft.

From Mr. Heinz paper: “For a long time, I’ve said that Hoerner wing tips should be used on most light aircraft designs, since they increase the effective wing span from 8" to over one foot without having to carry any additional weight: As we all know, there is low pressure on top of the wing, and higher pressure on the bottom of the wing, with the pressure difference creating the lift that allows us to fly. Toward the tip of the wing, the high pressure ‘feels’ that there is less pressure on the top of the wing (just around the tip), and wants to go there to equalize the pressure, thus creating a secondary flow out toward the tip of the wing. This secondary outward flow generates a vortex (a circular motion) behind the wing, as illustrated below.

Figure 5 – Wing Tip Vortices

With a rounded or squared wing tip, the vortex is centered around the wing tip, as shown above”

So what type of tip does Mr. Heinz recommend?

“If the wing tip is cut at 45-degrees with a small radius at the bottom and a relatively sharp top corner, the air from the secondary flow travels around the rounded bottom but can’t go around the sharp top corner and is thus pushed outward.

The performance of the aircraft depends on the distance from the right to the left tip vortices (the effective wing span), and not the actual measured geometric span. Hoerner wing tips provide the largest effective span for a given geometric span or a given wing weight.”

Based on Mr. Heinz article, the Hoerner tip increases the effective span of the wing and increases surface area slightly. That means slower stall speeds and less turbulence at the tip.

The other documentation I was made aware of by Derik Mackie was from Daniel P. Raymer's book Aircraft Design: A Conceptual Approach. The excerpt follows.

"...[the most important] effect is the influence the tip shape has upon the lateral spacing of the tip vortices. This is largely determined by the ease with which the higher-pressure air on the bottom of the wing can "escape" around the tip to the top of the wing.

A smoothly-rounded tip (when seen nose on) easily permits the air to flow around the tip. A tip with a sharp edge (when seen nose on) makes it more difficult, thus reducing induced drag. Most of the new low-drag wing tips use some form of sharp edge. In fact, even a simple cut-off tip offers less drag than a rounded-off tip..."

Based on the limited information I knew about airflow and wing tips, I had reasoned in the past that the rounded Cessna tip was no better than no tip at all. Mr. Heinz’s and Raymer’s writings confirms this hunch. As you can see by the above illustration, either tip, square or rounded allows the flow over the outer part wingtip to be disrupted thereby reducing the effective span of the wing.
 
I also decided on a modified Horner design  Unlike a true Horner tip, this modified design keeps the span of the wing consistent out to the very edge of the tip.

I do know they have no negative effects. I have read they are more effective on certain wings and only by trying them will you know if they have any significant effect.


« Last Edit: November 17, 2011, 04:37:23 PM by Doug Johnson »
Doug

Doug Johnson

Re: Wing Tips:
« Reply #1 on: November 17, 2011, 01:46:19 PM »
I was looking through old posts and ran into my post on wing tips since I now know how to put pictures in I decided to edit the post.

I tried these tips don't believe they actually do what Metcoaire, says they do, but do beleive at slow speeds in turbulence they may make airplane a little more stable.

I also believe I liked to think they helped, and besides I needed to replace my tips and I liked their looks. The tips I was building would have included landing/taxi lights in a Hoerner style tip.
 
« Last Edit: November 17, 2011, 01:49:32 PM by Doug Johnson »
Doug

Louis

Re: Wing Tips:
« Reply #2 on: November 17, 2011, 03:28:19 PM »
A lot of work on wingtip is centered around making better of the wing surface available.  Better take-off, better high speed, better slow speed.  However, for having crashed lately with one of the reason being to have a very good augemented wing tip, i am suspecious now about all these reasons.  The tip of a wing is where the roll control is most effective.  Aileron are put at this place for that reason.  Making too good wing tip without looking at roll control can change the roll charateriticc to a point that you don't have it anymore.  Particulary if you wing tip becomes wings extension.  I lost a friend in a 206 on floats with these.  With the plane full of children.  In six feet of water.  And i had a good time lately with a lack of roll control in a cub.

I know an Helio will never have problem with slow speed control, and it will be the only plane i would fly with augmented efficacity wing tips, or wing extension.  I hope in evaluating wing tips, a pilot will check the new roll control.

http://www.tc.gc.ca/eng/civilaviation/publications/tp185-2-98-008-3599.htm

You can see the wing extension after the aileron resulting in low roll control on crosswind of the 206 of my friend



You can see mine:






Doug Johnson

Re: Wing Tips:
« Reply #3 on: November 17, 2011, 04:29:35 PM »
Louis,
You posted a couple pictures at the bottom they didn't come through for some reason.

I can't remember if the cargo door on my Helio opened all the way with 40 degrees of flaps, I think it did. I had the style of door hinged at the top with the shirt tail catcher.

Does the 7/800 style cargo door that opens to the rear have any interference with 40 degrees of flaps?

Sad accident latch should probably be redesigned. Is this a good reason not to have a 206 on floats? I almost bought a U206 instead of a Helio. Since I had so much time in a 172.

I also carried 4 of those co2 inflated life jackets in the rear pouches of the seats. I probably should have had 2 for the rear seats, but I almost never had passengers in the rear seats.

Doug
« Last Edit: November 17, 2011, 04:50:39 PM by Doug Johnson »
Doug

Doug Johnson

Re: Wing Tips:
« Reply #4 on: November 19, 2011, 07:53:03 PM »
Most people think the 7/800 tips are strange how about these.
Doug