Philippe Vigneron's drawing of the Russion Experimental glider BP-3.
(See Letters to the Editor for a little more on
this interesting looking flying wing.)
THE WING IS THE THING
The Wing Is The Thing (T.W.I.T.T.) is a non-profit organization
whose membership seeks to promote the research and development of flying
wings and other tailless aircraft by providing a forum for the exchange
of ideas and experiences on an international basis. T.W.I.T.T. is
affiliated with The Hunsaker Foundation which is dedicated to furthering
President: Andy Kecskes (619) 589-1898
Editor: Andy Kecskes
The T.W.I.T.T. office is located at: Hanger A-4, Gillespie Field, El Cajon, California.
Mailing address: P.O. Box 20430
(619) 596-2518 (10am-5:30pm, PST)
Subscription Rates: $18 per year (US)
[Effective January 1, 1999 - $20 per year]
Information Packages: $2.50 ($3 foreign) (includes one newsletter)
Single Issues of Newsletter: $1 each (US) PP
Foreign mailings: $0.75 each plus postage (table below is approximate
PERMISSION IS GRANTED to reproduce this publication or any portion thereof, provided credit is given to the author, publisher & TWITT. If an author disapproves of reproduction, so state in your article.
Meetings are held on the third Saturday of every other
month (beginning with January), at 1:30 PM, at Hanger A-4, Gillespie Field,
El Cajon, California (first row of hangers on the south end of Joe Crosson
Drive, east side of Gillespie).
who might be interested in taking on building this aircraft, so maybe something will eventually come of Al's research work.
The SHA Western Workshop at Tehachapi over the Labor Day weekend was well attended and the speakers all put on a good show. The highlight of the Saturday night auction was the purchase of a Mitchell Wing that had been donated for the cause by Bob Chase. The flying weather was good, especially during the afternoon sessions and the temperature was nicely moderate for this time of year. Everyone I talked with really enjoyed it. The only thing missing were some flying wings on the flight line.
Access to the new TWITT web site appears to be brisk, although I haven't been able to get statistics from my internet service provider for about a week now. The site was down for about 10 days due to a software problem on their side, but it was back up and running in early September. I have been doing some behind the scenes upgrades to the various pages and will re-publish them in the next week or so. I have received several e-mails from strangers who have found the page and asked for more information or had a specific question about an aircraft or on how to get a hold of someone about a project.
The November meeting is looking like it will be a good one. We will be concentrating on the work of Witold Kasper and I will be putting some of the material we have in the library in next month's newsletter as a primer for the meeting.
This was a blessing since we would have to close the doors for your featured speakers view-graphs. After going over the usual housekeeping items, Andy talked a little more about the new TWITT web site pages that were currently out there for viewing. He explained the rationale for what would be in it for the future which is mainly to contain major items that are not already on someone else's pages. He will be putting out a page of links to other sites so anyone accessing the TWITT site could navigate to other related sites for more information on flying wings. He would also be adding the member's projects page as soon as he is able to purchase a scanner to convert some of the pictures into an electronic format.
Bruce Carmichael was asked to promote his latest booklet Ultralight & Light Self Launching Sailplanes. This was an outgrowth of his research for a speech he gave earlier in the year. Bruce also mentioned he had gone back to Elmira after the SHA Workshop to attend a meeting of the International Sailplane Design Board. He had been asked to give a presentation along with two others from SHA on light and micro-lift sailplanes and where they are going. This is probably the prelude to developing international regulations for these types of aircraft in the future.
Bob Chase had a little historical footnote for us. In his early years he had gotten interested in model airplanes through what he learned in the Book of Knowledge. While at Oshkosh this year he came across a book called Model Airplanes and the American Boy, 1927-1934. It illustrates paper airplanes designed by William B. Stout, who was responsible for the Ford Tri-Motor.
At this time Andy introduced Al Bowers who was going to talk to us today on what has turned out to be his favorite Horten sailplane, the H Xc. Andy mentioned we would be video taping Al so that others can share this experience from afar, and he asked everyone to ask plenty of questions.
(ed. - Due to the length of Al's presentation and the need to get other material into this month's newsletter, the minutes have been broken down into two parts, with the remainder to be published in November. We have also tried to make them as detailed as possible so you can get full affect of Al's work in this area. We will be releasing information on the availability of the video tapes as soon as they have been reproduced in sufficient quantities to meet the anticipated demand.)
As background into what got him started
preparing this presentation, Al said it all started when he heard about
the 1997 National Soaring Museum Flying Wing Symposium in Elmira, New York.
With his fascination of flying wings since his childhood days, he decided
to get his foot in the door and sent a letter to Paul Schweizer to see
if he could get a slot on the podium. Al had been working for the
past couple of years on the blended wing body which is a flying wing design
NASA has had some interest in. After consulting with Bruce Carmichael
and several others, Paul approved Al's request to put on a presentation
on the history of Horten flying wings.
| The next area to be covered is some history
of the Horten's sailplanes over the years. He believed Peter Selinger
had identified 43 particular sailplanes the Horten brothers had built and,
he felt this had a strong influence on how they ended up where they did
when compared with others of the time like Jack Northrop. This history
would include the high performance sailplanes, some of the later designs
while Reimar was living in Argentina, and in particular, the foot launched
Horten H Xc which is the ultimate goal of the presentation.
He then began talking about the analytical span load history. The original formulation for this comes from Ludwig Prandtl who came up with a paper published in Germany in 1918 and in an English version by NACA in 1920, called "Applicationds of Modern Hydrodynamics to Aeronautics". In this he explained how to calculate induced drag based on spanload using a lifting line theory which assumes all the lift occurs along a single spanwise line called the Line of Aerodynamic Centers. The way he accomplished this was with a series of chordwise vortices along the wing's span. He mathematically modeled these horseshoe or closed loop vortices going all the way back to where the wing first develops lift which is a starting vortex. If you moved the wing in a perfect fluid without viscosity this vortex would remain there as has been shown in some experiments. However, it is difficult for most people to visualize a wing and think about the flow going backward underneath it, so it is really more of a mathematical concept with some basis in reality.
Max Munk applied calculus to this theory and one of the things he came up with was the optimum span load that minimized the induced drag. The optimum span load turned out to be the elliptical span load distribution. This theory is taught all through aeronautical engineering school as the optimum so everyone is inclined to accept it as the best way to go as long as you are working in an inviscid world. However, there have been some recent developments done by a small group of people at NASA Langley where they have applied viscosity to this theory and it turns out that the optimum is almost, but not quite purely elliptical. So for all practical purposes, modern designers still use the elliptical theory and it works very, very well.
The problem was this is a very mathematically intensive way to try and calculate the spanload in order to get a beautifully elliptical span load that is desired. Oscar Schrenk came up with a very simple method of predict what span load is, but Al warns that this method is what would be called a "Rule of Thumb". It works very well, but there is no firm theoretical basis for the way it works. There is some empirical evidence that it works very well, but it just happens to work out that way. Referring to the Analytical Span Loan History chart, Al described the individual lines representing twist, taper and surface
deflections and then that they look like when combined under Schrenk's method. The twist line has a distinct jog in it that is the result of a flap being deployed in the inboard section of the wing which is representing mechanical twist, so this method deals very well with control surface deflections.
| Unfortunately, Schrenk's formula
didn't give the full picture since there were some problems with it, and
one of the people who came up with a solution for this was Hans Multhopp.
He simplified it mathematically by adding control points in his wing which
allowed him to get a product condition. This is were the flow comes
off the upper and lower surfaces cleanly and joins the airstream.
These control points are simply vortices going the other way and Multhopp
put them coincidence with the circulation vortex along the line of aerodynamic
center. In 1944, Laska and Weissingger move the control points back
to the 75% chord position versus the 25% position of Multhopp's which is
where the normal aerodynamic center is assumed to occur, however, this
makes the method even more mathematically intensive. Don't forget
this is at a time before digital computers which made performing the calculations
much harder accomplish with accuracy.
Multhopp's "simplified" theory came out in 1938 and the Horten brothers saw it as a big jump forward in being able to understand the span loads of their airplanes. You can understand why when you start thinking about the bell shaped span load. The bell shaped span load by definition goes to zero at the tip, so Schrenk's method which has a finite value for span load at the tip is very difficult to deal with. This made Multhopp's method a big break through for the Hortens and all their designs since 1938 used his theories in the design method.
In talking about bell versus elliptical span loading, elliptical is the optimum since it gives you the minimum induced drag and for sailplane designers this is a big deal. The Hortens thought that may be there are times you don't want the optimum for one thing, but a sub-optimal solution for many things will solve more problems so they came up with the bell shaped span load. Al referred to the Bell vs. Elliptical Span Loads slide to illustrate this point. Both the elliptical and bell shaped curves come to a finite point at the tips which is very important. Once you have these span load distributions, the fascinating piece is that you calculate the induced drag for each of the little vertical areas on the chart as you progress across the span.
On the elliptical curve the induced drag continues to build all the way across the span always represented by a negative value, which is drag. On the bell shaped curve you notice there is a positive area out near the tip that has become what could be called induced thrust versus being drag. This allows you to do things like proverse yaw with the roll command, which is based on the amount of lift that is generated. By making more lift at a tip then the value of the induced thrust will increase at that tip. Phil Burgers noted that this induced thrust condition is why birds fly in the "V" formation. The birds at the tips of the "V" are actually achieving forward thrust, whereas the lead bird is not but does benefit from the significant upwash from the others. So, in 1938 the Hortens are using this induced thrust at the tips, but we don't see it again until the 1950's when Dick
Whitcomb came up with the winglet designs. Phil Burger pointed out that the wing tips on Horten's aircraft are similar to "flat winglets", which Al agreed with.
The one thing that Multhopp's method cannot account for is the sweep angle, so there is a residual value out there that the Hortens called "mitteleffekt". This is purely an artifact of their calculation method and it doesn't really exist since it involves a problem in the analysis technique, but not in physical reality. As you sweep the wings back on any type of wing upwash from the center influences the tips differently so there is a small increased load at the tips and a decreased load at the center line. In Multhopp's technique the upwash for sweep is unaccounted for and the next slide showed what this looked like. If you took a Horten wing and un-swept it the results would be shown as the solid line on the chart which has a fairly low lift value at the tip but a much higher value near the middle relative to the swept case and this is the mitteleffekt. Bruce Carmichael commented that Irv Culver's approach to fixing this problem was to increase the angle of attack of the center section, whereas, the Hortens fixed it by increasing the chord at the root section. So, mitteleffekt is not the sag in lift distribution at the middle, but it is the unanticipated sag in the lift distribution in the middle, just to clarify the point.
There is one other piece of the puzzle in the calculation method used by Multhopp. Al had seen it in many of the Horten papers, but it wasn't explained very well. Then he ran across some unpublished papers by Dr. Edward Udens in Germany, who has a lot of information on the Horten designs. The Calculation Method (Multhopp) slide shows the analysis derived by Dr. Uden's (see next page for an illustration of this technique). It maps the wing out using a uni-circle arc that begin with a value of zero at the root and rotates around to a value of one at the tip. This 90 degree segment is then divided up into equal
angles and then the arc intersection points are mapped down through the wing's chord. These give you the spanwise locations that are called control points for analysis and are labeled as the central difference angle. These sometimes showed up in the Horten papers as a delta. What Horten found was that when you raise the power of the transcendental (sine) function for the value of 'n', you get closer to a bell shaped lift distribution curve. If you make the 'n' value 1 then you end up with an elliptical distribution and, when you raise it to 2 it becomes bell shaped but you still don't have induced thrust at the tips. As you get to a value of 2.5 there is a cross-over from adverse yaw to proverse yaw and, as 'n' increases towards 3 you get increases in induced drag which is the penalty for this method. So you want the minimum value of 'n' you can get away with and for the Hortens most of the time in their designs this value was 3, which is near optimum.
At the bottom of this slide is a span versus twist graphic
which represents a correction for the chord length. The graphic is
the twist distribution for the Horten H Xc and was Multhopp's Calculation
Method provided by Reinhold Stadler in Germany who has a program for calculating
it quickly and easily. The fascinating thing about all this to Al
is that there is washin for about the first 20 percent of the wing, so
the wing is twisting the wrong way. Then it goes out to about 10
degrees of washout at the tips, but overall it has a twist range of about
11.7 degrees due to the washin area.
Enclosed is $36 for 2 year renewal to your
organization. I always enjoy your articles on flying wings.
Living in Arizona doesn't allow me to attend your meetings. I have
actively looked at building a PUL-10, but am waiting until it is a more
flight tested product.
(ed. - Thanks for the nice letter on your activities
and collection of aircraft. You should be commended for taking on
the task of starting a new EAA chapter, and you're right about the amount
of work it takes. It seems like the work is never done and now with
the web page another aspect has been added that requires continual attention.
Sorry I haven't submitted anything in a
while, but I have been busy traveling (mostly work) and trying to get a
sailplane recovered and repainted (my trusty old 1-26 is just about airworthy
(ed. - As usual Kevin comes through again with some very good material. I have listed what he sent below. Included was an article on the Komet, but I don't believe we have ever seen a write-up on what the final outcome of the project was and what Kevin has done with any prototype that may have been built. Perhaps his next communication will relate this experience.
"A Wind Tunnel Investigation of the Kasper Vortex Concept", by Edward W. Kruppa, University of Washington, Seattle, WA 98195, AIAA, Inc., 1977, pp 10. Includes text, charts, graphs, illustrations and a references section.
"A Brief Wind Tunnel Test of the Kasper Airfoil", by Daniel Walton, Soaring, November 1974, pp. 26-27. Text, pictures and graphs.
"Some Ideas of Vortex Lift", by Witold A. Kasper, Engineering Consultant, SAE, Inc., Warrendale, PA, pp. 12. Line drawings, charts, graphs and text material, including some handwritten notes of unknown origin. Photocopy quality in some areas is poor.
"The Monarch", by Jim Marske, Soaring, (issue unknown), p. 28. A brief article on the thoughts behind the Monarch and some on the construction and flying.
"Flying the Pioneer II", by Rick Apgar with commentary by Paul Bikle, Soaring, July, 1974, pp. 22-25. Nice article on the finishing and flying of a Pioneer flying wing.
"Renshaw Komet", (author/source unknown), pp. 282-286. Concept
article on the initial development ideas for the Komet, including model
picture, 3-view and statistics.
Date: Fri, 25 Sep 1998
HELP NEEDED, Please
New kid on the web (E-mail is now available
here in Saudi Arabia and full Internet services are promised for next year).
P.S. Attached a file with my drawing of the Russian experimental glider (this month's cover picture) Belyayev BP-3 (BP for Beskhvostyi Planer: tailless glider, also referenced as TsAGI-3), designed by Victor Belyayev and tested in 1936. Her wing platform looks like the one of the "Genesis I" (Slight forward swept, separate horizontal rudder). More to come.
(ed. - After receiving this e-mail I wrote back and asked Philippe for more information on the Ring Wing and Pelican, which he quickly did by return message. This method of communicating is just super, since he was able to send the 3-views that had apparently gotten lost in the regular mail. The descriptions and drawings are included below.)
|Dehn "Ring Wing": This aircraft was designed
by German born designer Karl DEHN, in Australia. Flying tests were conducted
in 1982 by Ben Buckley, but were stopped after Dehn's death, at the age
of 67. Project of a motorized version not carried out. No spec available
here. This glider is now preserved by the Airworld Museum of Warangatta.
(*-Photo Allan Bell/Airworld Museum).
Debreyer "Pelican». This aircraft has been designed by Jean Claude DEBREYER and is now manufactured and marketed in kit form by the company AIR EST SERVICES, Marly, France. (3V drawing of the prototype JCD-02), (*-pictures of the production aircraft JCD-03/ Photo Air Est Services).
Specifications JCD-03: Span : 7.20m, Length : 3.10m, Area : 12m2,
Main chord : 2m, Thickness : 17%, Empty Weight : 80/85kg, Max. Weight
: 175kg, Engine : One Solo 210cc (15hp), Pusher propeller 0.75m Dia, Cruise
speed : 75km/h, Landing speed : 45km/h, Take-off run : 150/200m,
Autonomy : 3 hours. Fuel consumption : 3 l/h, Structure : Wings :
Foam and Dacron, Fuselage : (Prototype : wood), Production aircraft : Composite
materials (Molded fiberglass shells).
(ed. - This is the second part of Lloyd Watson's recount of his experiences in test flying his Pioneer IId flying wing. The first part was printed in the September '98 newsletter.)
(At the end of last month we read:
I stepped in the cockpit and for some reason felt calm and warm.
Everything slowed down. Even with all the activity around the
world got quiet. My spirit was calm and I proceeded with the
check list step by step. Radio check, Release check, Control check,
seatbelt check, thumbs up from my brother on the wing and the radio crackled,
N86TX on runway 17 New Braunfels for glider tow and test flight.
With that the rope pulled and we rolled down the open runway.
My self was focused on deciding the first 200' if it was going to be stable.
Then the noise of the skid stopped. Calm, quiet, and peaceful.
|NOTE: The remainder of each newsletter is composed of the Classifieds section, which provides our members with various products related to flying wings. These can be seen at the Classifieds page on this site.|