Airchair Q%A Page 3

I do appreciate comments, new questions, and corrections, but please read the website first and ask questions that show me what you already know (otherwise I'll just be referring you back to the website, which you may have already seen). I know it's easier to send me a list of questions than to read my (poorly organized) materials or to search the web, but I can't allow e-mail to take up all my lazy time. My e-mail address is "m--sandlin" followed by "@sbcglobal.net " (I give my address in two parts to confound harvesting by advertisers).

..................................................................................................................................................................................................................................................................................................

June 14, 2017 "...the super goat guys use foam ribs in the wing. It seems that foam would be an easier material to build ribs from than the small aluminum and not to mention cheaper. What is your take on foam ribs and would you suggest them for the goat wing? I know the tail feathers already have a similar design..."

Response: As you can see on my drawings, the main wing rib for the Bug, Goat, and Bloop is just a formed tube that shapes the upper surface of the wing. This is strong and simple, and has always worked well. I'm not sure what people are trying to accomplish with the built-up ribs, I doubt that trying to rigorously control the contour of the lower surface is worth the effort or the weight. On the Bloop 4 I stitched an undercamber into the lower surface to help tension the fabric, but that was quick and easy work with a long needle and thread (see B4A10). Go to the photo album "Bloop 1 & 2" and look at the wing frame on the lawn, it is ready to cover, there are no built up ribs. The Goat wing is the same. I would use this system again.

March 30, 2014... "I have a private pilot's license....and ... a few questions. First, can the Goat4 be built solely from the technical drawings provided, or are there other plans out there? Also, is there a complete build log I could view, so I know what I would be getting into?"

Response: Do a web search for "Goat Glider build blog", there are some out there. Also look at the Airchair Yahoo Forum for alternate drawings and opinions (better yet, join and ask specific questions). Generally, each homebuilt airchair is different, but I haven't seen anything much better than my Goat1, 2, or 4. My drawings are a description rather than a plan, but they have been used as a basis for building (but they get changed, as noted above).

February 8, 2014......... "I am an experienced sailplane pilot / instructor with over 500 auto tow launches. My planned launch method for the Goat 1 will be a similar launch process with lighter line, 90% gross weight weak link, and much slower launch airspeed. Without data, and only prior sailplane experience to rely on, I estimate tow NEVER EXCEED SPEED to be 30 mph airspeed. Do you have any experience with this launch method that might define safe launch airspeed and / or other procedures that differ from sailplane launches?"

Response: 500 auto tows! Launching the Goat should not be much of a challenge after those. I expect a slow and casual climb, so if the truck speeds up so I can't climb without a lot of airspeed and back stick, that's too fast, and I release. This may be different for you, depending on your weight and whether you have moved the hookup point back from the nose, as some people have. I favor the nose hookup for the initial ground tows because it gives lots of feedback, a tow that is too fast will pull your nose down, keeping down the line tension for the release. I've flown the Goat with an airspeed indicator because somebody else put it on, I don't use one for airspeed control, just for comparisons to other aircraft. I don't recall reading the airspeed on ground tow.
If the tow is too slow, I can't climb or maintain normal airspeed, and again I release. I agree that about a 30 mph airspeed on climb should work.
The standard weak link strength would be 100-120% gross weight, but I see no problem with being a little weaker, as long as you are prep ared to respond quickly to a line break.

Answer: "Differential aileron deflection" usually refers to rigging the controls so that the upward moving aileron goes way up while the downward moving aileron only goes a little down. This is intended to reduce the adverse yaw in turns, so you won't need as much rudder deflection to get a coordinated turn. It's the normal setup for conventional sailplanes and airplanes.
The Goat already has some differential aileron deflection, but it is small because a big differential would reduce the rolling power of the ailerons, which I don't consider a good trade off. The Goat ailerons are sized for keeping the wings level in a moderate breeze while sitting on the ground before takeoff, so you don't need a helper to run with the wing tip and keep it level until a higher airspeed is reached.

July 2, 2013 "How do the controls fell on the goat 4 glider, de they have any slack or play that is unconfortable, how do they do in time, do they gain play because or the wearing of aluminum parts in the sistem?

I prefer the cable braced wings than the strutted version, is it that much draggier that everybody chouse the strutted version?
the thicker wall ..., i mean will it create any problems oather than weight?
Being heavy it means tall, and that means longer legs also, so the control stick is a litle (4 inch) shorter fo me intend to make it longer, but that will limit a bit of control surface moovment, my qestion is how much (aproximatively in any measture) you think the ailerons and elevator shoud move in each direction?
The goat 1 flyes for a wile (10 years o so) do you know what problems or maintenace dit it need ( weared parts or so) exept fome fabric covering wich i know it was changed."

Answer: The Goat and Bug control lines can develop slack due to stretching of the Spectron lines, which is minor. The control lines can be re-tensioned anytime, or just use the new type lines which are a Vectran/Dyneema mix and don't stretch (see G4A9). This control line hardware is just sailboat running rigging, these problems were encountered and worked out by sailboaters. There is additional slop in the controls due to elasticity of mounting and structures, but I do not find it "uncomfortable". Stiff controls are better, but if the plane does what you tell it to do that is of greater importance.

No wear of aluminum, steel, or control line has been detected, just busted up landing gear and worn down skid plates. Maintenance might involve control line tension adjustment, lubrication of moving parts (silicone spray on control lines and pulleys works well), and air in the tire (take a hand pump).

Wing struts versus cables has been discussed elsewhere. I will not comment on design changes such as control modifications.

1. What about building an airchair, making design changes and using different materials? Will you help me? (April 2009)

Answer: For liability reasons I will not endorse specific design changes or material substitutions. I may be willing to make some general comments as long as the question has not already been asked and answered on my website.

The main issue with regard to design changes (or even without them!) is pilot confidence when it comes time to fly. You won't get much airtime if you have doubts about your glider, especially if you want to soar and stay up in turbulent conditions. We airchair pilots are aviation pioneers, and courage is required. Even without innovation, when you soar an ultralight you will, at times, get thrashed and trashed by the atmosphere, so get ready!

My confidence in my gliders (Bug, Goat, Pig) is based on using structures well proven in hang gliders. I have not done any large scale structural testing, but tubing ladder frames like mine, braced by steel cables, have been used by rigid wing hang gliders for many years with satisfaction. I fly at a hang glider wing loading, with about the same weights and speeds as a hang glider, so I feel that by applying a small additional margin of design strength I can use similar structures and take advantage of the history of safety that hang gliders have provided. Well known hang gliders with structures similar to mine might include the Fledglings, glider Quicksilvers, Icarus 2 & 5, Voyager, etc.

A flap might be useful to lower the stall speed for a rolling takeoff, but the effect would be marginal and I doubt that it would really make much practical difference.

In the landing pattern, using flaps for glide path control might be a good thing, but I don't favor them.
First, at hang glider wing loadings there are no devices that will allow any airchair to fly a fixed pattern in afternoon turbulence without maneuvering for approach control, so why install complex flaps which cannot serve as the primary method of glide control anyway? Even if you did have landing flaps that were powerful enough to overcome lift and sink at low wing loadings, they would be too powerful for any low time pilot (or maybe any pilot) to safely use. Only a few sailplanes use landing flaps as the primary glide control because they are tricky and require somewhat involved and critical procedures.

Secondly, even though the Goat is not high performance even by hang glider standards and doesn't really need special devices for getting down, there are already ways of adding drag. Some like to slip (flying slightly sideways to add drag), but I avoid anything requiring skill, so I use a drogue chute for almost every Goat landing. Of course, in addition to slips or a drogue, you will still have to maneuver to a landing under some lift and sink conditions, but this is just what hang gliders and paragliders have been doing all along.

The loads produced by my use of a drogue chute attached outboard on the struts or flying cables are not known to me, there have been no tests or structural calculations. I expect 30 to 60 lbs. of force on the chute bridle, and, as you see from my frequent use of it, I have decided that this is acceptable. Concern over drogue chute loads might seem to favor flaps, but the flap loads are also unknown and untested.

Answer: In response to this question I expanded section C3 of the Goat Construction Notes. The new text is: "Holes are drilled with a hand held power drill using a self centering drill bit. Every hole is marked from the outside and drilled separately (see reference line note .....). In tubing, matching holes are drilled through in pairs for final finishing alignment after they are drilled from the outside, unless there is an access problem. My holes tend to be sloppy and oversize, which makes assembly easier."

11. "...any idea of what Extrusions Floyd used to create the new struts on the now red goat (and where he got the material)?
They look good and are flatter than the extrusions I have been exploring for use (some made for Struts / jury struts on PMA Taylorcraft parts etc). I can see how they will allow folding for easy transport - and it looks like a simple and elegant solution to the strut constructions." (February 2010)
Answer: Floyd Fronius used faired cross section extrusions for the wing struts on the Red Goat. This aluminum stock was originally produced for use as hang glider "down tubes", in this case for Seedwings of Santa Barbara, California. There are various versions of faired down tube stock for the various hang glider manufacturers. I don't know if they want to sell it, or in what lengths.
The extruded struts, with heavy internal tubular sleeving for strength, added about ten pounds to the weight of the Red Goat relative to the tubular struts I used originally. The sleeved tubular struts with applied fairings, as shown on my Goat1 drawings, would still be my favorites because they are lighter, and probably easier to repair or replace if damaged.

12. "Why are the bug2 and bug4 wings inclined at an angle, and the goats' wings are fixed without any bending, but are straight all the way across?" (March 2010)
Answer: On my gliders the dihedral angle of the wings is often related to ground contact. The Bug biplane dihedral is set high mainly to provide ground clearance for the lower wing tips while rolling on the single wheel during launch or landing.
The strut braced Goats have a small dihedral angle (the wing is not straight, see the drawings). This allows short, and thus lighter and less bulky struts, as well as a reduced sideways tipping angle when not flying, making it easier for the pilot to sit down and strap in when the wing tip is on the ground. Aerodynamically the wing when flying will be more efficient, less stable, and the control might not feel as good or be as easy.
On the cable braced monoplane Goat wings the dihedral is intermediate, about 4 degrees, a good all around compromise. The dihedral provides good yaw/roll coupling for easy flying, making the rudder more effective in turns, probably reducing the need for precise stick/rudder coordination.
These dihedral effects are small and usually not noticed, at least not by me. I once tried steering a cable braced Goat using just the rudder, and it was okay but slow turning. I suspect that the Goats with less wing dihedral will not steer as well using just the rudder.

13. "WHERE I CAN FIND THE PLANS TO BUILT THE SUNDOG, DO YOU HAVE THIS IN YOUR WEB ?"

Airchair Questions & Answers