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Metal Wings: (information from Fred Hinsch)
Many people are now building metal wings for their BD-4s. There is no ready source of information for doing this so I have decided to include the basic technique in the newsletter. Fred Hinsch built a metal wing for his BD-4 and has supplied the following methods, weights, and techniques.

The specifics are:

• Spars: two tubes 10' x 6.80" OD x 6.41 ID, 2024-T3
• Spar extension: 2024-T3, 0.032" thick, rolled to fit into wing spar, riveted and bonded
• Rear spar: 2024-T3, 0.032" thick
• Ribs: Murphy. 0.025" thick, 6061-T6, spun flanges riveted to ribs, bonded and riveted to spars
• Skins: 3 sections, 0.032" thick inboard, 0.032" thick center, 0.025" thick outboard each wing
• Skin riveting: solid countersink rivets, 2" spacing except in fuel tank area, 1" spacing
• Tank sealant: PRC 1422-A2 and 1422-82

Wing renewal (Ardis Almond):
I thought you might like this information on this work on my BD-4, Pat's Patience, N71 AG, since it might apply to others with the same problem.

I finished my plane in 1979, I had the white wing panels that were of low quality. At the time I was building my wings, builders were recommending that the fuel tank area be overlaid with dynel cloth and polyester resin to help the leak problem most builders were experiencing.

I used this method in my construction and still had leak problems from the beginning. Over the years, I worked on the wings several times. I made many surface patches with ProSeal. I also cut inspection holes in the wings and tried to seal the problems from the inside. It continually got worse. I found that the dynel started delaminating and any pinhole leak traveled between layers until it found a way out. These pockets caused further delamination. I finally had to bite the bullet and do a permanent job.

In February, I brought the wings into my shop. I removed the flap/aileron assembly. I peeled, scraped, and sanded off the dynel layer. This got me back to the original panel surface. Isophtalic polyester resin (fuel tank resin) was used to patch any abraded spots on the panels. ProSeal type fuel tank epoxy was used to seal any suspected joint leaks.

The fuel tank area panels were heavily sanded. Then a very thin film of ProSeal was spread over the surface. While this was wet, a single piece of 6 ounce fiberglass cloth was wrapped completely around the wing and overlapped on the trailing edge. The glass cloth was pushed into the ProSeal by a small roller until it was smooth and the ProSeal went into the weave from the back side. This was allowed to cure.

The Isophtalic resin was then applied to this glass cloth. Traditional composite methods of micro slurry buildup and sanding was used to get a smooth finish. Featherfill was used for final finishing and then the entire wing was repainted.
The plane was put back into service in mid-June. At this time (September) I have had no leaks or blisters in the paint. I feel this method will work because the ProSeal will seal the tank and the cloth will keep the ProSeal intact, as well as strengthening the wing panels.

I will be glad to discuss my method with anyone that is interested.

Inspections Before First Flight:
We all know the importance of good inspections before first flight and we know it helps to have a couple different people go through the 'check list'. There is a check list in the Bede plans (at the back of the pilots handbook and on page 165 of How To Build Your Own Airplane) but it gives only general topics (not which way what should move, for instance).

A recent incident has reminded us again that "Murphy" will always be with us. Question: how would you check to see if your (anti-) servo trim was working correctly (not wired backward)? It takes a little bit of mental gymnastics to get to the answer so maybe a checklist is needed that gives more explicit directions.

In the incident in question, the first flight went fine until trim was needed to ease the stick pressure. The trim wheel was turned (grunt, ugh) but the pressure was not relieved on the stick. The decision was made to land and then sort out the problem. This was easily accomplished. Apparently, it was not noticed that the trim caused greater stick pressure or it would have been recognized that it was just wired backwards.

It is the small things that seem to pervade our minds and keep us from trouble shooting correctly. In this case, the builder was already concerned about the CG position. This expectation of trouble with CG pushed out all thought of other things that could make it seem that there was a CG problem. This prevented him from experimenting with rolling the trim the other way.

By the way, if you pull the stick back (the anti-servo will come up), and then roll-in "up" trim (move the top of wheel back), the anti-servo tab should go back down some (at least that is how mine worked just now!).

Thoughts on Iron Mike (Autopilots):
How good are you at flying with your knees and your peripheral vision? Most pilots have been doing that for years while they scrutinize their maps for whatever (just wait until you need bifocals!). Every time you think you have found the answer, the airplane gets out of whack enough that you have to look up and get things back under control. Don't even blame it on not having the proper dihedral (us BD guys are sensitive about that)!

Ever been flying at the higher altitudes and find that the heading is 30° off every time you look at it (you could have sworn that you just looked!)?

It is so much nicer if the airplane remains stable while you perform your map functions. A decent copilot is the best solution as he can fly an scan for threatening traffic. This doesn't always work as most copilots are trying to help you look at the map (they always think they can find 'it' better). What I am trying to get at is the (almost) 'need' for an autopilot.

How well does the autopilot meld with the BD-4? A lot of BD-4s have sported autopilots at one time or another. Remember the NASA generated system that used an enclosed air stream, fly-speck varistors and the 'water-hose-effect'? This was commonly known as a 'Fluidic Inertial Rate Sensor'. It generally used clothes dryer flex hose and a vacuum source for actuation of the control surfaces rather than the more common servo motor or the model airplane servo moving a trim tab.

You probably never heard of the 'Electrostatic Autopilot'. This one used the earth's electro-potential field at the wing tips to determine which was higher'. I had one of these working in the lab but never got it installed. A method of ionizing the air surrounding the wingtip probes was needed so that static build-up would be prevented. This required the use of radioactive alpha sources (I always wanted to go to Oshkosh with "Radioactive Hazard" stickers on my wingtips!).

The most common of the autopilots are those that use a gyroscope to measure motion (or attitude). The error signal is then used to drive a servo-motor that in turn drives the control surfaces. There are also lots of things to worry about like over-shoot, loop gain, loop bandwidth, and several others that we will ignore for now.

More of a worry to builders is: required BD-4 modifications to make an autopilot work.

The easiest method is probably moving the control surfaces by brute force. This requires a Servomotor that can generate a substantial force. One large disadvantage of full force servo-motors is their WEIGHT.

Trim-tabs must be added to the aft side of the control surfaces or they must be built into a 'cutout' in the control surface. Tabs mounted on the aft edge will have more moment arm and therefore can be smaller. Trim-tabs almost always require the Radio Control servo-motor to be mounted inside the control surface which adds to the weight required to be counter-balanced in airplanes that require statically balance surfaces.

Mounting The System

Now Neale is not the first to think of a BD-4 biplane (there is one newsletter member who is working on one - I just forgot who - sorry) but the loose connection to the Beech Staggenwing is clever. This might be the answer for those of you who want a lower stalling speed! Of course, you will also be the slowest BD-4 around.

The Beech Stagger did get great speed but at the expense of a lot of horsepower (and fuel consumption).

Where to go from here is the question.

1. You will immediately pick up 200+ lbs of added vehicle weight (not including the cute inter-wing strut). The lower wing spar really doesn't have to be equal in strength to the top wing (we still only have to lift the same weight) and we would get some 'spar strength relief' as the lift produced by the inner part of the lower wing will be put into the lower cabin area (and not have to be carried by the upper spar). This does mean that the 'cute' inter-wing strut has to be functional. It is probably best to just make the lower spar equal to the upper.
   
2. The lift will not be doubled as there is substantial interference flow problems with wings in close proximity however, there will be substantial increased litt. Our short wing chord will be a benefit in a bi-plane configuration. We could shorten the lower wing to get rid of some of the excess lift (and drag).
   
3. The center of lift will move forward but I am not sure quite where. This means that things have to be moved around to get the balance back within reason. The passengers are not a good option unless the firewall gets moved (and it might have to). The engine can be moved forward for improved access to the rear of the engine.
   
4. Increased lift says increased wing pitching moment. This means we have to revisit the tail volume - but if the center of lift and center of gravity move forward, the tailboom effectively becomes longer and therefore already has a better mechanical advantage. The tail volume might be fine as it is (except for that ugly fixed tailwheel).
   
5. The main gear would have to be moved forward to keep up with the Center of Lift / CG movement.
   
6. This airplane just wouldn't look right with a fixed main gear - although I believe the early Staggewings were fixed. The lower spar could be used for the main gear carry-through, but where would you tuck the wheels away?
   
   BD-4 owner David Dotson immediately decided that the lower wing should be below the fuselage (ala Paul Kauffman and his main gear box) to get more distance between the wings. This would give a nice hollow belly (about 7 Inches deep) which would allow the wheels to tuck below the front seats. The rear seat passengers could sit more upright as their feet could be 'down in the belly'.
   
   This dropped belly modification adds more drag due to the increased wetted area and also the weight of the structure - not to speak of matching the tail boom to it (might require moving the tailboom back 20").
   
7. It might be a good thing that we need more weight forward as we might desire a larger engine to pull all of that drag around. Now that Russian radial engine comes to mind. It would really make the airplane resemble the Staggenving. Or course, the gear might have to be lengthened some to get the prop clearance necessary.

I don't know - sounds do-able to me - but of course, We Are Experimenters!! It kind of makes the
heart pound and the blood race!
It may be time to put a basic configuration into the EGADS program and see what it comes up with. I do
plan to work at it a little but will let Eyler and Dotson do the building.

You can't go home again - or can you?
I received a letter from Joe Thalman who now owns his father's BD-4 and is slowly refurbishing it. He is putting on metal wings and will install a Lycoming 10-360 to replace the 165 Franklin. Joe soloed in N14BD and now flies F-16 Fighting Falcons and actually got to fly one to the '95 Oshkosh. I guess sometimes dreams can come true! Can you imagine getting to fly one of those (with free fuel) and then coming home to play with your BD-4? I expect there are a few fewer rules to adhere to with the BD?

Welcome to our group, Joe! It is nice to hear of 'kept in the family' BD-4s.

Paper Airplane BD-4?
John Brecher's BD-4 has found a new home. Ken Blackburn has purchased N186JB and is 'allowing' John some time in it if he helps with the maintenance (kind of like having your cake and eating it tool).

The 'Paper Airplane' comment in the title is due to Ken's major interest in life - that of designing paper airplanes, flying them (setting world records), and writing books about them so we can have fun too. You might visit his web site at: http://www.geocities.com/CapeCanaveral/1817/

LightSpeed Ignition:
Carlos Serodio also had me order an ignition setup from Klaus Savior. Steve Mahoney has a slightly earlier version of this system and recommends it as the best thing since sliced bread. He was miffed at all the time he spent fairing in his airplane to get a couple of more mph. He installed this system and picked up a full 5 mph (and probably with better fuel economy). Steve said that there was a noticeable difference in climb capability. He also idles verrrry smoothly.