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BD-4 NEWSLETTER #18
March 1991

Roger D. Mellema
17605 SE 288 PI., Kent, We 98042
PH 206-631-5324

Dues: It you have a'+' or an '--', you are good for more letters. An '@' says you owe $5.00.

Dear Friends,

Winter is over and it is time to get to some serious airplane building. The V-6 is hanging on the BD-4 now and I just brought Jim Huber's dynamometer out to the hangar. Jim is slowing a bit on his Mazda engine development so that he can get his airframe done and flying. He is hoping to get everything ready enough so that the FAA will sign him off for test flight. He isn't ready to risk flying the engine without more tests but the dreaded MODE 'S' transponder rule comes into effect in July. This rule says that any airplane completed after that date has to have Mode S. There have been some changes in the deadline but ft is not clear whether or not these airplanes will be forced to put In Mode S when they become available.

I plan to get the V-6 running within a couple of months and'want to do a series of tests on it to see how much horsepower I can actually get (the latest independent dyno run shows 191 hp). I think a complete exhaust system is necessary if you want to peak the power. 4200 rpm cruise is really not that high of an rpm and most experts I talk to, think that "short stacks" will cut into the power some. Walter Beecher, Galveston, TX says that his experts tell him that racers sometimes use short stacks but with a restriction in them. This is not optimum but is light and easy. I intend to try short stacks, stacks with restriction's in them, and 18 inch separate pipes from each cylinder. The dyno should tell me which does best.

Dave Blanton has made some recent changes in converting the Ford V-6. The original valve springs don't have to be changed, they are just fine for the small additional throw of the grind on the "Javelin Cam". The pistons should be forged and a good compression ratio is 9:1. I think this is because most people want to burn auto fuel some of the time. 10.5:1 pistons were tried and some bent wrist pins were the result. The wrist pins used were of a light racing variety so we really don't know if the high compression was at fault. Dave also recommends that a "Michigan 77" (same as Clevite 77) rod and main bearings be used. The original Ford bearings have not been a problem but the 77's are a bit harder. Lycoming does this sort of thing when 10:1 compression is used in the IO-360 made for the Helicopter engines (Firewall Forward also does this on the Mooney conversion).

I am still thinking about using a Holley Pro-Jection Throttle Body type carburetor and am happy that the fuel pressure required is 15 Ib/sq. in. rather than the 39 lbs fuel pressure used on the TBI injected Ford cars. The price for these Holley TBI's is $535.00. That includes all the necessary sensors, electronics control box, and an electric fuel pump. I don' know of an engine driven pump that has a 15 Ib/sq. in. pressure output, If anyone knows of one, please let me know. Can a regular pump be modified to get 15 Ib/sq. in.? The final pressure regulation takes place in the carburetor so the pump can put out a higher pressure.

A backup electronics module will be necessary. A Ford unit will run this TBI as it uses identical fuel solenoids. I could also put in a separate gravity flow cheater line. This method was actually certified (I believe) several years ago. A separate line is run from one of the fuel tanks. It has a shut-off valve, a needle valve, and runs directly to the carburetor. Small tubes are placed over each barrel of the carburetor. If a total fuel flow failure occurs, the valve is opened, and the needle valve adjusted to get smoothest engine operation for the present throttle position. The throttle can then be left where it is and the fuel shut off and on for power control.

     Flap Bearings

Richard Hedge is thinking of putting bearings in all of the flap ribs to reduce the aileron friction. He would like to know if anyone else has found this helpful? I believe the aileron friction is caused more by the aileron control cable going around the pulleys that are too small in diameter and having too much tension on the cable. The flap ribs 'float'.

     BD-4 on Water

If you will remember, many issues back I published some pictures of Bill deProsse's amphibious BD. Bill has not flown it as yet - it seems that he has had engine over heating problems during taxi tests. His O-360 is on a strut above the windshield and he has used the standard baffling and inlets. He is open to suggestionsl

I have had many people call me lately about BD-4's on floats. If anyone has information about someone getting ready to try this - please let me know. All I know of so far is the guy is Canada who was killed on his first landing, and I have a picture of George DeVauft's float structure (which looks very good).

     J R Metal Works. Inc

John Raffensparger is getting into the BD-4 metal business to a greater extent. I have visited him and have seen some of the products he has put out to the builder. Everything has been first rate quality and I would encourage you to use his services. He is the only businessman now supporting the BD-4. He now has a "how to do your own metal wing" set of drawings and they are only $35.00. This is by far the cheapest way to get metal wings. Stamped ribs are nice but are usually quite expensive. Many metal wings with homemade ribs are flying without a problem. John can supply large tail kits, main landing gear legs, aluminum angle of any variety, plans for a flap position indicator, copies of missing plans, etc.. John is now also supplying the curved windshield.

PO Box 375, Monkton, MD 21111 301-343-2159

     Concerning Letters

As you read through this newsletter, note how much of the material was sent in by you BD builders! I would like to thank everyone for their support. Of course there were about 4 times as many people who wrote in as are quoted here but it is difficult to get every little thing in. Your ideas are in my head and my files - so don't think you are forgotten. Keep up the excellent work.

rdm

     BD Jet

Jim's new address is: 18421 Edison Ave., Spirit of St Louis Airport, Chesterfield, MO 63005. He has plans for $220.00. He also has the original plates for "How to Build Your Own Airplane" book. He would have this book remade but there is a large minimum run requirement. How many of you need one of these (or a new clean one)? Maybe I can organize a new printing.

     Dunlap wind errata

I mistakenly said that the Dunlap wing is not the BD round spar. Noel did use the BD spar. He is using a 2.5 gal header tank but the normal fuel pickup locations. He has had a problem with the fuel vents: "An interesting phenomenon was the ability of the vents to pressurize the tanks sufficiently to cause transfer of fuel from the forward set of tanks to the rear set. Fuel would then flow in a large plume overboard, out the rear vent. If I placed a short piece of tubing over the rear vent and made it longer than the front vent, then fuel would transfer forward and the same thing would occur out the front vent. Needless to say this was the worst case situation since the fuel pickups were in the rear set of tanks. I tried adjusting tubing lengths which was kind of like trying to level a table by sawing small sections off the legs. Also this usually happened only if the tanks were over half full. My final solution is as follows:


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I have never had a problem getting all of the fuel from the wing tanks since they are pressurized from ram/wing pressure air. I regularly ran one wing dry as indicated on the fuel gage and engine power loss. Switching tanks brought restored power in about five seconds. This delay, I believe, was due to the header tank hindering the flow to some degree. The vent for the header tank has a small 3/16" vinyl tubing off a small brass fitting on the top of the tank to a valve and brass tube that was on the floor forward of the landing gear box. The line or tubing vent ran along the side of the center pedestal to the manual valve so that I could bleed the air out of the header tank with the fuel valve turned on: In theory the vinyl tubing vent would allow me to observe fuel/bubbles when the header tank was full. then 1 would close the valve and have an intact tank system. however, it only seemed to work that way part time on the ground and I never noticed any difference of operation in the air except fuel would siphon out the valve if it was left open. Now I have vented the header tank to the top of the left wing tank. Whether pressure from that tank will conflict with the header tank operation remains to be seen. I may retain the manual valve to close off that vent just in case."

Noel Dunlap

     V-6 Builders Newsletter (Javelin/Ford Builders Forum)

David Berelsman, 12333 Washington Brice Rd., Fairfax, VA 220033-2426, PH 703-620-1360 (7a-7p EST) is now editing a newsletter for the V-6. His interest is a Duflunky Cub project which is a Piper Tri-Pacer made over into an experimental 'Pacer' with a V-6 engine. This has been declared a legal Experimental airplane by the FAA. David would like people to send in their ideas and wants concerning Ford V-6 conversions.

If you have had trouble finding all the references to a specific topic in the Blanton newsletters, I (rdm) have made up a seven page index that helps. I will send you a copy if you will send in your request and $2.00.

     Aileron Gap Seals

Someone notified me recently that I have never supplied a drawing as how I sealed the ailerons and flaps against air leakage. If you will remember, I had the aileron gap seals fit much tighter to the control surfaces than the plans indicated (mine were less than 1/16"). I did this because it looks nicer and does stop some of the drag caused by the high pressure air on the bottom of the wing blowing up through the gap to the lower pressure air on the top of the wing. A friend who is an Aero Engineer said that I still did not do enough. He likened the jet of high speed air blowing up through the gap to a piece of aluminum sticking up 2 inches all along the wing. After thinking about it awhile and looking at several ways to do it, I chose the cheapest way. Figure 1 shows the rear part of the wing and the front of the aileron. You can see how the plastic seal is installed. I found that RTV (bathtub caulk) works very well for bonding the plastic to the fiberglass of the wing. It has been on for 7 years and nothing has ever come loose. The high pressure on the lower side of the wing will keep the seal rubbing lightly against the aileron/flap. When dust gets into the area you will hear (on the ground) a raspy sound when the controls are moved. I found that blasting water into the top gap will wash out most of the dirt.

The plastic is cut into long 2 inch wide strips. Use a straight-edge and a ball-point pen to make a light indentation in the plastic right down the center of the strips. If you push hard on the pen the crease will allow you to easily bend the plastic into the "V" shape. I then used a paper hole punch to put a lot of holes in the side of the plastic that was to be glued to the rear of the wing. I figured this would allow the RTV to squeeze out and would give a much better hold.


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     Memorial Day Fly-in

We had a great fly-in last year. We had 44 people total and the following families were represented: Dennis Love, Steve Mahoney, Rick Graf, Jack O'Keefe, the Mellemas, Jim Huber, John Dornbos, Waiter Beecher, Dick Gushman, Colin Powers, and 12 well wishers (a party at an airport always attracts extras). The Mahoney family was the largest there with kids, brothers, and parents. Everyone had a great time!

There were two BD's that flew in: Mahoney and Powers and one was trucked in: Graf. In fact Rick Graf's airplane was brought in during the day. In all 9 BD's were represented: 6 under construction or modification, 2 flying, and one taxiing.

We will again hold the fly-in on May 27, 1991. If you can possibly make it come on over. It is a pot-luck and we do have room for some to stay over night.

     GPS Update

For those of you contemplating buying a Loran - DON'T. The new Global Positioning System receivers are on the market and are fantastic. The satellite coverage is still not quite full-time but will soon be. The Soviets already have all of their system active and already are planning to dismantle their other navigation systems. The GPS receivers are now down below $2,000.00, are light (25 oz), are portable, have a very small non-crtical antenna, are usable anywhere in the world, are much more accurate, will give you altitude, have much less trouble with interference, and update quicker. BUT - they do not have all the bells and whistles yet that some Lorans do. It would be a good idea to wait a little while if you really want the fancy models.

     Fuel story addition

by Monroe McDonald

Re: your notes "more fuel flow words": It sounds like you did some careful work, and you came to similar conclusions as my experiments. One, obvious thing you didn't mention, however; the apparent attitude of the airplane is a gravity vector, the vector sum of pitch angle and acceleration. At lift-off, the acceleration is substantial, and fuel starvation will occur at somewhat lower pitch angle than in steadystate climb. In my tests (done on a long runway) I could induce starvation with no pitch up on level run at full acceleration with minimum fuel (less than 5 gallons total). With 1/4 full tanks it was almost impossible to unport except by very steep climb, and then pitching over level would quickly restore power. I believe all the header tank solutions are causing more problems than they solve, or solving problems that aren't there. As you pointed out, moving the T joint to a lower location is all that's really necessary.

Scott DeGaynor's rear-mounted header tank appears to be a move in the wrong direction - moving the tank aft and down is the wrong direction? He is ignoring the gravity vector.

Monroe McDonald

A Different Fuel System Approach

by Max Westin

Mack Weston sent me all the information about this extensive header tank system prior to the last newsletter. It was the first one I drew up and would you believe the only one I forgot to insert in the last newsletter? Sorry Mack! Ithas a lot of safety features to make sure the header tank isn't iust another Dart of the problem.      rdm


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I was particularly impressed by the number of fuel, or lack of fuel problems with the BD-4. I think this is caused by not only the flat wing, but more important is the fact that any system with a fuel pump that sucks as well as pushes will cause air, rather than fuel, to be drawn from any uncovered port that is connected to the system.

A totally gravity flow system (no pump) would let fuel run down any covered port. If there is a hump or high place in the fuel lines that is above the tank fuel level, gravity flow will not resume until the fuel level is raised above the hump, a slip will work to raise the fuel level to siphon fuel over the hump.

A fuel valve with all 'on' porting used in conjunction with a fuel pump is more dangerous than a left or right valve because you double your chances of unporting a pickup.

The answer to me is to use a totally gravity flow system or gravity feed a separately vented header tank and install a push only type pump (turbine) in the header tank to feed the engine.

Enclosed is a sketch of the fuel system in my BD-4, note the header tank fuel warning lamp. It is a combination lighted rocker switch that lights when fuel head pressure at the header tank is less than 12 inches above the header. When this low pressure occurs a small diaphragm opens a small tank vent valve to atmosphere and turns on the warning lamp. The switch function opens the vent manually and is also a system check lamp.

This feature lets me know when a tank is dry or a port becomes uncovered. I have had the light come on during initial acceleration with as much as half fuel, it goes out when the acceleration decreases, it also comes on longer with lower fuel level. The lamp will stay lit until level off when tanks are one fourth or lower. I have allowed myself sixty sends of continuous 'lamp on' operation then I will find a place to land before I use all of my one and one-half gallons in the header tank. There is a filter sock on the fuel pump in the header tank, screens on all six tank pickups, plus gascolator screen. The fuel pump is from 1968 to 1976 Riviera or early Vega. It must be in the tank as designed. Output is sufficient at approximately 7 psi. Do not run the pump without fuel as it cools and lubes the pump. The header tank vents into empty first bay of wing. If you do not use the vent valve shutoff, fuel will run out of it when the tanks are full.

You may use this information if you like but like all homebuilt systems, each individual is on their own, I will not assume any responsibility.

Mak Weston

     Another Fuel Story

by George Devault

The other day my insurance man told me I couldn't be covered anymore unless my BD-4 has a Header Tank. I wrote him the following letter; and much to my amazement, he called a few days later and said the underwriters (Eastern) agree with me!! - So now I'm insured for at least another year.

Dear Sirs,

Back in the 70's, when I was building my BD-4, I learned of a take-off accident at Long Beach caused by low fuel/ steep climb-out/ venting the forward fuel pickup port. l considered this very seriously, built simulator models, and discussed the problem with many knowledgeable people.

Finally, in July 1977, while in final assembly stage at Mojave, I had the opportunity to "brainstorm" the problem with Burt Rutan, who wasn't too busy in those days and showed an interest in my project during his lunch hour. Burt and I simultaneously came to the conclusion that the forward port should be eliminated. A most simple and obvious solution!

I don't remember any specific conversations with the FAA regarding this fuel system, but they did oversee my BD-4's construction and OK'd the first flight of Aug 3, 77. FAA inspector Bill Daniel issued my Airworthiness Certificate Dec 1,'77 after 50.5 hours of flight testing.

I have intentionally run a tank dry in flight with no problem, immediately re-starting by switching tanks. I've flown many skidding maneuvers and unusual attitudes with never a burp from the engine/fuel system. The only conceivable fuel-starvation would be at a negative angle of attack with very low fuel supply. And as Burt Rutan said to me" "Who cares you're going down-hill anyway." But to be safe, I'm happy to placard my panel with "This Aircraft not to be operated with tanks less than 1/4 full".

Finally, I don't think Header Tanks are good because: 1. They store fuel within the fuselage where the people are. 2. They are complicated and add extra weight. 3. People still get into trouble by taking-off with their main tanks empty or switched off and then getting just high enough to get hurt when the header runs dry.

George Devault

Ed. Note - Of course George takes no responsibility for the use of this modification. If you look at the last newsletter you will find a figure that shows fuel levels versus output port for various angles of attack.      rdm

     Engine Driven Fuel Pump Fallure/Gravity Flow

by Joe Gauthier

Tom Kulikowski recently had an off-airport landing due to fuel starvation. After much guessing the result was a failed engine driven fuel pump. The following letter was received from Joe Gauthier (see Feb 1991, Kitplanes, page 86).      rdm

A recent incident involving a fellow BD-4 pilot and an off airport landing caused me to modify my fuel pump installation. I have operated this, and one other BD-4, for many years (800+ hours) without an electrical backup to the mechanical pump. The theory being that; if the mechanical pump failed, gravity will takeover and continue to deliver fuel. My friend and his BD-4 proved that theory wrong! His mechanical pump failed and gravity alone did not provide the fuel to keep his engine running.

It appears that even if gravity delivers enough fuel for takeoff through an idle mechanical pump, a backup is still necessary. The failure modes for mechanical pumps obviously include situations where the fuel simply will not flow adequately. The failed pump would flow all the fuel necessary when sitting idle on the bench. The operational test, in our local engine shop test cell, revealed that it would run the engine at idle RPM with about 1 PSI at the carb inlet. However, it would not deliver enough pressure or volume to allow the engine to run higher than idle. When the electrical boost pump that the test cell is equipped with was turned on, the engine produced all the power it should have.

Before the fuel pump situation developed, I decided to look very closely at the.fuel delivery rates in our BD-4. I am concerned about the number of unexplained fuel problems. Originally I was interested in the effects of ram pressure on the tank vents. The fuel vent diameters, lengths and configurations were all areas that needed study. Recognizing that measurement of pressures so small would be difficult to read, I decided to temporarily install PYREX glass inline filters so I could actually look at the flow. The glass fitters were installed so they could be observed at all times during flight.

Other than my glass fitters, the fuel system that I tested is per Bede plans. It includes 3/8 inch aluminum plumbing, flush fuel filler caps and a selector valve that allows a choice between the right or left tank and not both, as well as 1/4 inch vent lines that faced down and slightly aft. Either tank is capable of holding 28 gallons of fuel and each has two pickups, one at the low point in climb. All four pickups are equipped with standard mesh screens to keep any debris out of the plumbing. This plane is equipped with a 180 hp Lycoming engine with a mechanical fuel pump with no backup during these tests.

I began by documenting the performance of the system as originally installed. As one could expect, the fuel level in the glass goes down to about 3/4 full with application of full power for the takeoff run. Reaching cruising altitude I reduced power and switched tanks from right to left and back, no change. Both tanks are nearly full. Fifteen minutes into my flight I began to notice that the fuel level in my PYREX filter is now down to about 1/3. After I returned to the traffic pattern and reduced power, the fitter level increased back to 3/4 full. After landing the glass is 7/8 full.

My next test was to see if repositioning the vent lines would have any material effect on the fuel level in the fillers. I bent them just slightly forward and filed a 45 degree angle facing into the slipstream. I flew it this way for a few months and no real change in filter fuel level.

The third item I tested was fuel caps. With the decrease in flow not occurring until after a fifteen minutes or so of flight, I began to suspect that 1 might be loosing some of my vent ram pressure through leaking fuel caps. I replaced the old "o" rings and increased the tension on the lock to be certain they didn't leak any air. This made my most significant change. The glass remained about 2/3 full all the time. It's hand to believe but, there appears to be enough air drawn out of the tank through the cap to significantly affect the flow. I expect that the combination of leaking fuel caps, and a long, (72 inches) small diameter vent line, (with a poor forward facing angle) caused the decrease in fuel flow that I observed. The faster and higher I went, the lower the fuel delivery rate became. The dynamics of aircraft speed and altitude, cap position, the condition of its seals and a small diameter, poorly placed vent lead to the significant reduction in the pressure difference which I observed in my PYREX looking glass.

In addition to tightly sealed fuel caps and forward facing vents, our BD-4 now has an electrical back-up pump as well as a mechanical fuel pressure gauge. The BD-4 that landed off-airport did not have forward facing vents or an electrical backup pump.

The BD-4 airframe did a great job of protecting the occupants In this incident. The landing was in small trees and heavy bushes in a swampy area., The airframe remained intact and there were only minor injuries and bruises to the occupants. The plane is repairable.

As with any newsletter article, my intent in submitting this is simply to alert other BD-4 owners (and others) in the same situation to a potentially hazardous situation, Looking forward to many happy hours in the BD-4. See you all at Oshkosh.

Joe Gauthier

ed. note: Joe didn't say just where the PYREX fitters were located, but it is obvious that he did not purge his fuel lines of air after the modifications. I say this because of the different amounts of air appearing in his fitters. I feel that the amount of air in the filter did not indicate just fuel pressure but also rate of fuel flow. With the size of fuel line we use, fuel will flow past an air bubble without pulling the bubble all the way through the system (self purge). What will happen is that the bubble will move down the fuel line in proportion to the amount of fuel flow. If the tanks are pressurized more, the air bubble in the line will be compressed some and this will result in less air in the fitters.

We believe it is always dangerous to have air in the lines because it makes the loss of siphon happen quicker. After running your lines dry for any reason, the fuel lines should be purged by opening the gascolator drain and blowing on the fuel filler hole.or the vent line to pressurize the tank slightly. Ray Ward and I learned this lesson at the CAFE 400 race a couple of years back!!

The size of the vent lines should not be a problem as long as the air flowing through them is very slow. Our fuel usage is so low that our vent lines are big enough. 20 gal/hour is .7 ounce per second, or 1/3 gallon per minute.

I think that pressurizing the fuel tanks is helpful. Of course this does not help as much during an 80 mph takeoff as it does during 200 mph cruise when you don't need it as bad (lower fuel flow). The pressure on the vent tube is from two sources: the higher pressure under your wing due to lift (0.16 lb/sq in) and the ram pressure due to facing the vent into the airstream (0.7 lb/sq in @ 200 mph). As you can see, the pressurization is very small, but helpful. Remember that you do not get much ram if you are inside the boundary layer. Make sure the ram port is below the wing by 1/2 inch or so.

  The fuel cap seal is something that several people have mentioned to me. This is the first time it was concerning ram pressure loss. Usually it is water leakage due to an old cracked "o" ring.  

     Cooling Fixes

by Joe Lienau

The information on cowling pressure was very interesting as I have been tinkering around with my cooling air exhaust and also the inlets some. I have the Brekke cowling installed and after fully enclosing the engine in a cooling shroud I am finally happy with the cooling. I have had two types of exit ramps installed so far.

 
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My next ramp installation will have the ramps moved further forward along with the exit area also moved forward. The first was a ramp on each side of the nose gear. I have since removed those and gone to a single exit ramp but am going to go back to the single ramp on each side. I've found there is considerable turbulence as the air exits around the nose gear area. Also the air flow pattern appears to flow out and aft in a drag producing pattern as shown.

I just got my BD-4 back flying after sitting since last October when I got the service notice from Ellison. It took 2 months from the time I sent it to them until I got the TBI back from them. I used the time to do a real good annual inspection and do some of the things I'd been putting off, like inspection of the bolts holding the main gear on. It's a good thing I looked at them cause all eight of the 1/4" bolts were bent. I finally replaced them with 5/16". I guess my next retrofit is going to be the 7075 gear legs.

Joe Lienau

     Wanted or For Sale

I have been corresponding with a BD enthusiast from Brazil. I am helping him to buy all the parts necessary for a BD-4. He is thinking about using 'a V-6 engine at this time. I am looking for a reasonably priced, complete kit that can be torn down for shipment.      rdm

     Fuselage Stretch

by Ray Ward

I've had numerous calls from people wanting to stretch their BD-4. I did it to balance a heavier engine and propeller. A welcome fringe benefit was a much larger rear seat area. Some people want to stretch for this purpose alone. Remember, the two are related; stretching requires rebalancing the airplane to maintain the designed Center of Gravity (CG) range which is 30 to 40 inches aft of the firewall. People going to heavier engines, particularly with radiator up front should consider the stretch. My tail and tailcone (fuselage aft of the rear door post) including cables and push-rod , weighed 200 pounds including the 17.1 pounds for the 18 inch extension. The CG of this mass was 41.25 inches forward of the stabilizer hinge pin. I found that an 18 inch stretch balanced the 475 pound 300 hp IO-540 engine and 72 pound 3-blade propeller. But I still had to put the battery as far aft as possible. A 24 inch stretch was considered, but rejected for cosmetic and strength concerns. I used double gusset plates in the cabin floor, and roof to attach the longer fuselage. These are gussets 3, 4, 5, and 6.

A heavier airplane should have a stronger spar, landing gear, and engine mount. Earlier Mellema newsletters show how to accomplish all except engine mounts. N62RW engine mounts were strengthened by lining inside of the rectangular engine mount brackets with steel plate 1/8 inch on top and bottom, and 1/16 inch on the side, that bolts to the longerons. A weld bead joins the plates.

The Super BD-4 has been a rewarding project. Initial climb rate is 4000 feet/minute. Cruise is 230 mph true, with plenty of room for 4 people and baggage. Flying against the worlds best airplanes, some costing $230,000, the Super BD-4 won the 1988 Tri-aviathon. It also holds the fixed-gear speed record around the CAFE 400 pylons at 214 mph.

Let me give you an idea what winning the Tri-aviathon means. Anybody can design a fast airplane; chop the wings down. The Granville brothers did it with their infamous GB racers. These planes are a death trap in forced short field landings. Kinetic energy goes up by the square of the speed. Squaring my 60.8 mph stall speed equals 3697. Burt Rutan's "safest plane ever buit" Defiant which stalls at 79 mph (Tri-aviathon 1986) has about twice the kinetic energy on landing (79 X 79 = 6241). To comprehend this, it means one would need a runway 6241 feet long to brake the same plane at 79 mph whereas only 3697 feet would be needed at 60.8 mph. These numbers must be brought to zero by your brakes if there's room, or by your butt and your head of there isn't. 

It takes an excellent all around airplane to win the Tri-aviathon. Not only fast top speed, but also good climb, and slow stall speed. Tri-aviathon score is top speed divided by slow speed, times average climb rate to 6000 feet. The Super BD-4 in Tri-aviathon 1989 had a maximum speed of 237.7 mph, min speed of 60.8 mph, and a climb rate of 3223 feet/minute. I could live with the Defiant's speed of only 215 mph, and climb of only 1923 feet/minute, but I would hate to have to live with an approach speed of 102.7 mph (1.3 X stall). Not without an ejection seat and parachute! Much simpler to build a BD-4.


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     Progress Report on the New BD-4 Wing

by Paul Kauffman

Projects such as this always take far more time to complete than one expels and this one is no exception. You will recall that a Wortmann airfoil (FX 38-153 is being used in place of the original airfoil and that the ribs are of PVC foam spaced at 4". Originally, I was planning to cover the wing with aluminum bonded with Dexter Hysol 9410 epoxy adhesive, using vacuum to hold the skin in place until the adhesive cured. The more I contemplated bending the leading edge radii in the aluminum skin to accurately conform to the airfoil, the more I woried about it. Laminar airfoils depend upon accuracy, especially at the leading edge and I found no source of information about how to accomplish this with resources available to me. Reviewing Alex Strojnik's publications on "Low Power Laminar Aircraft Design, Structures and Technologies" I decided to cover my wings with fiberglass skins using epoxy resin as described on pages 176 through 180 in his book on technologies. The skins are formed over an accurate male mold (smooth side out) after 3 layers of #7781 fiberglass have been layed out with epoxy on a sheet of plexiglass. When placed over the mold, the skins are weighted down until cured so that they then conform exactly-to the airfoil. The whole procedure is described in Alex's book, how to make the mold and the skins. As with the aluminum, the skins are four feet wide so they are joined using doubters under butt joints. Two are required for each wing.

In order to assure leak proof fuel storage, I plan to use Pro Seal both as adhesive for the skins to the ribs and brushable Pro Seal to seal the tank area.

Whether you plan to construct your wings in this manner or not, I recommend Alex Strojnik's three volumes on Low Power Laminar Aircraft. They are excellent books on 1. design, 2. structures, and 3. technologies. His address is 2337 E. Manhattan, Tempe, AZ 85282. His phone number is 602-838-1832.

I have just finished constructing the mold to form my wing skins and will start using it to make doublers with 3" tape and epoxy as a means of perfecting the procedure before I tackle the skins themselves. Let me know if you wish any more information on this adventure. PH 616-938-9152

Paul Kauffman


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     Super' BD-4

Ray Ward has been keeping me up to date on his Chevy powered BD-4. He is selling his IO-540. The Chevy has been on the dyno and it puts out 447 hp on 100 LL. Would you believe 470 Ib ft of torque at 4300 rpm (385 hp)? The engine has 10.1 : 1 compression and uses a 2:1 reduction drive. He will use the same 3 bladed prop as he did with the Lycoming.

He is having trouble getting his reduction drive. It seems everyone selling reduction drives has had trouble meeting delivery date of less than a year. Ray isn't in quite as much of a hurry as the CAFE 400 has been cancelled for this year. It will be run again in June of 1992.

Ray is putting his radiator (aluminum) in the rear of the BD in order to adjust his CG. He is designing a P-51 type of scoop to pick up and exit the cooling air. The cowling will have a bump on the top to enclose the huge 4 barrel carburetor. ft looks as if the thrust line will be a bit higher than the standard BD. The engine sure looks bigger than my V-6! It looks like Ray will have a hard time getting it to Oshkosh, but he has worked wonders before. 

     Rotary update

Jim Huber did some weighing lately that you might be interested in. The rotary without prop, spinner, exhaust, radiator, and coolant weighed in at. 383 lbs (a bare IO-360 weighed 337 lbs). This weight did include starter, alternator, 3 : 1 gear reduction, and constant speed prop feed. Jim has some hard running to do on the engine yet before he will commit it to flight. Hopefully, this will be done in late summer. The last run indicated that the maximum power output should be 180+ hp.

     Electric Elevator Trim

John Steere sent me some pictures of his electric elevator trim. It looks like something a lot of you would like. It totally replaces the trim wheel. The reversible DC motor is available from WW Grainger, the industrial supply house. It is a Dayton, permanent magnet gear motor, # 42835, costing $35.05. It develops 1/200 th hp at 4.5 rpm full load. It pulls 0.9 amps from a 12 volt supply while providing up to 38 in. lbs. of torque. I estimate the weight to be about 1.5 lbs. John machined a one inch diameter aluminum drum which is pinned to the shaft. The trim cable is wrapped around the drum one time. This will allow the cable to slip if the trim system is run against the stops. He is using a small turnbuckle to adjust the cable tension. The time required for the motor to run the trim system from one stop to the other is about six seconds. If this proves to be too sensitive, this motor is available with other gear ratios. The gear motor is mounted to a small aluminum plate on the inside of the gearbox in rubber grommets to provide a shock mount and reduce noise transmission when the motor is running. The control switch is mounted on the tunnel cover between the front seats. The trim control cable extends forward of the gearbox about ten inches to a pulley which reverses the cable direction. For the trim position indicator, he will attach a flag to this cable which will be visible through a slot in the top of the tunnel lid. If the cables have to be kept from rubbing on other hardware in the tunnel, cable guides of Teflon loaded Dairen or Micarta can be used. If you are interested in this idea you can contact John or I could send you the pictures he sent to me. 

John also has installed Cessna seat tracks right on the main landing gear box (tri cycle gear). The front of the tracks are supported by a 1" x 0.049", 4130 tube that goes from one side of the fuselage to the other. This looks like a very nice way to get adjustable seats. John is also short of a set of wing spars. He came up with the idea of bonding and a rolling thin aluminum (0.020, 2024 T3) around a mandrel. In this way the spar could be made the same thickness (aluminum minus bonding agent) or thicker than the original spar. Each 4 foot wide sheet will wraparound about 2.3 times. The original spar thickness is 0.195 inch and ten wraps will yield a 0.200 inch nominal thickness. A little over 4 sheets will be required for each spar. This didn't seem like the best idea at first but since then I have asked other engineers. They do not think there is anything wrong with the idea. It might be hard to get the outside exactly the right diameter, or to get the epoxy evenly spread between the layers, but otherwise it could be done very successfully. The mandrel could be a cardboard tube that could later be wetted and then stripped out. The aluminum could be cut at a taper so that the spar was thicker on the cabin end and thinner at the tip. There is possibly even a small weight savings or a strength increase. I hope someone tries it. Would you feel right doing it without test loading it to destruction once? 

     Gas Tank Repair

by Bill Kozak

I would appreciate your thoughts on how I rebuilt my wings to solve fuel leaks. I built new ribs and wing skins using fiberglass cloth and safety-epoxy. Then bonded the ribs to the aluminum spar using Pro-Seal and stainless steel hose clamps. I then bonded the ribs to the lower skins with safety-epoxy, having concerns that the bonding between the 1 1/4" flange on the outer edge of the ribs and the wing skins would not be sufficient to carry the weight of the fuel, I then added another layer of cloth and epoxy from midway down the rib across the bottom skin and midway up the adjoining rib, fuel tank ribs are on 7" centers. The top skins are bonded on the 1 1/4" flange of the rib only as I couldn't figure a way to get inside and do it better.

This is not a very scientific test but, with the wing suspended by means of a 2x6 through the spar and supported on two saw horses, after bonding the lower skins to the ribs I was able to stand with one foot (size 13 and 235 lbs) in one fuel bay and the other foot in another and had no sign of flexing or separation. I also had an A&P friend of mine inspect my lower skin to rib bonding job and he suggested that I had. overbuilt it, comparing it more to a "tank" than an airplane. My question is that after reading your newsletter page 16, (all rib cell to rib cell and cell to spar is now completely Pro-Seal, includes metal wing option). Why ProSeal instead of epoxy to epoxy?

Ed note: It sounds like you have done it very well. The reason for Pro-Seal is that it is strong enough, it bonds very well to clean fiberglass and aluminum (a lot of peel strength), is a good fuel sealant, and is never brittle. In your case, the use of epoxy is perfect.

     STOL Wing Mods

Fred Hinsch wrote to tell me of a modification that is being done to Cessna's to improve their short field performance. it involves a leading edge cuff that: increases the glide ratio from 7-1 to 13-1, improves the cruise speed 4 to 5 mph, increased spin resistance, softens stalls, reduce take-off and landing distances by 35%, and increases stall angle of attack to 30°. Ray Ward had Harry Riblett (416 Riblett Ln., Wilmington, Delaware 19809) do an analysis on our 64-415 (modified) airfoil. This is a quote from Harry's letter to Ray. "I checked the airfoil tracing that you sent me, and found that the mod to the 64-415 was all in the trailing edge - they raised the trailing edge 5/16 " (reflex T.E.) and then eliminated the underside cusp by drawing a straight line from 60% cord to the trailing edge, underneath. The top surface was just faired a little in the aileron area" "The mod is very good, and I agree with it 100%, since the 64-415 has too much aft camber anyway. This mod is remarkably similar to the changes I have made in my General Aviation airfoils compared to the NACA airfoils.

"I then tried 3 different types of leading edge modifications (cuffs) to try to improve your slow speed performance without affecting the higher speed end. As I suspected, I couldn't come up with anything promising. - - - - L.E. cuffs with a dish or reverse curvature under the L.E. Will have a bad effect on high speed drag. This one, and the ones on the recent Cessna Skyhawks are an example of this. - - - - The 64-415 section has a good leading edge on it now - it has enough thickness and enough camber forward that any attempt to patch on a cuff won't do much, if anything. - - - - - - For a new airfoil, however, it is possible to improve it slightly, for then you can make it smooth. Notice my GA37U-A215, which has a built-in leading edge cuff, but is smooth"

Ed. note: What do you know? Only the best money can buyl

     BD-4 Get Together

James Belknap wrote suggesting that we have a BD-4 get-together someplace other than Oshkosh. He had so much problem getting in there last year that he gave up and went visiting relatives. He suggests that we choose someplace near Oshkosh and at the same time so we get more participation. He suggests Dodge, West Bend, or Sheboygan. The first weekend would be good as working people can come and the Oshkosh scene is a wipe-out anyway (amen!).

I think this is an excellent ideal Does someone want to send in ideas or want to organize it? After my last trip, I have swom off the first weekend at Oshkosh.     rdm

     Better Visibility

John Fattaleh, who is one of our ancient, high time BD-4 owner/pilots, wrote to say that he has plexiglass in the lower part of his doors. He says it really makes for better viewing of all the scenery in Arizona.

Someone also wrote some time ago and said that they lowered the cross-beam of the door to get a larger window.

     BD-4 Parts Cross Reference

Bruce Labes has solved the hassle correlating Hex # to BD part # (I built mine so long ago that I forgot about all of this). The cross reference is included in this newsletter. Thank you Bruce!

Click here for BD4 Hex # to Bede Part # Cross Reference