BD-4 BUILDERS NORTHWEST
- - - - - - - - - - - - - - - - - - - - - -Dear BD-4 Builders and Owners,
Issue 11, August 1984
Issue 11, August 1984
Even though the newsletter before last was a double one, it is time to get started again. I have some exciting news to pass on about wing kits becoming available again and also raw material kits for the BD-4 and the BD-6. The BD family also had a very good year at Oshkosh and Arlington fly-ins.
Thank You to all those who sent in their money, some of you already had 4 free newsletters sent to you. If your name on the address label DOES NOT have an asterisk, you are far overdue and will not get any more issues.
Thank: You to those who sent in articles. I will print them when and where they fit best in the coming issues.
Roger D. Mellema
by: Bill VanNoyA fairly rigorous analysis of the BD-4 standard wing and long wing (24 inch extension per side) to determine the maximum operating weights each wing is capable of, has been completed. The theory used and the results obtained are as follows.
Airfoil section data used is for a NACA 64(2)-415. Mr. Bede says it is a modified airfoil, but any modifications would have minimal effect on those characteristics important from a structural standpoint, especially wing bending moment. The data for the airfoil is available in THEORY OF WING SECTIONS by Ira H. Abbott and Albert E. Von Doenhoff, Dover Publications, Inc.
The analysis method used to determine the spanwise airload distribution is from NACA TECHNICAL NOTE 3050, A METHOD FOR CALCULATING THE SUBSONIC STEADY STATE LOADING LOADING ON AN AIRPLANE WITH A WING OF ARBITRARY PLANFORM AND STIFFNESS, by W. L. Gray and K. M. Schenk, Boeing Airplane Company, Seattle, WA., December 1953. If one assumes a rigid wing, not a bad assumption for the BD-4, the equations of TN 3030 simplify considerably and lend themselves to solution on a home computer. In this case a 32K Radio Shack Color Computer. TN 3030 is really nice in that it solves simultaneously for the spanwise airload distribution, balancing tail load, and angle of attack of the root section zero lift line as a function of design speed, gross weight, and load factor. I might add that at least one very prominent transport category aircraft manufacturer uses computer programs based on TN 3030 to determine wing loads used for FAA certification.
Stress analysis methods and material strength properties for analyzing the critical spar section are found in ANALYSIS AND DESIGN OF FLIGHT VEHICLE STRUCTURES, by E. F. Bruhn, B. S., M. S., C. E., Professor (Emeritus) of Aeronautics and Astronautics, Purdue University, Chapter 4. This book is used by numerous engineering schools and an aerospace stress engineer is seldom caught dead without it in his possession.
The design criteria used in determining the design wing loads are from FAR part 23 Appendix. A, "SIMPLIFIED DESIGN LOAD CRITERIA FOR CONVENTIONAL, SINGLE-ENGINE AIRPLANES OF 6,000 POUNDS OR LESS MAXIMUM WEIGHT". The analysis was performed using normal category criteria only. No utility or acrobatic design conditions have been analyzed.
In an attempt to keep this report short, simple, and user friendly, I have produced two plots of maximum gross weight versus fuel load that if properly used will provide a 50 % margin of safety in the wing spar should a 3.8 G maneuver or gust be encountered. What the plots allow us to do is make maximum use of the spar strength by trading off a minimum amount of cabin payload for an increased fuel load (range) by increasing the maximum gross weight with increasing fuel load. You can use the plots in two different ways.
The first way is to determine the fuel required to your first refueling stop, or destination, plus reserves. Enter the chart at this location on the fuel axis. Proceed vertically to the maximum zero fuel weight line. Then proceed horizontally to the airplane weight axis. By subtracting the aircraft empty weight from the airplane weight just determined, you get the maximum allowable cabin load (passengers and baggage). The pitfall of this method occurs if you have not determined your maximum cabin load based on the longest leg of a multiple refueling stop cross country. Then you could end up having to off load cabin load to put in enough fuel to get down the road to your next stop. This could prove embarrassing.
The second method (more practical) is to determine the cabin load first, based on the number of passengers and baggage (junk) you really feel you must take along, then add this weight to the aircraft empty weight. Enter the chart at this weight on the vertical airplane weight axis and proceed horizontally to the maximum zero fuel weight line. Then proceed down vertically to the fuel axis and read the maximum fuel load. Then plan the route to include the needed refueling stops.
ED. NOTE: In both the above examples, the maximum gross weight for any fuel load can be found by going vertically from the fuel In gallons to the maximum gross weight line and from there horizontally to the left to the aircraft weight. You can see that for a fuel load of 60 gallons. The maximum gross weight would be 2340 for the short wing and 1880 for the long wing. An interesting side note to this is that. Mr. Bede says that one of the major general aviation aircraft companies tested a BD-4 spar to failure and determined the spar strength to be good for 2380 lbs. That's very good correlation between analysis and test.
Now having given out all these red-hot numbers its only natural that I should conclude with a disclaimer. Well I personally would feel comfortable operating a WELL BUILT BD-4 at these limits. I feel that the numbers are correct. But nobody has checked my analysis so there is always the possibility of errors. One should also know that all my analysis is based on theoretical aerodynamics. The big guys usually have actual wind tunnel tests on scale models to determine the airload distribution on the wing in the presence of the fuselage. The real significance of this is that all the stress analysis and static tests are worthless unless the actual in flight airloads ate reasonably close to those used in the design analysis. Again, the big guys with lots of bucks will strain gage the airplane and perform a flight loads survey to determine the accuracy of their analysis. Well we don't have the time or bucks to do this kind of check, although with the BD's tubular spar, I think it would be plausible to perform a limited flight loads survey at some time in the future. It is my feeling that the 1.5 safety factor was meant to cover these unknowns of actual airloads vs theoretical airloads, material differences and manufacturing differences from one airplane to the next. With this in mind, I don't think it's a good idea to consistently exceed the published limits of an aircraft thinking that you have a 50% margin of safety. You might only have 40% because of the difference between the theoretical analysis and the real world effects. In closing I would like to mention two areas that warrant some analysis in the future. First is the wing attachment structure. It is not going to do us any good to have the wing survive a 3.8 G gust at high gross weight and then flutter to the ground detached from the fuselage. It doesn't bother me too much because of all the beefing up by Bede after he experienced a failure in this area during a static test. However I would like to do some analysis in the future to get a nice warm feeling. The second area is the landing gear. Lots of people have told me of beefing up the gear box and attachment fittings and this is probably required to operate at the high gross weights. For those of you operating at these high gross weights with no gear beef up other than what Bede has put out, I would pay particular attention to this area during inspections and would consider doing some beef up according to what others have done in this area. For the time being, I need to devote more time to building and less to analysis but I will look at these areas as time permits.
Bill is rebuilding the straight backed BD-4 formally owned by George Mojonnier. Bill did a quick analysis as to what it would take (spar-wise) to increase the gross weight of the long wing BD-4 to about 2200 lbs. He found that a 7 foot center section would work very well. It is not practical to go higher than that in gross weight as the center section spar then becomes the weak link.
CAFE 400The CAFE 400 race wasn't as well attended this year. I guess that if a BD-4 can do so well, there must be somethig wrong with the whole concept. Rutan didn't show up with the factory team and neither did Mooney.
The competition for the 3 or more seat catagory was better this year even if there were only two of us in it. The Cozy prototype with a third person stuffed in back is good competition. The frontal area of a Cozy is much less than a BD-4 but he also uses a small engine (118 HP). I might have to start working on flight profile and optimum power settings for cruise and climb, etc. to stay ahead.
Needless to say, we did beat the Cozy and also increased our score over last year. We just missed the 3 million mark but I'll blame that on my aeronautical advisor-friend who doesn't like to ride in rough running (radically leaned) airplanes. After the race one of the pylon judges said that all the airplanes were coming by running very rough, but that my BD-4 was smooth as silk The Ellison Throttle Body Injector sure makes leaning an engine different. My leanest cylinder (#1) was 50 to 60 degrees F lean of peak EST and would still run smooth. The other cylinders were 5 to 10 degrees lean of peak. The distribution to the cylinders was much more uniform than with the MarvelSchebler MA 4-5. The improved distribution allowed me to run the engine at 1850 rpm during most of the race (last year I used 2000 rpm) and still run lean and smooth.
We learned during the CAFE 400 and Sens Selchow learned during the Oshkosh 500 that an Ellison isn't as forgiving about vapor lock as a float bowl carburetor is. If there is a bubble in the fuel stream, the Ellison will not "bleed it out" but will cause the engine to burp a bit. During the '400', the factory Glas-Aire, after a long, low power descent (slow fuel flow through the aluminum gas lines in the engine compartment) would not run after turning a pylon at 500 feet AGL. They tried everything and finally got it to start running again. It is absolutely necessary that all fuel lines be insulated when using an Ellison. This is no fault of the Ellison and it just shows us how near to the vaporization limit some people have been running (the float bowl has been saving us). The Glas-Aire has been having rough running problems for a long time even with the Marvel-Schebler. They have a very tightly cowled engine with minimal airflow through it.
The results of the race were: 800+ lbs cabin load, started with 36 gallons of gas, burned 16.97 gallons, 23.1 mpg, 161.6 mph. How about that - flew 400 miles with a heavy load and still had over half of the starting fuel left. We set the highest score ever set by a homebuilt, the highest score ever set by a four place, and also got the Tom Jewett efficiency award (payload X mpg) all in one fell swoop. When they gave me the Lopresti trophy, my friend asked why they couldn't have made it left handed so that I could have at least used them for bookends or something - ho hum. We won $400 for the best 3 or more seat, and $300 for the Tom Jewett award. The only disappointment was that no other BD-4's showed up.
Bill DeProsse (amphibious BD-4) and his family were volunteers at the race and son Brian Deprosse filled a seat for me.
I must thank my family for putting up with lots of nights out at the airport Geoff Sharples and Dave Dotson (BD-4 N313DR) for advise and help, and Marty Ellison for the loan of a 4-5 Throttle Body Injector.
OSHKOSH '84We had a record year at Oshkosh this year with about 16 BD-4's present and lots of interest. Scott DeGaynor even bullied 5 of us into going flying at the same time and giving some rides. Scott DeGaynor, Hugo Schneider, Deene Ogden, John Holland, and I flew loose formation up to Appleton and back. We of course had to compare airspeeds and also maximum speed. The airspeeds were very close and my BD is just a little faster - they said I had a light load. John Holland kept up for quite a while and he has a nose dragger and not all the fancy fairings.
On the way back from Appleton, Deena Ogden and I flew some close formation and 'Woody' Wood took some pictures from Scott DeSaynor's airplane. I hope we get some nice pictures to frame.
Hugo Schneider MC'd the BD-4 discussions and arranged for the banquet - Thanks Hugo. Hugo will send a transcript of the discussions to anyone who wants one (send money for printing and stamps).
Jim Bede was very high profile this year and announced that he was entering into an agreement with two individuals to supply BD-4 and BD-6 raw material kits. They will advertise in Sport Aviation and Trade-A-Plane soon. Lloyd Brekke and Val Bernhardt have also decided to start producing parts again. Val's fiberglass wing will sell for under $1000 (plus shipping, minus spars).
It is really nice to see the BD-4 come alive again. For a long time no fiberglass wing was available - only the excellent Murphy metal wing. Now Harold Pischke has developed an excellent wing to fix the fuel tank area (or could be used to replace the whole wing), Rick Graf is also developing a new wing here in Seattle, and of course Val Bernhardt. With all that competition and choice, BD builders with leaky tanks won't know what to do with themselves.
All of these wings look to be of about the same technique, appear to be easy to seal for fuel, are easy to finish to a very smooth surface, and should be easy to get straight. Jim Bede says he will use the "panel rib" design again but maybe a different airfoil and an injection molding technique.
SCOTT TAIL WHEEL (NOSEWHEEL) PROBLEMSI was happy that the Scott tail wheel on my BD was getting easier to pivot. That lasted about 10 hours before I started to get shimmy on landing. At the Oshkosh BD discussions, it came out that the Scott tail wheel is not inherently stable but relys on friction to kill the shimmy problems. Jim Bede said they could never put a wheel pant on 400BD because of the shimmy problem - that's why they settled for the little trailing fairing. I have a wheel pant on my tail wheel and until now it was OK.
The thing to check on your Scott wheel is that the 5 or more springs that push the brass plate against the fiber washer are in place. The castellated nut on the pivot bolt has nothing to do with the friction unless it wasn't tightened correctly in the first place. You will find that when it is tightenend too far, the wheel won't pivot at all. It should be loosened just enough so that the wheel pivot does not bind. The real answer is to put in stronger springs or take the grease off of the fiber washer as I did. I also put short sheet metal screws under each spring to make them tighter. The friction of the pivot should be checked regularly as a nose wheel (especially) shimmy can cause the nose gear to fail and then maybe a sommersault manuever. Don't be afraid to take the pivot assembly apart. It takes just a few minutes and is very simple.
OSHKOSH 500Gene Selchow had high hopes of running the 500 again this year in his newly painted, faired, and carbureted BD-4. He looked good on the first lap over Oshkosh but developed vapor lock problems on the first regular lap. He nursed it back to Fond-Du-Lac and insulated his fuel lines: He said that so far it now seems alright. Gene was running in the 3 place category which now has a minimum speed requirement as does the 4 seat category.
I was thinking of running the "500" this year but didn't like the trial speed run I did here in Seattle. I thought I had 80% power but apparently didn't as the fuel flow should have been 11.7 gph and I only burned 10.15 gph and got 184 mph. I'll have to check my gages and try again another year.
OTHER ITEMSJohn Hintermeister has his BD-4 for sale. All kits except for engine and mount, has Murphy's extended gear legs, and has conventional gear. A/C is on gear with all controls in. May sell piece-meal. Offers around $4000. RR 03 Box 34-A, Muscatine, IA 52761
Paul Wood, 5648 Armitos, Goleta, CA 93117, 805-967-3060 has plans for sale. $35 plus post.
Scott DeGaynor called to say he had a wind shear problem on the way home from Oshkosh, really wiped out his newly finished BD-4, and is now, looking for another one to spend the insurance money on. Scott and son Jon were not hurt. The accident happened on their home airport.
Stanley LaBore wrote to say that he finished rebuilding a BD-4 and that it flys very well. He had the airplane at Oshkosh and it really looked nice.
Fred Ninneman also had his BD-4 at Oshkosh this year. It is a rebuild of a BD he found in a junk yard and bought for the engine. The airplane is really pretty with a nice interior and his own metal wing tank system. Maybe Fred will write up his rebuild/modification of the tank system and send it to me?
Robert Ruff, 1443 N 61st PL, Mesa, AZ 85205 602-981-3595 would like information on the installation of the delux interior kit.
Malcolm Powell has a new process for putting the wings together. He bonded the clamps onto the wing-rib-spar-flange, cut a hole in the wing `skin' so a screwdriver blade could get through to tighten the clamp, and then he glued up the entire wing and tightened the clamps. In this way he could rotate and adjust the panels so that everything fit just right and was square BEFORE he had to tighten any clamps. If you use Pro-Seal for putting the wing together, there is plenty of time to glue everything up, put it together, and then adjust it.
Tom Metty recently purchased Bob Warden's BD-4. It was built for conversion to a seaplane, has Cardinal gear (very beefy), a twin-Commanche prop and cowl (extended 6 inches).
Jim Bede said that the Ultra-light he helped design used a BD-4 spar which was chemically milled to reduce the weight. The' BD-4 spars each weigh about 29 lbs. Chemical milling could reduce this by about 40 % without reducing the wing strength. The problem is finding someone to do it - outside milling is easy to get done but inside is a different problem. Jim will be looking at this and many other modifications to further improve the BD-4. If you have something you think would really improve the BD-4, please let Jim know.
D & R FIBERGLASSDuane Roberts has moved to Las Vegas and is no longer making parts. He returned all the molds to me and I am trying to find someone local to lay up those parts that people want. I am renting out the molds to builders in this area who have some fiberglass experience and want to lay up their own parts. rdm
(editors note: The actual title is "Turquoise Lament")
ARLINGTON FLY-INWe just completed a fantastic fly-in up here at Arlington. We had 8 BD-4's there - most of them on Friday before the fly-in had started. The following familied had BD-4's there: Colin Powers and Marilyn, Bob and Carol Hoey, Dick and Sylvia Marker, Dave Wesley and Nesa, Glen Dickenson, Glen and Randall Crouch, Roger and Verla Mellema, and Dave and Diane Dotson.
The following BD-4 builders attended: Rick and Darlene Graf, Dick and Cheryl Bushman, Jim and Leslie Parker, Cliff and Norma Poneness, John and Pat Spears , Fred Hinsch, and Bill VanNoy.
Glen and Randall Crouch had a hard landing about a year ago but they have everything fixed up and looking good again.. Remember Randall, 90 mph an short final!
Dick Marker didn't get done in time for Oshkosh but there is always next year. Dick's BD is really beautiful. We couldn't get him to fly in the fly-by pattern as he only has 30 hours an it yet and wants to get to know it better. He has an IO-360 in it and is going to work on some more details to really get the speed up there.
Bob Hoey's BD-4 looks good as always. Bob likes to keep his BD very lean. Anything that will not be needed in the next couple hours gets thrown out. I envy anyone who is so successful in keeping his airplane light - that really is the name of the game. The BD-4 was designed very straight forward and simple and should stay that way.
Dave Dotson who lives the closest of anybody, got there so late he got me out of my sleeping bag. I guess he likes those night landings (I know his wife doesn't). If it hadn't been for my lantern on in my tent, I wonder how he would have known where to taxi. Dave's BD-4 is a look alike to mine and Dave is working hard to get all the fairings on so he can keep up with me.
Colin Powers, David Dotson, and I went up and did some fly-bys. We had a lot of fun as the Arlington fly-by pattern is not nearly as busy as the Oshkosh pattern. We will have to talk over our fly-by plan better next time - I thought we were going to do a FAST fly-by!
(Removed for privacy. See PDF version.)
BD-4 WING COMPONENTS
Molded fiberglass skins and ribs for new construction or to replace existing leaking or deformed wing components. Designed to reduce weight, increase air speed, eliminate fuel leaks, provide uniform airfoil. Easy to assemble, 5 years
in testing. Complete with drawing $995.00
Custom figerglass droop wingtips $145.00 per pair with installation drawing. Designed specifically for the BD-4.
Click on image for larger view
Val C. Bernhardt, 12605 NW 99th Rd, Ocala, FL 32675