About Those Plans By Kent Hugus, EAA 15280 363 Knox Dr., Brunswick, Ga.

HE WRITER RECENTLY had occasion to review sixteen sets of plans currently available to amateur builders. The designs covered the entire fixed-wing spectrum, including several sailplanes. All of the plans reviewed are offered by aeronautical engineers, highly experienced amateurs or both. These comments are not directed toward the aeronautical qualities of any design, but are offered to those designers, professional or otherwise, who are presently working up a design to be offered in the future for amateur construction.

T

The Amateur's Investment

The purchase of a set of drawings marks the builder's decision to get the project off the ground. It is his first major investment and he expects to get what he pays for. The quality of the drawings is one first major impression of the design and is a strong factor in whether or not the design ever gets airborne.

There are several other ways to present ribs and bulkheads. One is to offer the necessary dimensions so that the builder can layout directly on the material or form block. The other is to offer the layouts on a minimal shrink plastic such as "Mylar." One reputable company will reproduce these, from a Mylar master, at about $1.35 per sq. ft. Outdated Specifications

Referring specifically to hardware, almost every item has an AN or MS number. The use of manufacturer numbers could lead the builder into difficulties finding that specific part. Giving the AN or MS number allows the builder to buy across the counter and choose his manufacturer. Of course where only one manufacturer's part will do, this should be noted on the drawings along with a current address. Metals (aluminum and steel) thicknesses have changed recently. Readily available stock thicknesses are shown in Table 1.

Bill of Materials

Only two of the sixteen plans included a bill of materials. The time required to derive a bill of course varies with the complexity of the design. Time required for the writer to derive a bill for one average design was 62 man-hours. Combining this time with the time requir-

ed to find sources for materials could mean a lapse of up to two months before the builder ever picks up the saw or snips. Upon asking one designer about the lack of a bill of materials, the writer was advised that the omission was purposeful. The designer felt that the omission would require the builder to study the drawing more carefully. A darn good reason! However, the more complex designs will require more than a casual look during construction. The inclusion of a bill of materials could save the builder many hours, and perhaps some expensive purchases. Format and Detail

Drawing size varied between the book size offered for a popular wood/fabric design and the continuous roll offered for a popular sailplane. Each has its advantages, but the designer must bear in mind the amateur's space problem — an auto, aircraft, work bench and 4 x 8 plans simply don't fit into a standard garage. General line quality of drawings was excellent with a few ghastly exceptions. Designers who realize that their draftsmanship is poor should hire a professional. This could pay dividends in longer reproduceability and in time spent answering questions forwarded by builders. One common mechanical fault is worth mentioning — that of placing sub-assembly or detail drawings on the same sheet as a major assembly. The draftsman usually backs himself into a corner and the result is a major assembly hidden in a maze of out-of-sequence detail draw-

ings. A better presentation might be the placing of major assemblies on sheets sized as appropriate, with detail and sub-assembly on a book of small size individual sheets. This allows easy cross-reference. Many designs offer full size rib and bulkhead layouts. This is a time saver, but the builder should be cautioned: 1. Work to dimension, not to scale.

2. That paper shrinks and expands with the humidity.

Thickness .016 .020 .025 .032 .040 .050 .063

.071 .080 .090 .100 .125 .187 .190

4130 X X X X X X X

X X X X X

.250

X

.375

X

6061-T4

6061-T6

X X X X

X X X X X X

X X

X X

X

X

X X (T651) X (T651)

2024-T3 X X X X X

X X X X X X X

X X

(T351) X (T351)

Table 1 Stock Thicknesses of Steel and Aluminum Sheet and Plate Vague Callouts

Vague callouts would seem the greatest single item worth correcting. Specifying a fastener as an "AN 3 bolt" leaves the builder to worry about length, how to safety it and the proper or intended nut to fit it. No problem? It is when 80-100 joints are considered! Far better to spell out the bolt, washer and nut sizes with AN or MS specs. Bolted joints are not the only example — corrective action can be applied to all hardware. A similar and far more dangerous example is in the callouts for aluminum extrusions. A callout may be shown as "1 x 1 x Va al." This leaves the builder a choice of three extrusion sections and normally three alloys (6061, 2024 and 7075). This could work out to one correct part — the one the designer had in mind — out of nine possibilities. Cats don't often fly airplanes. Extrusions should be called out by die or section number and alloy. Callouts are also the place to note substitutions. It would seem good sense to note a variety where applicable because it would simplify the builder's materials search. Due to the popularity of "pop" rivets, a table of the

hand driveable sizes is shown in Table 2. (Continued on next page) SPORT AVIATION

43

ABOUT THOSE PLANS (Continued from preceding page)

Rivet

diameter

7/64 1/8

Domed

head

Grip range

Countersunk head (120°)

MD319BS 321 MD419BS 424 429 435 440

.020— .070 .071— .090 .020— .070 .071— .120 .121— .170 .171— .230 .230— .280

MK319BS 321 MK419BS 424 429 435 440

Grip

range

.020— .090 .091— .110 .030— .100 .101— .150 .151— .200 .201— .260 .261— .310

Table 2. Grip Range of Pop Rivets Availability of Materials

Finding the materials necessary to build the design is one of the builder's major headaches. Items such as aluminum sheet, plywood and steel sheet are "garden variety" and available either at a local dealer or through the advertisers in this magazine. Others are not so common. Aluminum extrusions are never a "stock" item. There are few major suppliers in the U.S. and most will not sell to individuals. Advertisers in this magazine offer a small variety at a good price. Designers could do well to investigate availability of the specified item and offer substitute specs. An extreme example of this is an odd shaped extrusion required for the tail wheel bracket of an "all-wood" design which calls for five inches of the extrusion. The writer was able to find only one 20 ft. length in the U.S. and at a price of $248.00. The designer could have designed this bracket as a steel weldment or offered the weldment as an alternate. Another very popular all-metal design requires a handful of special high strength fasteners. The manufacturer of these, however, will only sell in lots of 100 or more of one size. Fortunately the fasteners are inex-

pensive and the builders have formed a club, allowing them to supply one another. Certain other fasteners seem attractive both to designers and builders because they can be set by hand. "Pop" rivets immediately come to mind. The pops outlined in Table 2 are specially made of monel with a steel mandrel, then zinc coated. The locally available do-it-yourself pops are simply not strong enough. Prospective pop users should note that the inexpensive hand tool will pull only 7/64 and V8 pops. A hand tool capable of pulling 5/32 and larger costs well over $50.00. There are other fasteners which can be set by hand but the tools cost $200.00 plus. Such is the case of the "Jo-Bolt." The manufacturer of Jo-Bolts advised the writer against their use in amateur construction, not only due to high cost, but also because professional quality control is required to ensure full strength. The writer would be happy to hear from readers with first hand knowledge of the other "hand" type fasteners available such as Deutsch drive pins, explosive rivets, etc. Of course design performance and flight safety usually take precedence over ease-of-construction. However, where safety is not compromised and high performance is not the design endeavor, minimizing the number of different items in the bill of materials is at least a part of ease-of-construction. Another is the substitution of inexpensive or readily available items. An example of this is steel tube. In the larger sizes, the availability is nearly nil and the price absurd. One could pay as much for one inch of torque tube support as for the entire torque tube. A less expensive and more available support would be a bolted metal or fibre block. A nice range of manufactured bearings are also available across the counter if the designer wants, or design strength requires. One last thought. The experimental aviation organization needs new designs — particularly those using the new materials. The new under-1500 cc racing class opens up all sorts of possibilities for use of Bondolite eooxy/stretch Dynel may improve the performance of sailplanes, there is no all-metal amphibian yet available, etc. Get back to that drawing board! *

Central States Aero Historians Meeting HE CENTRAL STATES Aero Historians Society will T hold its annual three day seminar on aviation history at the Air Force Museum, Wright Patterson AFB, Day-

ton. Ohio, on May 21, 22 and 23, 1965 (Friday to Sunday). The program will consist of registration and movies Friday night: introductory speeches and movies (or an unguided tour of the museum which will be closed to the

general public at this time, for those who wish to take photographs) on Saturday morning; speeches on aviation history Saturday afternoon; a banquet and after-dinner speaker on Saturday night; and speeches on aviation history Sunday morning. Among the speakers will be Grover Loening who will talk on his early amphibians; Dr. von Ohain who designed

and built the first successful jet engine to fly an aircraft

(Heinkel He 178, 1939); Charles D'Olive, a WWI Ace who

will speak on the problems of flying training in 19171918; George Page, one of the pioneers with Curtiss Aircraft who will describe his experiences as a pilot for the first commercial scheduled international airline flying Curtiss flying-boats from Florida to the Bahamas; Paul 44

MARCH 1965

Poberezny who will describe the new EAA Air Museum at Hales Corners, Wis.; Joe Fallo, a master model craftsman will describe the techniques he uses in making exhibition models for the Air Force Museum; Truman Weaver who will talk on air racing; and Fred Dickey, Jr., who will speak on the experiences of the U. S. Navy in flying aircraft (Hanriots and Nieuports) from platforms on gun turrets of navy warships. The registration fee of $1.75 covers all expenses except the banquet meal. Full particulars regarding accommodations, routes to the museum and program schedule will be sent with the registration form.

Mr. Richard Korns 470 W. Hudson Ave.

Please write to:

Dayton, Ohio 45406 The Central States Aero Historians Meeting is sponsored by the Miami Valley Aviation Historians Society with Ihe cooperation of the Air Force Museum and is a function of the American Aviation Historical Society, the Cross and Cockade Society of Aero Historians of WW I) and the Wingfoot Lighter Than Air Society. %