The Fine Old Art of Rigging a Biplane—Part 2
Contents
1. for a later check If there are two landing wires on each side use only the front one to rig in dihedral at this stage At this point careful center section adjustment and carefully made wing root fittings will be holding upper and lower wing panels at the correct angle of incidence at the roots Next step is to rig that angle into the panels all the way to their tips Place the incidence board under the lower wings at or just outboard of the interplane struts as the men in Fig 5 are doing If the ship has two landing wires use the rear one to raise or lower the trail ing edge Or perhaps the rear interplane strut has a threaded fitting Then rig incidence into the top wings with whatever strut or wire adjustments are obvious Then things can be tightened up turning each of the several wires about half or one turn at a time in orderly fashion Never use pliers or common wrenches on them Saw and file a half streamline shaped notch into the end of a brass or aluminum rod or bar to fit the wire section nicely and use that for turning them without causing dangerous scratches Don t pull wires up agonizingly tight for that will strain fittings and warp wooden struc tural members Fair tension is ample If a wire flutters on the test hop it can be tightened a little though you may find that has slacked off another one which will then start wiggling That s why they use javelin struts where the flying and landing wires pass e2. is such that trailing edges do not line up in flight adjust to correct 19 If in hands off flight one aileron droops and the other rides high the ailerons are unsymmetrical in contour the high degree of balance of these ailerons making them sensitive to changes in contour This produces an apparent wing heaviness that is corrected with the ailerons rather than on the wing rigging On the un der surface of the aileron near the outer end two ribs are provided with a variable camber device Cover is cut to reach them Two screws are turned to change camber backing them off until the aileron rides evenly in flight on the one which rides high Test fly until satisfactory WACO F 1 Remove streamline wire end terminals and screw them back on five complete turns to insure an equal amount of adjustment on each threaded end 2 Bolt center section struts to center section Mount center section on fuselage 4 Fasten center section wires w 5 Adjust center section wires so that the dis tances between pin cen ters are the same on both wires 6 Fasten front and diagon al interplane struts on upper wing with adjust ment ends at bottom Fig Qa 7 Mount lower wing on wing fittings on fuselage and insert 34 in bolts long one front short one rear Wing tip must be propped up in position until upper wing is mounted and landing wires are fastened and tightened 8 Fasten long interplane strut to rear of diagonal
3. stalling of the wing tip concerned so it would be well to divide corrective measures between some wash in on one wing and wash out on the other side Old biplanes with plain ailerons and unwarped wings can lose aileron control quickly and completely in a stall Read pages 163 175 of Stick and Rudder by Wolfgang Langewiesche before flying an old biplane Still talking of torque correction remember that when the wings are warped to counter it any particular adjustment will work only for one air speed Usually things are set to make the plane fly level at cruising speed but that can vary with load though the engine rpm is held constant Torque effect shows up more in big propellered short spanned biplanes than in today s small propellered large span monoplanes Odd things in an old biplane s flying characteristics often are based on the nuances of torque and those big propellers For ex ample if the engine is throttled back fully when gliding in to land the big prop will windmill and slow down the flow of air through it This retarded air stream passes over a sizeable proportion of the wing area and it makes the ship come down a lot faster than the average mono plane Carrying a small amount of power in the approach lets wind flow through the prop without retardation and the approach is less bricklike The same applies to to day s midget biplanes whose propellers are large in di ameter relative to the span One cannot ch
4. wing has no dihedral Center section of upper wing has been leveled as in 8 Level remainder of upper wing by adjusting landing wires L so that upper wing is straight taking care that flying wires F are slack enough to allow this Then tighten up flying wires F Lower dihedral may be checked if desired 11 Using incidence board Fig 6 adjust lower outer panel incidence to zero degrees via the adjustment on the rear interplane struts 12 All streamline wires are lined ip with the air stream and lock nuts tightened 13 Insert bakelite spacers at all streamline wire crossings and tape Use two of them at center section wire crossing and four on each side at flying and landing wire crossing 14 Grease hinges on wings and ailerons and inside of operating arm on inner end of ailerons 15 Approach wing with aileron from rear sliding aileron operating lever on aileron through opening in rear spar over operating lever tube in wing 16 Push aileron forward until hinges mate 17 Insert greased hinge rod through hole in wing tip bow Secure with two drilled head fillister machine screws at outer end and safety wire 18 Support ailerons with in droop on each Support stick in neutral and adjust fork ends on inner ends of operating tubes to match holes in operating lever in cockpit locking fork at proper adjustment with lock nut Connect operating tubes to operating levers with bolts and bushings If droop of ailerons on ground
5. PART TWO The Fine Old Art OF Rigeing A Biplane By Bob Whittier EAA 1235 57 Swift Ave Osterville Mass When the center section is all done and the lower wings are hanging by the landing wires it is time to in stall the upper panels Depending on the ship s size it can be easy or a struggle Lay a plank across two step ladders at convenient working height just outboard of the wing tip so that two men can lift the tip to proper height while a couple others raise the root end using the lower wing s walkway and the landing wheel for steps Have handy spikes awls drift pins Phillips screwdrivers etc to shove into strut root and wire fittings quickly and take the strain off the men Then one by one put the correct bolts in place Set the bubble protractor at the specified degrees of wing dihedral Place the straightedge on the top of a lower wing as in Fig 7 and by turning up the landing wire bring in correct dihedral Sometimes it s necessary to bring the bubble a little past the line to take into account wire slackness when the flying wires are tightened later dihedral will be pulled down to the correct amount Once the protractor has been set do not change it until di hedral rigging is done because one s hands and eyes are not sensitive enough to get exactly the same setting two or three times in a row Put pencil marks on the wing to show where the straightedge was laid so it can be re placed exactly if need be
6. ROD LENGTH Fig 8 Measuring an aircraft tie rod Note safety holes in terminals FLEET l Place upper panel upright on leading edge with pad ding on the floor 2 Attach all interplane struts 3 Raise panel above fuselage and attach center section struts to fuselage 4 Attach center section wires and tighten to fair tension 5 Attach lower panels to fuselage tighten and cotter nuts Lower wing to fuselage attaching bolts should be a snug fit without play use 1 64 in or 1 32 in oversize bolts in reamed holes if there is play Should be a light drive fit 26 MARCH 1963 6 Attach landing and flying wires left hand thread at upper ends 7 Level fuselage Top longerons and cross tubes in both cockpits may be used or both bottom longerons and cross tubes between front and rear lower wing spars 8 Drop plumb lines D Fig 4 from leading edge of upper panel at points in line with center section strut at taching points Measure distances X and Y from bot tom longeron to plumb lines and adjust wires A and B until X and Y are equal and center section is level 9 Drop a plumb line from leading edge of upper panel at outer strut attach points measure distance from leading edge of lower panel to plumb line for stag ger This should measure 23 in both sides symmetri cal within in and can be equalized by adjusting center section adjustable struts 10 Dihedral of lower panel is 4 degrees Upper
7. ach other as on the Waco 9 Fig 3 These are of wood taped on There is a difference of opinion in old texts on the question of rigging some wash in or wash out into bi plane wings to counter propeller torque s tendency to roll a plane in the opposite direction One school of thought points to the corkscrew path of the prop slipstream Ob viously it makes the relative wind blow up on one wing root more and blow somewhat down on the other one resulting in an automatic difference in lift changing with Fig 7 Measuring dihedral engine speed to counteract torque Others say to use wash in and wash out one old text recommending an inch of wash in on biplanes powered by 100 hp engines Some say to use wash in only others to divide the required corrective force between opposite lower wings with wash in and wash out It seems that the validity of the slipstream theory would depend on the relation of wing span to propeller diameter The eight and nine foot propellers on slow turning 100 to 250 hp radial engines obviously puts prop wash over a considerable proportion of the wing area in biplanes of 28 to 30 foot span But most texts describe the wash in wash out method Unless specific rigging data is available it might be best to test hop a biplane with no wash in or wash out note wing heaviness and adjust accordingly If an undue amount of wash in higher angle of incidence is needed to correct torque it can lead to premature
8. ange the length of a strut or wire with out changing others in its group to allow for the altered length If a terminal is screwed out too far too few threads do the holding job and there s danger of their SPORT AVIATION 25 stripping When starting to assemble the plane run end fittings on as far as common sense says they can or should go Frequently there is a tiny hole in the side of terminal barrels as can be seen in Fig 8 so that a wire can be poked in to see if threads have gone in at least that far from the end If after rigging you cannot feel the rod threads safety demands that rigging be changed to allow that minimum number of threads to be engaged Fig 8 also points out that there are two measurements to take into account when working with or ordering tie rods New streamline tie rods ere expensive but can still be ordered to fit through supply houses such as Air Asso ciates or from a manufacturer such as the Macwhyte Company of Kenosha Wis Match up left and right wires and struts to have them of equal length before starting Tie rods have left hand threads on one end and right hand on the opposite end It is standard practice to have the right hand thread ends at the lowermost innermost and forwardmost points so mechanics won t become confused as to which way the various lock nuts should be turned Lightly grease threads before installing terminals Do not jam lock nuts up very tight for that puts a concentrated
9. method of assembling wings on double bay biplanes such as Jenny Fledgling etc A good source for used textbooks of all kinds is Barnes amp Noble 5th Ave at 18th St New York N Y Also try book finding services in classified ads of Popu lar Mechanics etc l Centersectionwires 2 Front tiying vares exila actual wire length 3 Rear tlyng mires 16 09 4actual wire len grh 4 froni landing mires 44 x26 actual wire length S Rear landing wires 74x Y la actual wire kag th 6 Adjustment for short strut Adjustment for rong situt 7 8 Adjustment for Arleron strut Fig 9 Waco F rigging diagram 17 Cotter all fastenings 18 Connect aileron push tubes under fuselage so that both lower ailerons are even with the wing trailing edge when control stick is in neutral 19 Adjust aileron struts so that upper and lower ailerons are even with wing Herewith is a table of rigging specifications for sev eral biplanes reprinted from CAA Aviation Safety Re lease No 317 April 7 1949 The gap figures given for the Great Lakes biplane do not make sense to the writer but they are printed as given in that official release MODEL STAGGER GAP INCIDENCE DIHEDRAL degrees degrees lower upper lower upper 54 at Eaglerock A 1 10 tips 134 134 1 1 Fleet 1 2 7 23 1y om 0 0 4 0 Fairchild KR34C 9 63 6334 212 2 1 0 Fairchild KR21 14 63 2 2 2 34 Grecot Lakes 2T1 A 25 25 CS 3 3 2 3 12 8 IS Nav
10. pull on the wire at that point added to the normal flight stresses it could make a tie rod part Ailerons normally carry an up load and depending on the stretch characteristics of the control cable system will or will not be affected in flight Sometimes they are rigged so their trailing edges are even with the wing trailing edges on the ground In other ships they are rigged with their trailing edges from in to in low so that air loads in flight will hold them even with the wings Less frequently they are rigged to ride slightly above the wing trailing edges when in flight perhaps an eighth of an inch on the theory that this reduces overall airfoil incidence at the tips and causes that area to stall later than the rest of the wing so as to retain aileron control longer If rigging data is lacking rig them even with the wings and make test flights to decide if changes would help aileron effectiveness Some biplanes have no dihedral in the upper wing and in these it is often the practice to set the top wing in place rig it straight and use it as a reference point to get the proper dihedral into the lower ones The Fleet biplane is an example Partly to illustrate typical actual factory rigging instructions of the 1920 s and 1930 s and partly to make the information available to antique en thusiasts herewith are erection and rigging instructions for the Fleet and Waco F airplanes ee CENTER LENGTH
11. strut Fig 9a 9 Mount upper wings on center section using 5 16 in bolts with taper bushings 10 Bolt interplane strut on lower wing 11 Put on landing and flying wires with left hand thread to the top Don t tighten 12 Draw up front landing wire to 94 in between ter minal ends Fig 9d 13 Tighten rear landing wire until tension on both wires is equal 14 Tighten flying wires 15 Wings are rigged with no warp as no allowance for propeller torque is needed 16 Adjust interplane struts BIBLIOGRAPHY Aircraft Maintenance by Brimm and Boggess has a good chapter on rigging Pitman Publishing Corp N Y 1937 Aviation Service and Maintenance by James G Thomp son Aviation Press Los Angeles 1937 has service adjustment and rigging chapters on Wacos Fleets and Travel Airs Travel Air chapter has detailed rigging chart for all models A Text Book on Aviation Vol II Lt Leslie Thorpe Aviation Press Los Angeles 1935 has a chapter that reproduces entire Fleet service manual Also a good rigging chapter Part of Cadet Series of aviation textbooks Airplane Construction and Repair John E Younger McGraw Hill Book Co Vocational Texts series 1931 has a good rigging chapter with data on Fairchild 71 Fleet Waco F Fokker Universal Boeing 40 Aviation Vol 2 by American Technical Society Chicago 1945 has good rigging chapter including coverage of
12. y N3N 3 26 7 32 65 2 2 2 0 New Standard D 25 34 adie k 4 2 Bird A BK CK 30 58 2 2 0 0 Stearman C3R 224 63 atroot 134 134 2 1 Stearman PT 17 28 72 at root 4 3 1 1 Travel Air 2000 and 4000 251 58 2 RS 3 3 1 O0 5314 IS Trovel Air E4000 29 l 21 2 334 4 Waco GXE ASO 1014 621 0 0 0 0 Waco RNF INF 281 54 0 0 2 2 Waco QDC 33 5 16 5514 0 0 134 134 Waco QCF 3314 55 0 0 2 2 Waco UEC 31 5 16 5513 0 0 214 2 Waco UIC 33144 53 0 0 21 2 Waco UKC VKC VKS 31 5 16 53 1 16 0 0 2 2 Waco YKC YKS ZKS 31 5 16 53 1 16 0 0 21 2 Waco YOC 3834 49 RS 0 0 2 22 NOTE RS Root Section 1S Interplone Struts CS Center Section Great Lakes wing sweepbock in degrees lower O upper 9 deg 30 sec No data available Waco YOC wing sweepback in degrees upper ond lower 21 2 SPORT AVIATION 27
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