Rebirth of the Wooden Propeller

Rebirth Of The Wooden Propeller By Karl Yager (EAA 43131) 43 Victoria Street Lewisham Soutw Ne ,h Wales, Australia XjOOKIN E flee f ligho TH t T t A Gaircraf s i t i t indicated that the metal propeller is dominant. Only homebuilt d mor an sr les o e s antique aircraft featura e wooden propeller t ther bu e certai, ar e n signs around that the wooden propeller will gain ground. In 196 e 9Swedisth r ForcAi h e bega o discart n d e metath l propeller thein o s r Saa "Safir1 b9 " training aircraft equipped with the Lycoming 0-435 engine. e propelle Crackth e roo f th o t n i s r blades wer a econ - stant occurence in previous years. It was found that the non-elastic mounting of the engine was partly responsible for thise SwedeTh . s change o propellet d r blades from synthetics. But after a few years' service those cracks appeared also n theiI . r endeavo o overcomt r e these difficulties, they starte e manufacturdth woodef eo n propeller blades, usin e pasgth t experiences thewitd yha h such propellers in the 40's. Soon they found out it would cost them a considerable sum to achieve the desired perfection. As this kind of money was not available, they chose propeller blades manufactured in a composite way in West Germany. After lengthy type-certification and flight testing, those blades manifested the desired safety margin and are now standard equipment. The German Lufthansa re-equipped their Beech "Debonair" training aircraft with similar blades. But the reaso r thifo ns changa ver s y wa edifferen t one. These aircraft provecompositw ne o noisy to de Th .e propeller blades had a bigger blade chord, a considerably smaller Hoffmann built this 18-ft. composite pro- diameter, and brought about a noise reduction of four peller for the Rolls-Royce "Tyne" engine. decibels. Dr. A. Lippisch of EAA and NASA fame, the designer of the "Aerodyne", ordered the five-blade propelle r shroudefo r d installation froe compositth m e material. These composite propeller t onlno y e meanar s r fo t the smaller sized propellers, but proved successful also . drive ft a foRolls-Royc 8 ry 1 b ndiameter o t p u e f o s "Tyne 600f "o . I t 0hp shoul notee db d tha e developth t - ment of such blades was not easy, but proved a complete success. Wood, providing it is properly treated, always was d alwayan sa ver wile yb l suitable materia r profo -l pellers difference .Th weighn ei moss i t t obvious. Artificial resin weighs only 50 percent that of a metal propeller; balsa weighs only 7'/2 percent. Between them, a wide variet f combinationo y e possiblear s , offerin a subg - stantial reduction in weight which goes 'in favor of the The Fournier powered glider usee th s useful load. Hand in hand with the weight reduction Hoffmann HO V-42 feathering propeller. (Continue Nexn do t Page) SPORT AVIATION 51 WOODEN PROPELLER . (Continued from Preceding Page) goe e reductioth s e momenth f o n f inertiao t . Woos i d far superior against vibration. The lower weight and momen f inerti o e texcellen th s wela as a l t internal damping guarantees smoother running and less load on the crankshaft. This is rather a general story of the composite material as used on the propellers manufactured by the Hcffmann Propeller Werke in Rosen- heim, West Germany. It might be interesting to know a little abou e liff thith o et s company s formewa t n I i d. May, 195Ludwiy b 5 g Hoffmann n 191a I e fle. h s 2wa passenger in a Grade monoplane the remarkable dis- n a s wa e H . ft a heigh5 tanc 1 t a f f 150o o . et ft 0 observer in an aircraft during World War I. In 1922 e finisheh s studiehi d s wit e desige sailplanhth th f no e "Geheimrat" (F. Nicolaus was co-designer). The "Ge- heimrat e firsth ts glide"wa r which flew more thae non hour. In 1923, Hoffmann joined Junkers and developed the adjustable propeller as used, slightly modified, on the Ju-52. In 1928 Hoffmann joined Propellerwerk Schwarz in Berlin as senior designer. They developed e adjustablth e woo de "Leichtholz-Mante bladeth d an s l propeller", and finally wooden propellers pressed in a mould. Hoffmann's guiding principles were: "Ratheo t r do something wrong, as to do nothing at all". Tru thio t e s principle e begah , n 196e develi n th 5 - Older typ f Hoffmano e n pro- opment of a feathering propeller for powered gliders. peller on the balancing rig. This propeller, designate positiono tw V-42O s dH ha ,s— starting r positiofo s t laii d feathere ou dan d n an — d engines up to 30 hp. The movement is activated mechanically through the hollow crankshaft. In cases where this is not possible, a flange is provided so this propeller can also be used for the smaller Volks- wage f thio n sb enginestwo-positiohu e Th . n propeller is manufactured from Dural, the blades are wood, covered d hav e an leadinth e K bGF gy edge re-inforced with metal. These blades will give the same life span as e compositth e propellers e movemenTh . e bladeth f o ts s i accomplished with glide a fork-pieceblock d an s . e fork-piecTh s activatei e d throug e holloth h w shaft, or by means of a flange. The use of the glide blocks means smaller dimensions and simple activation. But it is t possiblno o altee t propelleee pitc th th rf o h r wita h running engine becaus e necessarth e y forces woule b d too high. The weight of the complete propeller of 53-in. diameter is 10 Ibs., 7% oz.; the 63-in. diameter propeller weigh 0 Ibs. 1 e scomplet ,Th 14Vf. oz e e spinner weighs Five-blade propeller developed by lb.1 , Thi8. 1Aoz s propelle typ s rvibratioi d ean n tested. Hoffmann for a shouded installation. Hoffmann did not rest on his laurels. With the HO V-6 wene h 2 stea t p further. This propelles fouha r w no r positions: start, climb, cruise d featheredan , e posiTh . - tionin s maintainei g y lockindb g devices which wile b l loosenee influencth y b df centrifugao e l forcese Th . 59-in. diameter propeller weighs 19 Ibs., 12 oz.; the weight of the spinner is 2 Ibs., 5 oz. This propeller is currently undergoing flight testin d wilan gl finally operationae b . hp 0 enginer 10 fo lo t p su These light-weight variable pitch propellers for engines of suchp-ratinw lo h g will certainly rejuvenate us e th e of woo n propellerso d wideA . r fielr sucfo d h light- weight propellers will be opened up with the further development of tilt-wing-airplanes. In such cases the lower weight and the lower moment on inertia will e greatesth f bo e t importance. Another field o lesn , s important in the future, will be ground-effect machines. e loweTh r momen f inertio t a wil n thesi l e f caseo e b s some magnitude and many more reasons will favor the wooden propeller. General aviation will think e woodeagaith n o nn propeller whe t e i comen th o t s Saab 91 "Safir" of the Swedish Air Force fight against excessive propeller noise. It might be said now fitted wite Hoffmanth h n propeller. that metal propellers s versatilcoula e come b dth -s a e 2 JUL5 Y 1972 Lufthansa airlines has equipped its Beechcraft Deb- onairs" with the Hoffmann composite propeller. 20 JU] * 18 •51.2- Moment of inertia 0.6 0.4- 02. 0-1 2.0 2,5 2,0 2.5 Artifici?l resin posite material. Partly true. The foremost disadvantage of the metal propeller is the fabrication; the propeller Bronze fabric must be forged in a mould and such a mould costs in Metal tipptng vicinite th $15,000.00f yo . This amount indicates clearly that a great number of propellers must be built to stay at a reasonable cost. Nearly every change of the pro- Solder peller blade asks for a new mould. To get the best Lacquer sheathng performance fro n aircrafma t very often e meanus e th s of tailor-made propellers. This is also a big field for the wooden propeller. O a nver y recent occasion Hoffmann said: "Every- thing that fliee th s s r losi faste fo h t rmp tha5 43 n propeller, but everything that flies slower will need a propeller." Q SPORT AVIATION 53.

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