Propeller Power and Efficiency

It 111111 liii WH111111 E F F Theres lot can learned article nomogra ph Give tryU John Brownlee THE SELECT-A-PROP NOMOGRAPH constructed using propeller thrust power coefficients CT Cp calculated Vortex Theory equations Assumptions 10% thick flat-bottom airfoil b constant nominal pitch along blades c blade chord/radius ratios measured standard lOx 6 Zinger HP values assume equilibrium flight J V/nD values equal pitch/diameter p/d viable condi tion optimum efficiency airfoil camber considered CT x J Efficiency ECp Eq 1 2 basis nomo graph Because deviations Cp blade shape nomograph should used propeller designs labelled wide extra-wide narrow Vortex Theory equa tions reputed give results close agreement wind tunnel tests Some small error inherent preparing print ing nomograph Deviations Cp model due dynamic solidity affect HP approximately linearly 10% higher value requiring about 10% power shown Small changes Cp effect E 1 significantly within reason E values should within about 1% actual bit deviation actual pitch nominal some commercial propellers measured pitch values 08 R should used possible 2 Assume RPM value calculate equivalent MPH using Eq 3 MPH h x RPM 1056 3 ENOY 3 Align straightedge between p/d J scale MPH value 2 MPH scale edge crosses L 4 Place T-pin etc L edge crosses pivot edge about pin align RPM value 2 Read HP required Cp x 002378 x n3 x D5The nomograph can used construct 5 Align edge p/d J scale soit HP 2propeller power curve followsmakes right angles scale lines 5501 Determine p/d Because quite Connnuedon16S place CL Scale muffler rule enforced Nats own experience East Coast contest circuit has sameno enforce ment muffler rule since its origination 1978 doesnt seem appropriate have use mufflers relatively quiet Scale models other CL models same contest flown wide-open exhausts Ed also asked what could done about revers ing rule suggested him anything done CL Scale modelers must let AMA Scale Contest Board know feel somewhere along line someone must submit rules change proposals Editors note Bill could nor have known about two rules proposals hare sub mittedforthe current cycle rules changes SC84-9 SC-84-10 propose delete re quirement mufflers CL Sport Scale CL Precision Scale respectively can read entire proposals summaries December Competition Newsletter RMcM might also appropriate write National Association Scale Aeromodelers C/O Bob Underwood 4109 Concord Oaks Dr St Louis MO 63128 enough pressure placed Scale board NASA maybe muffler rule CL Scale models can reversed last thought would like point Out writer Im sure Ed fellow modelers against use mufflers required preserve flying sites meet community noise standards makes sense we can keep aeromodeling everyones highest regard doesnt seem make sense have rule will way deter competition level noise does appear problem Perhaps solution would modify rule wording CL Scale entries meet levels Nats would need mufflers unless specified contest management meet flying site noise require ments New sanding tool Pete Bianchini Yonkers NY brought attention rather new hand-held sanding tool does great job tool made plastic has palm-size grip has built-in sandpaper supply receptacle tool made 3M Co found auto supply stores called Auto-Pak Pressn Sand sandpaper tool comes rolls vary length 55 85 depending paper gritwhich 100 180 320 usable sanding surface measures approximately 2 4 great sanding large semi-flat surfaces such wings tails Instruc tion applying sandpaper packag ing very clear easy follow Cost tool about $600 rolls ofsandpaper about $175 Bill Boss 77-06 269th St New Hyde Park NY 11040 Propellers Brownlee Con fin ued page 80 read E E scale Calculate thrust shown As pure calculations errors HP thrust will total inherent nomo graph caused deviation Cp propeller considered model used practical sense errors can shrunk substantially ac curate engine power curve used con junction calculations Continue steps 2 3 4 until propeller power curve intersects engine power curve may also use cube law after initial estimate optimum power usage intersection curves should near peak power RPM engine curve relatively flat Cp propeller measured say 10% higher model result will engine will turn about 32% slower intersection RPM will cause insignificant power loss Error calcu lated thrust value will principally error engine curve plus cube root percent deviation actual Cp model Obviously very accurate en gine curve propeller close model results will quite accurate Whether engine-propeller combination will reach HPMPH values indicated course contingent having appropriate air frame drag use nomograph power matching results will reliable variables Eq 4 accurately known MPH527 4 CD x Wing Areasq ft Pattern planes with retracts CD continued page 168 January1983 165 AC/DC AUTO CHARGER No 4005B liDS DELUXE HEAVY DUlY AC/DC AITFO CHARGER IS JUST PERFECT FOE SAFE REUABLE FAST CHARGING OF ThE NICAD DAFFERY IN YOUR PLANE BOAT OR CAR Fl HAS ALL ThESE FEATURES YOU ASKED FOR Has adjustable rate zero am amp charges 4 5 6 7 8 cells Charges 250 mahr up 18 ahr cells Works llOv house current Works 12v auto battery gel cell Has equalizer circuit pilot light Has jacks external voltmeter Use boats cars planes Use transmitter receiver Use motor break $6995 Astro flight Inc 13311 Beach Ave Vemice Cailfotnia 90291 2138216242 Solve Sanding Problems SPEED STIX Disposable Sanding Tools Inconvenient Hard-to-Sand Spotsl S Use Wet Dry @3 Sanding Grades 100 120 160 $485 Regular SPEED STIX 9 Stix 3 grade 1/4 3/8 1/2 diam $295 Mini SPEED STIX Set 6 1/8 3/16 1/4 diam 120 & 180 Orders Postpaid Order Direct Precision Sanding Tools 2930 Skyview Ave Pueblo CO 81008 Eve Phone 303 542-6200 $4995 KIT #12 51 Wingspan- 19-40 Engine Foam Wzng- Balsa Fuse Easy Picture Instructions Send Money Order- Pay UPS Ill Res add $2 00 Tax Dealer Inquiries Invited GT MODELS Pb 217-893-4136 P0 Box 869 Rantoul III 61866 TOLEDO/ 83 TWENTY-NI NTH ANNUAL RADIO CONTROL EXPOSITI ON TOLEDO SPORTS ARENA ONE MAIN STREET TOLEDO OHIO Reserve April 8 9 10 1983 attend wolds greatest radio con trol model show featu ring worlds largest Swap Shops no dealers complete ref resh ment centers Saturday Night Auction raffles complete nc systems accessories acres free parking Bring latest com pletely finished models display enter com petition exciting awards Complete nc systems will presented first second third place win ners new Video Cassette Recorder will awarded lucky winner Best Show Open public three great days 89& FRIDAY9amto6pm SATURDAY 9am to6pm SUNDAY 9am to43Opm presented Weak Signals RIC Club PO Box 5772 Toledo Ohio 43613 Propeller cont 0030 suggested Assume E 085 calculate MPH using HP value engine 10cc power curve proceed follows 1 Align edge HP RPM values taken engine curve 2 Place T-pin L intersection pivot edge right side aligns calculated MPH value 3 Read J J scale calculate diameter pitch shown 4 Determine F thrust before propellers will attain 85% effi ciency because low p/d general application MPH might need recal culated after first approximation results will quite accurate may proceed confidence carve oddball propeller described have accurate engine airframe drag data Just conform parameters defined earlier however play nomograph conjunction engine curve propeller efficiency curve will conclude typical 10cc engine Pattern airplane will get essentially equivalent performance using 10A x 7 .oranllx7.oranllx7.oran 11 x 8 About will change engine RPM Sky Baby/Scott Continued page 70 lot faster can run try land airplane about quarter eighth lap short him can save lot time round Tips pitmen model touches down will travelling pretty fast biggest target strongest part As engine its mounting seems pretty good trick field dead-stick though moving airplane its nose filled fuel syringe held left hand already wired starting thus leaving right hand free catching Fly smooth race Sky-Baby well soon see winners circle Materials list 1 x 3 x 36 Balsa hardFuselage 1 x 3 x 36 Balsa lightWing 11/16 x 2 x 18 BassTail 1 x Wing tail skid mount 1/32 PlywoodDoublers 1/12 PlywoodWing mount PlywoodFirewall 062 Diameter wireLanding gear 045 Diameter wirePushrod 032 Diameter wireTail skid 025 Diameter wireLead-outs 5-Minute epoxy glue Hot Stuff Goldberg control horn set Goldberg nylon reinforcing tape 2-56 Blind mounting nuts 5 2-56 x -in Screws 5 K&B Superpoxy Primer yellow clear Cox Black Widow engine Tomado 5-4 nylon prop FF Scale/Warner Continued page 57 prop shaft apply little heat match hot soldering iron contract neatly onto wire making hook wont cut rubber motor can used make winding tubes shrunk size bigger sizes used wiring hamesses retain flexibility toughness small bit shrunk end axle holds wheel Another hint Hot Stuff addicts involves what dam stuff wont set up youre tired waiting used blow fine baking soda dusting joint using just pinch between thumb first finger ground back forth blowing toward wet adhesive new product finding its way shelves hobby stores lifesaver time saver smell Ithink breathing may no good comes small bottle pump-tray nozzle used evapor ates almost instantly Although can used prep surfaces five bucks bottle prefer just save until need instant setting Its super-glue acceleratormakes cyanoacrylate glues set up almost instantly Several manufac turers ZAP Ace Hot Stuff market Make own planes own wheels local surplus auto parts store hardware store two can relied stock variety sizes 0 rings make great-looking tires gas jobs weight factor Peanuts dont recommend clever rubber-motor hook-ons some guys use have seen couple break very inopportune times figure has enough trouble adding another thing go wrong Like simple weird models Dave Aronstein Mid-Hudson Model Masters Baron Von Heinigrabbers outfit has plans ranging ultralight Goldwing Miles Libellula has Peanut plans HE 100 Gipsy Moth Stinson Reliant Goon Monocoupe others Ive seen ultralights Cloudbuster fly claim two-minute model exaggerated Send him buck plans list put some fun back jaded existence Dave Aronstein 50 Pasture Lane Poughkeepsie NY 12603 address final hint day comes other neighbor pages Bob Meuser Bob pre-shrinks superfine tissue frame takes Sharpie pen art-supply store saws open guts containing ink sloshed around small pan lacquer thinner about -in depth resulting mess swabbed onto tissue using absorbent material inside mop Bob says abbing back forth north south east west repeating plain lacquer thinner managed get fairly Somewhat similar results may obtained using Marks-a-Lot alcohol-based felt pen overlapping strokes fancy quick-and-dirty way get job done especially condenser paper Yellow seems work best Thanks great support 5 x 7 contrasty prints see too seldom hints share Bill Warner 423-C San Vicente Blvd Santa Monica CA 90402 SAFE FLYING IS NO ACCIDENT 168 Model Aviation