von klip tip : propeller performance

7/29/2019 Von Klip Tip : PROPELLER PERFORMANCE

1/16

Professor Von KliptipsTwelve All-TimeFavorite Questionsand Answers About

PROPELLERPERFORMANCE ON PERSONAL AND BUSINESS AIRCRAFT


2/16

2

About Professor Von KliptipIn 1903 as a young boy at Kitty Hawk,Professor Humperdinck Von Kliptip becamethe first person in history to yell, It will neverget off the ground! Though wrong aboutthe Wrights, the professor has been going

around in the best aviation circles since. As ateacher, he held the Wrong Way CorriganChair at Sopwith College for ten years. He isalso a renowned engineer and designer ofaircraft propellers. Professor Von Kliptip isthe author of many books, the most famousbeing Whatever Goes Up and its sequel,Back to the Old Drawing Board. He ismarried to the former Hilda Brinker, and theyare the parents of four flying Dutchmen.


3/16

3

1. Professor, what is a

propeller? The propeller is a twisted airfoil that convertsthe rotating power of the engine into thrust,which propels the airplane through the air.Sections of the propeller near the center aremoving at a slower rate of speed than those

near the tip, which is why the blades aretwisted. Modern propellers are fabricatedfrom high strength, heat treated, aluminumalloy forgings. Some are made up fromfiberglass resins into composite materials.

2. Can propellers beinterchanged amongdifferent engines?

Goodness, no! You want to end up in thecornfield? A propeller is designed to becompatible with a specific engine in order toachieve maximum thrust or efficiency andreliability from the aircraft. Even though thepropeller might fit another engine shaft, onlythe propeller manufacturer should

determine whether it is suitable for use on aparticular aircraft. McCauley has lists of theright propellers, governors and installationdata for all their props - both fixed pitch andcontrollable models.


4/16

4

3. Professor Von Kliptip,in your memorablelecture entitled Propsand the Single Engine

Aircraft you defined the basic types of propellers accordingto pitch. Do it again, please.

Fixed Pitch... one piece prop with asingle fixed blade angle. The pitch must behigh enough to offer good cruisingperformance and yet low enough to achieveacceptable takeoff and climb characteristics.

Ground Adjustable... blade anglecan be adjusted on the ground but cannot bealtered in flight. Once fixed, this propoperates like a fixed pitch propeller. Bladeangle can be set low for short fields and/orhigh terrain or for better load carryingcapability; it is set at a higher angle for longrunways, low terrain, or light loads when abetter cruising speed is desired.


5/16

5

Two Position... blade angle may beadjusted during operation to either a preset

low angle or a high angle setting. Low angleis used for takeoff and climb, then a shift ismade to high angle for cruise.

Controllable Pitch... within a presetrange, blades may be altered infinitely to anydesired angle during flight, starting with a

low blade angle and then graduallyincreasing the angle during takeoff, climb,leveling out and cruise.

Automatic Pitch... blade anglechange within a preset range occursautomatically as a result of aerodynamic

forces acting on the blades, and the pilot hasno control over the changes.

Constant Speed*... a governor isused in conjunction with the propeller toautomatically provide constant RPM as thepilot selects the proper setting. The governor

controls the forces acting on the propeller toautomatically change the blade angle withina preset range.

Full Feathering*... blades can berotated to a high positive angle to stoprotation (windmilling). This feature is

common on multi-engine aircraft, because itallows an engine to be shut down and theprop stopped to reduce drag and asymmetriccontrol forces.

Reversing*... blades can be rotated to anegative blade angle where they will

provide a rearward thrust to slow down, stopor move the aircraft backward. This capabilityis normally provided for turbine installations.

Beta Control... normally used forground operation, most often in taxiing,where thrust is manually controlled by

adjusting blade angle with the power lever.*Types starred are available in various models.


6/16

6

4. Why are some

propellers 2-bladeand others 3-, 4-,and 5-blade?

Multi-blade props are designed primarily,though not exclusively, for twin-engine

aircraft. The blades are shorter for increasedground clearance on all aircraft and to providemore fuselage clearance on twins. Otheradvantages over 2-blade props include higherand therefore less objectionable soundfrequency, less vibration, greater fly-wheeleffect, generally improved aircraftperformance, and a sharper appearance. I ampersonally designing a compromise-the 2 1/2 -blade prop, just as soon as I iron out the bugs...

5. Professor, what are thecorrect terms for thevarious parts of the

propeller? On the blackboard I will draw an enormouspropeller and label the parts with my chalk.


7/16

7

No horseplay, now, while I formulate mydefinitions:

Blade... one arm of a propeller from hub totip.

Hub... center section of the propeller thatcarries the blades and is attached to theengine shaft.

Blade Tip... that part of the blade furthestfrom the hub.Prop Diameter... the diameter of the circlecircumscribed by the blade tips.

Blade Root... section of a detachable bladenearest the hub.

Blade Shank... the thick portion of a bladenear the hub.

Blade Station... one of the designateddistances along the blade as measured fromthe center of the hub.

Blade Camber Surface... the cambered ormost cambered side of a blade (as seen fromin front of the aircraft).

Blade Face or Thrust Surface... the flat orleast cambered side of the blade (as seenfrom in back of the aircraft).

Blade Thickness... the maximum thicknessbetween the cambered surface and the faceor thrust surface at a given blade station.

Blade Leading Edge... the forward fullcutting edge of the blade that leads in thedirection of rotation.

Blade Trailing Edge... the continuous edgeof the blade that trails the leading edge inthe direction of the rotation.

Blade Width... the measurement betweenthe leading edge and the trailing edge at agiven station.

Blade Angle... an angle (less than 90)between the chord line of a propeller bladesection and a plane perpendicular to the axisof propeller rotation. The chord line is atheoretical straight line drawn between theleading and trailing edges of the blade.

Blade Angle Settings... low and highangle settings of a controllable pitch prop, asdetermined by built-in stops, for feather,reverse, latch and start locks.


8/16

8

6. What is the importance

of propeller diameter? Ideally, the propeller diameter should begreater for efficient low airspeed operationand smaller for high airspeeds. A propellerwith a variable diameter would solve theproblem, but the structural and controlproblems involved would increase the costand weight to a point where the advantageis not practical. The diameter of a fixed pitchpropeller is generally reasonably large tofavor low airspeed operation. At the sametime, the blade size is kept small to favor

higher airspeeds and permit faster turning atlow airspeeds so that higher power isavailable from the engine. The diameter andblade size of a constant speed propeller cangenerally be greater because of the variableblade angle provision.


9/16

9

7. Professor, it is a well-known fact that as a pilot you have pulled many a

blooper. Can aluminumblades on propellers becut back to fix nicks?

Yes, and am I grateful! The fact is, mostpropellers are produced with square tips

because it leaves extra material available forrepair. Material can be removed from thesquare tip to make it into a round or ellipticalform and still maintain diameter. My personalcollection consists of one prop with a squaretip and 43 with round ones. An approvedmechanic can correct minor blade surfacedamage such as nicks by dressing it out.Propeller performance is not impairedprovided the repair is within acceptable limits.


10/16

10

8. What are the effects of engine horsepower and RPM on the propeller,and vice versa?

I could take all day on that one, but thestrudels getting cold-so briefly, here it is. Forfixed pitch propellers, assuming a fixedthrottle setting, the propeller (and engine)RPM will change as the airspeed changes.With a constant airspeed, the fixed pitchpropeller (and engine) RPM will change ifpower is increased or decreased. Theconstant speed propeller employs an enginegovernor to automatically provide constantRPM at whatever throttle setting the pilotselects. The blade angle is changedautomatically and increases or decreases ifRPM setting is decreased or increased, or ifpower is increased or decreased. With fixedRPM and power setting, the blade angle willchange automatically as airspeed increases ordecreases. The RPM range is determined by apropeller control in the cockpit which may beadjusted to any setting between high andlow. Most governors are designed to returnautomatically to high RPM setting.


11/16

11

9. What is the effect of

balance on a prop? The mass moment arm of one blade of apropeller with respect to the other(s) is heldwithin reasonably close limits to avoidroughness. Since the length of a propeller isrelatively short in the direction of the axis of

rotation, as opposed to its length in the planeperpendicular to this axis, the balance can bedetermined and adjusted statically after thepropeller has been removed from theairplane. Dynamic balancing may also beaccomplished but is done with the prop onthe airplane.

10. How is propeller

resonance avoided? First I tell you a funny. I once designed apropeller with terrible resonance problems.When I flew it, every dog within miles wouldhowl. Such a racket! Anyway, a propeller hasnatural frequency, and it increases in

operation because of the stiffening effect ofcentrifugal force on the rotating blades. Toavoid resonance, forces which cause vibrationmust be studied so they do not coincide withthe propellers natural frequency. Some ofthese vibratory forces are engine torqueimpulses, engine shaft bending, motion ofthe engine on its elastic mounts, irregularairflow interference and many otherdisturbances.


12/16

12

11. Why is propeller overhaul needed?

A fixed pitch prop does not need overhaul. Itrequires blade reconditioning only, asnecessary. Constant speed and full featheringprops do require periodic overhaul. Overhaulof the propeller is needed to increase safety,prolong the propeller life, and improvefunction or operation. Overhaul is the

periodic disassembly, inspection,reconditioning, and reassembly of thepropeller. The overhaul interval is generallybased on hours of service (operating time)but a calendar limit also applies. After beingdisassembled, the propeller is inspected forwear, cracks, corrosion or other abnormalconditions. Certain parts are replaced, whileother parts are reconditioned and refinished.Reassembly and balancing complete the job.


13/16

13

12. Who is qualified to

overhaul a propeller? Overhaul should be performed by thepropeller manufacturer or by an approvedpropeller repair station* and followsmanufacturers service manual instructionsand service bulletins and letters as applicable.An approved propeller repair station is onethat is certificated by the Federal AviationAdministration to service, recondition, repairor overhaul propellers, in accordance withthe requirements established by thepropeller manufacturer or the FAA. These

firms have demonstrated that they haveequipment, technical information and skillsto perform such work. They are licensed and


14/16

14

limited to working only on specified propellermodels which are listed by manufacturer andmodel on their authorization.

*A listing of McCauley direct factory dealerscan be obtained by accessing our website at:www.mccauley.textron.com


15/16

15

A final serious word....McCauley takes flying very seriously. For thisreason we are anxious to disseminate helpfulinformation accumulated over years ofdesigning and manufacturing all kinds ofaircraft propellers. We urge owners andoperators of our propellers to read all

placards, operating restrictions andlimitations (including verifying enginetachometer) to assure product reliability andlongevity.

Professor Von Kliptip is our cartoon characterwho helps make the technical information alittle more interesting. Any resemblancebetween the Professor and a real person ispurely coincidental.


16/16

This booklet is presented in the interest of

happier, safer and wiser flying by

PROPELLERS SPINNERS DEICERSGOVERNORS & ACCUMULATORS5800 E. Pawnee, Wichita, KS 67218

Telephone: 800-621-7767 Fax: 316-831-3858www.mccauley.textron.com

von klip tip : propeller performance

Documents