Design => Stunt design => Topic started by: Will Moore on June 24, 2019, 09:14:11 AM

Title: 3 blade, or 2 blade props-which ?
Post by: Will Moore on June 24, 2019, 09:14:11 AM
(topic removed for another time)
Title: Re: 3 blade, or 2 blade props-which ?
Post by: Air Ministry . on June 24, 2019, 11:26:15 AM
You got something against 4 blades or something . ?  S?P

On the wonerous new Folkerts , the Yatsenko prop , 13.8 x 5.9 , with its wide thin blades , Thus lower airfoil % , seems most effecient .
Theyre Ash or something , very light .
14 or ditto Carbon trimmed to 13 , which is more of a toothpick , gets the nose twitching .Its around twice the weight . Not so uch Twich as Shift .

Tho this is early flights with the pilots brain at half mast , half the twitchings the Pilots hand . As a aside ,
whenever Id gone down the Big Smoke the General Agro carried home - had ' one ' giving harsh control movements . Centuries ago . On a .35 ship .
This'd have it cutting loose here there & everywhere , untill you regained your delicate sensitivities .  S?P or the fine figertip touch & ' in the zone ' .

Back to props , The 3 blade , ihem there days , was a 10 x 6 instead of a 11 x 6 . or 9 x 6 instead of 10 x 6 , tho a OS 35s much better on the 10 x 4.
diameter of center of mass of blade'd be lesser , but x 1 1/2 . I dont really think O.A. figure ( Resultant ! ) would be any less at all . Oranges & oranges .
As in wood for wood , Nylon for nylon. in 2 & 3 .

Now the chaps that use ONE BLADE props , apparenty do so as its running in cleaner air . Interfering with itself less . Less in its own disrupted air .
So conversly - we'd assume  the more blades the more adjacent to the previos blades progression .

But lo & behold . We are after consistancy & various other irregular things wot props arnt usually used for . Like vertical elevators & downhill brakes . etc etc .
So with a plane with a bit of weight & drag , or flying real slow . Like the 10 x 4 3 Bl on the blue plane , it keeps it moving , if not at warp speed .

My reason for nailing together a collection of Four Blades is just that . approximately . But also , to keep a load on a big engine ( a 51 was really big , once )
so its in its ' working powerband ' . Thus its load response , to gusts , holes in the air , and people throwing things , is on tap & available .
But also cusioned to an extent . When its important to keep the plane moving and overcome gusts , or hold out against them anyway ,
without turning the plane around a big clean effecient two blade propellor , or having its ' Bite ' steer the nose left right and anything but center .

Most Carbon 4 Bl. Bolly, apc  etc seem to go a bit ' toothpick ' in the blades . Having much the same effect . The air can fall off the blades easier than wide Yatesenko is ones.

So maybe blade aspect ratio and chord thickness % are differant relevaces / eqations , in the differing blade configurations . Someone chop up three Yatsenko 2 Bl
and build two 3 Bl , and ' one ' can draw direct comparisons . I suppose with the antique Tornados same blade & pitch / Dia , in 2 & 3 would give a more valid
or at least more easilly mathmatically deciperable equation . If we knew what we were decipering . But the two the same should let us figure that out .

The summary thus far being high pitch long props are more of a pain , in the wind , to me . The 4 in & let it revs having a more consistant torrque reaction,
thus a more consistant Gyro trip up front .
elaborating .
If a thing stalls out , like getting trown of a wave ( Im ' from the Coast ' , inlanders may take a while to get it - the Analogy . ) The Accelerative Load
even if its Relitive to the AIR , as in its fallen into a hole / hollow in a gust , and hit the other side , steady air moving harshly - The Engines PICK UP
to hold  is Reletive Accelertion , which produces a relitive Tourque Reaction .

Thus if the air is very much a mix of conditions - irregular sequences etc ( Just like waves on the coast in a storm . a irregular coast , if youre whingeing )
The Aeroplane maintaining a reasonable rate of progress - the engine may ( need to be ) all over the place in its efforts  .

A prop that has too much ' bite ' will tend to do the ' rotate the airplane around the prop ' trip and all sorts of other exciteing things , acting a bit like a power operated rudder up front working in three planes .

So its useability is far more important than its efficency per say . Or the piped .76 ships should approah 150 mph running well .
If you can manage to get a broader ( rpm ) responce range - The Inertial Reaction ( to rotational acceleration ( and deceleration ) is more .
But the AERODYNAMIC ONE , in rough air , is the killer .
A engine coming on hard holding the nose elsewhere than you would prefer, can be overly attention grabbing .

THUS . a prop that smoothly and calmly accelerates up & down the rev Scale without producing a great variation in rotationall resistance  :P will operate smoothr .
Or more effeciently in thgis case , in relationship to the conditions . Rather than in ultimate thrust . So ' Effecency ' unless defined in relationship to PUPOSE is perhaps MEANINGLESS !
 D>K S?P

As a aside , its possable to fit two 2 blade props tandem . One in front of the other , Visualiseing airflow on em at various seperations axially will boggle you further .

In fact ,  :P say weve got two 12 x 5s on the shaft , one in front of the other ;
we have options from a Bi Plane Prop , to one being ( theoretially or actually )
directly in the others slipstream . And much else besides .  :-\ ??? >:(

A possability it could be a good ajustable feature for variable conditions . Some irdiot'd wanna do a spring loaded automatic one ( patent applied for  >:D)
or could be totally useless . Tho appears not .

theres a few pictures of WW 1 props , one in front of the other - 4 blade . 90 degree seperation . Scimater Style . Like THIS .

You can see the rear outer edges are / would be Less Supported . TRhus would ' fine off ' under load . Keep you moving uphill rather than stalling .
Wood Props used to be a art , thinning and tuning to get'em to work up more pitch at speed centrifugally , for racing .
Or go flatter uphill under load for aerobatics .
Tho one can endevour to get similar results aerodynamiccaly on them . Using airfoil , blade distribution etc etc .
Used to be wierd offset Punctillos that were all the rage in the late 70s / 80s . in europe /

Im nervous of trying the heavier three blades on the big Folkerts in case I get the plane in the teeth , for multitudeinous reasons .
The Earlier 40 version was  less happy , seemed less bite , on a 10 x 4 3Bl  Vs 11 x 4 2Bl . Discenably , significantly if not astoundingly . the olde 3 / 5 % trip ?
tho the fall off in grip was likely proportional to the blade disc area .

Thus I think the only valid comparison ( on paper ) is of the SAME DIAMETER in the differant blade configurations . Perhaps .  S?P VD~ ;D
Whaderyer expectif ya getmeup at 2 inthemorning .

Thats o.k. looking at it . Thought I mightve had four pages there .  H^^ oops. didnt see the bit above the pitcher .  :-X
Title: Re: 3 blade, or 2 blade props-which ?
Post by: GERALD WIMMER on June 25, 2019, 05:25:17 AM
Matt you raise some interesting points in your discussion on props but my brain hurts now  ??? n~ have to re-read it in the morning
Regards Gerald