What determines which prop you use????

[aro]

In motor vehicles:

 

A vehicle with the highest torque will climb a hill fastest with equal gearing

 

"Equal gearing" - referring to gearing shows you are talking about power. Equal gearing means equal RPM, and at equal RPM power scales linearly with torque.

 

A Rotax 912S is quoted at 128NM of torque. On a bicycle, I can produce approximately 140NM of torque. RPM and therefore power are ridiculously low of course - there's no prospect of me powering a pedal powered aircraft. A GSXR600 motorbike has only 70NM of torque. I can guarantee it will climb a hill better than me on a bicycle, despite having only 1/2 the torque. Torque alone tells you nothing, torque and RPM together give you power.

 

Power is in fact defined by how fast you can raise a weight e.g. climb a hill. 1 (metric) horsepower is the power required to raise 75 kg 1 metre in 1 second. So climbing a hill faster requires more power, by definition.

 

 

[turboplanner]

Go to a drag strip and talk about a car's power in kilowatts and torque in Newton-metres. The rev-heads will direct you to the next village that's looking for an idiot.

 

Honestly, how do you visualise a kilowatt or a Newton-metre?

 

You’re kidding me????

 

 

[M61A1]

Honestly, how do you visualise a kilowatt or a Newton-metre?

 

Really easily.....Visualise a Watt and multiply by 1000 or if you need old terms visualise about 0.74 of a HP. For Newton Metres visualise about 0.1 Kg applying force at 1M. Simple.

 

BTW a lot of the modern hot rodders do use kW and NM.

 

 

[turboplanner]

"Equal gearing" - referring to gearing shows you are talking about power. Equal gearing means equal RPM, and at equal RPM power scales linearly with torque.

 

Yes it does:

 

500 Nm x 2000 rpm/9549 = 104.7 kW

 

500 Nm x 4000 rpm/9549 = 209.4 kW,   so 100% increase in rpm = 100% increase in power = linear progression

 

This is what I meant in my example:

 

500 Nm x 2000 rpm/9549 = 104.7 kW

 

600 Nm x 2000 rpm/9649  = 125.67 kW, so at equal gearing 2000 rpm the higher torque engined vehicle climbs the hill faster.

 

But a vehicle with LOWER torque can pass it by changing down a gear and revving hard

 

500 Nm x 2000 rpm/9549  = 104.7 kW

 

300 Nm x 4000 rpm/9549  = 125.67 kW

 

 

[aro]

This is what I meant in my example:

 

500 Nm x 2000 rpm/9549 = 104.7 kW

 

600 Nm x 2000 rpm/9649  = 125.67 kW, so at equal gearing 2000 rpm the higher torque engined vehicle climbs the hill faster.

 

Only because at the same RPM it has higher power.

 

But a vehicle with LOWER torque can pass it by changing down a gear and revving hard

 

500 Nm x 2000 rpm/9549  = 104.7 kW

 

300 Nm x 4000 rpm/9549  = 125.67 kW

 

In other words, it is power that determines how fast you climb the hill, not torque.

 

 

[turboplanner]

Only because at the same RPM it has higher power.

 

In other words, it is power that determines how fast you climb the hill, not torque.

 

OK, let’s take the torque out

 

0 x 4000. / 9549 = 0

 

 

[old man emu]

Power = Torque x velocity

 

Torque = Force x distance

 

Power = Force x (rotational distance/time)

 

Therefore, Power is a derived value (the product of) dependent on the magnitude of the torque AND the velocity of the "lever arm". Velocity is (distance /time). The "Lever arm" is the distance between the centrelines of the crankshaft and the connecting rod journal. The interval it takes to complete "suck, squeeze, burn, blow" give the time.

 

Given a fixed distance of the lever arm, and fixed dimensions of the combustion chamber, the only way to get high power is to increase the frequency of combustion events (revs). That means greater force must be generated by a bigger combustion event (more fuel/air).

 

 

[aro]

OK, let’s take the torque out

 

0 x 4000. / 9549 = 0

 

Take RPM out and you also get zero. You need non zero values for both torque and rpm, i.e. power.

 

 

[aro]

Power = Torque x velocity

 

Torque = Force x distance

 

Power = Force x (rotational distance/time)

 

Therefore, Power is a derived value (the product of) dependent on the magnitude of the torque AND the velocity of the "lever arm".

 

 

 

No, power is a fundamental concept in physics: the rate at which work is done. A rocket engine produces power (but no torque), a jet engine produces power, a man walking up stairs produces power. Your calculations are just specialized examples to calculate the power of an internal combustion engine.

 

It takes power for a vehicle to climb a hill. You can calculate the power required, and it doesn't matter whether it comes from an internal combustion engine, a rocket engine, or 4 guys pushing the car.

 

1 horsepower = the power required to raise 75kg 1 metre in 1 second.

 

or if you prefer imperial

 

1 horsepower = the power required to raise 550lb 1 foot in 1 second.

 

 

[facthunter]

The USA haven't gone metric as it's always been cited as "un American" by all bar the scientists there.. Is it because of the drag business being an american-based activity predominantly uses Horsepower and foot-pounds? Once, everyone was familiar with horses even if they didn't ride one had a rough idea what they could pull., how big a "foot" is and the weight  (Lbs) is a common usage in trade. Nev'

 

 

[turboplanner]

 

No, power is a fundamental concept in physics: the rate at which work is done. A rocket engine produces power (but no torque), a jet engine produces power, a man walking up stairs produces power. Your calculations are just specialized examples to calculate the power of an internal combustion engine.

 

It takes power for a vehicle to climb a hill. You can calculate the power required, and it doesn't matter whether it comes from an internal combustion engine, a rocket engine, or 4 guys pushing the car.

 

1 horsepower = the power required to raise 75kg 1 metre in 1 second.

 

or if you prefer imperial

 

1 horsepower = the power required to raise 550lb 1 foot in 1 second.

 

The thread is about props so we can dispense with expanding the thesis.

 

Once you understand the relationship between Torque and horsepower you can get an understanding of what prop will suit the engine characteristic.

 

For Example: 

 

You can nearly rule in or out a Wankel type rotary design on that basis alone, or

 

You will know why Douglas Bader crashed his Spitfire when he tried to take off in coarse pitch.

 

The first answer to the OP question is obtain the power, torque and fuel cirves of the engine.

 

 

[old man emu]

Sorry Aro, but there are only seven units of measure defined by the International System of Units as the basic set from which all other SI units can be derived. Those units of measure are:

 

Second, Metre, Kilogram, Ampere, Kelvin, Mole & Candela. All the other SI units are a combination of basic units by multiplication or division. Thus "velocity" is Metres divided by Seconds, Force is Kilogram multiplied by the rate of change of velocity per second. 

 

The first answer to the OP question is obtain the power, torque and fuel curves of the engine.

 

Bloody obvious. I must've had a Man-Look at the problem.

 

 

[aro]

Sorry Aro, but there are only seven units of measure defined by the International System of Units as the basic set from which all other SI units can be derived.

 

Whether the units are derived is irrelevant.

 

Energy is one of the fundamental building blocks of physics, but the units are derived. Are you proposing the laws of thermodynamics should be rewritten in reference to kg, m and s because they are SI units?

 

 

[aro]

The thread is about props so we can dispense with expanding the thesis.

 

Someone, earlier in the thread started talking about vehicles climbing hills...

 

Once you understand the relationship between Torque and horsepower you can get an understanding of what prop will suit the engine characteristic.

 

For Example: 

 

You can nearly rule in or out a Wankel type rotary design on that basis alone,

 

Tell that to the people running aircraft with Wankel engines e.g. 

 

https://www.airspacemag.com/flight-today/soundings-1-180969512/

 

On the subject of props, they had to limit the power because their prop was only good for 500HP:

 

https://woelfle-engineering.com/we/Wankel_Rotary_Time_to_Climb_World_Record_Presentation_Paul_Lamar.pdf

 

If you have a gearbox, you can have whatever torque you like. But you only have a set amount of power. A gearbox is never 100% efficient, it can only reduce the power available...

 

 

[spacesailor]

All props are NOT alike,

 

Many tinkerer's have spent lots of $ & hours, trying to get that last INCH per minute of climb, Or that last KNOT of speed from the very same engine & airframe,

 

SO

 

Weather it's Power Torque,  or another deity from whatever religion you like, The prop is what makes the airframe move thru the air.

 

SO

 

For the Same Power Torque & revs,

 

What prop is best for your aircraft.

 

"-what-determines-which-prop-you-use"

 

Single blade !, is scientifically the most efficient !.

 

Three blade seem more balanced & good for climb,

 

five blade seem to be in the realm of the most power-full.

 

Ducted fan are suddenly making their way in the modelling world.

 

And if any one knows who has the rego 55-3014, there's I picture of the BD-5  Jet motor in front of their plane .

 

spacesailor

 

 

[pmccarthy]

All props are not alike - well said. Here is Mike Patey's new Cub project.

 

[old man emu]

Everything old is new again!

 

 

 

 

 

 

This single blade has two features:

 

1. The blade is balanced by a counterweight on the opposite side if the hub.
    
   
2. The hub is connected to the propeller shaft through a bearing that allows the propeller assembly to rock back and forth on the mounting. 
    
   

 

 It works on centrifugal force more or less. There is no controls or linkages. On take-off it is flat (fine pitch), and in cruise it moves forward at the tip for more bite (coarse pitch).

 

     

 

The idea is that a single blade would be more efficient than multiple blades because the single blade is always travelling through undisturbed air. The propeller is counter-weighted and mounted eccentrically on the hub to keep it balanced. It also has fore-aft pivot so the prop pitch self-adjusts to the most efficient angle – you can move the tip of the blade forward and back several inches with your hand.”

 

“Apparently the design worked; in 1939 the Everel prop was tested on a Taylorcraft in a race and won by quite a bit. However, shortly after the introduction of the prop, powerful 50HP engines were developed which rendered the efficiency gains of the single blade moot. Considering that the balance of the prop was very fickle in changing weather, the already mechanical complex prop just wasn’t worth the effort, so the design never caught on. It’s a nifty bit of engineering and a cool piece of history.

 

Despite this bit about engines which could produce enough torque and high enough RPM to produce more horsepower being the killer of the single bladed prop, here's an article showing one fitted to a Cessna C-37 with a big radial engine. http://rexresearch.com/unibladeprop/onebladeprop.htm

 

Perhaps the single blade concept might be abandoned, but the floating hub assembly might be a simple way to get variable pitch.

 

 

[spacesailor]

It looks a certain winner for the Half VW 32 to 40 HP powered aircraft.

 

Any one willing to work out the hub mechanism, I haven't a clue on what's inside .

 

spacesailor 

 

 

[turboplanner]

Any one willing to work out the hub mechanism, I haven't a clue on what's inside .

 

Things

 

 

[facthunter]

Don't go there. Stick to a simple 2 blade with no hinges or gimmicks like the majority of engines have always had. Piston engines deliver torque with lumps in it and a loose prop is bad enough without making it more risky structurally. Nev

 

 

[old man emu]

Any one willing to work out the hub mechanism, I haven't a clue on what's inside

 

If you open that link I put in Post #42 and go through what it contains, you will see all the patent drawings for the idea.

 

 

[Yenn]

OME.

 

How can the kilogram be a basic measurement, when it is really 1000 grams. Surely the base is the gram.

 

What is the definition of velocity. I thought it was speed and direction. Not just speed.

 

You really opened up a can of worms with this subject and I don't think we have answered your original question, but it has kept us busy.

 

 

[facthunter]

Velocity has both speed and  a stipulated direction. Earlier when I was first taught it, the Metric system a was the CGS. Centimetre gram second.. Weight is subject to gravity. Mass is not.. A metre was a size related to the circumference of the earth so a metre has a more basic relevance. It didn't work out exactly but at least they tried. The Metric system has a lot more logic than any other (in my view). I still have to work in both working on old machinery. Nev

 

 

[old man emu]

How can the kilogram be a basic measurement, when it is really 1000 grams. Surely the base is the gram.

 

What is the definition of velocity. I thought it was speed and direction. Not just speed.

 

The base units have been set by the General Conference on Weights and Measures (CGPM), which is the supreme authority of the International Bureau of Weights and Measures, the inter-governmental organization established in 1875 under the terms of the Metre Convention through which Member States act together on matters related to measurement science and measurement standards.

 

The kilogram is defined in terms of three fundamental physical constants: The speed of light c, a specific atomic transition frequency ΔνCs, and the Planck constant, h. The International Committee for Weights and Measures (CIPM) approved a redefinition of the SI base units in November 2018 that defines the kilogram by defining the Planck constant to be exactly 6.62607015×10−34 kg⋅m2⋅s−1, effectively defining the kilogram in terms of the second and the metre. The new definition took effect on 20 May 2019.

 

The CIPM is constantly refining the precision of measurement. It is true that the system was once based on the centimetre, gram, second but that allegedly caused some problems in some fields of physics, so they went to kilogram, metre, second.

 

Yes. Velocity is a vector quantity, meaning that it has magnitude AND direction. Speed is a scalar quantity because it only has magnitude. Mass is a Scalar, but Weight is a vector for the same reasons.

 

 

[M61A1]

It looks a certain winner for the Half VW 32 to 40 HP powered aircraft.

 

Any one willing to work out the hub mechanism, I haven't a clue on what's inside .

 

spacesailor 

 

A Delta hinge perhaps?