Prop efficiency

[DieselFan]

A 4:1 ratio box should be pushing a 72" to 74" prop. the 65" would be highly inefficient.

Check out Powerfin's recommendations here. I see they recommend a 4 blade 65 for the 3.47 ratio but then the pitch must be quite high. They do not recommend the 4:1 or 3:1 ratios as they have harmonic resonance problem

Whats the definition of efficiency?

If I read it correctly, I see they recommend the 65" for the 4:1? In the B column. "Maximum possible diameter with this model is 65". I'm assuming the 5-65 means 5 blades.

What sort of tests / experiments can be done to show the prop is inefficient? Perhaps I don't know any better.

[Andre]

Hennie
Yes although I always had a short take off roll and good climb rate with the Airborne Edge with a streak 14 sq feet wing I find that I can get airborn 2 up in less than 50 m (dirt runway)with a 650 - 850 rate of climb. I have done approx. 50 hours with the new setup and the EGT's and water temp is still running low.
Prop noice is much less. The Brolca 4 blade was a 69" and the NC a 72 "
For me it was the best move but I am a bit worried about the high rev's

[Morph]

Whats the definition of efficiency?

On one of the calculations I saw a 2 blader is about 75% efficient. As you add another blade this drops to 72% etc. In the case of the 4 X 65" prop IMHO there is just not enough blade area to efficiently convert the rotation of the blade into forward movement. So you either crank up the pitch and load the motor or you add more blades to solve this problem, hence the 5 X 65" for the 4:1 gearbox.

What sort of tests / experiments can be done to show the prop is inefficient? Perhaps I don't know any better.

I would say that this will be an expensive exercise which is why we have to trust the suppliers to provide us with the best power/ratio/prop combination.

[smallfly]

What sort of tests / experiments can be done to show the prop is inefficient? Perhaps I don't know any better.[/quote]

I have an oppinion, and iff i'm wrong, feel free to stone me to death !

Tie a scale (skaap skaal) to a fixture (like a beam in you hanger) and the other end to a rope then run it through a pulley wich is fixed to your trike and again through a pulley fixed to the beam in your hanger, now tie the other end of the rope to your trike again.This should give you a ratio of three to one(because a "skaap skaal" usually only goes to 25 pounds.)

Now start up your trike and take the revs up to max static and take the reading of the scale(multiplied by three)

Repeat the procedure with the other prop.

It will not give you percentage of efficiency, but at least you will have a comparison figure of thrust.

[DieselFan]

Whats the definition of efficiency?

On one of the calculations I saw a 2 blader is about 75% efficient. As you add another blade this drops to 72% etc. In the case of the 4 X 65" prop IMHO there is just not enough blade area to efficiently convert the rotation of the blade into forward movement. So you either crank up the pitch and load the motor or you add more blades to solve this problem, hence the 5 X 65" for the 4:1 gearbox.

What sort of tests / experiments can be done to show the prop is inefficient? Perhaps I don't know any better.

I would say that this will be an expensive exercise which is why we have to trust the suppliers to provide us with the best power/ratio/prop combination.

So what would 100% efficient be? How do they get the figure, I also saw the sliding scale on the xls but wonder about the theory. I looked again this morning and compared to the other props mine starts broad thinning out, others start thin, broad then thin. So their surface area / bite is mid, mines closer to hub. Perhaps I can try one of the schools props to compare

My fuel tank is calibrated at 5l and 2.5l intervals by the manufacturer. I tried doing some tests this morning 45l fuel 1 person.

Engine idles too low for my liking 1500 and rattles, smooth is 2000 but then you ride the brakes
Takeoff rpm 6100
Climb at 850fpm@55, I climbed a 1000ft - max rpm on climb is 6000 til about 7500ft TMA...
Cruise rpm 4500@60, 4600 climbs at 80fpm
5000@73, 5500@79, 6100@90, 6400 at 100 but I only did this for a few seconds.
I did 4 landings and flew for 57mins, fuel used 8.2l

Without knowing the size or # of blades of my prop does this look efficient or isn't it so easy

I know that according to AC their 582 4 blade is almost 8db quieter than their 912 3 blade. 62 VS 70.

I remember the argument about "halt"ing my engine and pitched less yet cruise rpm is still low. My whole point to this is will my prop handle a higher speed as I'm looking at changing the engine and gearbox which would result in a speed of about 2000-2300 max.

Arplast have been - hard to contact.

[Morph]

From your figures the prop seems to be perfectly set up, if not a little (a degree perhaps) too course hence the static of 6100. if you decrease the pitch slightly and bring the static up to say 6400 then the cruise will come up little, the climb will improve slightly, fuel consumotion will increase slightly but the thrust at 2000 will reduce, allowing a higher idle and less holding on the brakes.

As far as I can see the 65" will happily run at higher rpm without the threat of disintegrating due to the tips nearing mach 0.92.