ok- bigger props are theoretically better -but in some cases they simply don't do the job -

Oh-My-God...this is going to drive Dick and me nuts. Or at least me
I'm gonna try to make my point one-more-time. Then, hell or high water, I'm quitting. ( I know Dick's thinking "finally!!")

Please picture in your mind any two identical props on two identical planes of identical 10.00000000 lb weights. Two identical engines burning...you get the point.

Hover them at the same time. Same TQ roll tendencies, right? NOW THEN, glue POPCICLE STICKS to the blades on one model. Sideways. THAT model now has a very inefficient , goofy prop. THAT one will use a lot MORE power to make the same 10 lbs of thrust due to the very draggy and goofed up prop. The extra drag being overcome at a higher rpm to make the same 10 lbs of thrust will burn more calories or amps or watts or joules or frigging dilithium crystals for all I care.

But it will, it WILL, according to none other than Mr. Newton's 3rd law, have MORE TQ ROLL.

There, I'm done. Whew...feels good

POWERLINES, in redneck-speak (as per your request) SWAP PROPS. Experiment. Enjoy. Bet your buddies beers on the outcome.

It's all your's now Dick. I'm worn out.

Thanks for indulging me, Don.

Hey powerlines. Perhaps we should get back to the plane? So now you know that it's possible that some other prop may produce a little less torque rolling effect. Not a lot less but enough to perhaps notice if your present prop is generating a lot of drag while doing its job.

But what about your aileron throw angles and aileron size? Are you running as much as the serious stunters or have you toned down the travel to be a little more gentle while you're learning to fly the 3D stuff and hover?

Makes sense to me -- you changed the setup - by adding the non lifting devices - changed the results
here is a bit of history-- to check the quality of a refurbrished aircraft engine -- the standard setup has been a large "load prop"--much like you mentioned a very draggy paddle thing -
IF the rebuilt engine turned that prop at a specified rpm (at STP) - it wa OK- This is the same thing a my electric motor /thrust tests
I found that X prop required a specific amount of power input (watts) to deliver Y thrust - Had I included rpm , it would be more useful info to other applications -but all I was after was power required to hold a model in a hover - all the props I used were basically of fthe shelf, low pitched props of differing diameters
No added paddles no grossly oversized or undersized stuff - and the results were as noted.
So power absorbed, indicated a particular load ( which I read as thrust)

Experimenting is what it's all about .
My own experiments showed mye my problem was NOT the props -it was the lousy batteries (lack of available power .)
for really good 3D flying an excess of power is needed - this allows you to juggle as may be necessary
a really sharp 3D flyer can hover with a 1-1 power to thrust setup -but trying to learn with that setup is veeeery tricky 2-1 or bette really helps -

Breaking my promise. Sorry Dick[8D]

Naw, no setup change. Just "created" an inefficient prop in an extreme example who's results should be extrapolated into a comparison between my new shiny APC and an old Top-Flite nylon that my dog chewed up, and further extrapolated into a comparison between my shiny new 18*6W APC and my shiny new Master Airscrew 18*8 classic.

The APC is a LOT more efficient at hover than the 8-pitch, uses less power to create more thrust, thus creates less TQ roll.

Yes, but it depends much on how you want your bird to fly with the power you have available.
Focusing only on thrust may be misleading unless you’re intending to fly like a helicopter hovering all the time…
As you obviously know, the diameter of a helicopter prop is much larger comparing with a conventional plane, but the helicopter’s forward speed is relatively much lower.

If you want your bird to hover but also to perform well as a conventional plane, you need to think about thrust and pitch speed.
Roughly, the power absorbed by the prop is equal to thrust times its pitch speed, which is equivalent to torque at the motor shaft times RPM.

Thus, for a given power, the more thrust you have the less speed you get.

Of course-
remember tho --The subject was about hovering a model

OK - Just putting in my 2 cents...

Torque Roll is caused by an equal and opposite reaction of the rotating propellor, right? Right.
How can you create the same thrust while reducing the torque? Use a propellor that is more efficient for the specific use.
They have several different diameter and pitch propellors for a reason.
Many people fly their planes in many different manners, one being hovering.
The most efficient pitch to hover with is a lower pitch and higher disk area, (diameter), than one used for high-speed flight.

A 17x4W is a wide blade prop. I used a 14x4W to load up my .65LA where I needed the ground clearance, and a 14x4 let the engine run a little high for my liking.
This is a power prop, and has a lot more engine load due to its WIDE blade. It has a higer rotational drag than a normal width blade.

You see, a larger diameter will have a greater static thrust using the same pitch because of the disk area that is covered when the propellor spins. Double the diameter and increase the disk area by 3 times.
Why is this important? The pressure differential can be less while producing the same thrust. The engine can spin slower and perform the same amount of work, (Dick, the watts consumed WILL be the same producing the same amount of thrust, but torque will change).


You can imaging the pitch as "shifting gears" in your car.
If you start in 1st gear, you will have lots of accelleration, but your top speed is limited. If you start off in third gear, you will have a good top speed, but your acceleration will be poor. This can translate roughly to your propellor pitch. A low pitch like x4 will have greater static pull than an equivalent loaded prop with a higher ptich like x8, (I use the term "equivalent loaded prop" because you need to decrease the diameter when you increase the pitch to obtain the same load).

Dick, with all due respect, you were measuring watts to thrust, not watts to torque, or thrust to torque. The question that was asked had to do with reducing torque while maintaining thrust, not changing power to change thrust. Please don't confuse the problem with a non issue.
You were measuring the efficiency of the prop, not the torque required to spin the prop.

Powerlines,

In simple terms, try a standard width blade 16x4. This will produce the same thrust for hovering while spinning at a higher rpm, but at a lower rotational force, or torque, because of reduced drag of the smaller prop blade.
If the engine revs to high, go up an inch in diameter while keeping the same pitch, (if they make such an animal).

Let us know how you make out.

Bob

[quote]ORIGINAL: bobmac010

.

The pressure differential can be less while producing the same thrust. The engine can spin slower and perform the same amount of work, (Dick, the watts consumed WILL be the same producing the same amount of thrust, but torque will change).


Iwill stop my comments at this point - I simply don't see how Bobs explanation (see above ) works

I think I have seen a 18x4W on Horizion.. I will look into it.. I am going to the field tomorrow and I will try a few things.. I did put a 18x6 prop on it yesterday and just held it in the air. It was still TRing but not bad.. I did not hold it like that with the 17x4W.. I will put it back on tomorrow and try agian..

LATER

Thanks guys for the info..

Dick,

I hate to keep beating this subject, and I respect your experience.
Maybe this will help...

Power = Power
Watts = Power
Total Thrust = Power
15 pound airplane hovering = 15 pounds of thrust.
Watts does not equal torque.
Propellor torque creates torque roll.

Torque required to spin a propellor to hold a 15 pound plane steady varies with the diameter, pitch, and blade configuration, (narrow blade, standard blade, wide blade, and 2 blades, 3 blades, etc.).
Different propellors require different torques to perform the same amount of work, just like different wings produce different amounts of drag to produce the same amount of lift.

Would you agree that you can liken the prop blade to a rotating wing?
OK, with a larger wing area, you do not need to produce as much lift per square inch to have the same lifting effect overall, right?
Example:
If you have 10 pounds of lift using 700 square inches, there is a larger pressure differential between the top and bottom of the wing than 10 pounds of lift using 1000 square inches.
The same applies to a propellor. A larger diameter propellor does not have to produce as much thrust per square inch as a smaller propellor to achieve the same overall thrust.
Make sense?

Powerlines,
The 18x4W may increase your torque roll because of WIDE blade has more rotational drag than the standard blade.
Try a 18x4, not 18x4W.

Bob

something to chew on--
1- props don't create torque - the motor (or engine) shaft torque ,can be measured )
2-watts simply are measurement the amount of power applied to the shaft
3- the torque roll is a reaction to applied force (from prop shaft)in opposite direction- on the prop
4 being an airscrew - the prop applies force (moves air) from front to rear and at an angle
When you add it all up - to hover 15 lbs takes 15 lbs of thrust --the prop had to slice the air is some manner to create a NET difference from above the blade to beneath them.
Short of using contrarotating props - that nasty old reactive force will still exist.
How efficiently you do this is up to your selection of prop and powerplant.
But make no mistake - the airscrew will always react (opposite force ) as hard as it acts. You can call that torque if you like but really -it is just reactive force.
Brer Newton had that one down cold


an electric motor driving a prop and a thrust stand (plus if you want it ,a reaction load meter) - will show you the relationships of
applied power measured in watts.
thrust -relative to power input
and reaction to thrust with various props -if you setup stand for measuring reaction .
but what the heck try different props-- that's the fun in flying models. I have a pot full of props from 32" long for 160cc down to 3" for tiny under one ounce electric models- I also swap props to find what I like best -

Ok.. I changed to a 18x6 pro zinger. It did hover at a lower throttle setting but did not wind up near as much. The wind was blowind 15-20 and I could not hold a steady hover with it.. SO I have no clue what it did. It did feel like it was lacking power with the 6 prop.. I will try this Sun with no wind and let ya'll know..

LATER

Keep in mind that with an engine you still need to be aware that the prop needs to be able to let the engine reach the power peak. So beware of putting too large a prop on the model. I only add this due to the fact that a few posts up you were working with a 17x4 and an 18x6 is a big jump up for pitch and diameter all at once. Generally as the size goes up we like to reduce the pitch and vice versa.

Hi Bruce,

He said he was using a 17x4W. This is a Wide Blade from APC. It loads up the engine considerably because of the increased blade area.

A jump to an 18x6 is not that much of a load difference from the prop he was using.
The prop specs for the Saito 1.80 engine are: 15x8 - 18x6

Just thought I would chime in...

Bob

I just tried the prop from my 220.. It spools up OK but not good.. I ran it rich and after the flight it was cooler with the big prop than the 17x4W.. I will get a Evolution 18x6 they are more efficient and look better too.. It should spool up much better on that.. I did have to open the high end almost 1/2 turn to run a little off peak RPM.. It was really cool. That was surprizing to me.. LOL

Will try more..

LATER