quiet performance props

[dick hanson]

Those who fly/flew lots of pattern over the years found that higher pitches are needed and power still remains but NOT at extremely low airspeeds
the answer is : there remains a pressure difference from front to rear of entire blade ,eliminating the Blaat of the flat tipped blades which quickly reach max forward speed and the tips are not pulling very much -if any .
In doing a simple test with MenzS 30x10 and ZM 30x14- the noise difference is impossible to ignore -- the Menz s will blatt , just pulsing the throttle in level flight
The ZM reaches the start of obvious blade noise at about 6600 in the air here at 4350 ft elevation
The Menz S blatted long before that rpm

My ignition has a tattletale which makes this testing easy -- just fly along and gradually add speed till the prop blatts, then throttle back and land --read the tach figure
the rpm tested on the ground is not much help in establishing best performance blade -- you can compare static loads but not dynamic (in flight) results
If you don't have a "tattletale ignition - there are some add on setups now which are not very expensive
Mine is on the 160J ZDZ-- MVVS is doing the same and 3W offers one
(the picture is of an 80cc on a 26x12- only decent sample shot--note the pronounced twist at the hub -the prop is very thick front to back -in this area on the 26x12 as well as the 30x14

[Bunky F. Knuckle]

WOW, Dick!!! That is a nice looking prop. Anyother info on it??? Have you compared that prop to a PT Model prop??? I'm curious as your results!!!

I've always been a follower of your writing. Enjoy it, frankly!!! Keep it up!!

Chris~

[Flyinrazrback]

http://www.rcshowcase.com/html/accessories/zmprops.html

[KrisW]

Dick, the Menz props are about the noisiest props out there, next to the bolly, ANY prop of comparable size should be quieter, especially if they are using more pitch, and consequently losing rpm out of the "rip zone". The big flexy blade of the Menz wooden props was the baseline many years ago, when that is all that was available. But, today, with at least 10 prop manufacturers out there it requires experimentation to determine which prop is correct. A difference of 100 rpm in the air, due to added or lessened airframed drag, and subsequent differing loads on the prop and engine (not to mention weight and engine size), can make or break a prop/engine combination

It still all comes down to combination. . . what you are trying to do with the plane (3D versus Sport flying versus IMAC/Pattern), and how good your throttle management is. Each application will require a different prop, with differing performance requirements, and higher pitched props will always have a tendency to be quieter than their flatter pitched brethren.

[dick hanson]

The use of the in air rpm recorder helped clarify why various props were noisy.
Was the noise simply rpm and diameter?
No
I think it is a handy tool

[KrisW]

	Quote: Originally Posted by dick hanson
	The use of the in air rpm recorder helped clarify why various props were noisy. Was the noise simply rpm and diameter? No I think it is a handy tool

Oh, I agree its a handy tool. . direct linked datastreams would be much more effective though.

At the Triple Tree IMAC we were discussing ways of monitoring the aircrafts actual sound signature, from the aircraft itself, instead of relying on the subjectivity of how it sounds in the judges chair or on the flightline. Couple such information with rpm, AOA, relative airspeed, and atmospheric conditions and you would have a very complete cross sectional overview of the conditions which were least desired, and be able to take steps to avoid noisy situations. You could literally design a throttle management program that would actively monitor and control the engine throttle, to keep the noise level very low . ..call it the computerized equivalent of a constant speed prop, in a fixed pitch situation.


This would be much more effective than a single "snapshot" of maximum rpm, taken only once during an entire flight, such as from "peak and hold" memory display from an ignition.

[dick hanson]

twood be nice -- - but this setup is sure better than not having any feedback - and it comes with the engine( s).
We went thru this in Pattern - I basically went to a bigger engine not working as hard - trouble is- as soon as more power was available - the guys just upped the size of the airplane ,opened the throttle and we were back to square one -

[KrisW]

	Quote: Originally Posted by dick hanson
	twood be nice -- - but this setup is sure better than not having any feedback - and it comes with the engine( s). We went thru this in Pattern - I basically went to a bigger engine not working as hard - trouble is- as soon as more power was available - the guys just upped the size of the airplane ,opened the throttle and we were back to square one -

Which is why I am trying to come upwith viable plane/engine combinations that fly just as well, but are less expensive, quieter, have a smaller noise footprint, as well as a smaller "Box" overfly area. It all comes down to accepting a different solution to the GSA and IMAC needs. The solution, IMO, is smaller, lighter, and quieter.

Camden S.C. IMAC is in 2.5 weeks . . we'll see how things are working out in that regard.

BTW. . my calibrated ear, and very capable left thumb are very adept at keeping things "on the edge" while not going into full-song prop rip. All it takes is discipline, and knowing when the plane is on the verge of getting noisy, then making sure it stays quiet.

[dick hanson]

good luck -
The great big planes are just soooo easy to fly and are sooo apt to impress -it is an up hill battle and without an equalizer - tough sledding
My son -who can frankly whip as s flying the box it came in- flew my 42 % piggy last week
His comment -" Chris-t --anybody looks good flying these -no wonder they are popular!"
The little 50 powered YAK as my Avatar flies any sequence with ease but to score well it must be way better than the big uns

[toprudder]

FWIW, I know of someone that is working on a throttle management system right now, for this exact application. It will be an rpm limiter that will allow a max rpm below the "rip" rpm.

I have seen something similar for helicopters, but don't know if it could be adapted to this application.

Bob R.

PS: Dick, I didn't recognize you without your old avatar.