noise-reduction, bringing down the prop rpm?

[Mario]

Hi canardians,

 

does anyone have experience in minimizing the noise-level of a canard aeroplane? Here in germany we have quite strict noise-regulations that seem hard to achieve just by muffling the exhausts.

 

The two possibilities I see are:

 

a) significantly reducing the rpm of the prop (just achievable by using a PSRU) to about 2000rpm or so.

 

b) avoiding the whole propeller-blade passing the trailing-edge at the same moment (bring it to "peel" along the trailing edge rather than "hit"). This can be done by curved propeller blades (I saw them on a pusher for purpose of noise-reduction but there´s no great assortment of these blades) or moving the prop-axis above the trailing-edge-level.

 

While the low rpm asks for significant increase in prop-diameter it would go well with rising the prop-axis. I know that would mean leaving the approved thrust-line but it should be possible tho correct that by adjusting the thrust-angle.

 

Any experience in this field?

 

Kind regards

 

Mario (is-it-possible?-phase)

[argoldman]

Hi canardians,

 

does anyone have experience in minimizing the noise-level of a canard aeroplane? Here in germany we have quite strict noise-regulations that seem hard to achieve just by muffling the exhausts.

 

The two possibilities I see are:

 

a) significantly reducing the rpm of the prop (just achievable by using a PSRU) to about 2000rpm or so.

 

b) avoiding the whole propeller-blade passing the trailing-edge at the same moment (bring it to "peel" along the trailing edge rather than "hit"). This can be done by curved propeller blades (I saw them on a pusher for purpose of noise-reduction but there´s no great assortment of these blades) or moving the prop-axis above the trailing-edge-level.

 

While the low rpm asks for significant increase in prop-diameter it would go well with rising the prop-axis. I know that would mean leaving the approved thrust-line but it should be possible tho correct that by adjusting the thrust-angle.

 

Any experience in this field?

 

Kind regards

 

Mario (is-it-possible?-phase)

You don't necessiraly need a longer propeller. Increasing the chord of the blade or increasing the number of blades will suffice.

 

As far as low RPM, Eggenflellner is now using very low RPMs in his Subary H-6.

 

He has had a 4 blade prop developed for his engine/PSRU combination. A problem for pushers is that the minimum diameter is 72" and untested in that environment.

 

It seems as Eggenfellner is uninterested in this market and is aiming primarily for the RV. Too bad.

[Nathan Gifford]

...It seems as Eggenfellner is uninterested in this market and is aiming primarily for the RV...

Well he had been developing one on a Defiant but he has put that on hold for some reason. I hope it wasn't abandoned.

[argoldman]

Well he had been developing one on a Defiant but he has put that on hold for some reason. I hope it wasn't abandoned.

In my last conversation with Jan, before the advent of his new gear box and expansion westward, (OSH 2005) I asked him about pusher application, at which point he stated in his typical matter of fact way that he has a defiant on which he is flying the Sube. Also in his typical way, he neglected to say that what kind of engine (h-4, or h-6) he was using, and he also neglected to say that he had less than 20 hours on it.

 

It's unfortunate that it seems like he has eliminated this market from his possibilities, as I was very interested in the H-6.

 

As I see it, he came out with this new belt reduction unit-- which self destructed due to FOD (easily avoided with a screen around the belts), determined that he could run the engine at various speeds to produce various max HPs. He then went to Sensenech to develop a 4 bladed composite prop. So far so good!. The testing is in a RV.

 

The minimum diameter, however is 72". When I asked him about the cozy market, he said that he didn't think that the new prop would be appropriate and gave me the number of an MT prop 11# heavier, and costlier.

 

It seems to me, that if he had a prop designed specifically for that engine, going to an MT prop, which he obviously rejected will be a step backward.

 

I respect Jan for zeroing in on a specific market (RVs, and eventually smaller HP engines for recreational craft), however I think that us pusher folks will be left out in the prop wash and will be the testers (been there done that---- sucks)

 

The rotary (crook, ET AL) is beginning to look better and better.