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Jan 04, 2019, 09:07 AM
gpw
gpw
“There’s no place like Foam”
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Question : As Noise goes up , doesn't efficiency go down ? Sorta’ like the unbalanced prop thingie … ???
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Jan 04, 2019, 09:55 AM
On the Edge of Space
dLdV's Avatar
Maybe, but from what I recall of the Zagi/Stryker/Funjet crazes at our field the ones that really scooted were ear piercing, screeching little boogers with tiny props spinning like mad. I don't know the principle behind it, but I think it was sort of what was found to work experimentally.
Jan 04, 2019, 10:58 AM
Kimbers Keeper.
BHOFM's Avatar
Quote:
Originally Posted by birdofplay
Oh , Sorry, I misunderstood.
You WANT to WAKE the DEAD !

70 yrs ago the guys would put playing cards in their spokes !

Lots of racket !
Now "We" are on the same page!

I am going to mark a couple different slot shapes, It will only take a couple seconds to
trim them out if needed. Ore tape back in as well.
Jan 04, 2019, 10:59 AM
Kimbers Keeper.
BHOFM's Avatar
Quote:
Originally Posted by gpw
Question : As Noise goes up , doesn't efficiency go down ? Sorta’ like the unbalanced prop thingie … ???
See above post!
Jan 04, 2019, 11:02 AM
Kimbers Keeper.
BHOFM's Avatar
Quote:
Originally Posted by dLdV
Maybe, but from what I recall of the Zagi/Stryker/Funjet crazes at our field the ones that really scooted were ear piercing, screeching little boogers with tiny props spinning like mad. I don't know the principle behind it, but I think it was sort of what was found to work experimentally.
One of our club members has a Glue and Go Mig-29 with a 3600kv Quad motor on 3s and the noise is
more than any gas plane ever built.
Jan 05, 2019, 12:47 AM
On the Edge of Space
dLdV's Avatar
Is it more prop noise or more sound board, vibration noise?

The ones at our field sounded like mini NASCAR qualifier laps. EEEEEEEENG YEEEEEE! EEEEEEEEEEENG YEEEEE!

Good luck with your earschplittenloudenboomer!
Jan 05, 2019, 05:56 AM
I Look, Listen, and Learn
Timbo383's Avatar
Quote:
Originally Posted by dLdV
Is it more prop noise or more sound board, vibration noise?
It's not the vibration of the foam that's causing the louder noise, it's the reverberation of sound waves hitting the foam and then back into the prop that causes the higher noise levels. I did some personal testing a while back by stiffening the foam slot around the prop and the noise actually increased. That's why the bow tie design works better...it changes the direction of some of the sound waves away from hitting back on the prop.
Last edited by Timbo383; Jan 05, 2019 at 06:02 AM.
Jan 05, 2019, 09:53 AM
treefinder
springer's Avatar
To support what timbo said, I recall reading a thread many years ago where the discussion was the opposite of this. I think gpw was involved. It wasn't the one Otto did, but came up with similar result. The objective to quiet down prop noise and increase efficiency, and the solution at the time was the bow tie - open up slot at tips. So conversely, I expect that keeping foam as close to prop LE will maximize noise. Maybe playing with bevels could push it a bit more.
I also have an FRC Alphajet that is really loud, (square slots top and bottom) and when spinning it up in hand, you can feel the very light, open box frame buzz and resonate as the prop passes the foam skin.
Last edited by springer; Jan 05, 2019 at 10:05 AM.
Jan 06, 2019, 12:01 PM
Kimbers Keeper.
BHOFM's Avatar
Little set back, the new Mig-29 was a failed maiden. I am redoing the elevron hinges.
The slotter is almost done. The tractor is all cut out.
Jan 07, 2019, 02:22 PM
Kimbers Keeper.
BHOFM's Avatar
Slotter is done!

This is raw crap video. It serves a purpose, not seeking any awards.!

sloter (1 min 51 sec)
Jan 07, 2019, 02:41 PM
flyin' fool
goldguy's Avatar
Quote:
Originally Posted by gpw
Question : As Noise goes up , doesn't efficiency go down ? Sorta’ like the unbalanced prop thingie … ???
A modeler who worked for a 1:1 prop manufacturer claims a loss of efficiency of up to 35% for pushers, so a prop in slot would be even more. I would think it's created by more restricted and disturbed airflow than noise.
Last edited by goldguy; Jan 07, 2019 at 06:47 PM.
Jan 07, 2019, 03:18 PM
Registered User
stillbents's Avatar

Slot noise


All I know is that the gas guys take notice when the F-22 winds up. This is a 1400kv pushing a 8X4 prop. Since the change over to a 9X4.5, it's even louder. I'm building another about 15% bigger and plan on experimenting with the bow-tie design.

https://m.youtube.com/watch?time_con...&v=K1vbzl2lLy0
Jan 08, 2019, 02:47 AM
Kimbers Keeper.
BHOFM's Avatar
The tractor version is well underway, basic airframe is done, motor mounted, esc mounted, CoG
is looking good, add some servos and the underbelly and it will be ready, but the weather coming
up don't look too great!
Jan 12, 2019, 12:57 AM
Kimbers Keeper.
BHOFM's Avatar
The three are done, all programed and ready, Rain, Rain Rain!!

I am working on X1-V5a, same basic air frame with a twist. Pictures later.

BTW, the three V4's came out at 330g, 330g and 331g., That is AUW! I am going to leave them
at that weight!


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