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Sep 26, 2008, 05:59 AM
Winging it Ò>
leadfeather's Avatar
Discussion

Slot design for "prop in slot"


Has any one done or know of any research on the slot for a "prop in slot" configuration.

What I'm interested in is minimizing the thrust reduction due to the slot, and also minimizing the noise caused by the slot. My guess is that a wider slot with more clearance behind the prop might be better. I also would guess that shaping the aft edge of the slot might help too.

Any data, research or theories out there?
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Sep 26, 2008, 06:14 AM
DroneWorlds - TEAM NEW ZEALAND
jackosmeister's Avatar
I dunno about any research or data, but i havent found any noticeable preformance difference in prop in the slot and straight pushers, Ive even modified an old prop in the slot delta pusher by cutting out the slot (so its a straight pusher) to see if it made any difference, it didnt.

Be interesting to see if anyone has any actual data on this though.
Sep 26, 2008, 06:54 AM
D'oh.. Dumb Left Thumb
dekan's Avatar
Dan. An Aussie guy makes wings with quite a big slot.... dunno if makes any difference. Maybe its just done for styling reasons or noise reduction?

http://www.tayloredtech.biz/TayloredTech/Home.html
Sep 26, 2008, 07:35 AM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
Lead, we thin the edges of the slot to provide the least resistance to airflow...
Sep 26, 2008, 09:30 AM
RIP Azarr - "Old age is not for sissies"
Azarr's Avatar
Quote:
Originally Posted by gpw
Lead, we thin the edges of the slot to provide the least resistance to airflow...
Does it make a difference in noise? Interesting thread, it will be fun to follow the responses.

Azarr
www.ecubedrc.com
Sep 26, 2008, 09:47 AM
D'oh.. Dumb Left Thumb
dekan's Avatar
Maybe most of the noise is produced by the front of the slot and the prop blade......as pushers can be just as noisy
Last edited by dekan; Sep 26, 2008 at 11:10 AM.
Sep 26, 2008, 10:02 AM
Registered User
don't have any first hand experience with prop in slot setups, but the noise issues is due in large part to the two flat edges running parallel to the prop. It creates a pressure wave the causes noise. if you angle the the slot (make it diamond shaped for example) you should see a reduction in noise.
Sep 26, 2008, 10:14 AM
My plans are in my blog
Rusty-Gunn's Avatar
IIRC, Kai, the designer is the Shuriken, an F-22 type prop jet, says he puts the prop closer to the rear slot edge to reduce noise.

Update... I checked Kai's thread, and he says putting the prop at the rear edge was an attempt to reduce the noise. First page, post 5 and 6.
https://www.rcgroups.com/forums/show...ighlight=kai+s
Last edited by Rusty-Gunn; Sep 26, 2008 at 10:25 AM.
Sep 26, 2008, 11:37 AM
Winging it Ò>
leadfeather's Avatar
For someone with a "thrust test rig" already in place, testing the slot variations might not be too hard to do but could give some really helpful data on thrust and noise.
Sep 26, 2008, 11:42 AM
D'oh.. Dumb Left Thumb
dekan's Avatar
I would be very suprised if there was any marked gain in thrust..... noise well?
Sep 26, 2008, 11:50 AM
7000mw of raw power!
rich smith's Avatar
This has always been of great interest to me so recently I built a series of mid-motor deltas to settle the issue. One design has a slot which is barely big enough to clear the prop. It produces a loud (but cool) noise and requires 8 of 16 throttle clicks to stay aloft. Another has nothing behind the prop and bigger space in front of and around the slot (like Jacko). It is almost dead silent and runs on 6 clicks. A couple in-between configs perform as expected.

Noise requires energy which is robbed from the prop. I also found this to be true for a full size pusher ultralight aircraft I fly which makes a lot of noise when the prop is nearer the TE and requires noticeably more throttle.

Any vibration or noise from things like unbalanced engine/redrive or badly tracked props take away from thrust. More than you might think.


Quote:
Originally Posted by leadfeather
Has any one done or know of any research on the slot for a "prop in slot" configuration.

What I'm interested in is minimizing the thrust reduction due to the slot, and also minimizing the noise caused by the slot. My guess is that a wider slot with more clearance behind the prop might be better. I also would guess that shaping the aft edge of the slot might help too.

Any data, research or theories out there?
Sep 26, 2008, 11:57 AM
D'oh.. Dumb Left Thumb
dekan's Avatar
Quote:
Originally Posted by rich smith
Another has nothing behind the prop and bigger space in front of and around the slot (like Jacko). It is almost dead silent and runs on 6 clicks. A couple in-between configs perform as expected.

Noise requires energy which is robbed from the prop. I also found this to be true for a full size pusher ultralight aircraft I fly which makes a lot of noise when the prop is nearer the TE and requires noticeably more throttle.

Any vibration or noise from things like unbalanced engine/redrive or badly tracked props take away from thrust. More than you might think.
Any pics of your "quiet" slot Rich?
Sep 26, 2008, 12:12 PM
7000mw of raw power!
rich smith's Avatar
I will take some as soon as the rain clears. I will also do a build log on my "One Minute One Buck Delta" when time allows.

Also should mention that shaping the edges had no noticeable effect on thrust. Don't remember if noise changes but I'm guessing it did.

BTW the "quiet" one actually had no slot.



Quote:
Originally Posted by dekan
Any pics of your "quiet" slot Rich?
Sep 26, 2008, 03:28 PM
Foaming at the mouth..
darksiede's Avatar
Quote:
Originally Posted by rich smith
I will also do a build log on my "One Minute One Buck Delta" when time allows.
Now that's something I'm highly interested in seeing.. Especially in this economy!

~Kev
Sep 26, 2008, 04:29 PM
"It's a Quad" :O
thewz's Avatar
Quote:
Originally Posted by rich smith
I will take some as soon as the rain clears. I will also do a build log on my "One Minute One Buck Delta" when time allows.
hey....wait a gosh darn second....if it only takes a minute why don't you do it now? jk


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