Whistle Sound on Torrent

I launched my new Madcow Torrent using an AT I-161 last week and was surprised (and pleased) to hear a whistling sound during the ascent after motor burn out. It was a cool high-pitched sound, like what you hear on war movies when a plane drops a bomb, and the pitch (frequency) dropped smoothly as the rocket went up (Doppler effect I guess). The whistle went on until the rocket neared apogee. I'm not sure what caused it. The Torrent has a fairly standard fin design. My best guess is that one or both of the two 1/8" vent holes in the body tube, one of which was in an empty payload bay, may have acted like a flute works and generated the whistle as the air rushed over the hole(s). I put metal eyelets in the vent holes to strengthen them which protrude out slightly from the body tube. Anyone have any ideas on this?

Several split fin rockets are known whistlers, but seem to do it best when the adjoining inner edges are square. Did you bevel the leading/trailing edges of the fins?

In the absence of split fins I think your empty vented payload bay is the likely culprit. Maybe try putting it outside on an especially windy day to see if you can duplicate the effect.

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Any pictures or video from the flight ?

Whistling fins and a muffled sonic boom are the coolest sounds your rocket can make (well, next to a N5800...). Estes made a rocket awhile back (Screamin Mimi) that had three whistle tubes on the ends of the fins, but it only worked if you put in an AT motor (F24 RMS worked great). D12/C11, forget it...

Here's a video of my L2 cert flight with a Madcow PAC-3. Split fins. Even the crowd comments on the whistle. https://youtu.be/maY9ePFqbaE

I've attached a photo of the Torrent. I "semi-rounded" the leading edge of each fin. It's not a split-fin rocket as you can see. Below is a link to the youtube video -- turn up the sound and you can hear the whistle.


https://www.youtube.com/watch?v=a_qLGOMQDqg&feature=youtu.be

Pushed hard enough, any thick, non-rounded fin will whistle to some extent. My MadCow Cowabunga whistles some. If you rounded the fins, likely it's the holes.

I've got the Torrent as well and launched it on an I170, J357 and a j530 imax 6xl cesaroni motor and never heard any whistle. I slightly beveled the leading edge of the fins. I only have a vent on my payload bay for the altimeter though. I followed the video construction instructions and that's all they called for.

My TLP Martel and my 24mm Crossfire both make a pleasing sound after motor burnout.

Ok guys... if you click on the filmstrip-like/ladder-like icon between the "Insert Image" and "Wrap |Quote| tags around selected text" icons in the menu bar when posting, we can actually watch the video in the thread (and avoid watching any commercials).

noffie79 said:

Here's a video of my L2 cert flight with a Madcow PAC-3. Split fins. Even the crowd comments on the whistle. [video=youtube;maY9ePFqbaE]https://www.youtube.com/watch?v=maY9ePFqbaE&feature=youtu.be[/video]

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clarinet said:

I've attached a photo of the Torrent. I "semi-rounded" the leading edge of each fin. It's not a split-fin rocket as you can see. Below is a link to the youtube video -- turn up the sound and you can hear the whistle.

[video=youtube;a_qLGOMQDqg]https://www.youtube.com/watch?v=a_qLGOMQDqg&feature=youtu.be[/video]

Click to expand...

K'Tesh said:

Ok guys... if you click on the filmstrip-like/ladder-like icon between the "Insert Image" and "Wrap |Quote| tags around selected text" icons in the menu bar when posting, we can actually watch the video in the thread (and avoid watching any commercials).

Click to expand...

Can't do that on the iPhone app. Sorry.

No whistles on my torrent either, but my e-bay has always been populated. Gotta hand it it you - that's an awesome paint design you came up with!!

noffie79 said:

Can't do that on the iPhone app. Sorry.

Click to expand...

Ah... didn't know that.

square edges, MC super Bat ray(with holes in the fins), Aim 54(4") (split fins), bt 70 size Hi flyer(rounded edges no holes). what do they have in common? they all whistle .
Rex

I must give my son the credit for the paint design, which he came up with based on the logo and images of his heavy metal band "Sacred Monster"

No whistle on my Torrent; but I second the awesome paint job. I've certified L1 and L2 on my Torrent, but it's still finished in solid gloss white waiting for me to decide what it should look like...

If your not worried about altitude, I love the whistle. So much that I wanting to create whistle on my L3 via some specially placed holes - which I need to research

Based on the responses, my leading whistle theory for my Torrent is the vent hole in the empty payload bay. (The payload bay was empty because I used Chute Release for dual deploy instead of the conventional method).

At the club launches, I hear quite a few HPR models with a whistle after burnout. It is very cool. Never really wondered about the cause?

Banzai88 said:

Several split fin rockets are known whistlers, but seem to do it best when the adjoining inner edges are square. Did you bevel the leading/trailing edges of the fins?

Click to expand...

I have a Binder Raptor with the dual split fins on the fin can, with about a 1 3/4 inch gap between.
The leading edge of the front fins and trailing edge of the rear fins were beveled - the TE of the front fins and leading edge of the rear fins were left square.
It used to whistle loudly after burn out...

Here's the Martel with it's whistley goodness.
Yes, like the other video here, you have to turn it up after motor burnout to here it, but it is good and wholesome.

[video=youtube;FHFeGZLoORE]https://www.youtube.com/watch?v=FHFeGZLoORE[/video]