Upscale Time!!!

[Steve Shannon]

Yeah but 4oz or 6oz cloth?

I used two wraps of 5.7 oz over PML phenolic years ago and it worked very well.

 

[pendrin2020]

Subbed. This looks like a really fun project.

 

[BradMilkomeda]

The Gardian has a split fin design which typically whistles. I presume the whistle is caused by increased turbulence. Which I also presume causes increased force and flutter at high speeds like in the transonic zone.

Can anyone lay down the physics of split fins, whistling and fin flutter?

 

[DM1975]

The Gardian has a split fin design which typically whistles. I presume the whistle is caused by increased turbulence. Which I also presume causes increased force and flutter at high speeds like in the transonic zone.

Can anyone lay down the physics of split fins, whistling and fin flutter?

I’d like to hear it too. The physics behind it that is. I sure don’t know it but I know my 4” Thor I made with 1/8” ply and did internal epoxy fillets. It’s been Mach 1.2 I believe it was on a Ksomething dark matter so it was too loud for me to hear the whistle if their was one.

 

[Andrew_ASC]

At the wing tips there are vortices. I’m not certain if that is the only factor. However the vortices are turbulent spirals that cone outward from the tip. I imagine the vortices contact the aft trailing fin set. The aft fin set tips also produce vortices. The elongation of the whistle is due to the Doppler effect of the object moving away from you. As to what theoretically causes the whistle in the first place I am theoretically lost as you guys are as a mechanical engineer student but I would blame the boundary layer flow separation happening at the surface of the fin from laminar to turbulent flow and subsequent interferences on the aft fin set. I have heard whistles on transonic jets landing not the engine noises such as fighter jets. It’s a unique sound effect. I’m not certain what exactly causes it and I know how to mess with math across shockwaves. That still doesn’t explain the whistle. But I tried. Maybe Winston or some Aero nerd knows.

 

[DM1975]

At the wing tips there are vortices. I’m not certain if that is the only factor. However the vortices are turbulent spirals that cone outward from the tip. I imagine the vortices contact the aft trailing fin set. The aft fin set tips also produce vortices. The elongation of the whistle is due to the Doppler effect of the object moving away from you. As to what theoretically causes the whistle in the first place I am theoretically lost as you guys are as a mechanical engineer student but I would blame the boundary layer flow separation happening at the surface of the fin from laminar to turbulent flow and subsequent interferences on the aft fin set. I have heard whistles on transonic jets landing not the engine noises such as fighter jets. It’s a unique sound effect. I’m not certain what exactly causes it and I know how to mess with math across shockwaves. That still doesn’t explain the whistle. But I tried. Maybe Winston or some Aero nerd knows.

I think it may have something to do with longitudinal pressure waves but I’m not sure

It sounds best when it’s incoming artillery that doing the whistle. Sounds nice and distinct lol.

 

[grouch]

Sometimes it’s enough to know of it rather than why.

 

[DM1975]

I would guess that the split causes the air to divert enough going over the rear fin that the attack angle of the wind induces the pressure waves.

 

[rharshberger]

I have noticed that not all split fin rockets that seem to have a history of whistling do so, my 3" Frenzy XL for example does not whistle, but other of my rockets without split fins do. I wonder if some motors as they burn out don't also create a bit of a whistle due to the base bleed caused by the burning tracking grain.

 

[jimzcatz]

Just found this thread. Die hard Upscalian here!

 

[DM1975]

View attachment 361881 View attachment 361880 Just found this thread. Die hard Upscalian here!

Nice! I love that black crossbow!!!

 

[Andrew_ASC]

What model is that red one upscale of?

 

[rharshberger]

Its an Estes Explorer Aquarius

 

[jimzcatz]

Nice! I love that black crossbow!!!

Shame on you... It's a gray SWAT!

 

[jimzcatz]

What model is that red one upscale of?

The red one isn't an upscale. It's an earlier version of my Starleopard. The orange one with black windshield is a 4.15X Explorer Aquarius

 

[Andrew_ASC]

Shame on you... It's a gray SWAT!

It looks cool regardless of what it is.

 

[rharshberger]

The red one isn't an upscale. It's an earlier version of my Starleopard. The orange one with black windshield is a 4.15X Explorer Aquarius

Sorry Jim, the Explorer Aquarius looks red in that pic...at least to me, its cool no matter what color it appears ( referring to the picture of the EAon the stands).

 

[DM1975]

Shame on you... It's a gray SWAT!

Ahh man! I knew it was another name but I could barely remember the crossbow. Lol. I want to upscale one of those as well.

 

[DM1975]

Fin templates ready to cut out. I know, not much progress but tomorrow I should make some.

 

[DM1975]

Fin templates are cut, just waiting for my son to come home from school so we can cut them.

Also, I am trying to figure out where and how I want to mount an electronics bay. I want the rocket to come apart at the transition and lower body tube only to replicate the Estes one. I’d thought about a JLCR but I’ve got another idea.

I plan on cutting the BT in half and making the fin can section like a zipperless design and was thinking about making that coupler the electronics bay. I want to offset a section of 54mm mmt inside of it as a stiffer tube kinda thing that I can place a charge inside of and then stuff the main into. Then have a charge on top of the bulkhead for apogee.

 

[DM1975]

Or I could do it out of the bottom of the transition with the e bay in the top 3” section. My only worry is if the sampling holes would be ok between those front fins?

 

[Wayco]

I built an avbay into the transition of my Estes Argent, you might take a look at this build thread:
https://www.rocketryforum.com/threads/waycos-dd-argent.60600/

 

[DM1975]

I built an avbay into the transition of my Estes Argent, you might take a look at this build thread:
https://www.rocketryforum.com/threads/waycos-dd-argent.60600/

Thanks, I’ll check it out. On this one if I do that I’d put my av bay in the upper body tube and put a parachute “canister” on the bottom of the transition so I can have the apogee charge open the body up for a drogue and the main would fire the parachute out of the bottom of the transition from said canister, kinda like a main parachute canon.

I’m fairly certain I can build it, I just want to check on the sampling holes being in between each fin if it would cause an issue from turbulence or not? I could probably use paper glued on the end of the canister as a seal/burst disk to keep from having a “premature inflatuation” so to speak...

I’d also build it to have at least a small amount of it stand proud of the bottom of the transition to be clear of the apogee charge. Doing this would allow me to use a motor ejection as a stand alone or backup which I like to do when I can. At least coming down cracked open it might be salvageable if the electronics fail.

 

[DM1975]

Like this maybe?

 

[rharshberger]

Like this maybe?

I don't think there is enough room to do it that way, most of the Argent/Ventris DD conversions put the electronics in the transition itself and the upper and lower airframes are the parachute bays.

 

[DM1975]

There is not enough room in the upper body tube for a parachute and bridal unless I cut the nose cone base.

 

[Andrew_ASC]

Like the hand sketches. I still sketch stuff sometimes before chunking it into a 3D program.

 

[rharshberger]

There is not enough room in the upper body tube for a parachute and bridal unless I cut the nose cone base.

In that case that's probably how I would do it but thats my style, I am currently building a 4" Loc V2 as dual deploy so the nose cone became the main parachute bay.
https://www.rocketryforum.com/threads/richs-4-loc-v2-build.147249/

 

[DM1975]

I think a foot of 54mm tubing will hold a thin mil parachute and Kevlar bridal. I could be wrong. I’ll cut a piece and test it out tomorrow.

 

[DM1975]

I know it may make no sense but I want it to look as much like an Estes model coming down as it does going up. If I could get a parachute the size I need printed and cut to look like one of those Estes plastic parachutes I would.