E3M ~ 4.5" O motor project

[patelldp]

I have been slaving away at this project the past couple days, fins will be attached tomorrow. They will be bonded directly to the case via 3M 8115 epoxy.

View attachment 278315View attachment 278316

My mom's chickens approve...

View attachment 278317

You sniped the top left corner so many times that you broke the cord holding the shooter tutor?

 

[mannyskid]

You sniped the top left corner so many times that you broke the cord holding the shooter tutor?

Not as good as the time my friend and I spent a whole day and sawed a door in half with pucks haha.

 

[pyrobob]

View attachment 278316

Sweet!

 

[butalane]

You sniped the top left corner so many times that you broke the cord holding the shooter tutor?

ahahahhahaa. Awesome.

 

[mannyskid]

First set of fillets down. The answer to your question is yes, I am crazy enough to epoxy the G10 fins to my case.

The epoxy is 3M 8115 panel bonding epoxy if anyone is wondering. It is very similar to another 3M brand epoxy you are all familiar with (proline 4500) but is a little thicker and had excellent adhesion properties with both Al and FG.

 

[bobkrech]

Quick question. Did you use a primer on the aluminum to enhance the surface adhesion?

Bob

 

[markkoelsch]

What is the Tg of the epoxy, and how hot is the case going to get?

 

[dixontj93060]

I looked it up last night and didn't find the Tg. There were only tests up to 180F for primed steel bonds (https://multimedia.3m.com/mws/media/443356O/tds-3mtm-automixtm-panel-bonding-adhesive-08115.pdf).

 

[mannyskid]

Quick question. Did you use a primer on the aluminum to enhance the surface adhesion?

Bob

No, I wanted to but my local Grainger didn't have it in stock and it would have had to been ordered. I am on a tight schedule, I am leaving for SLC tomorrow and the rocket has to be shipped to Houston. The launch is three weeks from today.

What is the Tg of the epoxy, and how hot is the case going to get?

The case shouldn't get hot enough to push the epoxy past Tg, it is 0.24" wall.

 

[watermelonman]

Any brainstorming for next Black Rock season yet?

 

[Solarover12]

Beautiful launch: [video=youtube;uFwnpFNn5A0]https://www.youtube.com/watch?v=uFwnpFNn5A0[/video]

 

[markkoelsch]

Very nice. All back in one piece?

 

[Solarover12]

The exit cone failed toward motor burnout, and likely effected peak altitude. Rocket also failed to separate at apogee. It was heard a short time later breaking the sound barrier and impacting the ground at over 700mph. It's off buried in the desert somewhere. Seems unlikely the two are correlated, but it can't be ruled out. We will likely never know.

 

[patelldp]

The exit cone failed toward motor burnout, and likely effected peak altitude. Rocket also failed to separate at apogee. It was heard a short time later breaking the sound barrier and impacting the ground at over 700mph. It's off buried in the desert somewhere. Seems unlikely the two are correlated, but it can't be ruled out. We will likely never know.

You heard it breaking the sound barrier?

 

[dixontj93060]

You heard it breaking the sound barrier?

op:

 

[Barkley]

You heard it breaking the sound barrier?

On the way back down I'm assuming...

 

[dixontj93060]

On the way back down I'm assuming...

Doesn't work that way...

 

[patelldp]

I'm guessing they heard the smack and the resulting echo.

 

[Reinhard]

Doesn't work that way...

View attachment 280368

The shock wave trails the rocket, but it doesn't move backwards. You can't hear the sonic boom of an object that is traveling away from you (unless reflected).

The recently landed booster of SpaceX is an example. There was no sonic boom during launch, but there was one during the landing. It reached many observers right after it touched down, fooling many of them (including Elon) for a moment that the booster had blown up on landing.

Reinhard

 

[dixontj93060]

The shock wave trails the rocket, but it doesn't move backwards. You can't hear the sonic boom of an object that is traveling away from you (unless reflected).

The recently landed booster of SpaceX is an example. There was no sonic boom during launch, but there was one during the landing. It reached many observers right after it touched down, fooling many of them (including Elon) for a moment that the booster had blown up on landing.

Reinhard

Not only is the sonic boom spread too far out and occurs too high on ascent (https://www.apogeerockets.com/education/downloads/Newsletter265.pdf), on descent the terminal velocity is far too low to cause a sonic boom. A 30lb sleek rocket 4.5" in diameter has a terminal velocity of less than 400mph--no where near the speed of sound.

BTW, there most definitely is a sonic boom on launch of a Space-X booster, you just aren't in a position to hear it.

 

[G_T]

Also at sufficiently high altitude, the rocket can accelerate above mach on the way down. But as air thickens, the rocket will decelerate to subsonic.

Gerald

 

[Barkley]

Not only is the sonic boom spread too far out and occurs too high on ascent (https://www.apogeerockets.com/education/downloads/Newsletter265.pdf), on descent the terminal velocity is far too low to cause a sonic boom. A 30lb sleek rocket 4.5" in diameter has a terminal velocity of less than 400mph--no where near the speed of sound.

BTW, there most definitely is a sonic boom on launch of a Space-X booster, you just aren't in a position to hear it.

I had forgotten that decent terminal velocity is subsonic, but knew the cone didn't go backwards. I figured it had to be on the way back down.

 

[jsdemar]

Some at the launch thought they heard the nozzle hit the ground. I was out on recovery 3 miles away and just heard the motor.

Rockets of our size do not make a sonic boom signature, up or down. On the way up, the cone is dispersed sideways, outside of where we're standing, and also masked by the sound of the motor. On the way down, if terminal velocity allows it high up, the Mach shock is outward and weak, dissipated before reaching the ground very far away. A horizontal craft with a large cross-section is needed to hear a "sonic boom".

 

[bobkrech]

The exit cone failed toward motor burnout, and likely effected peak altitude. Rocket also failed to separate at apogee. It was heard a short time later breaking the sound barrier and impacting the ground at over 700mph. It's off buried in the desert somewhere. Seems unlikely the two are correlated, but it can't be ruled out. We will likely never know.

If the rocket was not recovered: 1.) how do you know the exit cone failed; and 2.) it is unlikely that the rocket was supersonic on impact.

Manny appears to have used RASAreo to simulate the flight and that will provide a velocity versus time and altitude for any flight profile including a ballistic flight profile. Ask him to run the sim with no deployment and you'll get the actual impact velocity which will not be supersonic.

Bob

 

[Solarover12]

If the rocket was not recovered: 1.) how do you know the exit cone failed; and 2.) it is unlikely that the rocket was supersonic on impact.

Manny appears to have used RASAreo to simulate the flight and that will provide a velocity versus time and altitude for any flight profile including a ballistic flight profile. Ask him to run the sim with no deployment and you'll get the actual impact velocity which will not be supersonic.

Bob

The rocket was indeed supersonic on the way down. We definitely heard the boom and for a minute thought a bomb went off. The telementrum sent a couple packets on the way down and clocked it at over 700mph (I think the actual number was 760, I'd need to double check though). My guess is that the .25" wall case helped lol. Strangely enough the exit cone was heard falling and found just 300ft or so from the tower.

 

[dixontj93060]

The rocket was indeed supersonic on the way down. We definitely heard the boom and for a minute thought a bomb went off. The telementrum sent a couple packets on the way down and clocked it at over 700mph (I think the actual number was 760, I'd need to double check though). My guess is that the .25" wall case helped lol. Strangely enough the exit cone was heard falling and found just 300ft or so from the tower.

The only way that would happen is if the rocket was unstable, flipped 180 degrees in flight and was still under thrust on the way down. Beyond that what you describe breaks all laws of physics.

Maybe your boom came from a mid-air CATO and the sound reached you as the rocket was in ballistic descent.

 

[jsdemar]

Saw the space shuttle land before and it gives off a double sonic boom.

I heard a sonic boom when a little Estes Space Shuttle glider was landing near White Sands. It was during one of our Apollo 40th anniversary public demo launches. At the exact same time, an F22 Raptor flew over the launch site.

 

[Burner]

The stratofox webite is no more however they used to have an absolutely awesome recording of the CSXT rocket in 2004 IIRC coming down with two distinct sonic booms from the booster and payload section. It was a much larger rocket than this obviously, but if anyone has it I’d love to hear it again.

 

[Xrain]

The only way that would happen is if the rocket was unstable, flipped 180 degrees in flight and was still under thrust on the way down. Beyond that what you describe breaks all laws of physics.

Maybe your boom came from a mid-air CATO and the sound reached you as the rocket was in ballistic descent.

If the rocket has a small enough cross sectional area, a high mass, and goes high enough that it goes supersonic in the thin air on the trip down; It's entirely possible for it to be going supersonic when it hits the ground. This is because it has enough momentum and the drag force is low enough that it doesn't slow down much.

We did a sounding rocket launch and on the return trip it hit the ground doing ~mach 2. We had both radar and vehicle telemetry. Granted this went to 99.8km but it was also 14" in diameter.

[video=youtube;SjV8fdqVZ2g]https://www.youtube.com/watch?v=SjV8fdqVZ2g[/video]

Not sure if their rocket actually hit the ground above mach as some simulations would be needed. But hitting the ground much faster than terminal velocity is very possible. Especially if the rocket did a ballistic arc over.

 

[dixontj93060]

If the rocket has a small enough cross sectional area, a high mass, and goes high enough that it goes supersonic in the thin air on the trip down; It's entirely possible for it to be going supersonic when it hits the ground. This is because it has enough momentum and the drag force is low enough that it doesn't slow down much.

We did a sounding rocket launch and on the return trip it hit the ground doing ~mach 2. We had both radar and vehicle telemetry. Granted this went to 99.8km but it was also 14" in diameter.

[video=youtube;SjV8fdqVZ2g]https://www.youtube.com/watch?v=SjV8fdqVZ2g[/video]

Not sure if their rocket actually hit the ground above mach as some simulations would be needed. But hitting the ground much faster than terminal velocity is very possible. Especially if the rocket did a ballistic arc over.

Of course, but do the math. I already did it 8 or 10 posts back. Estimate 30 lbs with just the case no propellant, 4.5" dia. and I gave them a generous Cd of 0.6. Terminal velocity is still less than 400mph.