Supersonic Rocket

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William Carter

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Hello. I'm looing to buy a supersonic rocket for my L2 certification. With the word supersonic and going above Mach 1 I'm sure there are many things the rocket would experience that it would not usually going subsonic. Is there anything I should know about? Thanks.
 

GalantVR41062

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I have my L2, but have only achieved transonic speeds.

The airframe will need to withstand the shock wave as the vehical crosses from transonic to supersonic speeds. Cardboard is normaly not strong enough and will result in a shred.

Also fin flutter analysis, watching the Cg and Cp change during flight to maintain a safe margin of stability and other construction techniques can be helpful for a successful flight.

What other rockets and projects have you done? What was your L1 rocket and motor? What motor are you looking at for you L2 flight? Do you have a budget for your L2 rocket? What club/field/waver are you planning to fly at?

There are a lot of fiberglass, carbon fiber, blue tube, phenolic rocket kits and the L2 motor line up has a lot of good options. From the lowly 38mm AT J270w to a AT 75mm L2200 green motor.

~John
 

Zeus-cat

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A guy in my club hit supersonic, just barely. He thought just touching Mach 1 was the way to go to minimize stress on his rocket. The rocket didn't think so when it shredded. Punch through Mach 1, don't just graze it. That transonic region is nasty, don't sit in it.
 

Exactimator

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I sent a Madcow 2.6" DX3DD to Mach 1.5 once (see info in my signature). It flew well and came back just fine. I built it stock with Rocketpoxy on the fin joints and fillets. You could do the same with a 2.6" Tomach DD.


Make sure you have at least 2 calibers of stability for mach+ flights.
 

William Carter

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Thanks everybody.

Answering these questions:

What other rockets and projects have you done? I have mainly bought and built custom low power rockets. I have only recently started to build and fly high power rockets due to the cost.
What was your L1 rocket and motor? Peregrine (Apogee) motor, H182 with a 6 second delay
What motor are you looking at for you L2 flight? I would be looking at any suitable kind of J motor (for high power I bought my motor at the site of the day based on the weather and how high I wanted it to go.) I'm not really concerned about the motor because first I just the want the rocket to supersonic. L2 isn't my main focus, so I would be okay with any motor that could achieve supersonic speeds.
Do you have a budget for your L2 rocket? Anything under 350 USD
What club/field/waver are you planning to fly at? I don't know yet but there is a launch I believe with a 12,000 foot height limit so I am planning to launch there if I can.

Also I was wondering why I can't fly in the transonic regions for too long. Its not that I don't believe everyone, but that I like to know why when I do something. Thanks!
 

GalantVR41062

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Max q being the highest dynamic pressure for the airframe as it goes supersonic.


Screenshot_20210303-193928_Chrome.jpg


Screenshot_20210303-194134_Chrome.jpg


I would us Open Rocket to build a couple rockets, select a few 38mm J motors and see what combination will achieve your super sonic goal.

I would pull up a wildman black hawk 38, and a mid sized J motor, but watch the altitude, 12000' comes quick with a project like that.

My general thinking is a rocket that is lighter will go faster then a heavier rocket with similar air drag and motor selection.

~John
 

cbrarick

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[QUOTE="GalatVR41062, post: 2110630, member: 27144"
The airframe will need to withstand the shock wave as the vehical crosses from transonic to supersonic speeds. Cardboard is normaly not strong enough and will result in a shred.
John
[/QUOTE]

sorry, no. This is misinformation. I've flown a LOC cardboard rocket (the vulconite) to 1150 mph. Completely bone stock. No glass, no carbon, just cardboard with plywood fins and paint. AND I got it back and still fly it - proof cardboard survives mach. I know I'm not alone. I also hit 1000 mph on a loc big nuke 3e. Yet another cardboard rocket.
price?
vulconite 68.5 (loc price)
J600 Red 86.96 (Wildman)
CTI 38 6GXL Case 71.07 (Wildman)

Mach at 226.53 although you might want a ebay.....it's gonna be over 7000 feet......
 

OverTheTop

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You can fly transonic for as long as you like. It can chew up a bit of energy with the turbulence. If you have any resonances in the fins that are excited by the turbulence then things can get ugly. Normally when going for high altitude flights you punch through that quickly so as to keep the energy for going higher.

Remember that the definition of "transonic" is that the airflow somewhere around the vehicle is supersonic. It might only be a small area or pocket somewhere but it still counts. That's why the speed range of what people consider transonic can be quite wide.
 

OverTheTop

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A guy in my club hit supersonic, just barely. He thought just touching Mach 1 was the way to go to minimize stress on his rocket. The rocket didn't think so when it shredded. Punch through Mach 1, don't just graze it. That transonic region is nasty, don't sit in it.
My Velociraptor sits in it for most flights. Top speed is normally M0.98 or a shade over. Never had a problem with transonic.
 

Kelly

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Max q being the highest dynamic pressure for the airframe as it goes supersonic.
Is that really true? The actual definition of max q says nothing about speed relative to mach; it's just the point in the flight where the combination of air density and velocity reaches a max. It seems to me this could happen subsonically - if it doesn't hit mach until it's gone very high (probably rare). Or it could happen well above mach, if it continues to gain velocity - at low altitudes - after going past M1 (which probably happens on many supersonic flights).
 

rocketace

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The drag coefficient spikes during the transition though M1. The build up of the pressure wave isnt perfectly even and as its building up it is creating random turbulent flow. The increased drag and the random turbulent flow is the worst place for any flight vehicle. As you get closet to M1 the Cd maxes out but the random flow decreases a bit as the shock wave has already built up. Once through M1 everything gets smooth! I remember a Bell X1 documentary where they were talking about how violent the aircraft was shaking during transonic speeds and after M1 it was just smooth and relatively quiet.


Sonic.jpg

chapt5 (nasa.gov)

I had a professor that worked on the moment of inertia equations for the Saturn V. The computers and equations back then could not predict how the vehicle could act during transonic speeds. So they calculated and graphed the sub and supper sonic and then just drew a line to connect the two for transonic.....It worked.
 

GalantVR41062

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I do not know. I have heard these terms, did a quick search, applied what I thought I have learned sense being a BAR and was quick to respond.

I was trying to stay on topic with the OP, supersonic level 2 attempt.

I have had a pressure seperation and only sub sonic or transonic flights. I would not feel comfortable flying a cardboard kit to mach 1.4 on my level 2 certification flight. I feel its important to fly to your ability for the certification, then branch out to more difficult and extreme flight profiles.

~John
 

jd2cylman

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Get a Wildman Mach 2 kit or Mach 3 kit.
The Mach 2 was designed strictly with the L1000w dms in mind.
 

dhbarr

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Both things are true: there is a period of maximum dynamic pressure, and there is a pressure rise between ~M0.8 and ~M1.2. Sometimes they are the same occurrence, sometimes not. Successful recovery requires withstanding both :)

There are parts of the airflow in this transonic regime that are supersonic, and there are parts of the airflow that are subsonic, and there are shockwaves forming and collapsing here and there, mostly around things that stick out and/or have square corners.

All of this causes stresses on the airframe that are different to those experienced when it's all subsonic or all supersonic. A lot of this buffeting compresses against the tip of the nosecone which isn't usually much of an issue; but when it causes fins to start fluttering they often decide to tear off in a big hurry.

A LaserLoc163, for example, will break mach on almost any 38mm J, many I's, and a few H's as long as you keep the weight down. I might shy away from the CTI i540 or Loki K's though 🙃 At the other end of the spectrum, of course, you can buy a carbon kit and an L2200G
 

Kelly

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All of this causes stresses on the airframe
What kind of stresses? I know how to predict/handle axial forces; and I'm familiar with the concept of fin flutter; anything else?
When someone says "you can't take cardboard supersonic" (which I know is incorrect) it makes me wonder if there is some kind of radial force that one would need to deal with.
 

dhbarr

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What kind of stresses? I know how to predict/handle axial forces; and I'm familiar with the concept of fin flutter; anything else?
When someone says "you can't take cardboard supersonic" (which I know is incorrect) it makes me wonder if there is some kind of radial force that one would need to deal with.
Messrs Prandtl, Glauer, Navier, & Stokes could tell you; but alas I cannot. However! I do know that tubes are pretty strong except at the ends or cuts.

Tip-to-tip and a wrap of tape or glass near each moving joint could give peace of mind. A stuffer tube is probably overkill given the wall thickness and small diameter, but if you choose one use epoxy otherwise you'll get stuck :)
 

teepot

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I built a rocket with the aim of going supersonic on an I 500. I used a 2.2" heavy weight tube from BMS and a full length coupler. It has 1/4" Birch ply fins. It came in at 40 ounces with chute and no electronics. On an I 500 Thrustcurve says it will go 974 fps and make 6000'. So its too heavy. On a J 435 it will make 1121fps to 7300'. So I'll just have to wait until I get my level 2 to try for supersonic.
 

dhbarr

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I built a rocket with the aim of going supersonic on an I 500. I used a 2.2" heavy weight tube from BMS and a full length coupler. It has 1/4" Birch ply fins. It came in at 40 ounces with chute and no electronics. On an I 500 Thrustcurve says it will go 974 fps and make 6000'. So its too heavy. On a J 435 it will make 1121fps to 7300'. So I'll just have to wait until I get my level 2 to try for supersonic.
How does a CTI i540 or AT i600r sim for you?
 

SkywackerJim

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If your goal is supersonic why not do a L1 supersonic or wait and do it after you get your L2? I myself would prefer not to be pushing limits more than necessary on a cert flight.
 

SDramstad

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I built a rocket with the aim of going supersonic on an I 500. I used a 2.2" heavy weight tube from BMS and a full length coupler. It has 1/4" Birch ply fins. It came in at 40 ounces with chute and no electronics. On an I 500 Thrustcurve says it will go 974 fps and make 6000'. So its too heavy. On a J 435 it will make 1121fps to 7300'. So I'll just have to wait until I get my level 2 to try for supersonic.
Try an Aerotech H999
 

teepot

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I have only been using SU motors. I haven't bought a casing yet. Maybe it's time.
 
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