Tips for first supersonic flight?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
Feb 10, 2017
Reaction score
Thinking about trying a launch where the rocket will break the speed of sound. I've heard these can be tricky, any tips?
1) Make sure you can find it
2) Make sure the fins don't rip off
3) See (1)
4) Allow enough CG-CP margin. One cal is usually classified as not enough. YMMV.
5) See (1)

Don't sweat too much. Have fun and learn stuff along the way, then enjoy the flight :)
What motor class power threshold are you planning for? High power? Mid power?

I only as as I’ve mentioned playing with mid power Mach flight / it’s been fun so far leading up to it - one of these days I’ll get more than a GPS tracked nose cone back... [emoji12]

Sent from my iPhone using Tapatalk Pro
It would be a Wildman Darkstar Jr on a CTI J530. Would launch with 2 trackers and a screamer.
Ok - I’m yet to venture into HPR so I’ll now promptly close my yap and learn along with you, from those who have a clue!! [emoji16]

Sent from my iPhone using Tapatalk Pro
How fast are you talking Bill, Mach 1? Mach 2? mach 3?
I have hit mach 1 many times with doing nothing special to build.
I've played around with speeds just past mach a handful of times. 2.6" fiberglass rocket, didn't really do anything crazy or special to it. I've been told/seen LOC cardboard on kits like the Vulcanite and Nuke Pro Maxx are fine past mach built stock.

In very general terms, getting through mach quickly is preferred, the larger the fins, the thicker they'll need to be, and it's very dependent on just how fast you mean. M1.2 is a lot different than M2, and 7 seconds over Mach is a lot different that a half a second. And punching right up to 1.2 is different than a slow climb in speed.
The sim says it should go to 7900' at 402 m/s (mach 1.17).
The sim says it should go to 7900' at 402 m/s (mach 1.17).

I've been in that region a few times. As long as your fins are attached well, a WM kit should do just fine. The advice I got on those speeds from our resident mach guru is to shoot for 2 calibers between the CP and CG for stability. The CP moves forward at high speeds.

The only other thing I would add is to make sure your altimeters have a mach lockout. Perfectflite Strato's, Missileworks RRC2+ and RRC3 and I'm pretty sure all the Eggtimers have that feature pre-programmed in so if you're using those you don't need to change anything.

If you download the data and look at the graphs after your flight, you'll see just how noisy the velocity trace is during boost. The mach wave really messes with the barometric sensor. And if you deploy your laundry at Mach 1, you'll be raining parts onto the range.
One of our students built a nice machbuster from 54mm LOC cardboard tubing and 1/8" plywood fins, with 5-min epoxy fin fillets. It went ~Mach 1.5 on a 38mm J. As I understand form experts on the forum here, you start needing special techniques once you hit Mach 2 or so. Fin shape can be an issue at lower speeds, but a kit designed to go supersonic should be fine there.
Run a stability sim in OR or RockSim to make sure you are not going unstable during mach transition.
It is easy to get a rocket stuck in the transonic region (say, M0.9 - M1.2) and not get beyond by not having quite enough thrust. It is easier to go through with higher thrust motors than lower thrust longer burning motors. But M1.2 is no big deal if the rocket is decently built. As mentioned, a little time a little bit over mach is quite different than a lot of time way over mach!

AeroFinSim is a helpful program to determine fin flutter. Or you can look up NACA4197TN methods if you are beyond say Mach 1.5 and are concerned of fins failing due to harmonic vibrations. Supersonic multi stages with supersonic booster stage attempting to separate can be a very daunting challenge the first time due to unique shockwave and turbulent flow properties that even a university research center would struggle to answer until it's test flown.

Suppsedly RAS Aero II is excellent for supersonic flights. Designed two multistages this year with OR with one planned for M1.7 and that one didn't survive past the audible sonic boom. One thing I never got a good grasp on is the stability margin recommended range beyond Mach 1.5. I've always kept designs between 1.7-2.2 per stage. I don't know if it's better to try a sustainer stage with 1.9 stability cal then an overstable booster at say 2.5+ for a Mach 2 application???

Literally had had a competition judge tell us that over 2 stability cal would crash. We found out that he wasn't exactly right in all cases. We knew we were pushing edge of weathervaning. And what worries me is the L-2/L-3 builds often have way higher stability cal for really higher Mach flights. Heard Barrowman wasn't accurate in supersonic flight which is why RAsAero is preferred over OR for that stuff.
The problem is CP shift with angle of attack. On separation of a 2-stage for instance, there is going to be some wiggle. The sustainer is going to see a few degrees of wobble. Hit wind shear, same thing. Fin flutter, same thing. Coning - big time off axis alignment is possible (3 fins has higher chance of coning than 4). So what happens to the CP when mach > 1 and alpha is not zero? Here is an example, from a sketch up of single stage very aggressive 88mm rocket design. Rasaero plots.

11-14-2017 5-18-39 PM.png11-14-2017 5-19-15 PM.png

What happens is going to depend on your design.

here's a post from a year ago on stability ..

I've seen way to many rockets with 1 cal stability not "go so well". At Balls one year I saw a long hybrid rocket with 14 calibers fly..just fine. I have no idea how many calibers is too many.
My builds for the fast few years have had fin spans of 1 caliber+ (a little) and a stability margin of 2.5 calibers on the pad. I've been calling these rockets "AeroPac Sport Flyers". They are not the best for altitude records, but they're not glass slippers either! Attached is a video of a 3" version of this type of rocket. Shortly into the burn...1.5 sec.. It lost one side of the exit cone of the nozzle. The rocket was able to get corrected and still flew to 24,449'.


Also look at Chris 54mm M project thread
Chuck Rogers has added some very good info....



broken noz.jpg
As noted above, just make sure that the altimeter has a mach lockout and the switch band vents are not directly below the rivets (or other fasteners) and it will be fine. I have not pushed my DS Jr. over Mach (don't have the 6XL case or know anybody who does) but we've put the 54mm Darkstar 3 to Mach 1.2+ several times with no problems running the 54mm 6XL Imax. Stock build, no extra reinforcement.

If my sims are working correctly it looks like the 15 second maximum delay will not be long enough, and you will need to remove the motor deployment charge. In that case, I would recommend putting two e-matches into the apogee deployment charge, wired in parallel, so that if one match fails the other can still light the BP. You should test that your setup (altimeter, battery, and matches) will work with a second match wired in parallel, or find someone with the same equipment who can confirm that it does.

I used to not worry about this until I got a batch of matches that had an unusually high failure rate, and I got religion after my L3 cert rocket was saved twice (including the cert flight) by the backup apogee event. A fiberglass rocket can survive a botched main deployment, but if the apogee event fails and the main deploys during the ballistic descent, it's ugly. You wouldn't think that a parachute could scream but that's what it sounds like. And you'll lose a lot more than just the parachute. And it's just plain dangerous if there are humans in the vicinity.