18mm supersonic build (1st attempt)

I have read several articles and post about going "supersonic". A few of them were with an 18mm motor however most seem to be build threads and they say they are going to launch them and then they never post the results. Obviously they probably shredded or lost the rocket, but seriously post your results. Well after a lot of studying, research and playing on RocSim I have decided to try it for my self. First I feel I should state my intentions of this build. I would like to go supersonic (who wouldn't?) but I'm a little more realistic my aim is to survive transonic and learn what works and what doesn't perfecting my build skills so I can put it all into the real deal like an Apogee Aspire and make it boom. To start I went to rocsim, I can make a Yankee break mach all day so I thought maybe that's where I should start. Then when I was standing in line at Hobby Lobby with my 40% off coupon looking at the Yankee I noticed that the nosecone was fairly blunt when compared to the mach busting rocsim version. So I backed out. I went with a balsa nose coned Semroc Rawhide instead. The nosecone is super sharp the way it needs to be.


The build started with shrinking down the fins to get my drag down. On rocsim I could keep my Cp 1 inch aft with a 1"root 45 degree leading edge sweep .75" tip and a 1" span. I stated with the supplied balsa to be coated with fiberglass.


However I had very poor results

The fiberglass delaminated as it dried.

I happened to stumble across an old plastic clip board. Trimming and airfoiling was a beast but I'm happy with the results.



I reinforced the body tube with CA, I wrapped it in wax paper before it dried with good results.



To strengthen the fin joint I poked holes in the body tube for the epoxy to seep into. I wrapped the motor in wax paper and placed it inside for the fin gluing to avoid any innertube sanding.



I also tapered the launch lug. My next build I will probably try a tower.

Fins are all glued on. You may also noticed that the D21 is flush with the tube, this was to help push the CG forward. I figure I will be lucky if I get it back so if I need to swap in another engine I can use pliers on the nozzle.



I mixed lite balsa filler with epoxy to make fillets, worked pretty well, very sandable. I would rather have used micro ballons but I live in an apartment and those things are nasty.

Is it possible the larger less aerodynamic cone reduces the load on the fins? Everything has a give and take.

I built the Apogee Aspire and attempted to go supersonic...

The poor thing just wasn't up for the task & re-kitted itself about 80' up. I recovered the nose cone and most of the body tube.

It was probably the single most insanely fun launch I've had !!

It was not long after this that I discovered that Apogee had a set of instructions on how to toughen the rocket to survive going transonic

The plastic fins look cool What motor are you looking to launch on ?

Krusty

View attachment Boomhower1(Semroc-Rawhide).rkt

^Here is the simroc file^





It claims Mach 1.05, but my goal is survivability. I wont be doing any type of verifying with onboard instruments as that would just add weight. If I get it back, I may work something in later.

The plastic fins look cool What motor are you looking to launch on ?

Krusty[/QUOTE]

Thanks on the fins, I have three single use Aerotech D21-7s

ChesleyB said:

If I get it back, I may work something in later.

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Use some mylar survival blanket as a streamer - you should see it glinting as it comes down, well, as long as you launch on a sunny day

ChesleyB said:

Thanks on the fins, I have three single use Aerotech D21-7s

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Make sure you buy yourself one of these before the launch :wink:

Krusty

I plan on standing really far back. Mach is about 1130ft/s and a 45 auto goes about 850ft/s the rocket should be close to mach in a half a second so I'm sure the sights wont be as good as the sounds. I probably wont see it leave the pad.

You probably won't see it until slows down enough for you to see the delay smoke. I used a D21-7 on an Estes Rampage (2061) and did not see it until the delay smoke appeared a few seconds after launch.

krusty said:

The poor thing just wasn't up for the task & re-kitted itself about 80' up.

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That is classic. I scratch built one and tried the same thing. Same results. I shredded the fins.

Good luck.

mwtoelle said:

You probably won't see it until slows down enough for you to see the delay smoke. I used a D21-7 on an Estes Rampage (2061) and did not see it until the delay smoke appeared a few seconds after launch.

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How well did that work? is it super stressful on the rocket or can you do it over and over?

mwtoelle said:

You probably won't see it until slows down enough for you to see the delay smoke. I used a D21-7 on an Estes Rampage (2061) and did not see it until the delay smoke appeared a few seconds after launch.

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How well did that work? is it super stressful on the rocket or can you do it over and over?

I built my "mongoose 18" about 2 years ago. It was standard unreinforced paper tube, a plastic Nose Cone and sheet styrene fins. Assembled all with 5 minute epoxy.
It just disappeared on a D21 at Hellfire 16. Someone found it and left it at the LCO table, The tube was dented a little, but other then that, no damage.


Alex

Lots of sanding and painting complete, these pics are pre clear coat. The lighting may not do it justice but its a bright pink. I did end up using a space blanket for the streamer, I had one laying around for that purpose. My original plan was to use a fishing lure swivel and fold the plastic in a way that would cause it to spin like fishing lure in the the air hopefully making it "flash". I may do this an the future.



I have been doing a lot of research on CP as I am a little fearful of this rockets stability. Rocksim and the barrowman equation confirmed that its about one diameter aft of CG but the sting test is a little finicky. Basically to get it to fly strait i have to start it strait and go real fast at first, however if it starts backwards it will stay that way. I have read that due to angle of attack the string test can give false negatives on marginal rockets due to angle of attack. The engineer in me thinks it will fly strait even though its close because numerical methods say it will. Also its going to be going fast off the rod so I believe it would react the way it did one the string, staying the way it started and as it burns propellant it will become more stable. I wish I could try it on weaker engines but that wouldn't be accurate since the weight is not the same. Any advise?

The streamer will flash ok just by itself

Can you post the rocksim file for us to poke around in?

Krusty

ChesleyB said:

How well did that work? is it super stressful on the rocket or can you do it over and over?

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These flights can be very stressful on the shock cord and streamer. I managed to retrieve the bottom part of the rocket, but lost the payload section shock cord and streamer. I replaced the top part of the rocket and still fly it, but not on D21s or D24s (reloadable). You should wait for a near perfect day with clear sky and calm wind. Note that this flight was made in April of 1995 before the availability of RockSim and of myself having internet access, so I went with the best guess method based on the flying experience that I acquired over the years.

krusty said:

The streamer will flash ok just by itself

Can you post the rocksim file for us to poke around in?

Krusty

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Its in the sixth post down, its a link. says "Boomhower1"

ChesleyB said:

Its in the sixth post down, its a link. says "Boomhower1"

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Well, so it is!! Sorry, I missed it before!

Stability margin is 1.3 - that's going to be fine. Adding 3g to the base of the nose cone (ie. next to the screw eye) bumps the stability to 1.85 but drops your speed to 1131fps - much closer to mach transition. Everything's a trade-off!

Should be an awesome flight as-is

Krusty

I think I'm interested in trying this. How loud would the sonic boom be from a minimum diameter try?

Mojo_wire said:

I think I'm interested in trying this. How loud would the sonic boom be from a minimum diameter try?

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It may not matter if you're not in a position to hear it anyway: https://www.apogeerockets.com/downloads/Newsletter265.pdf

ChesleyB - are you going to put a logging altimeter in there to see how fast it really goes?

edit: if you want to see a 24mm cardboard and balsa re-kit itself in the middle of a 220g boost, go to the mid-power forum and look up Don't Blink. the Mk II updated and better constructed, but not strengthened much) and Mk III (carbon fiber) versions are languishing on my build pile at the moment. When I get a break from work, I'll get back to them.

Heh, I am building an F240 (and later an H410) powered model... It'll leave this baby in the dust!

blackbrandt said:

Heh, I am building an F240 (and later an H410) powered model... It'll leave this baby in the dust!

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Congrats for you. That's not really the point of this thread though is it?

I think your F powered rocket is a tad bigger than 18mm

blackbrandt said:

Heh, I am building an F240 (and later an H410) powered model... It'll leave this baby in the dust!

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You never miss an opportunity to remind people how old you are, do you?

Green Jello said:

You never miss an opportunity to remind people how old you are, do you?

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And, all of a sudden, I realize why we should have a "like" button on TRF. :-D

Could the addition of a small altimeter in the nosecone offset the need for added nose weight? Just a thought ,but that info could be quite useful for future builds

paul.nortness said:

Congrats for you. That's not really the point of this thread though is it?

I think your F powered rocket is a tad bigger than 18mm

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only 6mm... .

You shouldn't need to add nose weight - the rocket simmed fine.

However, if you want to add an altimeter, take a look at these - www.apogeerockets.com/Electronics_Payloads/Altimeters/MicroPeak_Altimeter they're only 2g and should keep the rocket in the transonic region.

Krusty

Green Jello said:

You never miss an opportunity to remind people how old you are, do you?

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JordanT said:

And, all of a sudden, I realize why we should have a "like" button on TRF. :-D

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:rofl:

Krusty

paul.nortness said:

Congrats for you. That's not really the point of this thread though is it?

I think your F powered rocket is a tad bigger than 18mm

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I did this about 18-19 years ago using SU E45 and F55 motors. After several failed attempts and a bit of a learning curve I finally managed to launch one that held together through the entire flight. Unfortunately I had no way of measuring anything so I could only assume that the rocket went super sonic.

Really, what else are you gonna do with 18mm E and F motors but push the limits of min diameter design. If I'm not mistaken I think I still have either an E45 or a F55 in my motor box. Hmmmm, should I? Nah!

Since I've been a TRF member I've seen a few people try out the 18mm D21 Mach Roc, it's good to see folks pushing the limits of paper and plastic. Good luck ChesleyB, punch a hole in the sky!