Is it possible?

The Rocketry Forum

Help Support The Rocketry Forum:

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

rockets

Well-Known Member
Joined
Nov 18, 2014
Messages
1,274
Reaction score
56
Location
Denver, CO
I've been looking into some HPR rocket recently.
I found the Madcow 4" Super DX3 with a 38mm diameter.
How about sticking a 75mm motor mount in it?
I'd glass it completely, and reinforce it in any other way I could.
I'd maybe stick some nice 75mm L motors in there.
I'm sure it would go really high and pretty fast, but is it a good idea.. Would you do it?

Or I could get a 4" Madcow Frenzy and modify to have a 75mm motor mount??


Thanks,
 
I don't have either of those kits. I'm sure it's possible to machine or cut your own centering rings from 4" to a 75mm MMT. You may be adding a lot of aft mass to the rocket which you would need to balance out by adding nose weight. The longer casings wouldn't hurt CG too bad. The short ones may really hurt. You will want heavier and stronger centering rings that are thicker. You will likely lose visual sight and require a inexpensive GPS tracker or at least some kind of chute release electronics like a JCRL if you want it back after it's blown past 8,000ft depending on grains in the 75mm motor. You may need a bigger chute to account for the mass increase. It may put a huge grin on your face if you do all this. You are making a kit relatively more expensive. You might want a flutter sim calculator like AeroFinSim by Dr.Cipolla for free, or read up on a NACA 4197TN flutter test to make sure the big honkin' motor doesn't rip the fins off when this thing passes the sound barrier and keeps accelerating.

You can get a Loki 38-1200 casing which is a L-2 K load for about $90 a flight with $120 hardware. The K loads by Loki have roughly three time the specific impulse of the I motors. My L-1 Aerotech 38/480 RMS casing was $115 and the I class reloads were $50 each plus hazmat. The price nearly doubles each time you increase the diameter, so keep that in mind. It uses more material simply put and costs more.

If you trying to go L-2 to L-3 faster it may make sense to use a 75mm hole... I'd want to look into a length of airframe and length of the shortest L-3 75mm casing or single use you could get. You may find out kit is too short. This is completely possible, but it may take more money than you find "worth" it to achieve whatever you want to do. Some people spend it anyways just because they want it.
You may break way past 15,000ft and struggle to find places year round to fly it with a long enough 75mm motor. Hard to say without a sim of it first. Other people with more experience should chime in.
 
I mean, you CAN glass a pringles can and fly it, so sure.... it's more than possible.... it's likely been done.


Personally...I'd just get a 4" FG kit, or something 4" from MAC....
 
I found the Madcow 4" Super DX3 with a 38mm diameter.
How about sticking a 75mm motor mount in it?

I'd glass it completely, and reinforce it in any other way I could.
I'd maybe stick some nice 75mm L motors in there.
Would you do it?

Or I could get a 4" Madcow Frenzy and modify to have a 75mm motor mount??


Thanks,

Yes, you could go 75mm.
And stick "stiffy" couplers in it full length.
Then glass airframe & fins.
Fill the plastic NC 1/2 full of foam, to stiffen it, so won't collapse under L motor flights.

Easy option, just order them with a 75 mount.
Would I do it NO!

I would save my money & simply buy a 4 in fiberglass rocket that's designed to fly 75's.
Too much time, material costs to do mods to a paper rocket.

Wait till another round of deals comes by. Get a 100-130.00 fiberglass 54mm airframe/38 motor dual deploy something, learn how to build and fly it. Fly the heck of it & learn all that's needed to move up to a full blown 4in L-M capable rocket, for 225-300.00.

You will be amazed at how much your thought process's change in just a year or so.
Probably look back & think how silly this idea was & how cost ineffective it is.

Wisdom is just getting older & realizing how dumb we were in our youth. Happens to ALL of us!!!!:smile:
 
I've been looking into some HPR rocket recently.
I found the Madcow 4" Super DX3 with a 38mm diameter.
How about sticking a 75mm motor mount in it?
I'd glass it completely, and reinforce it in any other way I could.
I'd maybe stick some nice 75mm L motors in there.
I'm sure it would go really high and pretty fast, but is it a good idea.. Would you do it?

Or I could get a 4" Madcow Frenzy and modify to have a 75mm motor mount??


Thanks,

You are just now looking into HPR? You haven't flown a Lvl 1 motor yet and already looking at 75mm L's. I'll try to keep the sarcasm down and let sensible Mike take over.

You absolutely can do it. Just like BlackJack says. Couplers inside, glass outside. By the time you gather all the stuff, you will come out cheaper just paying ~250 for the glass version, already with a 75mm hole. Unless you are after the challenge or have patiently amassed all the parts, your route really isn't practical or cost effective. But...if we were looking for a cost effective hobby, we have failed already. We pretty much just burn money anyway, and usually don't even get to push the button ourselves.

Buy the 4" paper. Build it and fly it on H and I motors. When you are ready for the 75mm Ls, build something suited for them. You are talking about some pretty extreme forces that you likely don't yet understand. Not saying that I do mind ya, only up to a J myself.
 
Last edited:
People like a challenge, and for each person it's different... that's cool.

If this is something you want to do just because, go for it. But if you're thinking "man the cardboard Dx3 is like $80, I can do this 75mm thing SO CHEAP" ..... well...yea no that's not going to work that way.
 
OK, I'll hold off on the big stuff.
I got a lot of 29mm motors and a little bit of 38mm, with that being said, I'll fly the heck out of those, and after about 2 or 3 years, start into 54mm, and after I turn 18, I get into the 75mm stuff.
How does that sound??




Thanks,
 
You are talking about some pretty extreme forces that you likely don't yet understand. Not saying that I do mind ya, only up to a J myself.

It's hard to have a physical grasp of the forces until you launch something in HPR. Even for engineering students doing math word problems about forces nearly daily. You can stack an H onto a I in multistage and touch 22,000ft in a sim and in reality you can bust the sound barrier in boost mode of booster 0.3s. Seconds after launch then implode an interstage between the sustainer and booster on a MD CF rocket. Conservatively speaking the kinetic energy of the SEDS competition rocket for attempting record altitude for specific impulse was exceeding a light 37mm AA flak gun at the muzzle comparing to max sustainer mach and mass. A university research center predicted the nosecone would implode. They were wrong. And we were even more wrong as students. The CF tubing sheared in half due to sanding it down fingernail thin from zero experience at this and not having a true earned respect for forces involved. We had a 340 lbf thrust booster motor acting on a 2 lbm rocket. It was a bloody miracle it made it to 2,500ft flew straight, then interstage implosion from wobbly connection. The whole airframe simply shredded above a case bonded casing to airframe tubing section. Oddly the fins well some of them were somehow still attached despite being airfoiled and too thin. Shoulder cracked at nosecone, oddly nosecone survived, electronics fell to earth no chute and survived the fall with batteries disconnected. Could not turn head fast enough vertically to track acceleration off pad. 168G's pulled on a whimpy "pud knocker motor" as this 14 year old thinks ( not trying to insult, he just hasn't tried one and seen it first hand), 38mm I1299N-P Aerotech just a lowly L-1 motor... It was touching a K class thrust curve for that puny third of a second. No one on TRF was posting MD multistages with it. Shared the same fuel composition as Orbital Peagsus with a fast burn time. Triple the thrust curve of the other I motors for class. Saw one thread disappearing act, how it ripped apart another single stage rocket no recovery or something from G forces involved. We found out hard way why. We lost tracking with FCC GPS tracker with a group of satellites. Not even a full I. The other was a CTI 29mm H motor which didn't light from robust raven logic. We'd spent months and thousands of dollars not having experience to get that far to make UROC launch date from nothing. It wasn't a kit you could go buy anywhere. It was our first design and clearly we were over our heads experience wise. Not treading water. Learning by Drowning. We didn't have mentors and reality was a hard teacher on forces in forced involved on HPR materials.

Halved the altitude expected, went to smaller airframe diameter, used two H motors, built something simple for a fifth the cost, and it worked well enough to meet mission requirements by competition on fiberglass airframe not sanded on a single stage then went third nationally. The old geezers in Utah had told us to our faces do not maximize thrust on rockets anymore, you want maximum burn time for altitude. We did not know that previously. I maximized the specific impulse as close to 640Ns with a maximized thrust on the lightest smallest diameter and most aerodynamic design I could do and that was a very poor decision for zero experience. We never had get there itis. It was a poor mistake from zero experience in HPR. First HPR I had designed and it had to be a multistage for the senior design class/comp, bad combo. It sure wasn't like any Estes low power flight I'd previously done as a child. Now the second iterations of nosecones worked as designed, but a commercial reload exploded from wiring lack of experience head end ignition.

Now David is going to tell me to go take my meds... I thought my personal story of screwup may someday save this 14 year old kid a moment from dreams being crushed by physics, budgets, and reality. Not what happens on paper, but what real world can throw your way when your wrong. You gotta get back up and try again. Just because you can computer model then manufacture a NACA 65A supersonic airfoil on a hobby rocket doesn't mean you should. Just because you can stuff a 75mm motor into a DX3 doesn't make it wise. And you can implode HPR's into tiny little carbon fiber fragments on a lot less thrust than a 75mm.

The closer to pushing a altitude record the more exponentially wrong things can go badly and you won't get your rocket back. Purdue also shredded a 20,000ft SEDS rocket this year named Proton or whatever...
Unlike Purdue, We had the guts to launch something lower performance a second time around at own expense and in a very humbled attempt to learn from our mistakes. Only 20 of 88 teams actually made it past launch phase into HPR multistages. Because the competition asks complete noobs to "just try it bro" and it's just hard enough to get a basic design subsonic to work on smaller L-1 motors and get past paperwork. And engineering students are naturally slightly arrogant thinking we think this will work the math theory says this. Then reality just slaps them real hard because its not always a cute theory.

Heard a story of $100,000 liquid rocket Vulcan 1 at UCSD had crashed because one altimeter wire disconnected. Heard another story of another team's liquid rocket having fin stabilized canards and ripping itself to pieces at 8,000ft. The engineering students didn't know the bending moments exactly in reality that were to occur during flight on the angled fins. They knew there were forces in component directions.

We had met L-3 guys and gals at UROC with rockets longer than our vehicles, airframes imploded, and they had more experience than us. Complete aluminum and fiberglass glassed shattered airframes and casings dented from forces involved. Even saw a huge sugar rocket explode at Hellfire 22 first hand. The forces involved threw a flaming sugar grain possibly 50-60ft into air from the pad, and popped the nose off. It was 12ft tall. The forces involved are mind blowing and the paper values do not reflect the true consequences of mistakes seen in person.

Start with the 29 or 38mm H or I because the forces only get greater. Still had to sign a death release and insurance health form waiver to do anything for college competition. Thankfully on your own you don't need to sign that form. Everyone that has pushed the limits has a shredded, exploded, or imploded rocket to show for lessons learned. Lessons that no book will teach you.
 
OK, I'll hold off on the big stuff.
I got a lot of 29mm motors and a little bit of 38mm, with that being said, I'll fly the heck out of those, and after about 2 or 3 years, start into 54mm, and after I turn 18, I get into the 75mm stuff.
How does that sound??




Thanks,
Sounds fairly reasonable. I'd challenge you not to worry too much about anything after flying the heck out of mostly 29's & 38's.

Build a rack rocket & work up to 5-stage. Do NARTREK. Try a PML Ultimate IO. Recover a d21 with a takeoff weight <1oz. Make a mach-breaking tubefin.

If all these ideas sound like crap, that's because they're mine and not yours. You do you, and don't worry so much about spending budget you don't have on rockets you can't fly with motors nobody can sell you.
 
Sounds fairly reasonable. I'd challenge you not to worry too much about anything after flying the heck out of mostly 29's & 38's.

Build a rack rocket & work up to 5-stage. Do NARTREK. Try a PML Ultimate IO. Recover a d21 with a takeoff weight <1oz. Make a mach-breaking tubefin.

If all these ideas sound like crap, that's because they're mine and not yours. You do you, and don't worry so much about spending budget you don't have on rockets you can't fly with motors nobody can sell you.

Do tell good sir! 6" riding a 75mm? Now I want one! I love the look of IO, just haven't got one yet.
 
I think the 4" cardboard DX3 is an excellent first high power rocket. I would highly recommend getting the avionics bay and start with using an altimeter like a Strattologger for deployment and using the motor as a backup deployment. Built with a motor installed it will almost certainly be too heavy to fly as a low or mid-power rocket. Looking at your website, I would also suggest taking advantage of the sale Estes has right now for three mid power rockets, pad, and launch controller for $45. https://www.estesrockets.com/clearance/000-2017-bundle-8-1 Mount an altimeter in one. Strap a camera on the outside of one. Get a 'low cost' GPS tracker from missile works, Eggtimer, tracker, featherweight, etc. (you'll need it for high power eventually). Learn how to use it. Fly those much less expensive Aerotech loads for the 24/40, 24/60, and 29-40/120 case for a year or two, then build & bring that Super DX3 to the field and totally own your level one flight.
I've attached an open rocket model of a DX3, and pictures of my son four years ago with is first mid power rocket, and last year at Midwest power with his first big project (he was finally old enough for the Tripoli mentor program), and his Mentor level one project last fall ('Reddy' was too big for a level 1).View attachment superdx3sm.ork

16159886353_2be1cd1caa_o.jpg30546981290_a77a391b38_o.jpgOrion cert flight.jpg

P.S. Orion had 40-50 mid-power flights using an Altus metrum altimeter/GPS and looking at the data of every flight, including 3 scratch built mid-power rockets each flown a half a dozen or more times before he flew his first high power rocket.
 
Last edited:
It's hard to have a physical grasp of the forces until you launch something in HPR. Even for engineering students doing math word problems about forces nearly daily. You can stack an H onto a I in multistage and touch 22,000ft in a sim and in reality you can bust the sound barrier in boost mode of booster 0.3s. Seconds after launch then implode an interstage between the sustainer and booster on a MD CF rocket. Conservatively speaking the kinetic energy of the SEDS competition rocket for attempting record altitude for specific impulse was exceeding a light 37mm AA flak gun at the muzzle comparing to max sustainer mach and mass. A university research center predicted the nosecone would implode. They were wrong. And we were even more wrong as students. The CF tubing sheared in half due to sanding it down fingernail thin from zero experience at this and not having a true earned respect for forces involved. We had a 340 lbf thrust booster motor acting on a 2 lbm rocket. It was a bloody miracle it made it to 2,500ft flew straight, then interstage implosion from wobbly connection. The whole airframe simply shredded above a case bonded casing to airframe tubing section. Oddly the fins well some of them were somehow still attached despite being airfoiled and too thin. Shoulder cracked at nosecone, oddly nosecone survived, electronics fell to earth no chute and survived the fall with batteries disconnected. Could not turn head fast enough vertically to track acceleration off pad. 168G's pulled on a whimpy "pud knocker motor" as this 14 year old thinks ( not trying to insult, he just hasn't tried one and seen it first hand), 38mm I1299N-P Aerotech just a lowly L-1 motor... It was touching a K class thrust curve for that puny third of a second. No one on TRF was posting MD multistages with it. Shared the same fuel composition as Orbital Peagsus with a fast burn time. Triple the thrust curve of the other I motors for class. Saw one thread disappearing act, how it ripped apart another single stage rocket no recovery or something from G forces involved. We found out hard way why. We lost tracking with FCC GPS tracker with a group of satellites. Not even a full I. The other was a CTI 29mm H motor which didn't light from robust raven logic. We'd spent months and thousands of dollars not having experience to get that far to make UROC launch date from nothing. It wasn't a kit you could go buy anywhere. It was our first design and clearly we were over our heads experience wise. Not treading water. Learning by Drowning. We didn't have mentors and reality was a hard teacher on forces in forced involved on HPR materials.

Halved the altitude expected, went to smaller airframe diameter, used two H motors, built something simple for a fifth the cost, and it worked well enough to meet mission requirements by competition on fiberglass airframe not sanded on a single stage then went third nationally. The old geezers in Utah had told us to our faces do not maximize thrust on rockets anymore, you want maximum burn time for altitude. We did not know that previously. I maximized the specific impulse as close to 640Ns with a maximized thrust on the lightest smallest diameter and most aerodynamic design I could do and that was a very poor decision for zero experience. We never had get there itis. It was a poor mistake from zero experience in HPR. First HPR I had designed and it had to be a multistage for the senior design class/comp, bad combo. It sure wasn't like any Estes low power flight I'd previously done as a child. Now the second iterations of nosecones worked as designed, but a commercial reload exploded from wiring lack of experience head end ignition.

Now David is going to tell me to go take my meds...
I thought my personal story of screwup may someday save this 14 year old kid a moment from dreams being crushed by physics, budgets, and reality. Not what happens on paper, but what real world can throw your way when your wrong. You gotta get back up and try again. Just because you can computer model then manufacture a NACA 65A supersonic airfoil on a hobby rocket doesn't mean you should. Just because you can stuff a 75mm motor into a DX3 doesn't make it wise. And you can implode HPR's into tiny little carbon fiber fragments on a lot less thrust than a 75mm.

The closer to pushing a altitude record the more exponentially wrong things can go badly and you won't get your rocket back. Purdue also shredded a 20,000ft SEDS rocket this year named Proton or whatever...
Unlike Purdue, We had the guts to launch something lower performance a second time around at own expense and in a very humbled attempt to learn from our mistakes. Only 20 of 88 teams actually made it past launch phase into HPR multistages. Because the competition asks complete noobs to "just try it bro" and it's just hard enough to get a basic design subsonic to work on smaller L-1 motors and get past paperwork. And engineering students are naturally slightly arrogant thinking we think this will work the math theory says this. Then reality just slaps them real hard because its not always a cute theory.

Heard a story of $100,000 liquid rocket Vulcan 1 at UCSD had crashed because one altimeter wire disconnected. Heard another story of another team's liquid rocket having fin stabilized canards and ripping itself to pieces at 8,000ft. The engineering students didn't know the bending moments exactly in reality that were to occur during flight on the angled fins. They knew there were forces in component directions.

We had met L-3 guys and gals at UROC with rockets longer than our vehicles, airframes imploded, and they had more experience than us. Complete aluminum and fiberglass glassed shattered airframes and casings dented from forces involved. Even saw a huge sugar rocket explode at Hellfire 22 first hand. The forces involved threw a flaming sugar grain possibly 50-60ft into air from the pad, and popped the nose off. It was 12ft tall. The forces involved are mind blowing and the paper values do not reflect the true consequences of mistakes seen in person.

Start with the 29 or 38mm H or I because the forces only get greater. Still had to sign a death release and insurance health form waiver to do anything for college competition. Thankfully on your own you don't need to sign that form. Everyone that has pushed the limits has a shredded, exploded, or imploded rocket to show for lessons learned. Lessons that no book will teach you.



My turn!! The kid wasn't asking for your life history.
 
Now David is going to tell me to go take my meds... I thought my personal story of screwup may someday save this 14 year old kid a moment from dreams being crushed by physics, budgets, and reality.
Start with the 29 or 38mm H or I because the forces only get greater. .....Still had to sign a death release and insurance health form waiver to do anything for college competition. Thankfully on your own you don't need to sign that form. Everyone that has pushed the limits has a shredded, exploded, or imploded rocket to show for lessons learned. Lessons that no book will teach you.

Andrew- naw, that story was relatable to the topic at hand. I agree too.

My turn!! The kid wasn't asking for your life history.

Meh, it related.
 
The old geezers in Utah had told us to our faces do not maximize thrust on rockets anymore, you want maximum burn time for altitude. We did not know that previously. .

Sounds like some folks needed to read G. Harry Stine's book.

The basics haven't changed since 1965, despite the fact available motors and materials have.
 
OK, I'll hold off on the big stuff.
I got a lot of 29mm motors and a little bit of 38mm, with that being said, I'll fly the heck out of those, and after about 2 or 3 years, start into 54mm, and after I turn 18, I get into the 75mm stuff.
How does that sound??




Thanks,

That sounds like a much better plan. I would suggest not even going to a 54mm motor mount until you're nearly 18 and ready for L2 certification. 29-38mm will let you learn on relatively cheaper loads with hardware you already have. You're probably not going to fly 54mm motors much on I's after you cert L2, so you'll have an orphan casing. At least on the CTI side, 54mm assembles just the same as 29mm, so there's not much to learn by stepping up a case size for practice until you're ready for J's and K's. You can do your L2 on the very top end of 38mm if you like, then jump straight to 75mm.

+1 to getting a rocket designed for your goals in the first place instead of hacking it to suit. By the time you glass a cardboard rocket, you'll have spent more money than just buying a glass one for a heavier rocket that doesn't perform as well. The only reason to do it is as a relatively cheap intro to learning how to glass a rocket.
 
If the OP picks up either a Aerotech 38-720 or CTI 5 grain casing only either should screw into the existing brand of 38mm closures he already has for an L-2 motor in J level. He could use a disposable DmS 38mm H motor for the L-1 flight or pick up shorter casings for either H or I loads. The I loads in 38mm are 480 casing AT or 4G CTI if he wants more thrust before trying an L-2 load.
 
And the cheapest I can find a AT 75mm hardware set for L-2 is $420. That doesn't even include the reload. At which point I could build, equip, and fly a 38mm MMT L-2 Kit complete with casing, reload, and hardware in 38mm.
I won't even touch 75mm until L-3. Supposedly Loki has a 54mm M load somewhere.
 
Here's all of the sweet motors and hardware I have:
AMW/KBA 38mm 640 hardware set.
CTI Pro 29 3 grain set.
CTI G106SK & H163WT.
Aero-Tech G53FJ, E18W, F40W, G75-7M, H115DM.
___
So, I have a LOT of AP to burn. :p
And for big rockets, here is what I have:
Estes Partizon.
Estes Mammoth.
LOC Precision with 38mm MMT & DD.
And.. That's all!!! :)



Thanks,
 
Hey kid, have you even gotten your HP junior cert yet ?

Working very hard on that.. I'm going to be going for NAR L1 and my TRA Mentorship in a week or so.
Otherwise, my L2 brother has really helped me out, and he's helped me out with my large G motors. And, he could even support me for a small little H motor, too!



Thanks,
 
Working very hard on that.. I'm going to be going for NAR L1 and my TRA Mentorship in a week or so.
Otherwise, my L2 brother has really helped me out, and he's helped me out with my large G motors. And, he could even support me for a small little H motor, too!
Thanks,

Good Luck!
 
Working very hard on that.. I'm going to be going for NAR L1 and my TRA Mentorship in a week or so.
Otherwise, my L2 brother has really helped me out, and he's helped me out with my large G motors. And, he could even support me for a small little H motor, too!

So how is it you aren’t even a junior L1 and you have in your possession a few HP motors?
 
It’s permissible for an “of-age” certification candidate to acquire a motor for the certification flight. It’s wise to have a spare. However, legally they should be in the possession of someone 18 or over. His brother is L2.
 
Last edited:
Didn't know L-0s could own spares on certification attempts. Explains how prof had enough for the multistage project before he certified at UROC. He certified at UROC prior to project launch. That was stressful. I failed two certs already this year and bought three motors tot. Burned one I300T-14. The other I 1299 had a charge pop early before on pad so it was unburned. Then ordered a H219T-14.
 
Didn't know L-0s could own spares on certification attempts. Explains how prof had enough for the multistage project before he certified at UROC. He certified at UROC prior to project launch. That was stressful. I failed two certs already this year and bought three motors tot. Burned one I300T-14. The other I 1299 had a charge pop early before on pad so it was unburned. Then ordered a H219T-14.

Not necessarily. Although I strongly believe college students and professors benefit from the certification process, NFPA exempts universities from many of its requirements.


Steve Shannon
 
Working very hard on that.. I'm going to be going for NAR L1 and my TRA Mentorship in a week or so.
Otherwise, my L2 brother has really helped me out, and he's helped me out with my large G motors. And, he could even support me for a small little H motor, too!

Thanks,

Sorry to burst your bubble, but look at the weather. I launch with WSR and our field is 11 miles from yours. Right now I expect our launch on the 16th to be cancelled. Near 100% chance of snow Tuesday, Wednesday, and Thursday, dropping to 60% on Friday and then the killer, 50% chance of rain on Saturday, but even worse, the low is 33. All that wonderful snow is going to melt and make a lot of mud.

I think TMO is done until March after this launch. However, at WSR we don't take off for January or February. You could always come over to our field and try to cert. We are a NAR club by the way and have lots of L1, L2 and L3 members. We even have the odd Tripoli L3 member (and I do mean odd!).
 
Back
Top