There is no way that this rocket is successful, but darn it I am going to try! (Mach 5+ Composite Case 38mm rocket)

[Brainstormz123]

My goal with this rocket is eventually to compete it in hamster dance at Balls next year. I have had 3 attempts at this so far. The first one immediately burned through as the propellant is basically an I1299 but a bit longer. I don't have a liner because that would be too much mass (definitely one of the choices you can make). The second one, I remade the first one and static fired it, and it also immediately burned through.

My third attempt I bonded the grain faces together to not have flames touching the casing, and that appears to have allowed the motor to work. Some pics of that flight here (https://www.rocketryforum.com/threa...se-i1400-rocket-launched-last-weekend.183053/). Last weekend, the nosecone was stumbled upon not attached to the rest of the rocket and that tells me it didn't work.

Video of the most recent flight, it moved pretty quick (Listen with sound on)
View attachment 531222-d2cba970f1aaf2e0d4f8f4e016403732.mov

 

[Brainstormz123]

That leads me to the build for this weekend, I've decided to get greedy and openrocket and rasaero are both saying 2800 m/sec (mach 8.3) with the roughest settings with my current rocket. The reason it sims to so fast is because the rocket weighs like nothing. I've also added more propellant and we shall see how this works.

The parts:

Casing-
Composite carbon sleeve wrapped on a mandrel and then removed. It has 2 layers of thin glass and then 1 layer of thick carbon to hold the pressure and act as a sort of liner. Propellant pictured next to casing in the picture below



Fins-
Compressively molded carbon. I made a lot of them and quality controlled my way into the best 4 fins that have ever seen this planet. The molds are PLA and carbon + epoxy hairballs get put in them and squeezed. For quality control, I am looking for 4 fins that I put on the scale and they all are the same weight (to the hundreth of the gram). Pictured are half of the reject fins I made


Nosecone-
Made on a printed male mold with 4 layers of fiberglass using condoms as mold release. I wanted to do an integrated shoulder, but due to a severe oversight (should have printed in ABS if I wanted to dissolve out the mold), I ended up chopping off the coupler and laying it up separately.


Coupler-
Made the same way as the nosecone, but only 3 layers of glass. Follows the internal geometry of the nose at the top and will fit inside the body tube.


The rocket-
Fins bonded on and coupler bonded to the nosecone. I got to sand everything smoother and shorten the body tube by around 8 inches (I made it too long so I had room to mess up). Also, I will be painting it white so its easier to see. Lets see how it goes.

 

[Brainstormz123]

This rocket will be flying with live telemetry as well as custom tracking (shameless plug https://www.rocketryforum.com/threads/custom-comspec-receiver-compatible-beacons.183577/) so should get some good data on speed no matter what happens. Will be single deploy with a tiny chute since it will not weigh very much post burnout (sub 100 grams)

 

[Brainstormz123]

Oh I forgot to mention, that even though the sims say mach 10+ if I set the surface finish to smooth paint, it also simulates to only 5000ft apogee. This is because drag is crazy high and it claims to slow down at 500 Gs. I have 0 faith in these sims, but would be a really fun hamster dance rocket for next year.

 

[Rocketjunkie]

You are probably way under optimum weight. Have you simmed it with more weight?

 

[Brainstormz123]

You are probably way under optimum weight. Have you simmed it with more weight?

Yeah ive simmed it with more weight, but my goal isnt altitude, its speeeeeeed (optimal weight puts me at 25k ft)

 

[Rocketjunkie]

Yeah ive simmed it with more weight, but my goal isnt altitude, its speeeeeeed (optimal weight puts me at 25k ft)

OK

 

[3stoogesrocketry]

Oh I forgot to mention, that even though the sims say mach 10+ if I set the surface finish to smooth paint, it also simulates to only 5000ft apogee. This is because drag is crazy high and it claims to slow down at 500 Gs. I have 0 faith in these sims, but would be a really fun hamster dance rocket for next year.

You must me measuring speed m/s/s. Meaning IF the motor burned for 1 second theroeticly* it might go that fast. But your motor might burn for .3 tenths of a second if it holds.

 

[Brainstormz123]

You must me measuring speed m/s/s. Meaning IF the motor burned for 1 second theroeticly* it might go that fast. But your motor might burn for .3 tenths of a second if it holds.

oh by 500 Gs I do mean 500Gs (or apparently more?), open rocket says 6000 m/s/s deceleration post burnout and rasaero says 500Gs which is why I have decided that simulation software is not up to the task of this rocket. As for max speed, if the motor burns faster than simulations, the rocket will have a higher top speed because similar impulse but much much less drag

 

[Neutronium95]

For context on just how ridiculous this project is, I ran the numbers on the overall Delta V of the rocket. This was done with some mass estimates from early in the build, so I don't know how closely they match the final mass numbers.


This is for the entire rocket. I've run the numbers for a number of commercial motors, and the highest number I've seen is 2221.6 m/s for the old O5280. A common rule of thumb I've seen is that you need about 2km/s to get to space. Of course that usually assumes a sensible burn time and twr, so that you don't hit reentry speeds at almost sea level...

I'm really interested to see where very mass optimized rockets and motors go in the future. Long burn motors are great for altitude, but I want to go fast as well.

 

[Bill S]

Wow, that is a wild project.

 

[pugachu]

That's awesome. it's been a long time stretch goal of mine to get a rocket hypersonic. I thought it would take 2+ stages of all W9 propellant. hope it holds together!

 

[3stoogesrocketry]

oh by 500 Gs I do mean 500Gs (or apparently more?), open rocket says 6000 m/s/s deceleration post burnout and rasaero says 500Gs which is why I have decided that simulation software is not up to the task of this rocket. As for max speed, if the motor burns faster than simulations, the rocket will have a higher top speed because similar impulse but much much less drag
View attachment 619832

I'm not doughting several hundred g's of acceleration. You claiming hypersonic velocities are where you are wrong severely wrong.

 

[Brainstormz123]

I'm not doughting several hundred g's of acceleration. You claiming hypersonic velocities are where you are wrong severely wrong.

Yeah I’m fairly confident its not gonna happen/work, but all the math I do and sims I run says that its very very possible to far surpass mach 5

 

[3stoogesrocketry]

Yeah I’m fairly confident its not gonna happen/work, but all the math I do and sims I run says that its very very possible to far surpass mach 5

Not a chance. Again, you cannot use M/s/s on a 3 tenths if a second burn. 6000 M/s/s is over 13,000 mph.......
Mach 5 is 3700 mph.......
Once you realize that your burn time of the motor is only burning for 30 percent of the time the sims are estimating it to go, then you will get better numbers.
3700×.3 =1100 mph or just under mach 2.
Look up Dissappearing Act on this forum. Its a virtually identical project.

 

[Brainstormz123]

Not a chance. Again, you cannot use M/s/s on a 3 tenths if a second burn. 6000 M/s/s is over 13,000 mph.......
Mach 5 is 3700 mph.......
Once you realize that your burn time of the motor is only burning for 30 percent of the time the sims are estimating it to go, then you will get better numbers.
3700×.3 =1100 mph or just under mach 2.
Look up Dissappearing Act on this forum. Its a virtually identical project.

Openrocket and rasaero both say mach 8 on the roughest settings and similar numbers if I plot it (ill send a picture later today). Im not at my computer right now, but ill send it later.

The key difference between my rocket and disappearing act is that my rocket is composite case instead of I1299 aluminum case, and more optimized for mass (about 700g lighter at burnout and 88% propellant mass fraction vs 50%). Additionally, mine has approximately 50% more impulse than the I1299.

Integrate the acceleration in that plot and youll get similarly silly numbers if you wanna compute it for yourself

 

[Brainstormz123]

Im also uncertain why you think that the motor burning faster than expected is gonna make it go slower? The same amount (or actually more impulse) is gonna come out the back, which means it will have a resulting higher speed than if the motor burned slower. Both due to reduced drag and also more impulse.

For example, what takes your rocket to a higher max speed, an I1299 or an I211? They both have similar amounts of impulse, but the I211 should have a much lower top speed

 

[3stoogesrocketry]

I don't need to run sims to know your way off. I used to fly my Shadow Aero Raven EX that was a minimum diameter carbon fiber beast that weighed 500 grams loaded no motor. Even on 38mm K motors it would barely hit mach 2. Change your units of measurement from M/s/s to M/s or MPH

 

[3stoogesrocketry]

Im also uncertain why you think that the motor burning faster than expected is gonna make it go slower? The same amount (or actually more impulse) is gonna come out the back, which means it will have a resulting higher speed.

You acceleration will be higher , but as you mentioned, the total impulse is roughly the same . So no the speed will not be faster, but it will just get there quicker. If anything your speed may be slightly less due to the extreme drag on the 1299 flight vs the 211 flight. Again your units of measurements are off. Wait till you can access your sims and change your units of measurements. Your sims are assuming your motor will have 1299 Newtons of thrust for 1 second, not 1299 Newtons of thrust for 3 tenths of a second. Your numbers are 300 percent over.

 

[FredA]

Yeah ive simmed it with more weight, but my goal isnt altitude, its speeeeeeed (optimal weight puts me at 25k ft)

So not really a Hamster contestant since that's all about altitude.
And agree, the sim's are not realistic.

 

[-Slick-Ice]

How well does OR model CF melting?

 

[Brainstormz123]

So not really a Hamster contestant since that's all about altitude.
And agree, the sim's are not realistic.

In my opinion, hamster dance is about the funny, not about winning. And I think this is really funny.

 

[Brainstormz123]

You acceleration will be higher , but as you mentioned, the total impulse is roughly the same . So no the speed will not be faster, but it will just get there quicker. If anything your speed may be slightly less due to the extreme drag on the 1299 flight vs the 211 flight. Again your units of measurements are off. Wait till you can access your sims and change your units of measurements. Your sims are assuming your motor will have 1299 Newtons of thrust for 1 second, not 1299 Newtons of thrust for 3 tenths of a second. Your numbers are 300 percent over.

Here we go, just arrived home and can now send velocity plots. Here is the raw openrocket output (with the roughest settings for drag), plotting both velocity (in red) and acceleration (in blue). The peak velocity is 1900 m/sec.


Here is the output with speed in mph:


and here is the output with the speed in mach number:


I have also made an example openrocket file (clone of the wildman mini mach) to put the I1299 and I211 into to show you the difference in peak speed. The peak velocity on the I1299 is 500 m/sec (1118 mph) compared with 388 m/sec (868 mph) on the I211. The I211 has 431 NS of impulse, while the I1299 also has 431 NS of impulse. You can see that a faster burn with similar isp and prop mass fractions results in a higher max speed. I attached the mini mach openrocket if you would like to see this for yourself.

As for your reference of your own Shadow Aero Raven EX being carbon fiber, that rocket has a metal motor case, is considerably larger in diameter (probably around 40mm OD if its proper min diameter) compared with my 34mm OD. Also, that flies with a liner and thick metal motor casing, which adds a ton of dry mass. On my rocket, the carbon "airframe" is also the motor casing. This means that my dry mass is crazy high. In addition, there is no length of body tube above the motor longer than the coupler, and the nose is also custom fiberglass composite. Where your Shadow Aero Raven EX has a non-propellant mass of around 800 grams (500 grams of rocket + 300 grams of casing+liner), mine is 110 grams. Following F=MA, having an M that is much lower, you get an A that is much higher for the same force.

The lower dry mass coupled with the smaller diameter of this rocket is the reason it is able to get so fast in simulations, which you wont see in the Shadow Aero Raven EX or really any other rockets ive seen (Andrew Reilley's GEM withstanding).

 

[Brainstormz123]

Oh and here are the plots in rasaero if you think that openrocket models high speeds poorly:



Again the stupidly high speeds are probably not gonna happen in real life (hypersonic at ground level is unreasonable), but the simulation software does claim it to be true. This is basically an I1299 rocket with 1.5x the amount of impulse, and 15% the non-propellant mass of disappearing act. Thats where the silly speeds come from.

 

[drewnickel]

There's also the factor that a shorter burn time = less impulse lost to gravity. If you have a thrust to weight ratio of 2, half your impulse is bled off by gravity during the burn. If it's say 500, you are losing a fifth of a percent of your total impulse to gravity (granted you will lose it to aerodynamic drag as well, but for a shorter burn you are still losing less of the impulse to drag until burnout). My guess is if it actually held together (which is a BIG if at those speeds), going hypersonic isn't unrealistic.

 

[Neutronium95]

I think that the intuition that a lot of people have built up with regards to amateur rockets starts to break down when the mass ratios start to get higher. Looking at the Northrop Grumman solid rocket motor catalog, pretty much every solid motor they make has a propellant mass fraction greater than 80%, and a few of them manage to exceed 90%. In contrast, the best mass fraction for a commercial motor that I'm aware of is the new Aerotech O6000, at just a hair under 70%. Per the rocket equation, delta V is dependent on just mass fraction and isp. I think that it might be possible for amateurs to get close in terms of mass ratio, but that would require a radical rethinking of motor construction, like this project.

I think that the numbers in the sim are correct. The bigger questions are if it is possible to hit the planned mass targets, and if a rocket that meets those mass targets is actually capable of surviving flight at the speeds it can hit. I am not very confident in the success of this particular flight, but am very interested in seeing where this leads.

 

[rfjustin]

OP, pull the trigger on it and find out.

 

[kramer714]

How well does OR model CF melting?

before or after the flutter....

 

[Brainstormz123]

before or after the flutter....

I checked the flutter on these fins and it claims to be good to mach 10 (I think that has to do with the really short height and them being randomly oriented carbon, but we shall find out).

T- 45 hours to launch

 

[kramer714]

I checked the flutter on these fins and it claims to be good to mach 10 (I think that has to do with the really short height and them being randomly oriented carbon, but we shall find out).

T- 45 hours to launch

I'm curious to see how the fins hold up / hold on. The motor case diameter is gonna grow quite a bit with thin fiberglass and a sock under pressure, preloads the joint - ignoring temperature. From a flutter standpoint the rigidity of the joint is part of the factor.

At the day job using 55% fiber by weight (careful about by weight and by volume) 1" long 'chopped' fibers we were getting around 5MSI as the tensile modulus, and around 4 MSI for the flex modulus (D790). Molded at about 1,000 PSI and 350F. I'm guessing you are around 2-3 MSI tensile and 2MSI flex.

Look into wetting agents and vacuum impregnation if you are trying to get higher fiber volumes.

Launching at FAR this weekend?