Hypersonic and Fiberglass--how????

Hello all!

In May, got my level one high power certification. Since then, I have begun to scratchbuild my rockets, and, lately, I have been fascinated with extreme speeds.

One of my goals is to build a 38mm or 29mm minumum diameter rocket capable of reaching hypersonic speeds (mach 5 and up). I will most likely be using blue tube material or hawk mountain fiberglass tubes for the airframe, and G-10 fiberglass fins. This brings me a problem--I have never made a high power minimum diameter rocket! I have researched fair bit, and have learned a lot about attatching fins to minimum dia. rocs, (dado slots, f-glass, etc) and have decided that fiberglassing the fin joints would be more than appropriate, but I cannot seem to find a guide to fiberglassing that pleases me.

So... how do y'all do it? Suggestions and walk thru's are welcome, etc.

Vipe

Honestly, I don't see any real way to reach mach 5+ with 29 or 38mm, pretty much regardless of motor (unless it's staged on top of a very large booster).

Viking3 said:

Hello all!

In May, got my level one high power certification. Since then, I have begun to scratchbuild my rockets, and, lately, I have been fascinated with extreme speeds.

One of my goals is to build a 38mm or 29mm minumum diameter rocket capable of reaching hypersonic speeds (mach 5 and up). I will most likely be using blue tube material or hawk mountain fiberglass tubes for the airframe, and G-10 fiberglass fins. This brings me a problem--I have never made a high power minimum diameter rocket! I have researched fair bit, and have learned a lot about attatching fins to minimum dia. rocs, (dado slots, f-glass, etc) and have decided that fiberglassing the fin joints would be more than appropriate, but I cannot seem to find a guide to fiberglassing that pleases me.

So... how do y'all do it? Suggestions and walk thru's are welcome, etc.

Vipe

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To start with, I don't think you can reach mach 5 with a commercial motor. Run them through Rocsim, but even with a nose cone and fins attached to the motor tube the CTI I-800 or the AT I-1299 (largest thrust motors I can find) won't get close.

I'm pretty sure you have to mix your own propellant to get anywhere close. That means TRA L2 certification, and only at research launches.

Once you've found a motor that will take you there, search for Jim Jarvis, who wrote great article on using carbon fiber, and the techniques he uses to reinforce leading edges for high speed flight.

As for actually applying fiberglass, it boils down to this:
1) put glass on surface
2) saturate with epoxy
3) compress the surfaces together and squeeze out excess epoxy.

How you choose to do these steps is entirely up to you, and can vary significantly depending on tools and materials on hand.

Cheers,
- Ken

Would a I1299 to a I200 get anywhere close
Maybe a better choice for booster would be a J825 to I200

I don't have rocket sim on my phone but maybe I'll try it when I get home

I've heard that RAS Aero is better than RockSim when it comes to simulating supersonic flights. Use RockSim for design and to get in the ballpark, then RAS Aero for final tweaking.

Breaking Mach 2 with a commercial motor is difficult; breaking Mach 3 likely isn't possible. The folks I know who go anywhere near those speeds are using custom-built motors.

In addition, the people flying those speeds are using aluminum components, because the atmosphere friction generates enough heat to cook composites. It even erodes the leading edges of aluminum fins.

-Kevin

Also, be prepared to spend some bucks. As in all racing, the old adage applies: "Speed cost money, son. How fast do you want to go?"

IMHO, it is a logarithmic cost curve for every Mach number achieved.

Also, I think it's better to take projects like this in phases or steps rather than an "all up/all in" flight.

A few weeks ago at a club launch, I talked with Jim Jarvis and he mentioned one of his latest projects that went south after Mach 2. He is not quite sure what happened, and this is from one of the premier rocket builders in the country.

Also, you may have to think about staging. Asking a rocket to plow through the denser atmosphere near sea level is turning a lot of speed into friction. Better to have a long-burn cruise to thinner atmosphere with a booster before "putting the spurs to it" with the sustainer.

:2:

Kevin is correct. You will be doing well to bust mach 2. You will have to keep your rocket as light as possible. I have heard of guys shreading Blue Tube when past 1.5 mach but that might be from fin flutter or something like that.

The easisest method of fiberglassing for me is to spray the rocket with 3M adhesive and then paste the cloth on the rocket. I then brush thin epoxy, I use West System, over the cloth until it is good and transparent. After it dries I go over it with West System epoxy with 407 filler to smoothe out the finish. After that it is just a matter of sanding and finishing which may take several layers to get the finish you desire. Hope that helps.

My USC group almost touched Mach 4 at Balls this year. This was with a carbon fiber-cased 115mm O motor; the vehicle's mass fraction was just over 0.6, and it had an insane internal motor geometry to get the thrust profile where it needed to be to achieve that speed. Also this year, Jerry McKinlay achieved Mach 3.2 with a 98mm O motor that he designed and built, and Ed Enyart busted Mach 3 with a Mongoose and an Al Goncalves 98mm O. All of these rockets suffered severe aerodynamic heating; any decals that were applied were ripped off, paint on the vehicles was bubbled and removed, rail buttons were melted off, and fin leading edges were burnt to a crisp. Photos attached of each of these attempts (USC fin can, note charred leading edges and peeling carbon fibers; Ed + Ed's rocket after flight, there used to be a decal and clear coat on the airframe; Jerry's fins with carbon peeling off; Jerry's nose cone with serious ablation.)

If you look at the common denominators of these rockets, they were all at least 4" diameter, with O motors or bigger. All of these rockets had major structures built from composites to save weight. The USC vehicle, in particular, was all composite, with phenolic leading edges incorporated into the autoclaved prepreg carbon fin laminate to protect them from the severe heating. All of these flights worked, but this was the first year that was the case -- everyone here has shredded in the past, multiple times, trying to break the Mach 3 barrier. Approaching even Mach 4 at low altitudes is *hard*.

cjl is correct -- you won't be able to get there with a 38mm motor; the drag and weight barriers are simply too high. Use 29mm and 38mm rockets to develop construction skill, and become good at composites. Step it up to 54mm; with a well designed 54mm bird, Mach 2 can be had. Then work slowly up to big motors and high speeds. It's a challenge, but it's really really cool when it works! Hypersonic flight is an awesome goal to have.

Sorry to say, but asking a question like how to break mach 5 on a 29/38mm motor that an L1 cert can buy is like asking how to drink lava and survive. just not possible.

The Space shuttle achieves mach 5 somewhere in the mesosphere i think, and it has heat shielding that can survive the drop from 17500 mph into the upper atmosphere reaching temperatures upto 3.5k degrees F. Maybe you should try building a kit that can break mach 1 and work up from there. this rocket is the one i'm going to be getting my L1 on breaking the mile high barrier at the same time. It can hit mach 1.5 if you build it strong with the provided fiberglass, but that's pretty much the best you'll do with a 38mm diameter unless you make your own propellent, which like the guys above said takes L2 at least, but usually the guys are L3 and have spent months/years developing the perfect formulas.

You could certainly put enough thrust into a rocket that it could reach that speed, but there's nowhere near enough burntime. The H999 burns for about 0.4 seconds, but has a per second thrust of about 2500 newtons.

Also, before you try breaking mach even 1, get rocksim or another program and learn to use it.

:y::y::y::y::y:!!!!!!!

WOW!

Thanks for the tips. Seems mach 5 is.....impossible. A little too ambitious on my part!
Anyhoo, thx for the pics and advice.

David: How the #$@% did they get that lawn dart out? Must have been tough!

Thanks again for all,

Vipe

Viking3 said:

Thanks for the tips. Seems mach 5 is.....impossible. A little too ambitious on my part!

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Now, all that said...

If speed and performance is your passion, there's absolutely no reason you cannot pursue machbusters in the Level 1 range, or whatever range of rocketry you decide to pursue.

-Kevin

29mm diameter rocket w/a g80T can mach bust. The apogee aspire built well can mach bust on a G77R. Machbusting definitely requires extra careful construction and planning, but is in no way impossible. Busting the hypersonic barrier is a little more difficult. NASA does it with two multi million lbF thrusters and liquid fuel engines

Viking3 said:

Seems mach 5 is.....impossible. A little too ambitious on my part!

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Not at all. One of my goals is to make a reliable hypersonic testbed vehicle. It's taking some thinking though. (And lots of MATLAB.) Build a lot of rockets, practice your techniques, it'll eventually work out. Keep in mind that this goal still evades guys who have been doing this hobby for 20+ years (I'd name names but I don't wanna piss anyone off ), so don't get discouraged when it works out to be harder than expected.

Viking3 said:

David: How the #$@% did they get that lawn dart out? Must have been tough!

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Lots of undergrads, a few shovels, and a cooler of beverages. And a minibike. Gotta have something to take off the ramps that get built from the dirt that comes out of the hole :duck:

Viking3 said:

Hello all!

In May, got my level one high power certification. Since then, I have begun to scratchbuild my rockets, and, lately, I have been fascinated with extreme speeds.

One of my goals is to build a 38mm or 29mm minumum diameter rocket capable of reaching hypersonic speeds (mach 5 and up). I will most likely be using blue tube material or hawk mountain fiberglass tubes for the airframe, and G-10 fiberglass fins. This brings me a problem--I have never made a high power minimum diameter rocket! I have researched fair bit, and have learned a lot about attatching fins to minimum dia. rocs, (dado slots, f-glass, etc) and have decided that fiberglassing the fin joints would be more than appropriate, but I cannot seem to find a guide to fiberglassing that pleases me.

So... how do y'all do it? Suggestions and walk thru's are welcome, etc.

Vipe

Click to expand...

well if you really want to make Mach number 5 with just a 29 or 38 mm mmt,
you need for sure a customized motor, XXL Length something like 1200mm long, also you need to make special propellant, really powerful like perchlorate or something, thats also expensive,
your motor case needs to be strong, really strong, so only the motor without propellant weight above 2kg,

and if you have that done, its still really hard to be sure if your motor doesn't explode,
and whit speeds up to Mach 5, your rocket gets really hot temperatures at the airframe, I believe close to 700 Kelvin.

There's a real neat equation that shows you exactly what you're dealing with here: the Tsiolkovsky rocket equation. It goes: , where delta-V is the change in velocity, Ve is effective exhaust velocity (specific impulse times gravitational force), M0 is mass of rocket plus propellant, and M1 is the final mass.

For an absolutely ideal rocket with optimized APCP propellant, specific impulse is around 250 seconds, and propellant mass will be close to half of total mass. That works out to 1700 m/s of delta-V, or exactly Mach 5. But the Tsiolkovsky equation ignores drag, off-center thrust, and other frustrating realities of real-world atmospheric rockets. So, you're not going to get Mach 5 out of a single-staged composite-fueled rocket launched anywhere in the atmosphere.

(How do professional rockets go Mach 5 and faster? Leaving the thick lower atmosphere, absurdly high propellant / mass ratios because of the economy of scale, and fuels like hydrogen/oxygen and boron slurries (missile fuel) with much higher specific impulses).

And, to an extent, the larger you can go, the better. Drag goes up the the square of size; propellant mass with the cube of size. Double the diameter and you only quadruple the aerodynamic forces, but you get eight times the propellant. Plus, casings are pretty much the same thickness from 29mm up to 98mm or so, because the issue there is not aerodynamic forces but internal pressure, so larger casings have more propellant per unit mass. For example, a loaded N3300R is 61% propellant, whereas an H165R is 41% propellant. That's why all the above-listed high-supersonic rockets were above 4" diameter.

:eyepop: My brain hurts now...

If you aren't aware of them, consider the Wildman Blackhawks. They come in 24mm, 29mm, and now 38mm min diameter carbon fiber. I haven't built them, but they look like a good intro for an L1 looking to get experience in low-weight, high-speed rockets at reasonable cost.
https://wildmanrocketry.com/default.asp?groupid=1&groupid1=612121482&groupid2=104274618

It seems like the production motor you need to go fastest in 38mm is the Aerotech J510-W in an optimized rocket. The motor is insane, with a peak thrust somewhere close to that of an I1299-N (not confirmed, but both give similar G forces in the same rocket). After that, it tapers off and burns a decently high thrust for about 2 seconds.

Even with all of that, I wouldn't expect more than mach 2.

You should be able to hit mach 2.5 or so - Adrian hit mach 2.2 on his J530 Imax altitude shot (if I remember right), and you could probably build a rocket that would be lighter than his if you were going for speed rather than altitude.

Lot's of posts debating on if it's possible to attain multi-Mach but few on construction.

To attach the fins on a minimum diameter rocket I'd try to find the Fusor epoxy trial kit for a start. To attach the best way is to use carbon fibre or fiberglass and build up 3 to 4 layers starting with a small piece and each succesive layers bit larger, running from fin to body tube, of course. Sand with a fairly rough sandpaper to provide "tooth" for the layer being applied, 120 or so. If you use carbon fibre the last layer should be fiberglass so it can be sanded smooth.

No launch lug or rail buttons, speed demons fly out of towers

dave carver said:

No launch lug or rail buttons, speed demons fly out of towers

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If you do it right the buttons melt off

Erik Hall from Ozark Aerospace managed to reconstruct the ARTS from the USC flight; we just got the data this weekend. 59,000 feet at apogee and Mach 4.2 max top speed Both the apogee and backup charges (in surgical tubing) fired -- they appeared on the accel plot -- but for some reason didn't separate the vehicle.

daveyfire said:

Both the apogee and backup charges (in surgical tubing) fired -- they appeared on the accel plot -- but for some reason didn't separate the vehicle.

Click to expand...

Maybe the air density in the tubes was so low at that altitude that the normally overpressurization BP charge that would have worked for say 20k or 30k feet was too small to overpressurize the tube? The pressurization wave dissipated before reaching the seperation point? :confused2:

daveyfire said:

If you do it right the buttons melt off

Erik Hall from Ozark Aerospace managed to reconstruct the ARTS from the USC flight; we just got the data this weekend. 59,000 feet at apogee and Mach 4.2 max top speed Both the apogee and backup charges (in surgical tubing) fired -- they appeared on the accel plot -- but for some reason didn't separate the vehicle.

Click to expand...

Probably a little off topic, but I'm curious on your ST charges if you had them sealed or if the air in the tubing could leak out. I've started making mine so that the air can leak out so the balloon doesn't burst on the way up.

Jim

JimJarvis50 said:

Probably a little off topic, but I'm curious on your ST charges if you had them sealed or if the air in the tubing could leak out. I've started making mine so that the air can leak out so the balloon doesn't burst on the way up.

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Hey Jim,

The charges were sealed on both ends with zip ties, as per standard procedure. I like the idea of letting the air leak out; how do you ensure that it's leak-able, but not such that black powder can make its way out? I figure that the hole's gotta be small enough that it won't make much of a difference once the powder has fired!

cjl said:

You should be able to hit mach 2.5 or so - Adrian hit mach 2.2 on his J530 Imax altitude shot (if I remember right), and you could probably build a rocket that would be lighter than his if you were going for speed rather than altitude.

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Yes, I think the top speed was around Mach 2.5 on the CTI J530. I didn't get any damage on the leading edges, but I did delaminate some strips of unidirectional fibers where I had some flaws in the original layup. I've been curious how fast I could push a 38mm airframe. Maybe just under Mach 3 on a single stage with less nose weight. Maybe over 3.5 or even Mach 4 using multiple stages, if the airframe would hold together.
My 3-stage rocket was going to use some really long delays to keep the speed (and drag) down, but the sustainer was still going to go over Mach 3.
The best motors for top speed will have a high thrust to reduce drag losses, but just as importantly, have a lot of impulse for their mass. That tends to make the largest motors of a given diameter work best, because there's more oomph to push the forward and aft closures up to speed.

daveyfire said:

Hey Jim,

The charges were sealed on both ends with zip ties, as per standard procedure. I like the idea of letting the air leak out; how do you ensure that it's leak-able, but not such that black powder can make its way out? I figure that the hole's gotta be small enough that it won't make much of a difference once the powder has fired!

Click to expand...

I plug each end of the tubing with a small piece of the little plastic cylinder that comes with the ematch. This is recessed a little, and then I plug the end with a little epoxy. I then zip tie each end around the epoxy plug. In the end without the ematch, I drill a 1/16 hole and then cover that with a tiny piece of masking tape. The air can leak past it, but it keeps the powder in.

I got to thinking about how much air is in there with the black powder and how big it would get, say, at 80K feet (it could happen). In rough numbers, use 2 grams of black power with 30% void (a wag). That's 0.6 cc's. At 80K, it could "balloon" up to as much as 29.92/0.8 x 0.6 = 22 cc's. I thought that would degrade the effectiveness of the charge, if not burst the tubing, so I started using a little hole to keep it from being air-tight.

Jim

JimJarvis50 said:

Probably a little off topic, but I'm curious on your ST charges if you had them sealed or if the air in the tubing could leak out. I've started making mine so that the air can leak out so the balloon doesn't burst on the way up.

Jim

Click to expand...

Interesting. Have you had problems with premature over-expansion of surgical tubing in a vacuum chamber? I would expect that even in a hard vacuum and wih a perfect seal that there wouldn't be enough gas sealed up to burst the tube. But maybe my intuition is off.

Adrian A said:

Interesting. Have you had problems with premature over-expansion of surgical tubing in a vacuum chamber? I would expect that even in a hard vacuum and wih a perfect seal that there wouldn't be enough gas sealed up to burst the tube. But maybe my intuition is off.

Click to expand...

I don't know if this would happen or not. But if the tube expands at all, it would defeat the purpose of keeping the powder contained. I just think of it as cheap insurance. On the other hand, I just bought a vacuum pump ....

Jim

JimJarvis50 said:

I got to thinking about how much air is in there with the black powder and how big it would get, say, at 80K feet (it could happen). In rough numbers, use 2 grams of black power with 30% void (a wag). That's 0.6 cc's. At 80K, it could "balloon" up to as much as 29.92/0.8 x 0.6 = 22 cc's. I thought that would degrade the effectiveness of the charge, if not burst the tubing, so I started using a little hole to keep it from being air-tight.

Jim

Click to expand...

I think as the outside pressure goes down, the tubing will provide a significant portion of the pressure, sort if like a space suit. I wonder how much pressure a partially-inflated section of surgical tubing applies. Maybe 1 or 2 psi?