How fast is too fast?

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Justin Horne

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Hi all. Will be starting to build a Binder Jaguar Extreme soon. I was thinking of various motors so I ran over and played with rocksim. An I284 gets it near supersonic, so i'm sure a J350 could push it over. A what point does the speed become too much? By the suggestion of another on this forum, I will build it with 1 or 2 layers of 6oz cloth, then 2 oz for less sanding. it is fully double walled. What is the maximum you think it could go for speed? Also, the fin can will have glass strips to anchor in the fins. For those not familiar with the kit, here is a link:

Jaguar
By the way, in the link it is 38 mm, but the extreme has G10 fins, 54 mm mount, and couplers to double wall the tube.
Thanks,
Justin Horne
 

Johnnie

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How fast is too fast??? When it comes apart as it hits MaxQ at 500 ft or less :D

The Jaguar is a beautiful rocket, can't wait to see some build pics.


Welcome to the forum, I'm JohnnieRKT...

I opted for the VBR Javelin, with a 54mm mount...kit bash for myself, kinda like sticking a Chevy smallblock 350 in a 79' Manza Spider...sweet!!
 

Justin Horne

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I didn't know the javelin could handle a 54! Should be something to see too! I don't have a digital camera yet, but am getting one in a week or so, so i'll take pictures. :) I've heard on this forum you could be killed for not taking them. :p

Justin
 

firemanup

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Justin,

I'll be watching your build also, I've got replacement parts for mine coming soon from Binder.

What weight are you using for your sims, also if ya have time could you give me the specs you're sims are showing for the I284 and J350. Max speed (mph or .?? mach) max altitude?


My rebuild will be double walled throughout, weather I glass it or not i've not decided, i'll be keeping track of yours and how it turns out weight wise.

I think you'll have no trouble with the I's or J350 the way you're building it.
 

LMazza

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Keep in mind that with all these reinforcements the weight will not be what you see in the stock rsim file from binder. My finished weight with all but the motor came out to 57oz. At that weight it would just touch mach on a J570 and might not even get there. Good luck with your build and keep us updated.
 

firemanup

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Yeh,

Mine without glass or couplers came in at 50 oz with everything but motor...
 

Justin Horne

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Oh, okay. My simulation jaguar weighs 47 oz, i'll go up that to 56 and report the sims back here..
 

rocwizard

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How fast is too fast? umm Mach 5 might give you some problems, but with enough reinforcement, anything is possible. A toaster could be flown to Mach 3 if you really wanted to do it:kill:


Anyways, it sounds like it will be very stong. Pop in a L730 and see what gives:D

we want flight pics!
 

Justin Horne

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OKay, weighing 56 ounces it goes to 4682 feet at 521 miles per hour. The optimal delay is just under 14 seconds. For a J350 It reaches 5736 feet and peaks out at 625 MPH. Using the weights that are more actual, I guess it won't quite get to mach (with 38's).

So I'm assuming it will handle this just fine? Thanks. Using the dual 6 oz cloths and a 2 oz, is there a rough number that i should not go over? In case you can't tell, this is my first rocket that is actually trans sonic or super sonic able...

Justin
 

Johnnie

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Justin,

To answer your question, a 54mm fits nicely into a Javelin Worth while mod, as a 4.5 pound rocket os the HyperTEK K240 would rock!!!

I had the cjoice to get the Jag or the Jav, and the Jav won, but if I had gotten the Jag, it would have a 54mm stuffed in it.
 

firemanup

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Justin,

Yeah with the double wall and the glass on top of that i think you'll handle the J350 just fine..as long as all stability issues are in check... should be good to go..
 

lalligood

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...and don't forget that if you're going to beef up the rocket with all that 'glass, you'll probably have to upgrade the chute.

IMHO, 'glassing the rocket seems unnecessarily redundant. After all, you're going to reinforce the tubes by adding all those couplers. Maybe 'glass the fins (only) but only then if you're going to be flying it somewhere that it can land on hard surfaces (like playa out west). Save your time, effort, & materials...build it stock so you have a rocket that performs!
 

Justin Horne

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Yep, main is a ballistic skyangle Classic II. I'm glassing it so that i don't have to anything when i put a 54 mm in it. Other than that i'm cautious. :)
 

DynaSoar

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Originally posted by Justin Horne
A what point does the speed become too much?
Too much for what? If it's built well it should handle transonic speed fine. Breaking Mach will probably be your max q (maximum pressure) so over Mach should be no more difficult than breaking it.

Now, if you're planning on breaking Mach 2, maybe you'll want to use some heat proof paint.
 

Justin Horne

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No, I'm not, but is there a reason for this? Obviously heat proof paint implies high temperatures... does it get hot enough to require these?! Just my curiosity.:)

Justin
 

LMazza

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High drag areas such as the nose cone and fin tips have been known to have scorched paint at supersonic speeds. A member of our club flew his Shadow Composites Raven on an I435 last weekend and when he retreived it the paint on the nose cone was scorched. I'm not completely sure but it would be my guess that this is a purely cosmetic problem.
 

BlueNinja

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Originally posted by DynaSoar
Too much for what? If it's built well it should handle transonic speed fine. Breaking Mach will probably be your max q (maximum pressure) so over Mach should be no more difficult than breaking it.


I would think transonic would be more of your problem after reading about supersonic rockets. Stay transonic too long and you will probably shred, after mach you should be OK excpet for the scorching thing. Anyone know why it heats up anyway? You would think the air rushing by would help to cool it down, unless that creates the heating.

Blue
 

DPatell

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I know this much:

At the mach wall/transition, drag is very high. I believe it is due to the expansion of air...but there is also condensation forming around the body moving that fast. There is also a lot of turbulence here, increasing drag significantly.

This increased drag is the reason many rockets don't break the barrier. They accerlate right up to it, but the increased drag does not allow them to go any faster.

Once you break through the barrier, the air is thinner and allows more acceleration. Less drag and turbulence.

So if you're gonna do it, do it low to the ground, about mid motor burn in order to go the highest;)

K1100!!!! K1275R!!!!
 

Todd Knight

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Originally posted by Justin Horne
I will build it with 1 or 2 layers of 6oz cloth, then 2 oz for less sanding. it is fully double walled.
Justin Horne
Justin, This is almost to the extreme of overbuilding:) With that much fiberglass and cardboard you will probably need an I-284 to get it off the pad. With the weight distributed right it will fly any motor you could fit in it (including Ks).

As a learning project, build and enjoy it. There are plenty of people here to help out. This rocket would probably be fine with no reinforcment going thru MaxQ. Larger fins are usually the culprit (fin flutter) of breakups thru MaxQ.

Post some build pics and then flight pics and then some recovery pics then repeat.

Welcome to the forum.
 

sandman

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I am no expert but I do read a lot.

Here is my view on high speed.

Transonic is the biggest problem. This occurs on the Shuttle when it experiences "maximum aerodynamic stress" but the transonic period is short. You just have to get through it.

The major reason for "aerodynamic stress" during transonic flight is due to the fact that as the air travels over the aerodynamic surfaces and has to divert around things like fin airfoils and launch lugs and around the nose cone, it has to actually speed up and slow down, so there are locations on the rocket body where some of the air is moving faster than the speed of the shockwave generated (sound wave) and other areas where it is slower than sound.

This is what causes the buffeting and vibration that can shred a rocket.

After the "sound barrier" has been crossed you're done...finished...there are no more barriers.

Mach 2 has no barrier and has no aerodynamic significance at all.

The next aerodynamic "barrier" is hypersonic speeds (above mach 5 I think) but you're not gonna get near that.

As for friction heating...well, that depends on surface prep and nose cone tip angle and stuff we can't be too worried about.

But it would be neat to tell people that the rocket went so fast that it burned the paint off of the tip.

sandman
 

firemanup

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I agree with Todd that you're probably going over board with the couplers and the glass...

But I think mine's flight shows that you need one or the other if you're gonna have the weight of electronics up top..
 

Justin Horne

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Really? Overbuilding, all right. So this means a 6 oz layer and a 2 oz would be suffiecient? I saw what happened to one Jag (I believe yours, firemanup?) and that disapointed me. I feel really sorry for whoever's owns that. I saw the pics on your site before shred, nice looking rocket! I actually learrned quite abit about high speed rockets here! It seems interesting that after breaking through it is clean sailing, but I dunderstand why. Still interesting to think about. :)I geuss one or two flights to test it out, then just go ahead and throw in something big and break mach.. Sounds fun. :) Am I correct in thinking there will be no sonic booms due to that the booms go out (ie, to the sides of rocket) not down? Oh well.:) One more question regarding supersonic/transonic flight. For the altimeter, if it is going transonic, do i need to do a mach delay adjust? Alos, the mach timer, does that mean If it goes mach in 4 seconds, and drops out in 6, I should set it to the nearest setting over 6? Thankws again so much, I'm feeling really ready to go build. Just waiting on cloth now...


Justin.
 

bobkrech

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A good simple illustration of aerodynamic drag can be found here.

https://aerodyn.org/Drag/speed-drag.html

While the drag coefficient changes as a function of velocity, vehicle shape, length and surface roughness, the total drag always increases with the velocity provided you are comparing two vehicles at the same altitude (constant density).

The Total Drag Force is proportional to 1/2*rho*A*Cd*V^2, where rho is the atmospheric density, A is the cross-sectional area of the rocket, Cd is the drag coefficient and V^2 is the velocity squared. All other things being equal (density kept constant), the total drag forces at M=2 is 4x that @ M=1.

So despite rumors to the contrary, the sound barrier really isn't a barrier at all. A rocket will accelerate to a peak velocity where the drag forces equals the motor thrust. Breaking Mach isn't that complicated. All you need to break mach is a motor that burns long enough to accelerate the rocket with sufficient thrust to exceed the drag forces at Mach 1. (or Mach 2, 3 etc.)

Max Q is the peak dynamic pressure (in pounds per square inch)that occurs in a flight. Where it occurs depends on the rocket speed and altitude, but since most model and HP rockets don't really go that high for the atmospheric density to change significantly, for practical purposes, max Q occurs at the peak velocity which for many, but not all rockets, occurs at peak motor thrust.

If this is the case, the max Q (in pounds/square inch) can be simply calculated by dividing the peak motor thrust (in pounds) by the rocket's cross-sectional area (in square inches). (I'll leave it to the readers to do the mathematical proof.)

Furthermore, the peak thrust of the motor defines the aerodynamic structural loading on a rocket ascending vertically. If your motor develops 1 pound of peak thrust, the maximum structural load on the vehicle is 1 pound. If the motor develops 1000 pounds of peak thrust, the peak load on the vehicle is 1000 pounds. The peak loading on any one cross-section of the rocket (in PSI) is simply the peak thrust (in pounds) divided by the cross-sectional area (in square inches) of the member carrying the load. Provided all the structural components have a yield strength (in PSI) greater than this peak loading, the rocket will not shread. (Yes, it's really that simple.)

The only fly in the ointment is aerodynamic heating. Materials loose strength at high temperature and eventually fall apart, so there is a limit to how long and fast above Mach you can go at a given altitude before you have a themally induced material failurebut no model rockets and virtually all HP rockets don't have to worry about this.

Bob Krech
 

Todd Knight

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I will expand on Bob's explanation a little. The sound barrier arose (from the math side) from an equation for drag vs. Mach number. The drag increases towards infinity on the square vs. the Mach number and the equation fails when Mach number reaches 1, hence the sound barrier. It is very similar equation that proves we cannot travel faster than the speed of light.

These equations actually work very well up to .8 Mach then they begin to fall apart. This is where transonic aerodynamics take over with a very messy set of equations. The time one of our rockets spends transonic is very short so there is no need to do the math. Once the rocket passes thru Mach 1 the drag is less of an issue.

Most of the shredding problems we have are created by ourselves. Misalignment of fins, no mach delay, loose fitting couplers and large span/short chord fins are the most common. Notice that I didn't mention airframe strength?

Great qoute from one of my professors.

"...anybody can build a bridge that will last forever but it takes an engineer to build a bridge that just barely lasts forever"

Mach delay? Most of the motors we use are very short burn. If the motor is finished in 2 sec. and speed is Mach 1.2, It will continue up for a long time so set delay for +4 or +6, the rocket will still be going up when the altimeter arms.
 
E

Evil Prince

Too much glass. You don't need glass at all if it's double-walled.
 

sandman

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Actually I think it would be cool to have a rocket that went so fast it burned the paint.

If it did...I'd leave it like that!

sandman
 

Elapid

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remember, drag = friction = heat

i agree with sandman, a scorched rocket would be pretty awesome!
 

rocwizard

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If you can get a rocket up to Mach 1.5 or so and keep it there for several seconds, you'll see some definite scorched paint on the nose tip and leading edges of the fins.
 
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