Level-3 high-performance design and build thread

Adrian A said:

Thanks for your help, Robert. A few follow-up questions if you don't mind:

On the fins that had the leading edge erosion, were you using high temperature epoxy and/or carbon fiber?
Where did you get your 1800F nosecone paint?
How smooth was the nosecone surface after the flight?
Do you have data on cooling of your av-bay during descent?
Was your av-bay connected to the end of your motor during the descent?

Thanks again.

Click to expand...

The leading edge of the fins was Cotronics epoxy and carbon.
Home Depot, BBQ paint.
The nosecone was not smooth after the flight.
https://www.geocities.com/rdh82000/NmotorRocket/images/Nose.jpg

av-bay was in the nosecone. No data on temperature.

Robert

BTW, Adrian, I want to add that I think this is the epitome of what a certification rocket should be.

Far too many people, in my opinion, advocate the KISS approach. I very much disagree with that.

Instead, I think certification flights should be typical of what the individual will fly, and what makes them happy.

It's obvious from seeing what you do, and talking to you, that you're all about performance, and that's what the rocket you're planning is.

It's not the perfect rocket for me, but it's definitely the perfect rocket for you!

-Kevin

rdh8 said:

The leading edge of the fins was Cotronics epoxy and carbon.
Home Depot, BBQ paint.
The nosecone was not smooth after the flight.
https://www.geocities.com/rdh82000/NmotorRocket/images/Nose.jpg

av-bay was in the nosecone. No data on temperature.

Robert

Click to expand...

Thanks, Robert. Great information.

troj said:

Instead, I think certification flights should be typical of what the individual will fly, and what makes them happy.

It's obvious from seeing what you do, and talking to you, that you're all about performance, and that's what the rocket you're planning is.

It's not the perfect rocket for me, but it's definitely the perfect rocket for you!

-Kevin

Click to expand...

Thanks, Kevin. Maximizing performance is what makes me interested in rocketry. I'm getting an L3 certification so that I can fly L3 record attempts. If I were a spectator or another flyer at a launch where I was attempting a level 3 record flight for the first time, I would want me to be doing it under TAP supervision. It would be kind of a wasted opportunity if I only had oversight on the most conservative rocket I could dream up, and I never flew a rocket like that again.

Edit: In other words, I'm looking forward to learning from my TAP and others to maximize the chances that my first L3 flight will turn out right.

op:

Early thoughts on the av-bay and chute configuration:

The details of the av-bay will need to wait until I have a motor end to play with, but the basic idea is that it will bolt onto the end of the motor, using a tool that will reach in through the end of the main chute holder. I drew this up to make sure I would have enough volume for everything, and I think it will be o.k. I'm planning to use a 30" semi-circumference chute I have, that packs down to about 2-3" of 38mm tube. It looks like there will be about an inch of radius around the 38mm tube, which would be plenty of space for a pretty beefy kevlar harness. On my other rockets that have this configuration I Z-fold the harness around the chute holder, taping it down as I go, and it looks like that would work fine here, too. I added the pusher to the end of the main chute holder so that I have a small, constrained volume for the apogee charge to fire into. That seems to be key for good use of BP at high altitudes. I might actually make it 24mm, which is the same size as my main chute holder on my 38mm birds. In that 24mm chute holder I get a lot of bang for a tiny charge.

Update: See post #96 for the design I built that worked on my 32,000 foot L shot

Adrian,

Assuming the rest of what I don't see is motor, and the airframe break at apogee is in the nosecone area shown, and there is no mention of a drogue chute... Aren't you worried by not breaking the rocket in the middle to distribute the falling mass on a drogueless deploy, that you will have a high probability of getting a ballistic recovery profile thus reducing your chances for an effective main deployment event?

-Tim

Another question.

Where will port holes be for apogee detection?

Or will deployment be solely based on the accelerometer?

Bryce

dixontj93060 said:

Adrian,

Assuming the rest of what I don't see is motor, and the airframe break at apogee is in the nosecone area shown, and there is no mention of a drogue chute... Aren't you worried by not breaking the rocket in the middle to distribute the falling mass on a drogueless deploy, that you will have a high probability of getting a ballistic recovery profile thus reducing your chances for an effective main deployment event?

-Tim

Click to expand...

The nosecone piece of the airframe will extend down somewhat lower on the motor than what I showed on the sketch, but even so it will be an 18" nosecone with about a 6" extension to make 24" (a lot of which is small-diameter). The booster tube would be about 36 inches, including fins. My 38mm rockets tend to fall straight down, fast, with the booster tube getting torqued out of vertical occasionally when the nosecone jerks it around. They descend around 150 feet/second, IIRC, and the main opening shock hasn't caused any issues. This is a heavier rocket though, so it's a good question that I'll need to look into. I know other people have gotten away with drogueless descent with heavier rockets than this one, which will be about 8-9 lbs at burnout.

bandman444 said:

Another question.

Where will port holes be for apogee detection?

Or will deployment be solely based on the accelerometer?

Bryce

Click to expand...

The 3" tube bolted onto the front of the motor would have shear pins and vent holes. I'll also probably put a pressure relief hole or two just above the av-bay. If it's sealed, there would be about 80 pounds of differential pressure trying to take the nosecone off at 50 kft. (google .75*15 psi *(3 inches)^2/4*pi in lbf)

A couple of things I know I still need to work out are how to attach the main and apogee shock cords to the front of the av-bay, and how to keep the whole thing from unscrewing itself from the motor if the shock cords try to do that. On my smaller rockets I've learned to tie the main and apogee cords together and run them between the main chute holder (which is bolted on with 4 threaded rods) and the av-bay. Here I'm not really planning on having a gap between those two parts, so I'll need to work out something else.

Also, you can see that the 3" coupler tube that forms the outside of the av-bay would be too wide at the top where the cone starts to neck down. I'm thinking of grinding down the forward corners and reinforcing it on the inside to make it somewhat-conical.

The above drawing assumes that I lay up my own 1-piece nosecone with airframe extension. If I use a standard cone with a regular shoulder, the length of the shoulder + av-bay would have to be added to the rocket length. That would add some strength to the cone and allow a purely cylindrical av-bay (and eliminate a lot of nosecone fabrication work) but it's not as efficient as if I do it as shown above. I haven't decided which way I'm going on that yet.

See, this is why I love this forum.

I don't foresee myself getting into doing a project of this ambition/scale for a LONG time. Perhaps never. I'd love to, but my own available time/money/experience/knowledge say otherwise. However, through this forum, I can live vicariously through Adrian's build/experience. It's fascinating and really fun to tag along here via this thread (and many others like it).

This is an extremely cool project. I'm learning a ton, as I'm sure others are too (including Adrian). Nothing beats building and flying them "for real", but I can't build/fly them all, and this "next best thing" sure is great.

Thanks Adrian for sharing this and letting us all watch & learn. And thanks to all the rest of the forumites for joining in.

clear skies to y'all, s6

adrian that nose bay is possibly the most amazing thing i've ever seen on this forum!

so much packed in. this thing is going to look like a goblin or squat or something

one question though, what size chute are you thinking of for the main deploy? because i've seen this on giant leap (go down to GLR slider). It butts up against the chut material and makes the shrouds open more slowly, making the main act as its own pilot to help slow it down before full inflation.


this is going to be one amazing build

stealth6 said:

See, this is why I love this forum.

I don't foresee myself getting into doing a project of this ambition/scale for a LONG time. Perhaps never. I'd love to, but my own available time/money/experience/knowledge say otherwise. However, through this forum, I can live vicariously through Adrian's build/experience. It's fascinating and really fun to tag along here via this thread (and many others like it).

This is an extremely cool project. I'm learning a ton, as I'm sure others are too (including Adrian). Nothing beats building and flying them "for real", but I can't build/fly them all, and this "next best thing" sure is great.

Thanks Adrian for sharing this and letting us all watch & learn. And thanks to all the rest of the forumites for joining in.

clear skies to y'all, s6

Click to expand...

Thanks. This design part is actually my favorite part of the whole process. Well, that and when I first see my rocket again after it lands. I'm only a so-so craftsman. I'm hoping that with this relatively simple prep (compared to multi-stage) and with plenty of time, the prep and flying part will be more enjoyable this time around.

edwinshap1 said:

adrian that nose bay is possibly the most amazing thing i've ever seen on this forum!

so much packed in. this thing is going to look like a goblin or squat or something

one question though, what size chute are you thinking of for the main deploy? because i've seen this on giant leap (go down to GLR slider). It butts up against the chut material and makes the shrouds open more slowly, making the main act as its own pilot to help slow it down before full inflation.


this is going to be one amazing build

Click to expand...

Thanks. I have a minimalist chute that I made from a single piece of nylon, with darts cut out and sewn to make it hemispherical. I just re-measured it and it's 32" along the fabric over the top, and it fits into a 3" long section of 38mm airframe. It might be a touch small for this 8 pound descent mass. For the playa I would shoot for about 30 feet/second descent rate.

I haven't tried a chute slider so I'm a little hesitant to try it for the first time here. But maybe I should get over that. I might be more inclined to use a single metal ring that I have heard described, since the Giant Leap sliders look like they take a lot of volume for small chutes.

The sliders sold by GLR are large and bulky for this.
they are ment to keep a Skyangle XXL or Tac-9B from snapping open on a 80lb rocket.
I have some neat accellerometer data of one opening with a slider.. it takes a fraction of a second more than normal.


Adrian, With just seperating the nose cone, on a Large rocket, how confident are you on the stress the nose cone is going to put on your main tube? And in that, it wont want to come in on a ballistic profile at 300fps(just a nice round number)

Adrian A said:

I haven't tried a chute slider so I'm a little hesitant to try it for the first time here. But maybe I should get over that. I might be more inclined to use a single metal ring that I have heard described, since the Giant Leap sliders look like they take a lot of volume for small chutes.

Click to expand...

All a slider is really designed to do is reduce opening shock. You don't really need one in this design, I don't think.

You should be able to use a nutdriver to attach your av bay to the top of the motor -- it's a standard thread, and a bolt and washer can easily keep things in place.

What're you planning to do to keep the nosecone from drag separating? I'm not sure where you could install shear pins in there, or how easily it could be done.

-Kevin

ClayD said:

Adrian, With just seperating the nose cone, on a Large rocket, how confident are you on the stress the nose cone is going to put on your main tube? And in that, it wont want to come in on a ballistic profile at 300fps(just a nice round number)

Click to expand...

Could you describe more the stress you have in mind? It think the highest tube stress will be where the nosecone fits over the front edge of the motor. Wind shear can put a lot of bending forces on the tube. The thrust from the motor will be transferred to the nosecone through the booster tube front edge.

troj said:

All a slider is really designed to do is reduce opening shock. You don't really need one in this design, I don't think.

You should be able to use a nutdriver to attach your av bay to the top of the motor -- it's a standard thread, and a bolt and washer can easily keep things in place.

Click to expand...

For some reason I was imagining a hex nut in there, and a long hex rod to tighten it down. But a regular machine bolt head and a nut driver could be more straightforward.

I have seen an L3 attempt in which the shock cord was attached to the end of the motor, but it came unscrewed on the way down, leading to a core sample. I'll need to come up with a way to prevent that from happening.

troj said:

What're you planning to do to keep the nosecone from drag separating? I'm not sure where you could install shear pins in there, or how easily it could be done.
-Kevin

Click to expand...

Providing a spot for shear pins, plus providing a vent path, are why I'm planning the av-bay shell to be a 3" diameter coupler. I have some filament wound fiberglass coupler material on the way for that. the nosecone extension there will be a piece of 3" airframe, that will either be glued onto the nosecone shoulder, or incorporated into the layup of a scratch-built cone.

Adrian A said:

For some reason I was imagining a hex nut in there, and a long hex rod to tighten it down. But a regular machine bolt head and a nut driver could be more straightforward.

Click to expand...

How 'bout a machine screw that accepts an appropriately sized hex key to tighten it? This would allow for a smaller hole at the bottom than would be required for a standard nut driver.

I have seen an L3 attempt in which the shock cord was attached to the end of the motor, but it came unscrewed on the way down, leading to a core sample. I'll need to come up with a way to prevent that from happening.

Click to expand...

Easy. If the screw is appropriately sized, a simple lock washer on the top end will keep the screw from turning. Then, a bit of masking tape on the motor to keep it from spinning inside the rocket.

Just be careful not to over-tighten the machine screw, or the forward closure may begin to spin, at which point it can be very difficult to get them apart later.

FWIW, where folks have attachment unscrew from the motor is when the parachute is one that starts to spin (a properly made parachute shouldn't spin).

-Kevin

hmm, you won't have any room in the booster for any sort of attachment, so i think your only choice is what kevin said about the lock washer, but you may need some extra reinforcement along the base to be able to get it tight enough without any cracking or anything.

i hope you decide to make the nosecone yourself, that'll be a really fun process to see

troj said:

How 'bout a machine screw that accepts an appropriately sized hex key to tighten it? This would allow for a smaller hole at the bottom than would be required for a standard nut driver.

Click to expand...

The machine screw (the dark-grey object in the drawing) will be accessible from the front of the 38mm chute holder before everything goes in it. I don't think I'm following you about the hole at the bottom.

I may want to put in a feature on the bottom of the 3" av-bay coupler that engages the slot in the motor's lock ring. Then any torque from the recovery harness would have to spin the whole motor retaining ring in order for anything to come unscrewed.

I've been looking at the sim data on the M2020, and found that Rocksim has the wrong motor length for it, claiming it's a 5-grain instead of a 6-grain load. Lengthening the airframe 5" to accommodate that reduces the altitude in RASAero by about 1500 feet.

Another interesting result is that the drag at Mach 3 is about 140 lbs, and the acceleration when the motor completes its burnout is about 13 Gs. If all the drag were on the aft body, and none on the nosecone, and if the weighted cone weighs 2 lbs, then I would have 26 lbs of separation force plus the differential pressure. At 12,500 feet ASL when burnout happens, the air pressure is 4 psi less than at liftoff. If the venting is ineffective, then the area of the tube (7 square inches) x 4 psi differential pressure would add another 28 lbs of separation force, for a total of 54 lbs. This is conservative, because I would expect the nosecone to have a significant portion of the 140 lbs of total drag force. I bet it's much less than half, though, maybe 20-30 out of the 140 lbs. I think I'd like to design the shear pins to cover the dragless-nosecone case, just to be on the safe side.

If the venting is ineffective and the rocket gets up to 47kft (50kft ASL), there would be 11.3 psi of differential pressure. That's about 77 lbs of separation force. I think before this is all done I'll end up running my own sim of the depressurization of the cone volume through the vent holes.

Here's a good site on shear pin test strength.
https://www.rocketmaterials.org/datastore/cord/Shear_Pins/index.php
This is at room temperature, however, and I would expect them to get significantly weaker after aero heating.

Adrian A said:

The machine screw (the dark-grey object in the drawing) will be accessible from the front of the 38mm chute holder before everything goes in it. I don't think I'm following you about the hole at the bottom.

I may want to put in a feature on the bottom of the 3" av-bay coupler that engages the slot in the motor's lock ring. Then any torque from the recovery harness would have to spin the whole motor retaining ring in order for anything to come unscrewed.

Click to expand...

You'll need a hole at the bottom of the bay through which to insert the tool to do the tightening. An Allen wrench needs a smaller hole.

Protrusions into the closure ring would work but that ring turns more easily than the closure does on an assembled motor.

-Kevin

Looking good Adrian
Randall TRA L3, CAR L4

Adrian A said:

Could you describe more the stress you have in mind? It think the highest tube stress will be where the nosecone fits over the front edge of the motor. Wind shear can put a lot of bending forces on the tube. The thrust from the motor will be transferred to the nosecone through the booster tube front edge.

Click to expand...

I am talking about after apogee deployment. I am guessing you have a drouge shock cord attached to your nose cone, and attached to "where" on the av-bay...
If the fincan wants to go ballistic, and your nose cone is being dragged along behind it, i would think there could be some real stress where ever you attached the other end of the cord..

(the up part will be easy... its the down part you have your hands full with here...)

I have seen an L3 attempt in which the shock cord was attached to the end of the motor, but it came unscrewed on the way down, leading to a core sample. I'll need to come up with a way to prevent that from happening.

Click to expand...

Easy. If the screw is appropriately sized, a simple lock washer on the top end will keep the screw from turning.

Click to expand...

I wouldn't say easy, lock washers only work for an initial point, then its all over....
I would use Loctite- high temp... a lot of it where you practly glue it together... lock washer or lock nut..
.
PLUS, some sort of key way.... this could easily be a very small set screw that is put in next to the hex head... a physical retention of the head to keep it from unthreading...

ClayD said:

I am talking about after apogee deployment. I am guessing you have a drouge shock cord attached to your nose cone, and attached to "where" on the av-bay...
If the fincan wants to go ballistic, and your nose cone is being dragged along behind it, i would think there could be some real stress where ever you attached the other end of the cord..

(the up part will be easy... its the down part you have your hands full with here...)

Click to expand...

I see what you have in mind now. I agree, especially since there will be quite a bit of uncertainty in the apogee charge performance; I don't want to undersize that charge, so the nosecone could whack the end of the shock cord pretty hard. I've been thinking about using a small u-bolt attached at the base of the 38mm chute holder, one for each cord (apogee and main). Another alternative would be like what I do on my 29mm and 38mm rockets, and use one cord for apogee and main, that's threaded underneath the main chute holder. No hardware required for that route, which is a big plus in my book. I don't like concentrated loads or the bulk and weight of metal hardware. But with 2 u-bolts I could make the av-bay and main chute holder a well-reinforced, sealed, 1-piece unit and not have to bolt anything together, so I'm leaning toward that route.

ClayD said:

I wouldn't say easy, lock washers only work for an initial point, then its all over....
I would use Loctite- high temp... a lot of it where you practly glue it together... lock washer or lock nut..
.
PLUS, some sort of key way.... this could easily be a very small set screw that is put in next to the hex head... a physical retention of the head to keep it from unthreading...

Click to expand...

If I can restrain the whole av-bay from rotating, using something other than just the bolt preload and friction, then I'm not worried about the bolt backing out on its own. Locktite or a lock washer would be plenty. I've been toying with the idea of making the main part of the av-bay smaller diameter to slip over the smoke grain holder on the motor, and use a hose clamp to cinch it down tight. The downsides of this approach are: lot less room for electronics, still need a 3" donut at the bottom for shear pins and vent hole, need to make a vent tube to connect the av-bay volume to the vent hole.

Kevin Trojanowski generously loaned me his 3" 6-grain hardware set to play with, so I expect I'll have some other ideas once I get it in my hands.

Adrian A said:

If I can restrain the whole av-bay from rotating, using something other than just the bolt preload and friction, then I'm not worried about the bolt backing out on its own. Locktite or a lock washer would be plenty. I've been toying with the idea of making the main part of the av-bay smaller diameter to slip over the smoke grain holder on the motor, and use a hose clamp to cinch it down tight. The downsides of this approach are: lot less room for electronics, still need a 3" donut at the bottom for shear pins and vent hole, need to make a vent tube to connect the av-bay volume to the vent hole.

Click to expand...

I wouldn't use Loctite -- tightening it will be easy, but how are you going to keep the closure from rotating when you're trying to remove it?

-Kevin

Who says you'd ever have to remove it? Just leave it in the closure- if you ever fly a rocket where you absolutely can't have anything screwed into the forward closure, buy a new one.

Also Adrian, what about the 6GXL case? I hear CTI is working on a 9k+ Ns motor for it.

Mars any idea when that motor is expected to be ready?

troj said:

I wouldn't use Loctite -- tightening it will be easy, but how are you going to keep the closure from rotating when you're trying to remove it?

-Kevin

Click to expand...

Good question. That could be another good reason for having part of the av-bay protrude into the lock ring slot. Worst case, you could unscrew the av-bay together with the whole forward closure from the case in order to get access to grab onto the forward closure.

Here's a variation on the design that would allow me to use the existing Shockwave nosecone, with a carbon tube glued onto a shortened shoulder. The av-bay would have a reduced diameter to fit around the motor's smoke grain holder. The disadvantage of this design is that it would make the rocket longer, and I wouldn't have control over the nosecone layup. There are also some complications with the venting that I mentioned earlier, and not as much real estate to put u-bolts for the harness. On the plus side, I wouldn't have to make a nosecone mold or a new nosecone, and the part of the cone that goes over the front edge of the motor could be carbon fiber. I would probably add my own secondary layup of uni-axial carbon fibers to strengthen that area. I've recently seen or heard of too many shreds on high-performance flights not to overkill the strength there.



Update: See post #96 for the design I built that worked on my 32,000 foot L shot

Adrian A said:

Good question. That could be another good reason for having part of the av-bay protrude into the lock ring slot. Worst case, you could unscrew the av-bay together with the whole forward closure from the case in order to get access to grab onto the forward closure.

Click to expand...

The challenge there is that you then need to spin the closure as you tighten the av bay/retaining ring down, which means you're spinning the o-ring on it. That, to me, spells trouble as you're increasing the odds of the o-ring getting damaged.

-Kevin

troj said:

The challenge there is that you then need to spin the closure as you tighten the av bay/retaining ring down, which means you're spinning the o-ring on it. That, to me, spells trouble as you're increasing the odds of the o-ring getting damaged.

-Kevin

Click to expand...

Thanks for the input. The motor hardware is waiting for me at the post office, by the way.

I think I would just assemble the motor first, put the av-bay/chute holder in place with the nub in the retaining ring slot, and then install the bolt through the chute holder and tighten. I would only turn the retaining ring with the av-bay if the bolt were stuck.

If I go with option 2 shown above, I would have access to the forward closure so this wouldn't be an issue. A point in its favor, I think.

Adrian A said:

Thanks for the input. The motor hardware is waiting for me at the post office, by the way.

Click to expand...

Cool. Take your time with it -- not sure when I'll need it again. I have a 75-4 case, too, and I'm more likely to need that one sooner.

I think I would just assemble the motor first, put the av-bay/chute holder in place with the nub in the retaining ring slot, and then install the bolt through the chute holder and tighten. I would only turn the retaining ring with the av-bay if the bolt were stuck.

Click to expand...

Gotcha. I was thinking you were going to attach them together, first.

-Kevin