L3 Project - Modular 98MM

[ether]

There are three pressure relief holes, they also function as switch access ports for the two protons, the camera and deployment charges disconnect. They are sized a bit bigger than what is recommended to have a larger safety margin on pressure equalization.

The camera window sits flush with the airframe, should stay on sized it to have good amount of contact area with the coupler

 

[ether]

Here is the completed rocket

 

[OverTheTop]

Very nice. I like the woodgrain effect on the fins .

 

[ether]

someone asked me about the camera window size

its 30x40 cm and 1.5MM thickness with a radius of R50

have an entire set of windows from R40 to R120, can confirm the R40 works perfectly with a 3inch tube

hope to have the rockets shakedown flight next weekend at Tripoli Vegas launch, hoping for good on-board video from the flight, will be using a K1449 to make sure the cobwebs are shaken off

 

[ether]

Small change - will be using a beeline GPS 70cm tracker

Wanted longer range of 70cm and used it as an excuse to get the Kenwood th-d74 radio.

Nice solution, the d74a can display the coordinates, show distance and direction from the rocket. Since it has bluetooth built in, can connect it to my android phone and use APRSdroid app to view the incoming packets, see it on a map, and export the coordinates to google earth on the android phone.

Still have the eggtimer TX and LCD receiver, in fact have two sets, but both 900 - hence will use those for other rockets that don't go that high

realized vegas has waiver for this weekend launch - planning on trying for the L3 cert if the weather and waiver lines up

 

[ether]

here is the video of the cert flight attempt - successful video, but not the L3 flight - too fast horizontal speed (~280mph) at apogee resulted in a drogue shred, which led to coming in hot. Main deployed at low altitude, zippering the airframe, and the main parachute shredded a bit but stayed intact but could not slow it down enough and landed hard on its tail

thanks to Pat for watching/encouragement during the attempt and my TAPS for the review, appreciate the help / guidance throughout the process

couple of cool things - (1) sonic booms are awesome - went mach 1.6 - below the mach 3.5 limit at the range (2) polished fins reflect the sunlight perfectly during boost (3) speed rash on polished aluminum fins is awesome (4) fin can held up great - feel great it worked as designed (5) camera window worked perfectly

this is a great reason to fly another M motor (got the reload already) and try again - will take the best of what I learned, make it simpler to prep (this was a bit too complicated where the AV was located) and will try again

 

[ether]

here is the slow mo of the main deploying - drogue is supposed to be about 5 feet from the nose cone

video starts right before the tender descender activates - the small blur is the exhaust gases near the camera lens

 

[T34zac]

someone asked me about the camera window size

its 30x40 cm and 1.5MM thickness with a radius of R50

have an entire set of windows from R40 to R120, can confirm the R40 works perfectly with a 3inch tube

I’m curious, where do you get glass like that? I’d like to try it out for some of my own rockets.

 

[ether]

https://www.esslinger.com/watch-min...rved-rectangular-1-5mm-thickness-for-cutting/
Alibaba sells a packet of different sizes

https://www.aliexpress.com/item/329...98#741_4452#3098#9624#921_4452#3564#16062#969

 

[ether]

i glued them onto a coupler, it may work epoxing them by the edges top the airframe without using a coupler. Its glass hence epoxy works well. i sanded the areas to be glued and it worked great

 

[T34zac]

https://www.esslinger.com/watch-min...rved-rectangular-1-5mm-thickness-for-cutting/
Alibaba sells a packet of different sizes

https://www.aliexpress.com/item/329...98#741_4452#3098#9624#921_4452#3564#16062#969

Thanks a ton.

Ether, great job on the build. Unfortunate it has the problems it did. Looking forward to the next attempt!

 

[ether]

i'm not at all disappointed, learned a ton on putting it together and got great video

not sure if the next design will be modular from 75MM to 98MM. May separate out the 98MM fincan to its own dedicate motor case only design.

toying if I should make the next design around a 5G or a 6XL case, have both, or may repurpose my MacPerformance scorpion build into an L3 attempt

this design needed to be long to accept a future 98MM motor, but it made it more challenging in prep in a 75MM design. Got a blank canvas to do it again, enjoy the design of components as much as the flight. Got some new ideas on fin attachment and recovery to make them simpler and less weight.

 

[Dan Griffing]

fast horizontal speed (~280mph) at apogee

Have you assessed what the very high horizontal apogee velocity was due to?

Was it from a “gravity turn“ from the 4.7s M1101 motor burn or an inevitable component of going 1.4 Mach?

Can you open a drogue at 280mph without breaking something?

In July I saw the gravity turn from a Moon-burner motor that caused a drogue deployment at 170mph that landed without damage miles away. But it was a near disaster because it opened up a 3/8” SS quick link.

Horizontal velocity at apogee is a really serious concern.

 

[ether]

ended up flying with a CTI 1830, has a 3 second burn

It started to weather cock after taking off, while there was little wind at launchpad, believe there were winds higher up causing the issue.

if i had a stronger drogue maybe it would have been ok. will not use a drogue next time and make it survivable even if the same conditions happen again. even the main parachute could have survived if i had gone with a thicker material, did a trade-off between weight and packing size vs strength. for a nominal flight would have worked great, but i reduced the margin of error. will make recovery have higher safety margin

 

[Dan Griffing]

ended up flying with a CTI 1830, has a 3 second burn

It started to weather cock after taking off, while there was little wind at launchpad, believe there were winds higher up causing the issue.

if i had a stronger drogue maybe it would have been ok. will not use a drogue next time and make it survivable even if the same conditions happen again. even the main parachute could have survived if i had gone with a thicker material, did a trade-off between weight and packing size vs strength. for a nominal flight would have worked great, but i reduced the margin of error. will make recovery have higher safety margin

Good luck on your next attempt!

As an L2, I’m learning a lot from you that I hope will help me over the next year or two.

 

[ether]

happy to share, especially what did not work, better to learn from others. going with a proven kit and techniques is the more straight forward way - i just like piecing things together that others have done and trying to make it work

 

[ether]

initial design - will switch to 6 fins using composite vs the aluminum - polished looked great, but speed rash - hence a one time effect. also less weight with composites. moving the fins a bit more away from the end and with a slight angle to lessen damage on landing. will keep single break in the airframe, will not be modular fin can, will use mechanical lock of the fins lessening epoxy and motor tube (weight savings), moving all the electronics (altimeters, GPS and camera) to the nose cone, single parachute (couple of different ways i'm thinking about how to deploy - will separate nose cone at apogee).

 

[Dan Griffing]

happy to share, especially what did not work, better to learn from others. going with a proven kit and techniques is the more straight forward way - i just like piecing things together that others have done and trying to make it work

What attracted me to your thread, (aside from me being an L2 eventually working for my L3), was its title "L3 Project - Modular 98mm".

My nascent L3 project is currently targeting Contrail Rocketry's hybrid motors.

Fellow Big Sky Rocketry Assn (BSRA) club members have loaned me -- for the next couple of years -- complete sets of 38mm, 54mm, and 75mm motors, together with all of the ground support hardware. The reload kits for Contrail's 3.4s burn M1491 and 7.2s burn M711 is only $95 each. Moreover four of the other senior BSRA members went through their hybrid phases and at least two of them -- who have agreed to be on my L3 TAP committee -- got their L3's on hybrids too.

My reason for a modular design is to be able to have a modular development with my 38mm, 54mm, and 75mm rockets each with modular configurable lengths for the various lengths of hybrid motors, but while being able to manage the common subassemblies under RockSim10. I also want to be able to use my L3 rocket for smaller, less expensive AP motors, and I want to test each design in low power configurations before going for the "Big One". I'm also a retired engineer and the typical approach to professional project development is with modular designs and starting with working prototypes and versions of increasing scale to minimize risk.

The big problem with hybrid motors is their length. The maximum power 38mm, 54mm, and 75mm hybrids are 48, 48, and 54in respectively. Lesser powered hybrids are 20 and 36inches. So the trick is to have multiple RockSim10 design files, one for each length configuration, but which share the common subassemblies, and to test them with a common set of 50 or so rocket motors. The problem with this is that RockSim screws up the simulation configuration if you change anything about the motor mount in a subassembly, and editing 50 simulations is quite tedious.

 

[ether]

that would be fantastic please share as you progress your build. the modular design works, the modular aspect did not have a single failure, it held up great. i donated the airframe to another flyer to be re-incarnated, did not want to deal with fixing the zipper and its an opportunity to re-do the recovery/electronics setup.

 

[Dan Griffing]

I generally need to resist the temptation for sharing too much.

I'm currently working on three modular designs:

1) A modular design for an Apogee Peregrine with added sections for three lengths of hybrid motors, a 54mm MMT to replace its 38mm, wrapped with 5.7oz carbon fiber for added strength and durability, and a modified nosecone for an Eggtimer GPS TX, Proton or Quantum, and a Tinder Rockets CO2 ejection system. I also have RockSim modular designs and kits for 2) a ARR 3" Basic Blues, and 3) a Mad Cow fiberglass Super DX3, both with 54mm MMTs.

These are all the replacement and next step for the modular single/dual deployment Apogee Zephyr that I got my L1 and L2 certs at the BSRA May and June launches before destroying it at the July launch.

 

[ether]

Progressing the design of the next attempt, will be posting updates via blogger

https://rocketryprojects.blogspot.com/
Will retire this thread and no longer post in this thread, all updates will be via the blogger site

 

[Faroutspacenut]

https://www.esslinger.com/watch-min...rved-rectangular-1-5mm-thickness-for-cutting/
Alibaba sells a packet of different sizes

https://www.aliexpress.com/item/329...98#741_4452#3098#9624#921_4452#3564#16062#969

Thanks so much for posting this about your window glass - I've been looking for something like this. You wouldn't happen to know what radius would be the best fit for a 4" tube would you?

 

[Tobor]

Thanks so much for posting this about your window glass - I've been looking for something like this. You wouldn't happen to know what radius would be the best fit for a 4" tube would you?

[Full Disclosure] I had to use the internet to figure this out. [/Full Disclosure]

The question you are looking for is: What is the "Degrees of Arc" or "Measure of the Arc" needed for your application?

The formula for this is:
[(s/r) * 180] / π
Where
s = segment length
r = radius

So,
s = Length of glass crystal = 40.0mm
r = Airframe O.D/2 = 2in. = 50.8mm

[(40.0 / 50.8) * 180] / π = 45.114787018175055808502484105595 or rounded down = 45 Degrees

Therefore the crystal glass you need to select from that website is 40.00mm - 30.0mm - 45 Degrees (Second item on the drop down menu).

The website that helped me figure this out is (Here).

 

[Faroutspacenut]

[Full Disclosure] I had to use the internet to figure this out. [/Full Disclosure]

The question you are looking for is: What is the "Degrees of Arc" or "Measure of the Arc" needed for your application?

The formula for this is:
[(s/r) * 180] / π
Where
s = segment length
r = radius

So,
s = Length of glass crystal = 40.0mm
r = Airframe O.D/2 = 2in. = 50.8mm

[(40.0 / 50.8) * 180] / π = 45.114787018175055808502484105595 or rounded down = 45 Degrees

Therefore the crystal glass you need to select from that website is 40.00mm - 30.0mm - 45 Degrees (Second item on the drop down menu).

The website that helped me figure this out is (Here).

Ha that's awesome. Nothing like a google to make us all math geniuses! I just found a similar calculator and got the exact same results - thanks for confirming! I also think I can take this to my watch repair guy and have him cut it for me to make the exact size I need for the "porthole"

 

[ether]

Ha that's awesome. Nothing like a google to make us all math geniuses! I just found a similar calculator and got the exact same results - thanks for confirming! I also think I can take this to my watch repair guy and have him cut it for me to make the exact size I need for the "porthole"

it should be 45 radius per the calcs, that is also what I thought it would be when I tried it, but actually the R50 is the one that fits perfectly - good thing I ordered the full set. Do not order the R45 for 4" tube. I have all the sizes and can confirm from 1st hand experience.

R45 crystal - this is sitting on a coupler for a 4" tube


R50 - perfect fit. I have several R50s they all fit the same.


Also if you attach them in the same manner as I did, epoxied over a coupler, the crystal may crack from epoxy shrinkage - suggest adding filler to the epoxy to reduce shrinkage. Luckily the cracks on the latest install are not in the field of view of the camera - so no impact. I did use filler when I installed the crystal on this rocket and had no cracks in the crystal from the epoxy drying. Would also suggest installing them at the end of the tube or end of nosecone to help alleviate stresses on the crystal by having one edge not constrained, also makes cutting the porthole a lot easier.