O3400 Min Diameter L3

[airforcetp1991]

I wish I'd noticed that, and taken a look at the pad and rail after the fact. Those pads have been used without incident for rockets and motors in that size class for many years without incident...

It doesn't have a wide base, but its base is a truck tire filled with concrete.

I didn’t notice it when I went back to the pad to get my camera, only later when I looked at the footage.

 

[JoePfeiffer]

I didn’t notice it when I went back to the pad to get my camera, only later when I looked at the footage.

I meant noticed when the rocket was going up, so I'd known there was something to look for.
Oh, were you able to establish whether the main deployed at apogee, and why?

 

[airforcetp1991]

I meant noticed when the rocket was going up, so I'd known there was something to look for.
Oh, were you able to establish whether the main deployed at apogee, and why?

That footage was 120 FPS slowed down about 10x so I think it would have been nearly impossible to see it real time.

So I downloaded the data and the Raven4 functioned correctly in terms of the main and apogee charges. There was no damage to the airframe or avbay so it wasn’t a structural failure of any kind. These leads me to believe the RRC3 erroneously fired the main at/near apogee. This is the 3rd flight on this redundant dual deploy setup and the previous 2 were similar in terms of acceleration, Mach and altitude so I’m not sure what specifically caused the RRC3 to malfunction. I’ll plan to use dual Raven4s in the future.

Tony

 

[Hobie1dog]

Thanks for the pictures and videos.

 

[Hobie1dog]

Great build.

 

[Rocketjunkie]

Tower I used in 1990 and 1992 for minimum diameter O motors (4.5")
From 1992. Parts for the tower, 8' 2" conduit, plugs to fit the conduit bolted to the plywood top and base. Not adjustable. Saved the metal parts and made new wood parts as needed.

Here it is at the pad for LDRS XI. (L-R LDRS Launch Director Pius Morizumi, Earl Cagle with the camera, I'm installing the igniter, and John Cato keeping the rocket from moving.

 

[airforcetp1991]

Tower I used in 1990 and 1992 for minimum diameter O motors (4.5")
From 1992. Parts for the tower, 8' 2" conduit, plugs to fit the conduit bolted to the plywood top and base. Not adjustable. Saved the metal parts and made new wood parts as needed.
View attachment 465087
Here it is at the pad for LDRS XI. (L-R LDRS Launch Director Pius Morizumi, Earl Cagle with the camera, I'm installing the igniter, and John Cato keeping the rocket from moving.
View attachment 465088

Thats awesome, I love that it is so simple and purpose built for the specific rocket. Given how infrequently I’d use the tower that idea is becoming more and more appealing to me. Just priced a 1515 aluminum extrusion adjustable tower and it is like $700 with shipping…

 

[airforcetp1991]

Tower I used in 1990 and 1992 for minimum diameter O motors (4.5")
From 1992. Parts for the tower, 8' 2" conduit, plugs to fit the conduit bolted to the plywood top and base. Not adjustable. Saved the metal parts and made new wood parts as needed.
View attachment 465087
Here it is at the pad for LDRS XI. (L-R LDRS Launch Director Pius Morizumi, Earl Cagle with the camera, I'm installing the igniter, and John Cato keeping the rocket from moving.
View attachment 465088

Did you machine the top pieces that attach to the plate yourself?

 

[Rocketjunkie]

Did you machine the top pieces that attach to the plate yourself?

Yes. Used a piece of 2" 12L14 steel. Drilled and tapped for a 3/4" screw. Turned OD until it fit the conduit. About 3" long. 6 pieces, 3 for top and 3 for bottom. Bolt to plywood, then it will slip into the conduit.

 

[airforcetp1991]

Yes. Used a piece of 2" 12L14 steel. Drilled and tapped for a 3/4" screw. Turned OD until it fit the conduit. About 3" long. 6 pieces, 3 for top and 3 for bottom. Bolt to plywood, then it will slip into the conduit.

Thank you!

 

[ihavemanyquestions]

Awesome build!
I had one question though - what rail button setup were you using, since this is a min diameter design. Conformal guides?

 

[airforcetp1991]

Awesome build!
I had one question though - what rail button setup were you using, since this is a min diameter design. Conformal guides?

The plan would be to use a tower to minimize drag and any drag asymmetry as much as possible.

 

[airforcetp1991]

Over the past few months there have been a lot of developments with this build. I have been fortunate to learn a lot from many people along the way. While it is still my eventual goal for this rocket to fly on the O3400 I now understand that this flight will not be my L3 cert flight, nor with this rocket be allowed to be my L3 cert project. It is not my intent in posting this update to challenge these decisions, it is my goal to share what I have learned and continue to learn from others. I am embarrassed to say that along the way I have allowed my ego and frustration to get the better of me when talking with those who have far more experience from myself. I hope that my apologies to them and my continued work in this hobby will show I am better than that.

I would like to address upfront the rumor that I started this build without TAP approval, that is not correct, there were 4 on board at the start of construction.

As always, BS flags are always welcome.

-Tony

Deployment proof of concept - 17 April 2021​

Eagle CO2 System

• 35 gram CO2 cartridge
• Dual firewire igniters
• Test Device
• 4” diameter PVC pipe
• Lower cap interior was leveled with epoxy for ease of mounting and secured with 4x steel screws
• Upper cap is mildly friction fit and held with 3x #6-32 nylon shear pins
• A 1/8” vent hole was drilled in the tube

The Eagle system was ignited using my low power rocket launch box with a 12V battery. The test was conducted twice with a totally empty tube to allow for the largest margin of safety. A video of the test is located here:

Both tests demonstrated the 35 gram cartridge was more than sufficient to shear the pins, launching the cap over 20’ from the tube.




Mako Line Cutter

• Loaded with single firewire igniter and secured to an old DMS motor tube
• Zip tie was 0.05” thick and 0.2” wide and was tightly secured

Mako success severed the zip tie and functioned as advertised. Small amount of exhaust is not a concern as the chute will be wrapped in a Nomex blanket.

Fin Beveling Practice – 24 April 2021

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The rocket design calls for a 5 degree fin leading and trailing edge bevel. To accomplish this I will use my router table, a jig, and a 5 degree carbide burr.

Router Table

• Standard router table and a DeWalt ¼” shank router

Carbide Burr

• Foredom fine abrasive 5 degree carbide burr

Jig

• 8” x 24” white shelving board from Lowe’s
• 2x Toggle clamps from harbor freight

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Testing with ¼” thick woods and scrap fiberglass showed very good results. There will be plenty of cutoffs from the CF plate used for my fins so that will allow for additional practice when the fins arrive. The biggest advantages of the jig setup I have observed are

• Allows your hands to be further from the burr
• Allows for far better control of the fin as the clamps can hold it very tightly
• The clamps can produce a lot of clamping force so be sure to step up the pressure slowly to avoid cracking the material
• The wider edge at the bottom of the board and the larger contact area on the back with the fence makes it much easier to keep the fin path correct

I would recommend using at least to passes to remove the desired amount of material. This reduces stress on the material (tip can break off) and makes it easier to push the material through the machine. Some light sanding was required to remove the grooves left by the bit.

AvBay Prototyping – 25 April 2021​

First step in prototyping the AvBay assembly is to drill out the mounting holes for the 2 Eagle CO2 systems. This was done using a 1” hole saw and then a 9/64’ bit for the mount screw holes. The fit is good but I plan to use some tape on the face of the sled between the sled and the Eagle to create a “gasket” to help seal the NC better.



Next step in the Avbay prototyping was the “machining” of the fixed ring that the sled base will seat against and be screwed to. This started as an SC Precision 98mm-75mm thrust plate and using a Dremel and some files I reduced the diameter until the aft face seated ~4.3” inside the NC. This will allow the coupler to have 4” of purchase in the NC for epoxying and give about 0.1” of extra room for the sled base which is 0.25” thick. Obviously, this will need to be epoxied in before the coupler as it is larger than the coupler inside diameter. The thinking behind this is 4 fold.

• Give the sled base a positive seat closer to the aft end of the nosecone to ensure clearance for all AvBay components. If I did not have this ring the sled base, which must be slightly smaller that the coupler inside diameter to be inserted, would sit much higher in the NC (about 1.5” higher). This increased seating height doesn’t allow sufficient clearance for the Eagle CO2. Additionally, there would be a relatively small contact area between the sled base outside edge and the NC wall.
• I will utilize 2 of the pre-drilled 6-32 holes in the thrust ring to help hold the sled base secure during flight. This will also help to make sure the sled base is properly aligned for switch access during arming.
• By filling the unused screw holes in the ring and adding a layer of tape on the ring I will be better able to seal the Avbay components off from the CO2 systems at Apogee.
• The epoxied thrust ring in addition to being a positive seat for the sled base will help to distribute the large pressure loading at Apogee. ~200 pounds of force are required to shear the 3x #6 shear pins and while they will quickly give way there will be a small period of time where the sled base will have to withstand that pressure, and possibly a lot more if the CO2 systems fire near simultaneously. The surface area available on the FWD side of the thrust ring to apply epoxy will allow for a better distribution of that loading and reduce the chance of a sled base failure.

Following these proof of concepts wooden prototypes were ordered from SendCutSend and used to further refine the design and fit before ordering the final aluminum and titanium versions.

Motor Retainer Skeletonizing – 28 April 2021​

I got the Wildman order in the mail today and I am still waiting on the motor hardware and fins so I can’t start major assembly yet, but I was able to do the modifications I planned on the Aeropack retainer. Full disclosure this only reduced the mass by about 10% so take it with a grain of salt. Other than the weight reduction my goal in drilling out the material was to provide more bonding area/access for the epoxy. The fit in the Wildman tube was spot on but I wanted to give the epoxy more ways to get between the tube wall and the retainer. I felt this was more important given the retainer is ~48” from the aft end of the tube and I won’t be able to easily add more epoxy after the fact.

 

[airforcetp1991]

Fin Beveling – 3 May 2021






Wear a respirator and use a vacuum or do not do this at all!!!​

Fin beveling was done using the jig discussed earlier in this log. The jig worked better than I anticipated with only a few very small movements of the fins on one or two passes. Increasing the clamping pressure fixed this issue. The trailing edges of the fins were beveled first to allow for maximum unbeveled contact area on the jig, this allowed for better clamping. The finished LE and TE thicknesses are approximately 0.05”. The plate was 0.25” thick to start. The material was removed using two passes through the burr to minimize stress/heating on the material and to make the jig easier to move through the tool. After beveling grooves were left in the bevels as expected due to the design of the burr. Sanding with 100 grit removed the groves in a few minutes and left the bevels with a nearly smooth finish that will work well for fillet bonding and a coat of epoxy on the bevel area not within the fillets. The satin finish in the unbeveled area will be sanding down as well both for fillet bonding and high temp paint bonding considerations. Overall, this process took ~2 hours total and went very smoothly. I highly recommend this style of jig and burr beveling setup. The fins started out at 747 grams total weight before bevels and following bevels and the sanding are now 547 grams total. This is more of a weight reduction than expected.

The next day I went back with a sanding block and blended the beveled region and unbeveled region more cleanly. Additionally, I removed the satin out layer on both sides in the unbeveled region to prep for bonding. The fin roots were notched and then the fillet region was cross hatched to improve the mechanical bonding strength.

Fin Attachment 8 May 2021​

After final sanding of the fins I moved on to attachment. Overall game plan was to prep the surfaces, wipe down, tack with superglue and then pull the fillets. My goal was to get all of this done within 24 hours to maximize the effectiveness of the surface prep. This process was borrowed from Steve Heller who has used it to fly many times to > Mach 4, his help has been essential in this project.

• I prepped the tube and fins with 60 grit hand sanding. The intent here was to leave a VERY textured, almost grooved, surface so I was very directional with the sanding and did not use many passes. This did not show well in pictures of the CF fins unfortunately.
• Next, I did a dry fit up which was critical! I had to sand my alignment guides a little more to improve the fit. This should also be a dry run of your superglue, or epoxy, tacking method. Make sure you don’t need a third hand now as opposed to when the epoxy is on the parts…
• With the fit up complete I wiped done all the glued surfaces with Acetone and then isopropyl alcohol. Wear gloves and minimizing touching of these surfaces as much as possible.
• To tack the fins I placed in the fin in the guides such that I could lift the fin up about ¼” up into the guide holding it just above the surface but precisely aligned with the line on the tube. From there I applied superglue to the tip and tail areas and then slowly slide the fin down onto the superglue.
• I held the fin down with hand pressure for about 1 min then checked the alignment and allowed the superglue to set for 15 mins before doing the next fin. After the 4th fin was tacked I let 1 hour pass to make sure the fins were stable for fillet pulling. A test with 2 scrap pieces showed it took a lot of force to break the superglue bond after only 15 mins but I wanted to be sure.
• 
• After the 1-hour insurance cure I moved on to the fillet pull using Loctite (Henkel) Hysol EA-120HP that was de-gassed before the pulls. This is where I made a frustrating mistake. I used the rule of thumb of 4-8% of root chord for fillet radius to select a 2” diameter for my fillets. This turned out to be too small and I had to add another layer to the fillets to increase the radius to 2.8”. Below you can see the 2” diameter wooden ball tool used for the first pulls and the 2.8” diameter foam ball used for the larger pulls. I like the ball tool over a dowel as you do not need to keep the pull angle constant to get a constant radius like you do with a dowel.

This is the results of the first set of fillet pulls with the Hysol.

• Based on the sims and wanting to be on the conservative side for the fillet sizing I decided to add more epoxy. I chose RocketPoxy G5000 based on high shear strength. The first set of fillets and tube/fins were prepped with 60 Grit. The picture with the foam ball shows the increase in fillet size.

• After the larger fillets were pulled the Rocketpoxy was allowed to cure for 2 days before sanding began. The Rocketpoxy didn’t de-gas as nicely as I would have liked so if I had to do this again I would use either more Hysol or an epoxy that is easier to de-gas, maybe 3M 8115.

Fillet Sanding 15 May 2021

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The fillet sanding used a Dremel with a sanding drum/flap wheel/grinding tip and hand sanding with up to 220 grit though 80-100 was used to remove larger amounts of material. A time-lapse can be seen here: In total about 13 hours went into sanding. Part of that was due to tool selection at the start but overall I felt this step demanded some attention to detail and with 8 fillets to sand I think that is a reasonable period of time to spend over about a week. Given that the fins would be painted by objective was not to make them look good but to have the profile be consistent/symmetric and for the fillet to blend well into the tube and fin. My fillet pull taping was not as precise as it could have been but overall I was happy with the profile after sanding.

 

[airforcetp1991]

Fin Painting 21 May 2021

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Plan for fin painting is 4 coats of Rustoleum 2000-degree high temp paint as a base followed by 2 coats of standard black paint and then the blood splatter. This is all really just a cool looking ablative and I don’t expect it too look good after the flight but it should serve its purpose. At least one hour was allowed to pass between all the coats and the last coat of the standard black paint was allowed to dry overnight to reduce the peeling risk when taping for the splatter. To create the splatter look I used some water based hobby paint from Hobby Lobby and a cheap art brush. I got some paint on the tip of the brush and swung/flicked the brush toward the rocket. You can find good videos on how to do this on YouTube and with a little practice it is very easy. To create some smaller droplets I ran my thumb along the brush like a toothbrush. Here is the final result pre clear coat. I plan to use a 2-part epoxy spray clear coat to make it as durable as possible. The clear coat will be applied after the NC is complete and pained as well.

Retainer Prep 23 May 2021

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While I am waiting for the hardware to get here (Next week hopefully) I am prepping as much as I can. Today I secured the eyebolt in the FWD end of the Aeropack MD retainer that I previously skeletonized. I did this in 2 steps. First, I sanded the contact point between the bolt and the retainer and then wiped it down before applying superglue to the contact surface and threads. I then used a metal rod to tighten the bolt very tightly into the retainer. After the bolt was secured I used a small engine tube I had laying around to made a “mold” around the bolt. I surface prepped the area and then poured in RocketPoxy to act as further “Don’t have a bolt back out and ruin my L3” insurance.

Retainer Mounting 27 June 2021

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After receiving the motor hardware and checking the fit/marking the location in the airframe the retainer installation began. The skeletonized retainer was prepped with acetone and alcohol. The airframe interior surface was prepped using 60 grit and 220 grit sandpaper and then wiped down with acetone and alcohol. The retainer was threaded onto the FWD closure of the motor hardware using an old avbay lid as a spacer. This spacer insures that the motor thrust ring will seat against the aft end of the airframe (won’t run out of threads). Rocketpoxy G5000 epoxy was used for the bonding and the assembly was set at a 5 degree decline (aft end high) to ensure no excess epoxy moved onto the motor case. The excess epoxy on the FWD end of the retainer was removed with a squared off stir stick and gloved finger. The spacer was removed after the epoxy cured and the final length of coupler that will sit in the airframe is 5.75”.

AvBay Mount Ring Installation 27 June 2021


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After the Avbay prototyping discussed above the final aluminum mount ring was ordered and after final fitting was epoxied into the NC using JB weld based on possible high temperatures due to Mach heating. The aft surface of the mount ring is approximately 4.25” from the aft end of the NC.

AvBay Sled Assembly 27 June 2021

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The final versions of the Avbay sled base and mount ring were ordered from SendCutSend and are made of titanium and 7075 aluminum respectively. The Single all thread sled was 3D printed by Additive Aerospace and is a prototype of a product they are developing. After some final adjustments to the fit the CO2 systems, wire retainers and connectors were attached to the sled base. The connecters and wire retainers are epoxied in place with JB Weld 5 min epoxy. The CO2 systems are screwed in place and use electrical tape as a “gasket” on the upper edge of the bottom flange. The taped hole just above and to the right of the right wire connector shown in the right picture above uses an 8-32 hex head screw to help attached the base to the mount ring. The forged eyebolt and cotter pin are the primary load bearing components but the 8-32 screws help to seal the AvBay and aid in resisting rotation.

 

[GrouchoDuke]

So much awesome! That’s for writing all this up. Can’t wait to see it fly.

 

[airforcetp1991]

 

[airforcetp1991]

Tanto completed a test flight today at FAR. It was flown on a motor used for motor and igniter testing by a friend of mine, Steve, who has been incredibly helpful throughout this project. The rocket achieved ~90G of acceleration at launch and a max Mach of ~1.8 in 1 sec. Max altitude, though not the objective, was 23,000' AGL. CO2 and line cutter deployments worked as planned and the rocket was recovered with no more than minor paint scratches. At launch the rocket was 7.5' long an weighed approximately 40 pounds.




These flight loads are equivalent to:

120% max drag of O-3400 flight profile

225% max acceleration of O-3400 flight profile

100% Fin Flutter margin Mach of O-3400 flight Profile

My analysis of these data indicate the rocket is more than capable of withstanding the O-3400 flight profile and completing a safe recovery. This was intended to be, and executed as, an extreme test of the airframe and design. If this test is not sufficient to prove the design's integrity I am not sure what would be sufficient.

Go with questions...

-Tony

 

[boatgeek]

An excellent flame to rocket ratio! What was the approximate average thrust and total N-s?

 

[GrouchoDuke]

EPIC! Awesome photos. Excellent work digging into all the various design aspects, requirements and gotchas for a rocket like this. I can’t wait to see you fly it with that O3400!

 

[airforcetp1991]

https://youtube.com/shorts/slGQxhknq0U?feature=share

 

[FredA]

Nice flight Tony & Steve!

 

[airforcetp1991]

An excellent flame to rocket ratio! What was the approximate average thrust and total N-s?

I’m still traveling but the first look at the data indicates about an M9000 with ~9000Ns total impulse.

 

[levi seaton]

Job well done Success taste pretty good when others have to eat it as well.

 

[Cameron Anderson]

Looks like the boat tail got a little eroded there.

 

[airforcetp1991]

Looks like the boat tail got a little eroded there.

It did, though I expected it would be single use haha

 

[rfjustin]

Nice Flight!

 

[blackjack2564]

Great proof of concept.....now on to the big One....!

 

[NateLowrie]

Very nice flight! When is the next flight?

also, is there anyway to prevent the erosion on the boattail? Is erosion like that normal?

 

[airforcetp1991]

Very nice flight! When is the next flight?

also, is there anyway to prevent the erosion on the boattail? Is erosion like that normal?

Thank you, not sure about the date of the next flight yet but hopefully soon.

I would have to defer to someone with more 98mm boattail experience but I would say a boattail is very likely to experience some kind of erosion with a burn profile like this.