V For Velocity: Thin Wall Fiberglass 54mm High Velocity Rocket for LDRS

[patelldp]

I am not really 100% ready to start posting meaningful pictures for this project yet, but I would like to post pictures of some of the awesome custom made peripherals and components I have received thus far!

The background:

Over the past 3-4 years I have had an affinity for 54mm motors in minimum diameter rockets. This journey began back in 2011 with Crank. This rocket flew on a KBA K700F for the 54/1400 case to an unknown altitude. The Featherweight Parrot altimeter didn't function properly and the rocket flat spun in and broke a fin.

The next rocket in this series was a Mongoose 54 I purchased from Prophecy. This rocket put in 2 successful boosts and one successful recovery. The first flight motor was a clone of the 54/2550 Kosdon L850S and put the rocket to 17,142' and 1,431 mph, both personal bests. The next flight was a blue L1730 for the same case but an angled launch led to a lower altitude (13,483') and a lower speed (1,289 mph), both disappointments. The booster separated due to a high velocity at apogee deployment caused by the angle and the booster was shortened significantly.

That brings us to today. With the advent of thin wall FWFG tubing, I decided that I had to give this another try. This rocket will use 36" of red thin wall FWFG tubing, a CTI molded cone complimented with an ACE-RC altimeter sled arrangement, a Telemetrum 2.0, an Archetype cable cutter, 1/16" carbon plate fins from McMaster, and a linen phenolic nozzle from Loki.

Improvements over previous iterations:

1. The thin wall fiberglass tube is lighter per inch than standard thickness Performance Rocketry carbon fiber tubing.
2. The CTI cone is significantly lighter than FWFG cones and should perfectly house the Telemetrum.
3. The APE-RC assembly is free of all thread for the Telemetrum and is custom made to my specs. HUGE shoutout to Chris for his support on this!
4. I previously used a Tragic Little Aerospace GPS, a Raven, and RRC2+ to control tracking and deployment. This wasn't great as it was bulky and heavy. The Telemetrum and single battery will save on weight and space, as will the cable cutter in lieu of "Head End Dual Deployment (HEDD)."
5. The fins are THIN. I am a little skeptical regarding the adequacy of the 1/16" CF, but I plan to build it and assess the rigidity following the fillet application.
6. Said thin fins will be attached using fin guides made by Nat Kinsey at UpscaleCNC. Again, a custom made part at a good price with great service! Having those thin fins on super straight makes me feel a little better.
7. Lastly, the Loki phenolic nozzle will permit me another 1" in propellant over my graphite nozzle. I haven't ordered this yet, but I am sure Scott will be more than up to the task to provide great service.

I've attached a picture of the guides on the tube with a fin in place. These guides fit like a glove on the tube and the fin, thanks Nat!

More to come!

 

[patelldp]

Here's another picture of the fin guides, now with all three fins.

 

[rfjustin]

Bevels, what about bevels!

 

[CarVac]

Why would the angled launch result in lower velocity? Vertical velocity maybe, but overall without gravity I'd imagine that it would go faster. Except maybe due to increased air resistance?

Anyway, cool project and good luck.

 

[patelldp]

Why would the angled launch result in lower velocity? Vertical velocity maybe, but overall without gravity I'd imagine that it would go faster. Except maybe due to increased air resistance?

Anyway, cool project and good luck.

I agree, and my wording was a little off. There was a significant kick off the pad followed by a wobble. I imagine that the motor underperformed compared to expectations, as well.

 

[ChrisAttebery]

Subscribed!

I'm looking forward to building my own very similar 54mm project this year. Have you run Aerofinsim on this or any other project?

 

[4kids49]

Subscribed. Good luck with your project Dan. It is interesting to me that you are going with one altimeter. I am waffling on this topic for the same reasons that you mentioned. Bulky and heavy. I have a nice plan for small, light, single altimeter design. My two altimeter design is much heavier, longer, harder to setup etc. Now you have me thinking. Part of my decision will be on whether I can control CG favorably with a light nosecone and light av bay or not with large motors. If not, I will go to heavier av bay first, then heavier nosecone.

 

[patelldp]

Subscribed. Good luck with your project Dan. It is interesting to me that you are going with one altimeter. I am waffling on this topic for the same reasons that you mentioned. Bulky and heavy. I have a nice plan for small, light, single altimeter design. My two altimeter design is much heavier, longer, harder to setup etc. Now you have me thinking. Part of my decision will be on whether I can control CG favorably with a light nosecone and light av bay or not with large motors. If not, I will go to heavier av bay first, then heavier nosecone.

It's all a matter of comfort. I am not to that point yet with the Telemetrum as I have never flown it. I plan to do that a couple of times prior to this flight to work out any kinks and become proficient with it. Only then am I going to be okay with flying it solo.

While not redundant, I will save a significant amount of weight in batteries alone.

 

[patelldp]

Fins lightly beveled (yes Justin, lightly beveled), and everything scuffed for application. I didn't want to apply too heavy if a bevel as it's pretty difficult in this thin stock.

 

[4kids49]

Fins lightly beveled (yes Justin, lightly beveled), and everything scuffed for application. I didn't want to apply too heavy if a bevel as it's pretty difficult in this thin stock.

View attachment 254085

Nice bevel. Looks like the root edge based on your above photos. Or is the long edge just scuffed up for mounting?

 

[patelldp]

Nope, that's the the root scuffed up, 1/2".

The bevel is really just a broken edge. I may got back after and hit it with a sanding block.

 

[patelldp]

Third fin attached with RocketPoxy. I kind of wish that I used the black pigment for this application as it thins the epoxy slightly.

For the fillets, I will be precisely weighing the resin, hardener, and pigment with my TBB. I know the RocketPoxy is forgiving to slightly "off" ratios, but I want it all to look identical and behave the same. This project will likely be painted.

 

[conman13]

Subscribed. This is going to be an Interesting build!

 

[patelldp]

Guides removed, fins are straight as an arrow! Certainly better than I could ever do by eyeballing, needless to say I am quite happy!

The tube with fins attached now weighs 15.0 oz (427g) according to my kitchen scale. Figuring 10g per fin fillet (TBD), that puts me at about 490g, or 17.3oz! I think that making a sub-two pound rocket is feasible, but we'll see!

 

[RKeller]

Thats awesome. I would do black fillets and no paint. Looks killer as it is.

 

[ChrisAttebery]

Paint is just added weight. :wink:

 

[patelldp]

Fillet time!

First step is to choose a fillet tool. In my case, I am using a section of a retired 7/8" Delrin propellant mandrel. Using CJ's sharpie method, mark the boundaries of the fillet.



Next, you apply masking tape at this line.



And again. Also, you re-scuff the field and clean with acetone.



Mix epoxy! I overestimated my epoxy needs before. It looks like a 10g batch of epoxy is all I'll need for two fillets. Added the recommended 5% pigment, as well.

 

[patelldp]

Smear the epoxy into your crevice and push it in to avoid any air bubbles.



What follows is messy mayhem. Taking the tool, you spread out the epoxy until it's smooth and forms a nice fillet.

This is the result:





After you're satisfied, VERY CAREFULLY remove the masking tape. The epoxy may "string" as you pull the tape away and it can get everywhere. Not a big deal, I just don't want little black smears all over the place.





I'm now monitoring the fillet sag. I've never done a fillet in this manner, however I wanted full continuity around the fin. Seems to be working well with minimum sag thanks to the RocketPoxy, but we'll see!

 

[DizWolf]

I know the 38mm thin wall i have is a bit loose on motors... hows the 54 in that regard?

 

[patelldp]

I know the 38mm thin wall i have is a bit loose on motors... hows the 54 in that regard?

Slightly loose. Two wraps of masking tape on my 2550 makes it a nice smooth fit. I will need a little more to friction fit it for the flight.

 

[tim cubbedge]

Just my 2 cents but I found it best to do adjacent fillets at same time when using rocketpoxy. Found it to sag a bit the way you did it. Other than that, pretty cool build!

 

[patelldp]

Having a 65 degree basement affords me some interesting benefits when dealing with epoxy. The fillets didn't sag considerably.

I set the rocket on my boiler overnight (~72 degrees) and it cured up nicely.

Here's the result, along with the other two fillets taped off:

 

[patelldp]

Fillet #2 done. It's a little more rough than #1, but that could just be my OCD showing.



I'd be mistaken if I didn't send a huge thank you to Tony A for sending me a few items incorporated into this build. The tape used for the rounded fore and aft ends of the fillet is 1/4" wide and allows some simple curvature. Tony sent me a package with this tape and some Kevlar mule tape a while back. Thanks so much Tony, I'm putting it to good use!

 

[EeebeeE]

Subscribed. Good luck with your project Dan. It is interesting to me that you are going with one altimeter. I am waffling on this topic for the same reasons that you mentioned. Bulky and heavy. I have a nice plan for small, light, single altimeter design. My two altimeter design is much heavier, longer, harder to setup etc. Now you have me thinking. Part of my decision will be on whether I can control CG favorably with a light nosecone and light av bay or not with large motors. If not, I will go to heavier av bay first, then heavier nosecone.

I would seriouslt consider adding a Perfect Flite MT-4 timer as a redundant apogee deployment. I do this on my single altimeter projects for a few reasons.
1. The MT-4 is tiny, can be connected to the same altimeter battery, and gives you at least redundant separation so if the altimeter fails, the rocket at least does not come down ballistic. This is going to go out of sight, and if it were to come into a crowd ballistic there would be very little opportunity to get out of the way. Motor ejection as a redundant charge will not work because chances are the delay will be too short.
2. The MT-4 has an accelerometer on it that will beep out max speed in MPH and max Acceleration in G's. A baro altimeter on a rocket like this will be inaccurate past mach.
3. The MT-4 also beeps out battery voltage levels so you know whether or not you have a sufficient charge when you turn the rocket on at the pad.

Please seriously consider some sort of backup deployment. A rocket coming in ballistic from 20,000' could do a lot of damage.

 

[patelldp]

I would seriouslt consider adding a Perfect Flite MT-4 timer as a redundant apogee deployment. I do this on my single altimeter projects for a few reasons.
1. The MT-4 is tiny, can be connected to the same altimeter battery, and gives you at least redundant separation so if the altimeter fails, the rocket at least does not come down ballistic. This is going to go out of sight, and if it were to come into a crowd ballistic there would be very little opportunity to get out of the way. Motor ejection as a redundant charge will not work because chances are the delay will be too short.
2. The MT-4 has an accelerometer on it that will beep out max speed in MPH and max Acceleration in G's. A baro altimeter on a rocket like this will be inaccurate past mach.
3. The MT-4 also beeps out battery voltage levels so you know whether or not you have a sufficient charge when you turn the rocket on at the pad.

Please seriously consider some sort of backup deployment. A rocket coming in ballistic from 20,000' could do a lot of damage.

Duly noted.

The Telemetrum reports its status via RF to a base station, live, throughout the time it is on the pad, in flight, and during recovery. This includes its current state of operation, GPS coordinates, GPS readiness, battery voltage, and charge continuity.

I don't dispute your call for redundancy at all, however the Telemetrum is a well proven flight computer that has successfully recovered rockets that have flown to far greater altitudes and velocities than this one. The fact that it displays the status of essentially all possible "points of concern" directly to my computer or droid device will permit me to make very informed "go/no-go" decisions should something appear out of sorts.

Also, as you mentioned it, utilizing the same battery to run the altimeter and the timer isn't true redundancy. I'd recommend that you have a dedicated battery for each unit and treat each unit as its own independent "system."

 

[patelldp]

One more point on the MT-4. I'd really doubt that the unit reports reliable velocity and acceleration data due to the limitations of its accelerometer. Its "optimum accuracy" rating is 15G, "acceleration limit" is 23G, and "timer function limit" is 100G.

While the 100G is a stretch, this rocket will crush 23G.

 

[EeebeeE]

Also, as you mentioned it, utilizing the same battery to run the altimeter and the timer isn't true redundancy. I'd recommend that you have a dedicated battery for each unit and treat each unit as its own independent "system."

Agreed, but unless you are using LIPOs or smaller batteries, room is a challenge. The voltage measurement at the launch site helps. I can tell you that in my configuration, I did have a timer fire the apogee charge when the altimeter didn't. While I use one battery, I do use separate charges. The apogee charge connection apparently came loose at launch, so it did not fire. The altimeter did fire the main.

As far as limits to acceleration is concerned, you will probably exceed 23 G with what you are building. I use this configuration the most in my Mad Cow Arcas, and I routinely hit 20+ G's with it on a 6XL CTI 38mm motor. I set the timer to fire 1 second after anticipated apogee.

 

[patelldp]

Came up with a name and finished all of the fillets! "v for Velocity" sounds clever enough for me.

Here's a picture of the complete airframe for your consideration. I have put a FWFG cone on for visuals, I will not be using it for the flight.

 

[RKeller]

looks great! don't paint it. the injection molded cones are considerably shorter and lighter than that one. that thing is going to scoot!

 

[3stoogesrocketry]

Looks good Dan. I'm looking forward to ldrs this year. What's your motor gonna be?

Eric