RW Fire Flyer – Planning, building, and questions

Moan2

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Hello all!
I am relatively new to HPR (four flights and an L1 under my belt), and would like some help with the construction of my most recent rocket purchase, a RW Fire Flyer. For those who don’t know, it’s a 2.6in thin-wall fg dual deploy rocket with a 54mm MMT, so this bird is going to soar. However, I am planning on overbuilding it somewhat, as in my four flights, I have trashed two rockets due to deployment issues. Since I am so new, I figured I would share my plans with all you fine folks in order to get your thoughts and ideas, and to make sure I don’t make any huge mistakes (its no fun without little ones though!). In return for your help, I’ll give you a build thread! Sound fair? Perfect!


So, on to the plan, from top to bottom:
First, the fin can. This is going to be a doozy! There is only about 1/8in between the outer wall of the MMT and the inner wall of the airframe. I have never really done internal fillets (or external ones, for that matter) before, and this doesn’t seem like a good situation to learn in. Therefore, I think it would be better to simply Rocketpoxy the fins to the MMT, foam the admittedly small space between fins, and make good external fillets. In detailed steps, here’s what I am going to do.

1. Figure out where the forward CR goes on MMT
2. Sand MMT and CR, then epoxy forward CR in place
3. Sand forward CR and inside of airframe, then epoxy forward CR to airframe. Aft CR will be in place for this step, but with tape tabs for easy removal.
4. Sand and line the bottom of the fin tab with lots of epoxy, the stick into fin slot. Repeat for each fin, then slide fin alignment guide in place
5. Foam the spaces between the fins
6. Sand aft CR and airframe, then epoxy in place
7. Sand end of MMT, and JB Weld motor retainer onto end

However, I do have a few questions here. First, I am using an Aeropack motor retainer, and the outside lines up almost perfectly with the airframe, so I would like there to be as small a gap between the two as possible. Is there a good way to find the right place to place the forward CR so that it lines up with the top of fin slot? Secondly, the fin slots are about 3/8in too long for the fin tab. I am planning on having the fins as far forward as possible, so that any force on them gets translated directly into the airframe, is that a good idea? Thirdly, recovery. The CRs are so thin that I don’t really want to sand them down to allow the Kevlar to pass under the forward CR. Therefore, I was planning on looping the Kevlar around the MMT above the upper CR and knotting it, then once again, similar to how you would truss a roast, pulling it tight, then liberally applying epoxy. Thoughts on this method? Fourthly, the two part expanding foam. I did a little test a few days ago, and mixed some. The foam is still fairly compressible and hasn’t stiffened up much at all, is this normal? Did I not get a good mixture ratio? How long does it normally take to cure? Fifthly, rail button positioning. I haven’t used thin-wall fiberglass before, how do I get a good mount of the rail buttons? Lastly for this section, epoxy choice. I currently have Rocketpoxy, JB Weld, and some standard Five Minute. The Aeropack retainer wants JB Weld for its heat resistance, is there anywhere else that needs that kind of heat resistance, or will I be ok using Rocketpoxy for everything else?


Next up, the electronics bay:
The basics here are that I am using and Eggfinder TRS as my main, and a Stratologger CF as my backup I have never used the TRS before, so I am planning on doing a couple low and slow flights to learn the GPS side before I do something crazy. I am comfortable using the Stratologger, so no worries there. Additionally, since I am keeping the TRS’s antenna inside the ebay, there won’t be any allthread rods running the length of the bay. Instead of the standard setup, I have decided to have a single length of Kevlar running from MMT to nosecone, running through the ebay, with knots on either side to keep it in place. This allows me to build the ebay without worrying much about its strength, as the only part of it that will be structural is the fg coupler portion, which will have shear pins holding either end of the airframe on until deployment.

The ebay itself will also be fairly non-standard. Instead of a single plane, the sled will be shaped like an upside down capital T. All electronics and hardware will be mounted to the vertical board, and the horizontal board acts to shield the electronics from any whipping of the Kevlar. Both boards will be swiss cheese’d to ensure the pressure is constant in each section, and to ensure that all four pressure holes are in use.
I don’t have a step by step plan for this part, because I don’t think the order of steps matters much at all, but essentially it will be assemble the two bulkheads, cut the two boards and epoxy them together, then fit all mounting hardware for electronics, then wire it all up.

I also have a romanticized vision of having a “Remove Before Flight” tag hanging off the side of the rocket, which gets pulled once the rocket is on the pad to arm the ejection charges. I think this can be done on the Stratologger easily, as described in the Stratologger manual. The TRS manual is less clear on how it would be done, would I have the limit switch short the reset pads? The TRS manual makes it seem like the TRS would have to reconnect to the LCD receiver at that point, but I would like to have had the connection between the two made before I leave my table. Is there a way to achieve this?
Also, batteries. I have never used LiPo batteries before, so guidance there would be appreciated. The TRS manual wants a 2S 7.4V LiPo battery with at least 350 mAH. It also mentions something about a “C” rating of the battery. What do these all mean? Some suggested batteries would be great also!

Lastly, is there a good place to calculate the size of black powder charges I need, and the number of shear pins? I would do tests, but I am bouncing between my parents’ house and my dorm room, and neither want me to keep black powder or live motors, and I don’t have any casings of my own (I use my club’s casings, or single use motors).


At the top comes the nosecone:
The nosecone is going to be a fairly simple, standard nosecone. I’ll have an eyebolt to hold it to the Kevlar, some method of holding the airframe to the nosecone shoulder, and a removable bulkhead in the nosecone shoulder. For holding the bulkhead to the shoulder, I was going to epoxy two nuts to opposite sides of the interior wall, then pass bolts through the bulkhead wall to screw into the nuts. This allows me to add nose weight, or other electronics like a screamer, to the nosecone at a later date. Also, I am cognizant of the fact that epoxying the Kevlar to the MMT means the nose cone end is the only way to get the coupler tube onto or off of the Kevlar, so I want this end to be removable.
What are some good ways to attach the upper airframe tube to the nosecone shoulder so that its removable, should I need to access the nosecone, but solid enough that I don’t need to worry about it breaking from the ejection charge? Also, how do I ensure that the bolt holes in the bulkhead line up with the epoxied nuts?


Lastly, recovery:
Not too much going on here, I’m having the15in drogue in the aft tube, 36in main in upper tube, nomex for each with quick links and swivels. I think my only question here is that OpenRocket is warning me that with large motors (6GXL, etc), the main chute is deploying at high speed. Is 60-75 fps too fast? Its going to end up weighing 4ish pounds empty. Also, am I crazy for doing the single line of Kevlar thing? I’ve never seen it done, on here or irl.


Sorry for the wall of text, there will be pretty pictures to come, I promise!
Thank you all in advance!
 

blackjack2564

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Here's how to build a 54mm motor in a 2.6 tube.
This is a scratch build, but has the same issues....thin CR's etc.


https://www.ausrocketry.com/forum/viewtopic.php?f=6&t=2564

Retainer: dry fit mm tube,with motor installed and cap screwed on. Insert into airframe so there is just enough sticking out you can unscrew the cap. Mark positions with pencil or blade through fin slots.

Remove Slide on Cr's from front. put in place with a fin between for spacing. Drop of CA on all parts to hold in place.

Slide assembly into airframe, check fit...put fins in slots..check fit. If all OK remove. Epoxy on rear CR and retainer.

Notch front CR for shock cord Y-harness. Slide CR on MM tube over cord. Be sure cordage is aligned BETWEEN fins. Only need 4-5 inches of cord glued on. All force is pull..no shear..
Put everything back on marks and glue up. Pics in the build thread above...but I don't use retainers on everything high perfrormance.

Move fins forward in slots. I don't have enough time right now to address all your Q's...that a build thread in itself buddy. Read my link...it will answer most of your Q's

Scratch the single cord thingie, where do you get that stuff...use a single rod through center of bay if you wish to have forces centered. Heck Goggle strength of threaded rod sizes. I'm not going to address all the Q's that what's called experience in build.

Good luck & have fun!

Edit: 2 small diam. all thread should not be an issue with GPS. I use #6 in bay this size, with 3/16 welded/forged eyebolts. Be sure GPS antenna faces away from launch rail.
 
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woferry

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Since I think you said this was your first FG kit, you did wash all of the parts to remove the mold release first, right?

Next up, the electronics bay:
I also have a romanticized vision of having a “Remove Before Flight” tag hanging off the side of the rocket, which gets pulled once the rocket is on the pad to arm the ejection charges. I think this can be done on the Stratologger easily, as described in the Stratologger manual. The TRS manual is less clear on how it would be done, would I have the limit switch short the reset pads? The TRS manual makes it seem like the TRS would have to reconnect to the LCD receiver at that point, but I would like to have had the connection between the two made before I leave my table. Is there a way to achieve this?
Also, batteries. I have never used LiPo batteries before, so guidance there would be appreciated. The TRS manual wants a 2S 7.4V LiPo battery with at least 350 mAH. It also mentions something about a “C” rating of the battery. What do these all mean? Some suggested batteries would be great also!

Have you already soldered the TRS? It has the option to use separate deployment power from the power for the rest of the electronics. This would allow you to either use a bigger battery for the electronics (so that it can run longer in case it takes time to find the rocket) while using a smaller one for the deployment charges (less stress on the TRS's transistors), and you could also switch the deployment power without affecting the rest of the electronics (even if both are still powered from the same battery). If you can find a dual-throw switch it can switch power to two batteries at the same time, or you may be able to put two switches in-line so that the same pin would release both switches.

But yes, any time the electronics side of the TRS is powered-up it needs to be re-sync'ed with the LCD unit, you generally want to power-up the LCD, wait for the 'Waiting for Sync' screen, then power up the TRS, should sync-up within a few seconds. Also be aware of the arming procedure for the TRS, there are multiple required 'holds' (long button presses) for it to be properly armed for flight, if it's not sending you GPS coordinates it's NOT ready to fly. I crashed a rocket once forgetting this detail, got to the screen that reports the Main/Drogue status, but never did the final step so the rocket came in ballistic since there was no backup.

The main thing to keep in mind with LiPos is when you're not using them they prefer to be left at ~50% charge, not fully-charged. And you never want to fully-discharge them as it causes damage to the cells (reduces their capacity). Any good balance charger with a 'storage' function (to set the 50% charge level between launches) should do the trick. I tend to use larger batteries (900-950mAh) on my electronics, so I'll let others make suggestions there. The "C" rating in a LiPo indicates how much current the battery is rated to provide during discharge, and it's a multiple of the capacity. So a 300mAh 10C battery could deliver 3A without damaging the battery. Higher currents (larger capacity and/or higher C ratings) can put more current through the altimeter's FET/transistors during the charge firing (especially if the charge ends up being shorted for some reason), which can cause the FET to fail. When ground-testing an altimeter I always suggest testing TWICE, as the first time may work but damage the altimeter such that it'll never work again, and without two tests you wouldn't know until the first flight. LiPos also do best (last the longest) if not charged above the "1C" rating, unless the battery says otherwise. So for my 900/950mAh LiPos I set the charger to 900mA, for my 1800mA battery that powers my LCD I bump the charger up to 1.8A.

I'll also note on the StratoLogger / Eggtimer combo that Eggtimer's deployment tends to be a bit later, the standard algorithm for 'nose-over' is actually 1s after apogee. So if you configure the TRS as the primary at nose-over and the StratoLogger for apogee + 1s I think you'll find both charges fire around the same time. I haven't done this particular combo, but I have paired a SLCF with an Altus EasyMini, and I left the SLCF set to its defaults and made it the primary, since I found it easier to tweak the settings on the EasyMini to make it the backup altimeter. Seems to me that the same would be true here, easier to tweak the TRS to be the backup (since you can do it using the LCD, and may want to leave the drogue charge at nose-over, as nose-over+1s may be 2s after the StratoLogger's drogue) and leave the StratoLogger as the primary with its factory default settings. I know whenever I fly my AltimeterThree along with a SLCF it always says the SLCF's deployment was early (before apogee), it never gives this complaint with the Eggtimers I have (TRSs and Quantums).

Lastly, recovery:
Not too much going on here, I’m having the15in drogue in the aft tube, 36in main in upper tube, nomex for each with quick links and swivels. I think my only question here is that OpenRocket is warning me that with large motors (6GXL, etc), the main chute is deploying at high speed. Is 60-75 fps too fast? Its going to end up weighing 4ish pounds empty. Also, am I crazy for doing the single line of Kevlar thing? I’ve never seen it done, on here or irl.

I haven't understood the knots-at-both-ends trick, maybe I just don't know the right knots but I don't see how you'd get the lids tight enough to seal off the bay from the charges outside. All-thread in the avionics bay doesn't mean the TRS won't work at all, it just can create 'blind spots' for the signal it's sending. The farther you can keep the antenna away from the all-thread the better, and personally I think having the antenna not parallel to the all-thread (i.e. tilted somewhat, easy to do if you're using the brass rod) would help also, though I don't have any proof for that.

If you're concerned about the drogue descent rate you could always switch to a larger drogue chute. Though personally, I'd suggest doing a less aggressive flight first just to try things out, and use the data from your altimeters to check the actual drogue and main descent rates. In my experience the parachutes come out quite different than the sim defaults, I've often had to modify my chute Cds and often significantly (anywhere from ~0.4 to >2) to get the sims dialed-in to my actual flights, but once I figure out the right numbers they've been very accurate. So you might find that it's computing the wrong speed just because the Cd isn't right for the chute you specified.
 

DavidMcCann

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foaming is likely to be an insane mess, for no benefit. Put some epoxy in the slots, put some on the fins, press them in...then do solid external fillets.

I've seen the kevlar thing done before... mostly on 38mm MD's In theory it can work, but I think trying to get knots that close the bay is going to be problematic. I'd also worry after apogeee, the caps would open on descent and the opening of the bay may cause issues with the altimeters inside. If you're concerned about the all thread that much, I'd get a separate tracker and put it in the nose with no all thread. Personally, I'd just leave the tracker in the regular mid-body av bay with all thread.


New ideas are good to try. Maybe it'll work out well. But it may be advisable to try a simpler method if you've been having issues with recovery. It's much easier, and preferable to focus ideas and energy on getting a good recovery, than on overbuilding for a bad one.
 
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Maxter

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Here's how to build a 54mm motor in a 2.6 tube.
This is a scratch build, but has the same issues....thin CR's etc.


https://www.ausrocketry.com/forum/viewtopic.php?f=6&t=2564

Retainer: dry fit mm tube,with motor installed and cap screwed on. Insert into airframe so there is just enough sticking out you can unscrew the cap. Mark positions with pencil or blade through fin slots.

Remove Slide on Cr's from front. put in place with a fin between for spacing. Drop of CA on all parts to hold in place.

Slide assembly into airframe, check fit...put fins in slots..check fit. If all OK remove. Epoxy on rear CR and retainer.

Notch front CR for shock cord Y-harness. Slide CR on MM tube over cord. Be sure cordage is aligned BETWEEN fins. Only need 4-5 inches of cord glued on. All force is pull..no shear..
Put everything back on marks and glue up. Pics in the build thread above...but I don't use retainers on everything high perfrormance.

Move fins forward in slots. I don't have enough time right now to address all your Q's...that a build thread in itself buddy. Read my link...it will answer most of your Q's

Scratch the single cord thingie, where do you get that stuff...use a single rod through center of bay if you wish to have forces centered. Heck Goggle strength of threaded rod sizes. I'm not going to address all the Q's that what's called experience in build.

Good luck & have fun!

Edit: 2 small diam. all thread should not be an issue with GPS. I use #6 in bay this size, with 3/16 welded/forged eyebolts. Be sure GPS antenna faces away from launch rail.

What he said. I built mine almost exactly like this. Read the Darkstar sticky, then read it again. Great info. Have fun.
 

Moan2

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I haven't understood the knots-at-both-ends trick, maybe I just don't know the right knots but I don't see how you'd get the lids tight enough to seal off the bay from the charges outside.
I think trying to get knots that close the bay is going to be problematic
My apologies, I wasn't clear. The sled will have bolts to hold the ebay bulkheads on, the knots on either side are to keep the ebay from sliding around on the kevlar line. The sled is technically structural, but doesn't feel the full force of deployment, just the inertia of the ebay, and those forces should be compressive rather than tensile.

Since I think you said this was your first FG kit, you did wash all of the parts to remove the mold release first, right?
Nope, good to know!

I'll also note on the StratoLogger / Eggtimer combo that Eggtimer's deployment tends to be a bit later, the standard algorithm for 'nose-over' is actually 1s after apogee. So if you configure the TRS as the primary at nose-over and the Stratologger for apogee + 1s I think you'll find both charges fire around the same time.
Interesting, so I should set the stratologger to +2s then?
 

woferry

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On the washing, I'd suggest downloading the instructions from any of Madcow's FG kits (on their website, like the 4" FG Nike Smoke). They have a recommended mix of water, alcohol and dish soap, it's what I use but I always have to download something to consult, I don't have it memorized. But you definitely need to remove the mold release before doing any epoxy, and I've heard it needs to be done before sanding also or it just rubs the compound deeper into the fiberglass and then it won't wash out (or gets harder to wash out). But since it's designed to get the molds to release easily, it will also make it harder for the epoxy to stick to the surfaces. And my experience with RW/Madcow kits is they're pretty generous with the compounds, you quickly get dusty dealing with the parts as-shipped (except for the fins which recently have been covered in duct-tape residue or something similar, for me acetone has worked the best to remove that gunk).

My apologies, I wasn't clear. The sled will have bolts to hold the ebay bulkheads on

Ah, okay. So there is still metal at the ends, just not all the way through.

Moan2 said:
Interesting, so I should set the stratologger to +2s then?

As I mentioned, I'd suggest leaving the SL to its defaults and using the TRS as the backup personally, but I guess you could try +2s on the StratoLogger, assuming it supports that option. Otherwise you can stick with +1s, I just think you'll find they're competing with each other, based on my own experience (and understanding of Eggtimer's algorithm/documentation).
 

FMarvinS

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I previously built the RW Blue Lagoon which has the same issues-namely a 54 mm motor mount tube in a 2.56 inch diameter body tube. I agree with the advice you got from CJ, woferry, and David which is excellent and reflects there vast experience. I combined the double dipping technique mentioned by David and the injection technique discussed by CJ. Most likely overkill-but after a dozen flights-no issues. The reference build from CJ is very good and as already advised review CJ's excellent DarkStar build -its a textbook on how to build fiber glass rockets which also . includes internal fillet injection technique. There is also a good RW Fire Flyer TRF build thread that you can look at (https://www.rocketryforum.com/showthread.php?142887-2-6-quot-54mm-MMT-Fire-Flyer-(MadCow-RW)).

With respect to single all thread AV-bays-you may want to review the advice available within another TRF thread (https://www.rocketryforum.com/showt...ll-thread-rod-to-secure-av-bay-sled&p=1753777), There are several perspectives discussed in this thread that may help.

With regards to the pull-pin switch utilization for an altimeter, you may find elements of the following thread also helpful:
https://www.rocketryforum.com/showthread.php?143967. I'd suggest you also look up Handeman's level 3 build in which he has excellent photos of his use of these micro switches.

Also, with regards to a nose cone electronics bay, there are several methods. An excellent post similar to what you outlined is found in the website describing the "Kate" altimeter in which 4 threaded coupler nuts are attached via epoxied kevlar cloth to the inner surface of the cone. Just using JB weld alone to hold the nuts is insufficient and risky. You are better off sanding all surfaces (with a dremel) then JB weld epoxying the nuts in place followed by 2 layers of fiber glass cloth (soaked in West systems epoxy) or utilizing kevlar cloth as outlined in the Kate altimeter commercial post.

Finally, with regards to your issues of parachute deployment-for the RW Blue Lagoon build I used a Jolly Roger chute release for main chute deployment and 2 altimeters (Stratologger CF and MW RC 2++) for streamer or drogue deployment. Since the length of the body tube is limited, the use of the chute release and the need for only one high end separation point, facilitates the use of larger motors than would be possible in traditional dual deployment.

CJ is one of the best sources for rocketry builds and David and Woeferry are also excellent sources. As a matter of fact, I have often sought advice from CJ and David in the past on rocketry questions. Essentially they are great reference sources. Before I put you to sleep, I'd just say-take your time in the build (there's no medal for a quick finish) and as advised by the others do low & slow flights first to work out all the potential kinks. Good luck!

Fred, L2
KG4YGP
member of ICBM, S.C.
 

Handeman

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Lastly, recovery:
Not too much going on here, I’m having the15in drogue in the aft tube, 36in main in upper tube, nomex for each with quick links and swivels. I think my only question here is that OpenRocket is warning me that with large motors (6GXL, etc), the main chute is deploying at high speed. Is 60-75 fps too fast? Its going to end up weighing 4ish pounds empty. Also, am I crazy for doing the single line of Kevlar thing? I’ve never seen it done, on here or irl.


Sorry for the wall of text, there will be pretty pictures to come, I promise!
Thank you all in advance!

I would recommend you don't put the swivels on the chutes, they don't do any good there, the chutes seldom spin nor the rocket under it. I have one swivel on all of my DD rockets and it's on the fin can. The longest part of the flight is when it drops on drogue, the fin can tends to spin and that is what twists up the cord. If it's a long fall, it can twist up the cord so bad it will twist your drogue right up inside it. A swivel on the chute only helps if the nose cone and fin can are spinning in a circle under the chute and that almost never happens fast enough that the chute can't spin with them. Also, get good ball bearing swivels. I tried the non-ball bearing once. It got replaced after that one flight.

I'm not sure where the idea of putting swivels on chutes came from, probably from the practice of using fishing snap swivels on the Estes chutes. The thing is, that is more for using the snap to make it easy to swap chutes than any benefit the swivel part provides.
 
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DavidMcCann

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One other thing I just noticed. A 36” main is likely to be too small. I use a 4’ rocketman in rockets this size. My screech is 7.5 pounds loaded on the pad with a 38/1200
 

Handeman

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The Fire Flyer is listed as 2 lbs. With gear and a spent motor case, maybe just over 3 lbs.

I think a 36" chute will work for the main, if it's a spherical or elliptical. If you get a Rocketman, Sky Angle, or cross type, it might be a little small. It all depends on design and actual Cd.
 
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