L2 Project: WM Drago 4 "EX-1127"

[Theory]

It is officially that time, time to kick off my L2 project. Before I get into that, I want to talk about how I came up with this and why I am doing what I am doing.

When approaching a new build I generally build to the motors that I want to fly. That said I have always enjoyed the sledge hammer quick burn motors, especially those with a high length to diameter ratio. There is just something aggressive about them, 100% unapologetic... to that end I knew that my next big project would be built for the Loki 38/1200 case and more specifically the K1127, but also wanted a 54mm mount for the J1799.

Enter the Wildman Drago 4! Its 48"airframe set up for HED and 54mm motor mount can easily accommodate most any motor I will fly. Its final weight of around 8.5 pounds (purely a guess based on what I have seen others come in at) will allow respectable flights on moderate 'I' motors at NOVAAR's obstacle filled field, and will return some serious performance when I let it rip at Battle Park.

To the build plan. Keeping this fairly straight forward, but with a few twists from stock as, well, that's what I do. The most dramatic change will be swapping the stock nose cone for more aggressive 6-1 version also from WM. I will also be using a 19" long motor mount. This affords me two benefits, one real and one perceived. First I am a fan of anchoring my rail buttons into the forward and aft centering ring. The longer motor mount and addition of birch ply rings will allow this. Also, and this is 100% on me, I like having my motors "contained" especially if using motor ejection as a back up. The longer motor mount allows for that. No not for the aforementioned 38/1200 case, but then I do not see me using motor backup there... after that that the major components are as follows:

-Birch ply forward and aft rings with the stock fiberglass ring acing as the center centering ring. (I strongly prefer 3 rings on my builds.

-A 10" long AV bay to hold an RRC3, RRC2+ and eventually the Missile Works RTx tracker. This will be spaced accordingly by the use of a 2" long switch band. Don't want to have a ton of coupler in the airframe and secured via 2-56 pins.

-Motor retention will be via a flange mounted Aeropack using a 38mm adapter when needed

-Recovery will be a combination of 1/2" Kevlar adhered directly to the motor mount and 20' OBH 9/16 3 loop nylon harness. To save space the nose cone HED will use a 3/8" nylon harness. Thinking now that the "drogue" will be a 70" X 7" streamer with the main being either a 48" crossfire chute or a 7' RM. I also have a 70" Top Flight X form in my rocket box from a previous project that will likely work for the time being so long as it will fit. All components will be protected with Nomex blankets.

-All structural bonding will be with T88 by System Three and external fillets will be made with RocketPoxy.

-Rail buttons will be a standard 10/10 affair with an 1/8" aluminum spacer to move the rail off the airframe a touch.

-And as always, graphics will by from StickerShock23. ...really goes without saying!

really going to take my time with this one. more than the whole measure twice deal... currently I am looking to have the first flight be at the NOVAAR July or August launch. Already have an I300 in the range box.

That's about it for now. Placed an order with McMaster-Carr for the electronics bay components earlier, and aim to have the WM order completed later today.

Stay tuned as this should be fun.

 

[Theory]

everything save for RRC2+ and a few other things for the electronics bay are on the way.

next task is to clear some room on the work bench...

 

[DAllen]

Interesting. Not sure I've ever heard of the T-88 adhesive.

RRC2+ has to be one of my favorite altimeters I've ever used.

 

[Speaknoevil]

Interesting. Not sure I've ever heard of the T-88 adhesive.

Top rated structural adhesive; never brittle. Easy to use 1:1 mix.

 

[Theory]

Top rated structural adhesive; never brittle. Easy to use 1:1 mix.

YUP!

Also has a long pot life allowing for lots of working time. Its of moderate consistency, thicker than say BSI 30min but nothing like RocketPoxy. Used it for the first time on my WAC Corporal project and then almost exclusively on my Caliber ISP build. Not great for fillets as its a little too thin. I am not a huge fan of adding products to epoxies, but in this case a little silica would have gone a loooooong way.

 

[boatgeek]

Interesting. Not sure I've ever heard of the T-88 adhesive.

RRC2+ has to be one of my favorite altimeters I've ever used.

I just started using it and am a huge fan for anything structural. I really like every System 3 product I've tried (and they gave our TARC team free epoxy twice!).

YUP!

Also has a long pot life allowing for lots of working time. Its of moderate consistency, thicker than say BSI 30min but nothing like RocketPoxy. Used it for the first time on my WAC Corporal project and then almost exclusively on my Caliber ISP build. Not great for fillets as its a little too thin. I am not a huge fan of adding products to epoxies, but in this case a little silica would have gone a loooooong way.

You could definitely add a little silica to this one. The other product they have that's really useful is the EZ Fillet. It's a 2:1 mix, but it already has wood flour mixed in to be the perfect consistency for fillets right out of the mixing cup.

 

[Flyfalcons]

Interesting. Not sure I've ever heard of the T-88 adhesive.

RRC2+ has to be one of my favorite altimeters I've ever used.

Been used for a long time in homebuilt aircraft, typically in wood construction.

 

[Theory]

It’s a good day!

 

[Theory]

Went through all the parts and began washing the fiberglass pieces with dawn and warm water. Also cut the motor mount down to 19 inches as discussed earlier. Notched the forward ring for the Kevlar harness and test fit. This will be epoxied tomorrow after I prep the motor mount tube

All fiberglass pieces will be roughed with 220, then wiped down with alcohol prior to bonding.

I did bond the aft birch ring to the supplied fiberglass ring. Tomorrow I will drill the holes for the flange mount Aeropack retainer.

 

[Theory]

laid out the motor mount for the forward and middle centering rings. Each ring has a notch to allow the Kevlar harness to pass through

Lined everything up. Fit a touch looser than I wanted so I opted to use rocketpoxy to tack them in place. T88 would have been a touch thin and would have likely flowed out of the joints. The rocketpoxy stayed put!

 

[Theory]

Went to the drill press and worked on the aft centering ring. Opting to use stainless screws in place of the cap machine screws

Hard to ask for much more than that!

 

[crossfire]

Are you having the wood CR facing out? I would have the FG ring facing out. Of is there no FG cr?

 

[jd2cylman]

The Allen socket screws that came with the AeroPack retainer were stainless as well.

 

[Theory]

Are you having the wood CR facing out? I would have the FG ring facing out. Of is there no FG cr?

The plan was to have the wood ring on the outside to allow the fiberglass ring to contact the fiberglass fins keeping that bond “glass on glass”

could easily flip it. Thinking the glass ring facing out would be more resilient?

 

[crossfire]

I think the bond might be better Fg to wood. There is no right or wrong to either way. Plus its easier to clean crud off FG than wood. It's just the way I would do it.

 

[Theory]

Rodger that

though it’s all going to be painted so “cleanability” will be equal.

yes, going to remove the retainer for painting

 

[Theory]

Woke up early and got some work in. Laid out the 1/2 Kevlar to ensure its long enough. Ran into an issue on another build so now I make it a point to confirm!!!



Mixed a batch of T88 and applied a good layer under the Kevlar then on top and also small fillets doing all I could to work any air out



Covered with masking tape to keep the epoxy where I want it. This will be left to cure for the majority of today.

 

[Handeman]

Did you sew the loop in the Kevlar? If so, what thread did you use?

 

[Theory]

I didn’t, purchased from Ken at performance hobbies. He told me it is Kevlar thread.

The stitching isn’t half bad. I saturated the bottom inch in fabric glue to control fraying.

If the entire recovery system has a weak point, this is likely it, however with a target weight of under 9 pounds, this should be more than sufficient.

 

[Theory]

The motor mount is in!

after adding a little reinforcement by the way of extra epoxy to the Kevlar I was ready to go.

Mixed up two batches of T88. One was poured to the forward ring and the other was injected into the slots right before the middle ring passed the very top of each slot. The viscosity of T88 combined with its ultimate strength is perfect for this



the middle ring ended up perfectly at the top of the fin slot. Measure three times...

 

[Theory]

...and yes. Was extra careful to ensure the epoxied Kevlar did not line up with a fun slot. Noticed that on the initial test fit and thought to myself “self, don’t do that when it matters!”

 

[Theory]

going to get to work on the fins today. my though is to "tack" them in place with a small (very small) amount of rocketpoxy along the root of each, then execute internal fillets followed by external. thoughts?

typically i simply "double butter" the fins and call it a day, however, as i am really looking to push this in the future, i want to add a little more in the way of strength.

the way i have it i set up (and yea i know this is common) the aft centering ring butts right up to the aft edge of each fin and the retainer seats right against the aft end of the motor mount tube. the forward edge of each fin then butts up against the middle centering ring. all of this should work together to distribute the "instant on" force of the K1127 / K2050.

 

[Theory]

First fin prepped and installed. My oldest helped

and no fancy fin jig needed here

 

[Theory]

Woke up early and got the third fin tacked in place. Going to let all of this sit till this afternoon then I will begin working internal fillets with T88



all of my electronics arrived as well so as soon as the fin can is complete I can work the electronics bay. The original plan was to add a missile works T3 in the future, but now I have my eye on an RTx set up... time will tell there

 

[Theory]

First set of internal fillets is curing. Mixed up some T88, filled a syringe and injected as far in as I could. Then, like others, I employed a 100% custom, and finely calibrated stick to move the epoxy where I needed it. T88 has a long cure time so that’s it for today

 

[FMarvinS]

Your build is looking good! If you do enclose the missleworks GPS unit, I'd suggest placing it in a nose cone bay. I believe the output is 250 mw which could possibly affect altimeter function. I'm completing a Drago 4XL and I built a nose cone bay following Crazy Jim's "glue-less" concept but I used a titanium allthread in lieu of stainless steel in order to minimize transmission signal attenuation. This obviously only works if you plan on classic dual deployment and not HED. If you do plan on HED, you'd need to ground test with both altimeters and the gps transmitter turned on (with electric matches attached) for an hour or so to make sure all is kosher.

Good luck with the L2 launch!

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

 

[Theory]

This will be an HED set-up so yea an good deal of testing will need to be done.

A review of the overall budget looks to show that the GPS tracker will have to wait. not sure I can justify another large expense at the moment. ok, thats not true, I cant justify it!

No worries though. I intend on creating an electronics bay for the near term for the RRC2+ and RRC3 then redoing it when I settle on the GPS solution. The final components for this have been ordered. Intend to get to this portion of the build as soon as the external fillets are complete.

 

[Theory]

All internal fillers are complete so it’s time to move on to the aft centering ring and flanged retainer.

this assembly is set in a manner that the flanged retainer sits on both the motor mount tube and the aft centering ring, and the aft rig sits up against the fin tabs.

after prepping the fiberglass (went with the original plan of having the glass ring on the inside) we were ready for epoxy


for this I opted for rocketpoxy and used it immediately after mixing to provide a little flow while still staying more or less where I put it. T88 would have been messy



the ring installed. You can see it’s position at the bottom of each fin slot. Gotta fill these voids

the whole thing was then turned upright to cure. First round of external fillets will be applied and pulled tonight

 

[HVArcas]

Personally i would save the K1127 for a thinner rocket or otherwise limited and hit this bad boy with a J820 or K960

They will all be awesome flights, though. Make sure your adaptor is up to the job!

 

[Theory]

idk man, theres just something about the K1127 that speaks to me. I have taken a long look at the adapter and retainer assembly and do not see that as a weak point. ...and no doubt there are several other short burn motors, the J820 is surely one that I aim to fly. The J1799 and K2050 are on that list as well.

Now to be 100% honest, the majority of her flights will likely be on full I class motors, I405, I366, I284, I377 etc. as the closer field, and the one that is available year round (during non-COVID times) has a good deal of trees and other obstacles. While the waiver is to 4500 feet, it is advisable to keep flights to 2000ish. IMHO 2500 is kinda pushing it, even with dual deploy

building her solid as she will be one workhorse of a rocket.