Experimental fighter build thread

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Bill S

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I recently posted a picture of the experimental fighter I was going to be working on, and once I started construction, decided to do a build thread. Mainly because one guy on Facebook wanted the file so he could build one too, and I wanted to show how I did it, and help avoid gotchas.

This is what I am building: EDIT... the rocket has 3 fins, but the initial picture only showed 2, so I got a better one that shows 3 to avoid confusion.

Rocksim file attached at the end of this post.
Experimental fighter scratchbuild.png


Okay, I assembled the body tube in 2 sections, one 14" and one 8" with a coupler in between. I previously had been using Bondo glaze putty, but found some CWF that wasn't grainy and nasty like the first tub I tried it with. I sanded it, etc, no pictures.

Motor mount, one error in the Rocksim file: I had the forward centering ring too far forward, and there wasn't a ring in the middle to help hold down the engine hook, so I used some aluminum duct tape (yes, the real thing, not the usual "duct" tape).

DSC02419.JPG


As for the rear transition, its the one from a package of BT-60 body tubes, the one they used on the Sprint upscale and has a slot for the engine hook.

Next up was the fins. I did them in 3 parts, using a posterboard cutout split into 3 parts, sanded and glued together. Pretty standard.

DSC02420.JPG


Onto the wing pods in the next post...
 

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BABAR

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Beautiful design. I’m thinking your are going to need some sort of vertical stabilizers either dorsal and or ventral (preferably both) to give it some yaw stability.
 

Bill S

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Wing pod construction. I hadn't tried anything like this, but my main goals were a) cool factor, and b) durable enough that if the rocket landed on the end of one, it wouldn't buckle.

I took one nosecone (ASP BT-50 X) and cut it in half length-wise with an Xacto saw.

DSC02455.JPG


I then put it on the fin to see where it would look good, and marked around the outside edge with a pencil.

Next up is to deal with the rear transition. Its an ASP BT50/5 transition. In the photo I used some ASP 50-T tube because I wanted to use it up, but discovered that it is a bit thinner than Estes BT-50 tube, and leaves a bit of a lip at the mateup point with the transition/nose cone. The other 2 tubes will be Estes tubes...

Firstly, I need to cut out the slot for the tube to fit over the fin, so I put a lengthwise line on the tube. I then held the tube up to the fin where the nosecone positioning markings were, and measured the length of the tube protruding beyond the rear of the fin (3/16" on one side, 3/8" on the other side. I marked the tube with the same lengths, and cut out with scissors an 1/8" wide slot down the length of the tube to the proper length.

DSC02457.JPG


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Test fit of the tube on the fin:

DSC02459.JPG


Next, prepping the transition. Cut off the smaller shoulder, as that will be the back of the "engine exhaust cone" (in the picture I hadn't done that yet, order of removal isn't important really). As for the larger shoulder, I initially made the mistake of cutting it straight across 1/4" long, then I realized the wing pod would be stronger if I angled that cut so that the rear transition butted up against the rear of the fin. I glued the shoulder stub back on, and cut it so that on one side of the transition shoulder it was 3/16" tall and the other side was 3/8". I did NOT glue the rear transition in yet, see why later on. See picture:

DSC02461.JPG


Next the fun part. I had to determine how much material from each half of the balsa nose cone sections to remove so they would fit into the body tube in the fin pods. Roughly 1/16" on the flat side. It resulted in a lot of sand and try fitting, pretty time consuming really. I used a ruler with 1/16" increments to measure and see when I was getting close, and a set of calipers to measure the diameter of the front and back of the pod to see when it was close enough.

DSC02463.JPG


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Once that was done, I took the rear transition out of the body tube, held it up against the rear of the fin, and put a pencil mark on the top of the shoulder. I also put a mark on the rear of the body tube so I could line it up properly. I wanted the angle on the transition shoulder to match the angle on the rear of the fin to give it something to butt up against and give it more strength. I plan to put a dab of glue on the rear of the fin in the correct spot when I attach the fin pods to the fins.

DSC02466.JPG


I then cut down the shoulder on the nose cone pieces down to 1/4" to save weight.

DSC02467.JPG


Time to put it all together. Cut off the small (BT-5 end) of the transition if you haven't already. Slide the slotted pod tube onto the fin and slide the nose cone halves into the front of the tube and check fit one last time. CAREFULLY glue on the nose cone halves, making sure no glue has gotten on the area that attaches to the fin - in other words, you want everything to fit together nicely but you don't want the whole pod assembly glued to the fin yet. I used some Tamiya yellow tape to hold the body tube to the nosecone shoulder until everything dried.

DSC02468.JPG


Continued in next post...
 
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Bill S

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Final fin pod assembly:

DSC02469.JPG


Put the pod back on the fin and make a pencil outline all around the pod. Some people might want to attach the fin pod at this point, but I won't. After building my Starship Vega rocket, which had rounded fin pods on it, and all the hassle puttying and sanding those fins, I don't want to go through that again. I had a miserable time with the sanding, accidentally scuffing up the fin pods, etc. So I'm going to try using CWF on the fins to smooth them, taking care to not get it on the area inside the fin pod attachment lines.

DSC02470.JPG


Do the other 2 fin pods. I numbered the fins and pods so they are a matched set. In theory one shouldn't have to do that, but I'm hedging my bets against Mr Murphy showing up. :)
 
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Bill S

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Beautiful design. I’m thinking your are going to need some sort of vertical stabilizers either dorsal and or ventral (preferably both) to give it some yaw stability.
I updated the description to show that the rocket has 3 fins but you can't see it in the picture.
 

BABAR

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Final fin pod assembly:

View attachment 459425

So I'm going to try using CWF on the fins to smooth them, taking care to not get it on the area inside the fin pod attachment lines.

View attachment 459426

Do the other 2 fin pods. I numbered the fins and pods so they are a matched set. In theory one shouldn't have to do that, but I'm hedging my bets against Mr Murphy showing up. :)
I think I learned this from @hcmbanjo , maybe he will chime in to confirm or refute me (he’s too nice to call me an idjit!). But i theeeeeeenk that you can use carpenters wood filler (CWF) with impunity over areas that will be joined with wood glue. Specifically you should not cover paper/wood, paper/paper, or paper/wood joint spaces with regular sanding sealer, primer, CA, epoxy, or paint, but IIRC wood glue will adhere right though CWF.

I think I see where your launch lugs are. They will certainly work fine there, although cosmetically you may want to hide them on the central side of the rocket. An added plus is that when you put the rocket on the rod, if it gets scuffed a bit against the rod, it’ll be the central side that takes the brunt. Also, if you take pad shots, since the dorsal side tends to be the “beauty side” you won’t have the launch rod between you and the camera.

given the wing surface area on this bird, it’s gonna get some blowing around by the wind. If you are at a club launch with staggered launches, it may be on the pad a while, and in any case with that much surface area prone to rod whip. Mini rail buttons might work nice for this bird if you have or don’t mind investing in the appropriate rail.

 

neil_w

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Very nice work so far, should be a beauty when finished. Great work on those pods.

This is my kind of build, lots of balsa work. :)
 

neil_w

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I think I learned this from @hcmbanjo , maybe he will chime in to confirm or refute me (he’s too nice to call me an idjit!). But i theeeeeeenk that you can use carpenters wood filler (CWF) with impunity over areas that will be joined with wood glue. Specifically you should not cover paper/wood, paper/paper, or paper/wood joint spaces with regular sanding sealer, primer, CA, epoxy, or paint, but IIRC wood glue will adhere right though CWF.
Generally true in my experience. I do not make any effort to keep CWF away from glue joints.
 

Bill S

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I was mainly avoiding using CWF under the fin pods to save sanding and weight. My rockets tend to be way overweight anyways, so I'm trying the CWF instead of the Bondo I usually use, in an effort to save weight. I'm going to sand the primer better, and try to use less paint and glue in general. We'll see how it goes. I plan to use the bare minimum sized fillets around the fin pods, as I don't want the pods to blend in too well; the same thing happened with the Starship Vega and I didn't like the effect - that and it was a pain to sand, putty, sand, putty, ad nauseum. :(

I'm hoping the rocket won't have rod whip, its got 3/16 launch lugs and will be using a 4' rod. I have yet to actually see rod whip, the worst candidate for it that I have is probably my Estes Interceptor, as it mainly veers one way or another (except with the C5-3 engines, which are the closest to straight up I've seen with it).
 
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Bill S

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While I was waiting for the motor mount to dry, prior to attaching the fins, I decided to make the fighter more "fighter-like" and add a cockpit and Interceptor-like decals.
As for the cockpit, I took 2 BT-20 plastic nosecones, cut off the shoulders, glued them end to end, and then cut in half to make a cockpit.

DSC02471.JPG


I then took some 220-grit sandpaper, put it on the nosecone where I intended to mount the cockpit, and moved the cockpit assembly back and forth until the bottom was shaped to match the nosecone contour.

DSC02472.JPG


I then glued the cockpit on with some styrene plastic cement.

DSC02473.JPG
 

Bill S

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I've been unable to do much with the project due to cold and windy weather preventing me from sanding the fins, etc. Got one done today, 2 more to go soon.
 

Bill S

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After a period of cold and windy weather, I was finally able to sand the fins and attach them.

DSC02491.JPG


Fillets (2 coats) with Titebond II. For some reason, I kept getting bubbles rising to the surface as it dried, more than usual. I ended up using some of my Bondo glazing putty to fill those in and touch up.
DSC02492.JPG


I then put the wing pods in place, and drew a faint pencil line around the outside edge to help me position them.

DSC02493.JPG


I put a thin bead of glue on the inside of the line, and then on the rear of the fin inside the lines where the rear transition cone would butt up against. I used q-tips to quickly remove any glue that squeezed out, touching up with some that were moist with water.

DSC02494.JPG


A little bit of CWF will be necessary to fill in slight gaps between the fin and pods. I will also need to do a little general touchup and sanding prior to priming it.
 

neil_w

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Looks beautiful.
Fillets (2 coats) with Titebond II. For some reason, I kept getting bubbles rising to the surface as it dried, more than usual. I ended up using some of my Bondo glazing putty to fill those in and touch up.
That is where Quick and Thick shines: no bubbles. I do one fillet of TBII, then finish on top of it with Quick and Thick. *Occasionally* Q&T will get a bubble here or there, but it's rare.
A little bit of CWF will be necessary to fill in slight gaps between the fin and pods. I will also need to do a little general touchup and sanding prior to priming it.
I would think glue fillets are all you need there, although obviously CWF will do the job as well.
 

Bill S

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Neil, I was going to skip the fillets on the fin pods; when I did my Starship Vega that had similar fin pods, it was a nightmare blending and smoothing them out, so I decided to skip them this time.

I may have to try the Quick and Thick if I can find some locally. Thanks.

Forgot a pic of the complete rocket (sans priming/painting):

DSC02495.JPG


As for an name, calling it the Enforcer-17 with Space-X logos on it (alternate future timeline where the fighter is an enforcer ship for the Space-X corporation that runs colonies on Mars and the Moon, plus many asteroid mining facilities - they are the dominant economic force in the solar system and need to defend their assets from Earth-based factions that are desperate for resources and try to seize them. 🙂

Nearly ready for priming and painting. I'll be borrowing many decals from the Estes Interceptor plus making some of my own as well.
 

Bill S

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After getting some weird numbers in Rocksim, trying to adjust the mass object to represent the weight of glue, I decided to try and figure out where the extra weight in the rear was coming from. The only items I hadn't weighed were the fins (forgot to weigh them before using CWF on them). Turns out that the balsa I got from Balsa Machining is of the "hard" variety, and so weighed about 2.3x the weight of the "medium" balsa I had gotten from SIG. So there was an extra .7oz in the rear just in balsa roughly. Once I adjusted that, I was able to tweak things so that it represents current weight and CG (assembled rocket, no primer/paint yet). That extra weight has thrown off my stability #s to the point where it won't be stable on E12 motors, so I will probably have to add a little noseweight.

So lesson learned, be more selective of source for balsa and ask what the weight/density of it is before you order it. And for sure, don't forget to weigh the fins BEFORE putting CWF on them. :(
 

Bill S

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After some delays due to funky weather, I have the Enforcer painted white. I will be handpainting the rear of the fin pods/engines a metallic dark grey, and the cockpit canopy will be sprayed a gold color.

I plan to wait until Monday to start applying decals. I had to apply 4 coats of paint to cover up the grey filler primer. I think I am going to start only using one coat of filler primer, sand most of it off, and then use some Tamiya white primer. My rockets always end up overweight due to having to use excessive amounts of paint to cover the grey primer. It took 2 cans of Tamiya Pure White to cover adequately.! :(

Decal-wise, once I figured out Inkscape, I was able to make up 2 decal sheets, borrowing many of the decals from the Estes Interceptor, plus a few of my own.

Gotcha was that for the second sheet, it had been sitting a few days after printing, waiting to be clear coated (it was rainy/humid for a few days and I didn't want to risk a problem). Forgot to give the decal sheet a quick blast of canned air to remove any dust, etc. Naturally after I clear coated it with the first coat, did I see some dust on the sheet, which I had just clearcoated. Trashed it, had to start over, won't be able to coat the replacement sheet until Thursday (again, raining today, bleh).

DSC02507.JPG
 

Bill S

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Yes they are pretty good. Glad I stocked up on white a while back. Need to check my inventory for future use though; hate to run out at the worst possible time. :(
 

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I've weighed the painted rocket and checked CG. I think I want to add some noseweight. Right now, when I put in motors and physically check CG , this is what I get:

D12-5 stability 1.23
E12 stability .94.

If I add .25 oz noseweight, those numbers for the E12 go up to 1.3. .50 oz = 1.44. My question is this: Is there an optimum stability, allowing for possible simulation inaccuracy in the Center of Pressure? I know the accepted minimum stability is 1, up to 2 is okay, above 2 you are asking for weathercocking issues. Is there any real benefit in using .5 oz noseweight, other than a little more insurance that it'll be stable? I give up anywhere from 15-20 feet altitude for the extra .25 oz, which isn't very much.

If I had used lighter balsa (8-10lb/cu ft), then no noseweight would have been needed, but I used the balsa Balsa Machining sent me which was 20+ lbs/cu ft and didn't weight it before attaching it. So that's an extra .8oz in the back of the rocket that I have to contend with. Lesson learned, check fin material weight before you use it.
 

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The rocket is done! :)

I've finally finished up my experimental fighter model rocket. Its now called the Space-X Enforcer class. Briefing follows:

It is 2072. Space-X has established colonies on Mars, Ceres, Titan, and numerous other facilities around the solar system. Space-X is the most powerful corporation in the Solar System, and is the most technologically advanced. As Earth's resources dwindle, the Earth powers begin to mount clandestine raids upon Space-X facilities and shipping to steal resources.

Space-X's CEO, Elon Musk the III demands that something be done about these illegal raids. The response is a new warship, Space-X's first independently built space fighter, the Enforcer class.
It is equipped for long duration flights, can operate in atmosphere, and is well equipped to deal with any opponents. Mounting 6 pulse lasers for missle defense and short range combat, 3 missile bays that can carry a mix of conventional or thermonuclear missiles, and a 6cm nose mounted railgun, it is an tough opponent. It is rumored to be able to carry the new AN-57 Anubis antimatter munition as well.

It is commonly seen escorting Space-X Longships (Estes Longship ), but is also seen in show the flag manuevers at Luna and Earth.

I used Estes Interceptor decals and some of my own. The rocket is 31" long, and flies on Estes D12 and E12 motors, as well as Quest D20-4, and Aerotech D10-5, E20-7 and E30-7 motors.

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DSC02518.JPG
 

BABAR

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That one belongs either in a museum or on a movie set! Great design and execution!

Hope you get a great flight!
 

Bill S

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Thanks, I appreciate it. I may build another one at some point (this version is tail heavy due to the very dense balsa I bought) with proper weight balsa and maybe tweak the decals a bit.

I've also fooled around with 25% and 40% downscales to give me more smaller rockets to fly, as my collection seems to be trending towards D/E engines lately. :)
 

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Slick looking bird. Would fit right in to an Atilla Hejja or a Vincent Di Fate sci-fi painting.
 

Bill S

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Stunning. I would be afraid to fly it because it might get dinged.
You have that right. It's in the same league as the Johnny Star Commander build I did; I flew it exactly once, and now it sits on the shelf looking pretty. This one, I think I may build a second one at some point. It was challenging, but the results were very nice I think. :)
 
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