AGM Pike NextGen, First DD Build

[geof]

I've finished the large fins. It's amazing how well that fin jig works. Now I'm starting to tack on the aft fins. Alignment is easy, now.

 

[qquake2k]

Looking good!

 

[geof]

Help!

Having a problem. I thought I loved the peel ply, but now I've got a complaint while filling the tube surface. There are tons of little pinholes that I can't get filled. I'm alternating fill,sand,prime,repeat. I'm using water-based wood filler, as always, thinned with water. With an ordinary fiberglass weave surface, the holes are big enough that they are easily filled by the filler. But with these pinholes, the filler won't flow down in them (I've tried thick and thin, and lots of brush-stroking/massaging).

Any suggestions for a different filler substance, or strategy? There's so many holes, I really need something that I can paint over then entire surface.

[Bondo, Kilz, and aeropoxy are not options.]

Here's a look at one of the tubes...lots of invisible pinholes, but the overall smoothness is good.

G

 

[CarVac]

I'm not sure (I have little personal experience here), but isn't this where high-build primer is the answer? Prime-sand-prime-sand.

 

[ksm2001]

I would suggest what CarVac mentioned or Bondo Glazing & Spot Putty. I use Glazing & Spot Putty on small pin holes on raw fiberglass RC boats and for filling spirals on rockets. Its easy to apply with a plastic scraper or plastic gift cards, bonds well and sands easily.

 

[CarVac]

...[Bondo, Kilz, and aeropoxy are not options.]...

...Bondo Glazing & Spot Putty...

I don't know the OP's circumstances as to why he can fiberglass and paint but not use Bondo but...

 

[neond7]

I feel your pain, I did a few builds using 6 oz weave and fought the pinhole issues - lots of high build primer and sanding was the answer, but it still didn't come out perfect.

To avoid that, I now use a 3 oz veil layer over the 6 oz, and on smaller rockets I'll even use 1.45 oz deck cloth. Both leave a much smoother surface and no pinholes.

You also might want to try the teflon release film vs the peel ply.....

 

[DRAGON64]

If you had used a 0.5 to 2oz veil over the 6oz glass, you would have solved many of the pin hole issues. I always veil my builds with 2oz glass. Then fill and sand as needed. 2oz glass helps get rid of spirals as well, if you do not plan to do a heavy glass lay up.

To fill, I use KILZ primer; easy on, easy sand.

 

[geof]

I don't know the OP's circumstances as to why he can fiberglass and paint but not use Bondo but...

Bondo:It's expensive and the working time is extremely short as to be impractical unless I make a zillion little batches.
Kilz (later poster): I hate it because it sands extremely poorly, IMO. Gunks up.

I'm trying the rustoleum high-buildup filling primer to see if that works.

neond7: yes, maybe I'll try the teflon film next time.

 

[DRAGON64]

Fair enough, I'm sure a solution will find you...

 

[geof]

Some ups and downs in the last week. On the good side, I solved the pinprick issue. I used 6! coats of the filler primer, and it turned the pinprick holes into dimples. Then my standard wood filler easily filled in the dimples and sanded smooth. It turns out that that portion of tube was my first peel-ply attempt, and it was the worst. I've filled the next piece, too, and it required much less priming and filling. Hopefully the main airframe will also be easy.

The other thing I've done is make interior fillets, both between the fin and the motor tube, and between the fin and the inside of the body tube. I used a spoon on a long dowel to spread thin epoxy around a bit, then tilted the tube to get good coverage. You can do 4 at a time.

Then I began the outside fillets, and had a problem. I decided to try a new method. I used carwax on a pvc tube, then wrapped peel ply around the pvc. Then I taped the fillet, applied the epoxy, and mashed/rubbed in the tube to shape the fillet. My idea was to get a truly concave fillet. With the standard finger method, I tend to get rather straight fillets which can then be rounded with some wood filler in the corners.

So, anyway, I used 15min epoxy and waited about 30min before trying to peel away the pvc. I thought it would release extremely easily, and then I could peel away the peel ply afterward. It turned out that the tube was very strongly stuck to the rocket. At this point I panicked a little bit because I was worried I would never get the pvc off. The epoxy still appeared a bit green despite the elapsed time, so I pulled hard and was able to remove the pvc. It turns out that I also pulled up some of the epoxy.

Entering damage control mode, I used an alcohol-wet glove finger to press the shredded epoxy down into the seam as much as possible. After it is fully cured, I'll put another fillet over the top, using the standard finger method.

This isn't a major disaster because the affected fin (aft) is small and sufficiently filleted already on the inside. Just a headache. I'll do the rest and come back to it.

 

[geof]

After finishing the fillets, it was time to glue in the aft ring. I needed to sand it to fit various irregularities inside the airframe due to drops of epoxy, etc. I inserted 3 screws into the ring to use as "handles" so I could repeatedly test the fit. Then I epoxied the ring in place and removed the screws.

There is a couple inches of airframe below the aft ring. I have had previous rockets where this gets dented on a hard landing so I decided to apply several layers of thick fiberglass matting to the inside. That stuff is hard to work with, especially in a tight little space, so I slopped it in there and I'll trim it down neatly later. To ensure good adhesion to the walls, I stuffed sandwich bags full of toilet paper into the space to press the matting against the walls. The result wasn't pretty, but it is very solid and I can trim it to make it pretty next.

The "upload attachments" tool doesn't seem to be working right now, so I'll add the photos later.

 

[new2hpr]

Here's a tip on fillets. Just do them your standard "finger" method, but strike them off with a short piece of pvc pipe dipped in alcohol. You'll get the perfect curve you were after with the clamped on pipe, but no adhesion problem. Works great with a peanut-butter-thickness epoxy.
-Ken

 

[geof]

In fact, that's exactly what I ended up doing. Thanks.

Here are the aforementioned photos.

 

[JohnCoker]

Kilz (later poster): I hate it because it sands extremely poorly, IMO. Gunks up.

Give wet sanding a try. It avoids heat build-up and airborne sanding dust.

 

[geof]

Sorry I skipped a lot, but here are a couple photos to catch up.

First, I made a mistake. Frankly, I can't remember what it was anymore, but it was fixed by adding another 11in of tube, epoxied to the nose cone, with an extra bulkhead/coupler as shown in the photo. No problem.

The OD of the nose is slightly smaller than the OD of the tube, so I filled and contoured the area with bondo to get a clean curve. All the holes were drilled: 2 at the top of the main tube for shear pins, 4 at the bottom of that tube for removable rivets, one in the middle of that tube for air pressure equalizing, one in the av bay wall for the altimeter, one in the aft tube for air pressure equalizing, and two for the rail buttons (which I installed).

The instructions wanted me to install the rail buttons so they could spin. I've never done it that way, but it made sense. The aft button was attached with a screw into a centering ring, with a little epoxy in the hole. The button spins. The forward button is attached with a sort of screw rivet. As instructed, I used threadlock on this, but it turned out that the button was stuck, too. No biggie.

I also made a detachable nose weight ring (with a hole in the middle for the bolt, since the forward coupler is non-removable). Finally, I grounded out a ring for my motor retention system.

There are only a few more steps before painting:
1. Install a switch for power to the altimeter. That's being shipped.
2. Figure out how the hell to attach my weight ring (a ton of BBs and fishing weights epoxied in a doughnut shape) to the forward bolt/coupler. (I'll take a photo to see if anyone has any bright ideas)
3. Sew the main chute.
4. Figure out what is an appropriate size for a drogue chute. Can anyone clue me in...what is a desirable descent speed under drogue?

 

[geof]

Working on the chute. It is 101" diameter. Usually I like color, but I decided to go b&w on this one for maximum contrast and just to be different. I use R. Nakka's pattern-maker for semi-ellipsoidal parachutes for a higher drag coefficient. I chose 12 gores because, based on past experience, it allows quite a round shape, is convenient for shroud lines, and is "pretty".

 

[ksm2001]

Very nice!
If your using this chute for the pike 33 you might have a bit of a walk though. A quick calculation based if the rocket weights 7 lbs will have a descent rate of under 8 ft/sec. I used a 60" Aerocon chute on my pike 33 and it was around 14 ft/sec which was a nice slow descent.


Sent from my iPhone using Rocketry Forum

 

[Buckeye]

Agreed on the chute size - looks way too big for this rocket.

Also, is the nose weight really needed?

 

[geof]

Yeah, it seems big to me, too, but remember that my extension is longer/heavier than the stock build. The web calculators indicate 13fps not counting the weight of the casing, shock cords, and chutes themselves. I like a soft landing (especially of this becomes my L2 bird), and nearest tree to our launch spot is something like 7 miles! The nose weight is not needed unless I fly the biggest, heaviest motors that would fit. I have no plans to do so anytime soon, so the nose weight should just collect dust on my shelf for now.

I'm thinking 50fps for the drogue. Is that about right?

 

[Handeman]

Working on the chute. It is 101" diameter. Usually I like color, but I decided to go b&w on this one for maximum contrast and just to be different. I use R. Nakka's pattern-maker for semi-ellipsoidal parachutes for a higher drag coefficient. I chose 12 gores because, based on past experience, it allows quite a round shape, is convenient for shroud lines, and is "pretty".

View attachment 246319 View attachment 246318

Is the 101" diameter the flat diameter as you have it laid out? If it is, I would expect an effective diameter under chute of about 72".

How big it the spill hole in the center going to be? I would suggest about 6" on a chute that size. The spill hole will help make it much more stable and won't reduce the Cd of the chute much at all.

 

[geof]

Thanks for the spill hole suggestion. I didn't know the reason for it. Is that 6" diameter or radius?

I understand your comment about the effective diameter. I wonder if the reduction in diameter is somewhat mitigated by the increased drag of the semi-ellipsoidal shape compared to round or x-form. I speculate this from experience: I've made the same pattern with several previous chutes, say 80", 65", and 50" (guesses) and have always found that the descent rate is rather slower than expected, leading to soft landings and sometimes long walks. Of course another reason for these past results could be that the rockets are lighter than my computations and weighing. Or drag of the rocket itself?

 

[Handeman]

Thanks for the spill hole suggestion. I didn't know the reason for it. Is that 6" diameter or radius?

I understand your comment about the effective diameter. I wonder if the reduction in diameter is somewhat mitigated by the increased drag of the semi-ellipsoidal shape compared to round or x-form. I speculate this from experience: I've made the same pattern with several previous chutes, say 80", 65", and 50" (guesses) and have always found that the descent rate is rather slower than expected, leading to soft landings and sometimes long walks. Of course another reason for these past results could be that the rockets are lighter than my computations and weighing. Or drag of the rocket itself?

I would do the 6" as diameter. That only reduces your overall 950 square inches of canopy by about 10 square inches. The extra stability you get from the chute will be well worth it.

 

[geof]

Still working on the chute. For adjacent panels, I'm using the following approach. Place the panels "back to back" with their outside surfaces sandwiched face-to-face inside, and their inside surfaces facing outward. Here "inside surface" is defined as "inside" because I already hemmed the bottom edges of the panels, and "inside" is the surface where the hem folds into. Now that the panels are aligned this way, I sewed a line about 3/4 inches in along one edge. This is exactly the way that you would sew any seam, e.g. for a pillow case. (For the pillow case, you sew the whole thing together like this, then turn it inside out). Anyway, next I fold the edge over on itself and tucked under the fold, and sew this in place. The photo shows me pinning this second step: in the distance the nylon has been folded and is ready for sewing, and nearer the camera only the initial seam is visible. This whole thing is a lot easier to see in a picture than it is to describe in words. The other photo shows the result after turning the panels inside out. There is no visible hem on this, the top side of the chute.

I have previously always used a zig-zag stitch for making chutes. However, I'm trying a straight line stitch this time. My wife googled it a bit and she says that there is not convincing evidence that one is better than the other for this purpose, and if anything the straight stitch is stronger. Go figure.


above is finished; below is sewing one edge

 

[Handeman]

I noticed the weave angles were different on the black then the white. The white has the weave 90 deg. from the seam while the black looks like 45 deg. Was there a reason for that? The angle of the weave does make a difference in how much the fabric can stretch under opening shock and loads.

You will get little to no stretch from the white at 90 deg, but the black will be able to stretch some and absorb some shock. The issue is if the loads are too high, they can permanently stretch/deform the black section.

check out this thread https://www.rocketryforum.com/showthread.php?69018-Constructing-a-Ringsail-Parachute-Canopy by jcato and some of the linked documents about chutes. It has a huge amount of useful info on parachutes.

 

[geof]

Thanks, I hadn't considered that. I was simply trying to waste the minimum amount of material.

 

[geof]

Finally finished the sewing. I'm going to ask my wife to make the spill hole since it will be pretty tricky since the chute is already together.

I decided to use the screw-type switch that someone here recommended. It's a lot smaller than I expected (that's a dime), but I think I can make it work. The challenge will be that my soldering iron is from about 1940 with a tip about the size of a used pencil eraser. Pairing that with my very limited experience, this won't be the most elegant part of the build.

 

[dixontj93060]

Finally finished the sewing. I'm going to ask my wife to make the spill hole since it will be pretty tricky since the chute is already together.

View attachment 246733

Nice job on the chute! Personally I would pass on the spill hole.

 

[geof]

I'm finally finished, and tomorrow I attempt my L2 with this bird. It will also be my first dual deploy, first electronics. Yikes.

This project started out as a nice Madcow kitbash. Then I happened to pick up a great deal on an altimeter, so I thought it would be a good opportunity to try my first electronics. Then the L2 itch strengthened and I figured that I might as well try that too. It has been a really fun build, and if it shreds or lawndarts tomorrow, I'll try to keep reminding myself of that.

G

 

[qquake2k]

Great looking rocket! Good luck on the L2!