Polecat 10" V2 Build

[smapdiage9]

I'm going a bit build crazy lately, and the combination of a full kegerator and internet access has really been fueling this fire. Recently I ordered a 10" diameter V2 sport rocket from Polecat Aerospace, fulfilling a build desire I've had for years but never attempted.

The Polecat kit is a pretty old school one, consisting of gel coated fiberglass nose cone and boat tails, a thinly fiberglassed cardboard body tube, a thin paper/cardboard motor mount tube, and plywood centering rings and fins:

It has some 1/4" allthread and u-bolts, 16' of 1" tubular nylon shock cord, and is designed for single deploy only. I haven't cracked the nut yet on how I'm going to get dual deploy into this thing, but there are many options. The parts are made pretty well though I will note that the fin slots were way too thin. Part of this may be that the act of cutting the slots causes the four sections of the tail cone to bow in, pushing them closer together, but the instructions explicitly warn you to avoid putting too much force into the boat tail before it's assembled as it can split, so I ended up widening mine quite a bit:

Construction starts with getting the aft centering ring mounted in the bottom of the boat tail. I beveled mine for more surface area of engagement as it comes squarely cut, meaning only the bottom edge would actually touch. Gaps are filled in with epoxy:

The boattail is provided extra long so that you can trim it to where your actual CR sits. I used my power sander to reduce some of the bumpiness and do surface prep, but like many gel coated glass cones the inside surface of the boat tail is very bumpy:

Once it was all prepped I stuck the CR down there, checked through the fin slots to make sure it was even, and reached my arm waaaay down to get coverage with rocketpoxy holding it in place.

Then I use the body tube and CRs to glue the motor mount tube into the aft centering ring and let it cure:

Then I used a cutoff wheel on a dremel to widen my fin slots as well as trim the boattail flush with the CR. This was the messiest fiberglass work I've ever done, and I've never cut glass that generated so much dust. I used a respirator, face shield, and gloves, but still had to separately clean my clothes and shower afterward because the dust was insane!

Used a 98mm aeropack as a drill guide to do pilot holes for the threaded inserts, then inserted them:

So here's where we are:

More to follow!

 

[fyrfytr310]

Looking good!!! What do you think of the finish on the pre-glassed BT?

 

[smapdiage9]

This is the first of two fiberglassed kits I've bought from Polecat and I haven't opened the other yet so just my first impressions:

I've never been impressed by factory glassed tubes from any manufacturer. This one is okay: the finish is very even, but notably cloth textured so if you were trying to get a perfect finish you'd either have to do a lot of filling or a lot of sanding. The amount of fiberglass seems really thin compared to the amount of relatively soft cardboard tube, and mine came with some dings in the end that I'll have to reinforce. I'm really used to FWFG tubes and wish that this one was as confidence inspiring with regards to strength as those, but again it'll be okay.

 

[mccordmw]

Ooh! I've been eyeing big Polecat kits for a bit. op:

 

[fyrfytr310]

That is pretty much the same impression I have gotten from other polecat fliers. I have a 10" Nike on the way and I think I will prepare myself to add a thin layer of glass on top of theirs.

 

[dixontj93060]

I have always found the Polecat tubes more than strong enough. I'm pretty particular about finish on my rockets so I would be using SuperFil anyway, so really no extra process steps for me.

 

[smapdiage9]

I don't doubt that the stock tube will be tough enough for normal duty, but I've yet to make a decision about final finishing. Some builds coat the entire rocket in extra fiberglass and make it weigh even more, while others seem to have flown stock without issue. Before I worry about that I need to make a decision about getting dual deploy out of this thing. The options seem to be chute cannon (never seen a build), chute tether (I've used one many times on small rockets with reliability being nowhere near what I want), or creating a rear-eject system for the drogue and forward eject for the main meaning the boat tail is not permanently glued to the body tube.

I've started modelling an openrocket file based on the measurements I've taken so far. Added a zero mass, 10" diameter cone to the aft end of the rocket pi calibers in length and it puts my CP around the same point that the instructions illustrate it should be. Sim flights on K's so far keep it around 2000' which is low and easy like I want for this big fatty.

 

[dixontj93060]

Polecat does sell av-bays, but to keep it scale you'd have to cut the airframe and may limit your motor length.

 

[GRIFFIN]

You can do the nosecone as the AV-bay like on my 8" gizmo. Gary T did a real nice build thread a few years ago. Let me know if you can't find it and if you are interested.

 

[smapdiage9]

Thanks for the tip, I found Gary's thread. I think I'll end up copying the nosecone chute cannon/avbay design, which means I'll need to cut a new centering ring for the nose cone, find an appropriately sized tube to contain what will probably be my 120" top flight main, and figure out where to position the sled.

Fins are tacked on. Realized I couldn't find the fiberglass tape that's supposed to come with the kit for internal reinforcement, but I've got a bunch of FG cloth laying around somewhere so it'll be easier to cut my own strips. This thing is starting to take shape!

 

[GRIFFIN]

Here are a few pics of my set up.

This is the nose with the glass cannon and the piston.

Here is the sled. I use a raven and have air starts on mine as well


The vent holes are around the shoulder and one of them is used as access to arm the electronics


You should have plenty of room in the nose for the canon and chute. Mine is a 4" tube and fits a 12' ultra-X chute.

 

[smapdiage9]

Thanks! That design looks great; what are you using to retain the chute until its charge goes off? Just masking tape?

 

[farsidius]

Been eyeing this kit for awhile as well. Thanks for putting this build up. I'll be following you to the end.

-brant

 

[GRIFFIN]

Thanks! That design looks great; what are you using to retain the chute until its charge goes off? Just masking tape?

Good question. I have used heavy masking tape but prefer the metal foil tape. I have unlimited access to the tape and it is super sticky and does a great job. I also make sure the chute (wrapped in a nomex blanket) is snug in the canon. The only time I ever had a premature main was the one and only time I didn't use the nomex blanket. I think the chute was too slippery on the walls of the canon and it slid out. I am going to fly this thing again soon and can post a few pictures of the prep if you are interested.

 

[smapdiage9]

Well now that all of my arm hairs have been fully wetted in aeropoxy the hard part of building this ridiculous fin can is complete.

Seal off them messy fin slots with tape:

Then perform the easy task of perfectly aligning a two foot strip of wet fiberglass along a narrow v-channel that curves gradually narrower within a 3.5 foot tube with an inner tube that makes any kind of hand movement impossible. Then do it seven more times. Easy!

Seriously this part sucked. I had to remove and realign every one of these eight strips at least twice. I cut my strips four inches wide which gave me a much better margin of error during alignment. The can is very dark inside unless you have a light directly overhead, I recommend a headlamp. I taped a chip brush to the end of a long piece of allthread and used that to pre-paint the fin and boattail with a thin layer of epoxy. Once I had a strip wetted out, I'd roll it up from the bottom then fold in half vertically. I used one hand to pin the running end of the fiberglass roll centered on the fin-boattail joint, then use the brush pole to unroll the cloth down the vee channel.

Now it's standing on top of a pile of newspaper, slowly dripping epoxy. Yeaaaa!

 

[fyrfytr310]

Lol. The pain of love!

 

[Tonimus]

I'm a little surprised you didn't go for the two part foam approach.

 

[gerbs4me]

Looks great so far, keep up the good work!

 

[smapdiage9]

Thanks. I have only seen other builds where people foam the fincan (for this specific rocket) on top of doing fiberglass. This kit is pretty low performance, so I bet it would work fine with just foam, but I already had all the stuff for fiberglass on hand. If I had foam at the ready, I probably would've done that for the inside instead, but I'd also want to consider the weight since adding more to the back would further affect the already weirdly low stability margin of such a fat rocket.

I'm gonna add epoxy fillets to the outside, so between that and fiberglass this thing should be plenty solid.

 

[smapdiage9]

Tonight I slipped the first of two big plywood centering rings down over my motor mount with the intention of installing the body tube and realized that my boattail's shoulder is about 8 inches longer than the instructions account for.

By the design, you're supposed to have a good foot or so of motor mount tube sticking up from the boattail. You glue one centering ring on at the top of the tail, build in a little compartment for an avionics bay accessed through a side hatch, then sandwich it under the top ring. My mmt only sticks a few inches above the boattail shoulder, meaning when I slipped the first one on there is little room above it. This is fine, since, I am planning on putting the avionics in the nose cone and don't need the room for a side hatch, but it's also kind of not fine since the two centering rings meant to support the lower half of the main body tube will now be only three or so inches apart. Also, when I did this initial slip-fit test, the centering ring so tightly friction fit onto the mmt that I can't remove it.

So my options are:
1) Screw it. Glue the CR in place, use the fiberglass boattail shoulder to support the bottom part of the body tube, get on with my life. This will probably work fine.
2) Cut the top 4" of the mmt off to remove the centering ring and sand it out to slip over easier. Cut the majority of the boat tail shoulder off and allow the CR to reside near the lower end of the body tube as designed.

The only advantage I see with option 2 is that I'll be able to put the lower rail button further down the body tube without issue. But if I cut the MMT to remove the CR, then the shortened tube ends up placing that upper CR within a couple inches of the lower one again. Secret option 3 is cut the boattail shoulder off in place, then push the CR lower without cutting the MMT.

 

[Mightyrocketman]

Put a couple of screws in the ring and use those to pull the ring off.

 

[ChrisAttebery]

^ What he said. Maybe use a couple lag bolts to get a good grip on it. You got it on there, it should come back off.

4) Sand the outside of the CR so that it fits INSIDE the shoulder of the BT shoulder. FTW!

 

[smapdiage9]

Thanks for the advice; I ended up using a putty-knife-like tool to walk the CR back up the MMT a fraction of an inch at a time until I could get my fingers under it and it came right off.

This is launch week so I have stepped away from this one while I prep my other stuff, but I think I'll follow Chris' advice and sink the CR into the boattail. Rather than sand it down I think I'm gonna get a sheet of 7 ply birch and cut out some new CRs with my Shapeoko. I need two to build the nosecone chute cannon, and then one smaller one that can ride on top of the fins inside the boattail creating a much stronger joint at the base of the body tube, and then use one stock one inside the tube.

To illustrate the difference in tail shoulder between what was intended and what I received, here's a pic: