Build thread: Aerotech HV Arcas

[Dane Ronnow]

Faced with a Las Vegas summer and temperatures too hot to launch rockets (too hot even to paint rockets outside), I decided to pass the time building a new rocket. I'd been looking at the Aerotech HV Arcas—I downloaded an ORK file from Rocket Reviews and instructions from Aerotech so I could see exactly how this goes together—then purchased the kit from Sirius Rocketry (thanks to David and Evie for a great price and fast shipping).



This is the new kit from Aerotech, boasting an aluminum motor retainer (replacing the motor hook), and conformal rail guides.

Other parts included: a 13" polystyrene nose cone, 19" upper body tube, 24" slotted lower body tube, 6" coupler, 12" thick-walled motor tube, three centering rings, bulkhead, four fins and two fin-lock rings, a baffle system, 30" nylon parachute and elastic shock cord, two eye screws for shock cord attachment, and launch lugs.There's also a cardboard sleeve that is used to cover the rear 5" of the body tube for a scale look. Further enhancing the scale appearance of the rocket is an aluminum Atlantic Research identification tag that attaches to the upper body.



The first thing I want to do is weigh and measure every component, and plug those actual values into the ORK file. The ORK file from Rocket Reviews was off, in some instances by quite a bit. The RR ORK file specs the nose cone at 12.5" in length, weighing 6.5 oz, whereas the cone that came in the kit is a full 13" in length, and weighs 3.18 oz. The fins in the ORK file are spec'd at 8.5 oz; the actual fins weigh less than half that—3.5 oz. And the fins that come in the kit have a flat trailing edge, square with the long axis, not slightly angled as they are in the ORK file.

I dug up a couple of other ORK files for this rocket, and they are all similarly off in weights and measures. I'm attaching my ORK file in case someone out there wants one that is accurate.

With the ORK file updated, and using my 36" parachute, a 12" Nomex blanket and Kevlar shock cords, I ran a few simulations with G74-6 and G80-7 motors, and ended up with a deployment velocity of more than 30 mph with the G80. It's on the uphill side of the flight, but still a little hot for my tastes. Adding a mass object of 2.5 oz for paint and adhesives, I was able to bring the deployment velocity down to 27 mph.

With that in mind, I decided to build this rocket using epoxy, rather than the medium CA that the instructions call for. The build certainly doesn't need epoxy, but it does need more weight.

Before test fitting the parts, I need to remove the mold flashing from the FL rings and fins. This is especially important on the inside of the FL ring fin channels, where the flashing prevents the fin tab from seating all the way. I used a hobby knife to clean up the FL rings, and #600 sandpaper on the edges of the fins.

Here's a pic of the fin showing the airfoil cross section:



Tube, CRs, FL rings and baffle:



After measuring and marking the tube, I slid the FL rings in place, using the centerline marked on the tube as a reference point to make certain the FL channels are aligned. Then I snapped the fins into the rings.



Here's the ORK file for this build:

 

[Dane Ronnow]

The instructions call for gluing the FL rings, the baffle, and the forward and mid CRs to the MT, then sliding the assembly into the BT, and using a long glue stick to apply adhesive to the CR/BT joints. Then adhesive is applied to the fin tabs, and the fins are inserted into the BT through the fin slots and snapped into the FL ring channels.

The problem with this—at least for me—is twofold: first, in test fitting the fins, they aren't perpendicular to the body tube once snapped into the FL rings. In order to straighten them, you have to push the fin sideways past the point where it's perpendicular, then let it flex back. It's push-then-release-and-repeat until it's straight. The slot in the body tube is not going to allow that movement. And the slot itself isn't going to move the fins into the proper position, because it's cut wider than the thickness of the fin tabs.

Second, it takes a lot of pressure to snap the fins in place. And that's much easier to do with the MT/FL ring assembly out of the BT.

So I'm going to glue the MT/fin assembly together outside the BT, then slot the BT all the way to the bottom and slide the MT/fin assembly in, like a fin can without the can.

I'm using blue masking tape as a cutting guide, then cutting the remainder of the slot with a hobby knife, making five or six passes to get a clean, straight cut.



I'm still test fitting here, so no adhesive. With the slots cut, I slip the mid and aft CRs into place, then slide the assembly into the BT.



Note the 1/32" recess on the forward end of the fin root chord.

I've got a spare tube coupler, from which I'll cut a 1" long section to insert into the rear of the BT to close the fin slots.



With the MT/fin assembly in place, I check alignment of the fins.

 

[Dane Ronnow]

Next up is test fitting the motor retainer. The retainer instructions calls for positioning the FL rings and CRs in such a way that the MT is flush with the bottom of the BT. My guess is that it will be easier to unscrew the retainer cap if it's not tucked up inside the BT.



Normally, I like the retainer butting up against the aft CR. It's a stronger joint. With this design, there's a half-inch of MT between the CR and the retainer. So I dug up an old tube I had lying around that was originally a carrier for plastic wrap. It's thick walled, and it's a perfect fit for the MT.

Using a razor saw, I cut off a half-inch.



Then I test fit with the retainer.



Probably unnecessary, but I like it. And I need the weight.

 

[Dane Ronnow]

The last component of the MT assembly is the ejection charge baffle. Aerotech's design uses a small wad of steel pad (think pot scrubber), and a plastic MT cap. When stretched out to five or six inches in length and inserted into the top of the MT, the steel wadding acts as a heat sink to cool the ejection charge gases. The plastic cap keeps the wadding in place, and diverts gases sideways into the wall of the BT, rather than straight up the tube. With an eye screw set in the top, the cap becomes the anchor point for the shock cord.



Here's a pic of all parts test fitted:



I'm ready to glue everything in place and install the assembly into the BT. But I need shock cord first. I've got a roll of Emma Kites 550 lb. braided Kevlar cord on order. It should be here by Sunday.

More then.

 

[Initiator001]

Back when I worked at AeroTech I did the prototype building, flight testing and instruction writing on the HV Arcas kit.
There are some good reasons for using CA adhesive instead of epoxy.

If you assemble the fins to the fin-loks with CA, if a fin hits the ground too hard it will pop out of the fin-lok ring and can be reinstalled. If you use epoxy the fin will break off where the fin tab exits the body tube. The best you can do at that point is just glue the fin to the body tube. The joint will not be as strong and the fin will randomly break off. We built two HV Arcas kits, one with CA and one with epoxy. The epoxy model often had the most damage and was more difficult to repair.

Do not use epoxy to glue the plastic baffle into the motor tube. We discovered if the cooling mesh was in contact with epoxy the heat from the cooling mesh could ignite the epoxy, and start a slow smoldering fire in the motor tube.

The HV Arcas is a fine model and if built per the instructions will provide many years of rocket flying fun.

 

[OzHybrid]

The last component of the MT assembly is the ejection charge baffle. Aerotech's design uses a small wad of steel pad (think pot scrubber), and a plastic MT cap. When stretched out to five or six inches in length and inserted into the top of the MT, the steel wadding acts as a heat sink to cool the ejection charge gases. The plastic cap keeps the wadding in place, and diverts gases sideways into the wall of the BT, rather than straight up the tube. With an eye screw set in the top, the cap becomes the anchor point for the shock cord.

View attachment 526452 View attachment 526453 View attachment 526454 View attachment 526456

Here's a pic of all parts test fitted:

View attachment 526457

I'm ready to glue everything in place and install the assembly into the BT. But I need shock cord first. I've got a roll of Emma Kites 550 lb. braided Kevlar cord on order. It should be here by Sunday.

More then.

Stainless steel scourer. I use the same for my baffle. Works well.
The Emma Kites kevlar is great. Just watch out for the weave. I think it's the 1500lb that has a really tight weave which caused a sort of internal knotting at the bends when you bunch it into sections.

 

[Dane Ronnow]

Back when I worked at AeroTech I did the prototype building, flight testing and instruction writing on the HV Arcas kit.
There are some good reasons for using CA adhesive instead of epoxy.

If you assemble the fins to the fin-loks with CA, if a fin hits the ground too hard it will pop out of the fin-lok ring and can be reinstalled. If you use epoxy the fin will break off where the fin tab exits the body tube. The best you can do at that point is just glue the fin to the body tube. The joint will not be as strong and the fin will randomly break off. We built two HV Arcas kits, one with CA and one with epoxy. The epoxy model often had the most damage and was more difficult to repair.

Do not use epoxy to glue the plastic baffle into the motor tube. We discovered if the cooling mesh was in contact with epoxy the heat from the cooling mesh could ignite the epoxy, and start a slow smoldering fire in the motor tube.

The HV Arcas is a fine model and if built per the instructions will provide many years of rocket flying fun.

I appreciate you posting this. I see now there are better reasons for using CA in this build than just preference. I'll proceed with the MT/fin assembly and baffle as you suggest, but build it outside the BT, then slide the completed unit in from the rear.

I plan to use epoxy on the portion of tube coupler that inserts into the upper BT, mainly because epoxy lets the tube slide in without seizing, unlike white or yellow Elmer's. But I've never used CA on a coupler. With regard to seizing in the first few seconds, does it behave more like epoxy, or Elmer's?

Thanks again for the post. I really look forward to flying the Arcas.

 

[Dane Ronnow]

The Emma Kites kevlar is great. Just watch out for the weave. I think it's the 1500lb that has a really tight weave which caused a sort of internal knotting at the bends when you bunch it into sections.

The Kevlar I'm using is 550 lb. So while there would probably be less chance of knotting, the problem still exists. Thanks for the tip.

 

[Dane Ronnow]

@Initiator001 -- Another question if I may: Without the motor hook piercing the tube ahead of the motor, there's nothing keeping the cooling mesh from dropping on top of the motor under acceleration. No problem with this? (I like the idea that I can pull it out from the rear periodically and clean it, though.)

 

[Initiator001]

@Initiator001 -- Another question if I may: Without the motor hook piercing the tube ahead of the motor, there's nothing keeping the cooling mesh from dropping on top of the motor under acceleration. No problem with this? (I like the idea that I can pull it out from the rear periodically and clean it, though.)

The cooling mesh does not move under acceleration.
Never been an issue for me and I have AeroTech models that have flown 50+ flights.

 

[Dane Ronnow]

Thanks.

 

[bronicabill]

Just for the record, I have built two of these now, both converted to dual-deployment. That coupler tube is the perfect diameter and length for the Apogee #10549 2.64" ebay kit specifically for Aerotech rockets. Both ARCAS kits have been 100% reliable with an RRC3 altimeter handling deployment duties, powered by a 3-cell 1,100mAH Lithium Ion battery pack. While many folks use 11.1V Li-Po packs, I prefer the Li-Ion because they provide all the necessary current dump, are nowhere near as volatile as Li-Po chemistry, do not "puff up" with age, and hold their charge for many months on the shelf (unlike Li-Pos that lose considerable power in only a few weeks).

Anyway, the conversion is easy, even after the rocket is built, so keep that option in the back of your mind!

 

[Dane Ronnow]

Anyway, the conversion is easy, even after the rocket is built, so keep that option in the back of your mind!

Will do. Thanks for the info!

 

[Dane Ronnow]

Okay, back to the build. I'm going to follow Initiator001's suggestion (post #5) to use CA instead of epoxy to attach the fins to the FL rings. I'm using thin (EM-02) to cement the FL rings to the motor tube, and medium (EM-150) to cement the fin tabs to the FL rings, and for the fillets along the fin tab chord.



Next, attaching eye bolts to the coupler bulkhead.

Later on, I'll be building an altimeter bay in the base of the nose cone, which means the nose cone needs to be removable. (Instructions call for cementing it into the upper body tube.) And to prevent an accidental loss of the nose cone and altimeter, I'll be running a tether from a second eye bolt in the bulkhead, up to the nose cone.

Here's the bulkhead with two #8-32 eye bolts attached. The main shock cord will attach to the center bolt. The nose cone tether, to the offset bolt.



Next, I'll attach a screw eye to the baffle. And here's where I ran into a problem. The screw eyes supplied with the kit have a minor diameter of just under 1/8", but the hole in the baffle is 9/64". To make matters worse, the threads on the screw eye are practically nonexistent.

I went ahead and threaded the supplied screw eye into the baffle, and there was almost no thread bite. So I'll be using a 10-24 x 1-5/8" screw eye.

The top screw eye is the one supplied with the kit. 10-24 screw eye on the bottom.



Before inserting the screw eye, I mixed up a small batch of J-B Weld to secure it, and to apply to the bolt ends on the bulkhead eye bolts.



Next up, finishing the motor tube assembly.

 

[n3tjm]

I have been thinking about getting myself a HV Arcas

 

[Dane Ronnow]

@n3tjm - I like the kit. The parts are good quality, good fit. The Fin-Lok system is nice. And the fins are airfoiled, but very stiff.. Nice nose cone. It comes with a 30-inch nylon parachute (I'm using a 36" semi-ellipsoidal of my own making).

My OR file has the rocket sitting at 28 oz., including a 2.5 oz. mass object to account for paint and adhesives. With a G74-6, it sims at 970 ft., 188 mph VMAX, 9.5G. The G80-7 sim is a little over 1700 ft., 277 mph, 10.8G.

Anyway, I've got high hopes for this one. It's my first kit since getting back into rocketry. And my view is it's a nice one. We'll see how it flies.

 

[rcktnut]

I would never replace the stock elastic shock cord with tube zippering Kevlar or anything else for that matter. I've always used the supplied elastic never ever had a problem with any breaking on any of the Aerotech kits I built. The cord on the Initiator (pictured) was cut buy me to retrieve from a tree and tied back together before its 10th flight. After another 40 flights or so it is still holding together just fine.

 

[DeltaVee]

Back when I worked at AeroTech I did the prototype building, flight testing and instruction writing on the HV Arcas kit.
There are some good reasons for using CA adhesive instead of epoxy.

If you assemble the fins to the fin-loks with CA, if a fin hits the ground too hard it will pop out of the fin-lok ring and can be reinstalled. If you use epoxy the fin will break off where the fin tab exits the body tube. The best you can do at that point is just glue the fin to the body tube. The joint will not be as strong and the fin will randomly break off. We built two HV Arcas kits, one with CA and one with epoxy. The epoxy model often had the most damage and was more difficult to repair.

Do not use epoxy to glue the plastic baffle into the motor tube. We discovered if the cooling mesh was in contact with epoxy the heat from the cooling mesh could ignite the epoxy, and start a slow smoldering fire in the motor tube.

The HV Arcas is a fine model and if built per the instructions will provide many years of rocket flying fun.

@Initiator001 - Thank you for your hard work on this one! It's one of my favorite items to fly... and
the HV Arcas is one of my most-flown.. It is a great kit. Mine is from the time of motor hooks, but I only got around to building it about 5 yrs ago or so! That said, I built it per the instructions with CA etc. I had no apparent alignment issues with the fins.... it was simple to put the mount in and align it, then drop in the CA etc. I've had a few hard landings though.... but it never ever popped a fin off. I've lost a chunk of the fin on an outside corner (evergreen plastic sheet, plastruct and bondo to the rescue) and a few small cracks on the trailing edge. I would have loved it if the fin popped out instead of having to repair the chip...

Over the years it's taken a beating but I still have a very high regard for the rocket.

 

[Dane Ronnow]

I would never replace the stock elastic shock cord with tube zippering Kevlar or anything else for that matter.

Personally, I like Kevlar better. I understand the potential for zippering, but I also know it doesn't snap back, it's heat resistant, and I think it will last longer. That's just me, though.

 

[waltr]

I also like Kevlar but since it does not stretch it is a very good idea to do taped bundles to absorb energy so there is not a sudden stop when it becomes fully extended.

It is this 'shock' that causes zippers and breaks parts of the recovery system.

 

[Dane Ronnow]

I also like Kevlar but since it does not stretch it is a very good idea to do taped bundles to absorb energy so there is not a sudden stop when it becomes fully extended.

Good idea. Feathering the brakes.

 

[rcktnut]

Personally, I like Kevlar better. I understand the potential for zippering, but I also know it doesn't snap back, it's heat resistant, and I think it will last longer. That's just me, though.

Out of hundreds of flights on Aerotech kits never had a "snap back" on them. Length of the cords is key. If using the labyrinth system, no need to worry about heat. These are not your typical LPR kits with flimsy low quality, way too short shock cords. I'm just sharing what has worked well/ perfect with me. Will be watching your build thread!!

BTW, you don't need the Nomex blanket.

 

[Dane Ronnow]

Out of hundreds of flights on Aerotech kits never had a "snap back" on them. Length of the cords is key. If using the labyrinth system, no need to worry about heat. These are not your typical LPR kits with flimsy low quality, way too short shock cords. I'm just sharing what has worked well/ perfect with me. Will be watching your build thread!!

I know the elastic that comes in the Arcas kit is plenty long. I just don't like elastic. The Kevlar works great on my previous build, so I'm sticking with it.

BTW, you don't need the Nomex blanket.

I use the Nomex to keep the parachute bundled as much as for heat. I've got a system for packing that works very well, and it includes the blanket. FWIW, I'm not worried about the weight, and using the blanket doesn't complicate anything (in my situation).

 

[Dane Ronnow]

Today I'm finishing the motor tube assembly, and cementing the bulkhead to the coupler.

First, the mid CR is cemented to the motor tube and forward FL ring using J-B Weld:



Next comes the baffle and forward CR. The cooling mesh is stretched out, then inserted into the forward end of the motor tube, leaving about an inch and a half free space above it.



After cutting four slits in the top of motor tube, the forward CR is placed on the tube, then the baffle is cemented in place using medium CA. CA is also applied to the four slits.



I'm going to sink two small screws into opposite sides of the motor tube, and into the baffle sleeve. I drill .063" holes for the screws, then cement the forward CR to the baffle plate using J-B Weld. I'll sink the screws after the epoxy is cured.

The forward CR is slightly warped, so I clamped it to the baffle plate, flattening it.

 

[Dane Ronnow]

Before cementing the bulkhead to the coupler, I need to string the upper shock cord tether. I want about 5" sticking out of the bottom of the coupler, so, allowing for two knots, I cut 20" of 2.1mm braided Kevlar cord (550 lb). I run that through the screw eye, slip a .75" piece of 5mm heat-shrink tubing on the cord, tie the ends with a square knot, then trim and finish the knot with the HS tubing.



Next, I tie a simple overhand knot to form a loop, and secure it with a piece of 6mm HS tubing.



I mix a small batch of BSI 30 min. epoxy and run a bead around the end of the coupler. Before placing the bulkhead, I bundle the shock cord, then lower it into the tube, place the bulkhead and position it, then wipe the excess epoxy with a paper towel wetted with isopropyl alcohol.



That's it for today. More later.

 

[Dane Ronnow]

Today I'm going to glue the coupler into the upper body tube, and attach two more Kevlar tethers.

First, though, I applied a fillet of J-B Weld to the back side of the forward CR, then sunk the small screws through the motor tube wall and into the baffle sleeve. This completes the motor tube assembly.



Next, I attached a length of 250 lb. braided Kevlar to the offset screw eye in the top of the bulkhead. This will attach to the nose cone.

(The nose cone will not be glued into the upper body tube as the instructions call for, but will pull out for access to the altimeter bay in the base of the nose cone. The tether prevents the loss off the nose cone and altimeter in the event of an unplanned separation during the flight.)

The process for making this tether is the same one used to attach the upper shock cord tether to the screw eye on the opposite side of the bulkhead (post #25 above).



I need to ensure that this tether doesn't come into contact with the epoxy that will be on the BT wall, both during insertion of the coupler, and when I flip the tube to let the epoxy cure (there will be a bead of epoxy around the edge of the bulkhead from pushing through epoxy on the BT wall).

I rustle up a couple of long, wide drinking straws, then thread the Kevlar through them end to end. Then I test fit the coupler to make sure the tether can't contact the epoxy.



Then I mix a batch of BSI 30 min. epoxy, apply two beads to the inner BT wall—one bead a quarter inch down from the top; the other 1.5 inches down—then slide the coupler in place.



This coupler is a fairly tight fit, so it should be straight in the body tube. To be sure, I slide the lower BT onto the coupler (being careful not to push it any farther into the upper tube), push the tubes together tight, then roll both tubes across a perfectly flat table top. It rolls smoothly with no flop at the ends, which tells me the tubes are aligned.

Finally, I attach the lower shock cord tether to the screw eye in the baffle.



Once the rocket is completed and ready for flight, I'll run 20 ft. of 350 lb. braided Kevlar from the loop on the lower shock cord tether, to the loop on the upper shock cord tether.

That's it for now. Next up, the nose cone altimeter bay.

 

[Dane Ronnow]

I've got to loosen the fit between the tube coupler I just installed, and the lower body tube. And I'm thinking of using a block sander with #320 paper to sand the coupler down, then, when it's a sufficiently loose fit, harden the surface with CA and sand it smooth. The lower body tube, which already has about a half inch inside coated with CA, would be coated down to the length the coupler would reach, then sanded smooth. Adjustments from there would be made with masking tape on the coupler, usually at the field.



Is this a good way to do this? I've never sanded a cardboard coupler to fit for separation. The nose cone has always been the point of separation for me, and it's been a simple matter of masking tape to tighten it.

Any advice would be greatly appreciated. Thanks.

 

[bibbster]

I'm curious as well. I've never had a coupler be too tight. Always had to add some tape. I use packing tape since it is more slippery than masking tape, to ensure a smooth ejection/separation.

 

[rcktnut]

Try "cutting"/rounding the inside edge of the BT and the outside edge of the coupler first. Sand your CA inside the BT first also. That might do the trick!

 

[Dane Ronnow]

Try "cutting"/rounding the inside edge of the BT and the outside edge of the coupler first. Sand your CA inside the BT first also. That might do the trick!

That's the first thing I did. (Great minds?) It's tight all the way in. I'm going to have to sand the coupler. I'm just trying to figure out a way to do that and get an even reduction in diameter. I'm thinking now of a sanding sponge, which will let me wrap around the coupler.