My Second Build - Estes Big Bertha

@Rex: was that a 2 stage Bertha I see on your youtube channel?

ayup, and I should have skipped a coat of paint , it is on the verge of being too heavy. I did however manage to get the booster to tumble.
Rex

Build Update..

Masked and sanded the missing launch lug spot - masking the area I wanted to sand (or didn't want to sand rather) made it super easy not to screw it up..

LL - I ended up using a waxed paper drinking straw. I cut angles on the ends (and dipped the rims in CA for a little more protection from wear and tear and put a light coat of flat primer on the LL before gluing... (I sanded the primer back off the contact spot on the LL before attaching)

Glued and filleted with epoxy.




Sanded everything down very lightly with 600grit. clean wiped with a fresh clean rag, then a only very *slightly* damp piece of high quality paper towel (the VIVA stuff you can wet, rinse and re-use - this stuff is amazing)

Base coat of orange is on.. a few small areas I need to fill in on the 2nd coat in about 20mins.. I found that one of the black plastic drinking straws I tried that was too small, actually fit into the inside of the waxed paper one perfectly, so I used that to mask the LL and prevent paint from gumming it up...



Then, I leave it 24hours, *maybe* smooth again with 600grit (if needed) and repeat, otherwise it will be masking and on to the blue, leaving the rings and fins orange...

My design didn't pick up that the LL will be in the middle of one of the orange rings - gonna have to figure out how to mask that properly for a clean finish or else I will have to move the rings up a little...

I originally toyed with the idea of having a masked stripe spiralling around the body - decided to test it in real life on an old kitchen cardboard tube..

glad I did...

It was a HORRIBLE idea... I think it looks boring and just a little stoopid...



I like the more traditional type of design I settled on MUCH more...

But for the budget for frisket film, go I..

Build update...

1) Leave the orange base coat for 24hours [ YES ]

2) Mask stripes and fins [ YES ]

3) Paint the Blue coat [ YES ]

4) Take the masking tape off straight away or wait at least 24hours [ FAIL ]



I was super keen to see the finished paint job, and I pulled the tape off after about 2 hours..

Most of it lifted perfectly, but one of the edges on the fins came up a little jagged where the blue ripples off the edge of the tape as I lifted it..

I should not have rushed it, and I also should have broken the edge of the paint line with the back of a craft knife..

All in all, I learned my lesson the hard way (why does the lesson always stick better in your brain when you screw it up, even when you KNOW you shouldn't be doing what you're doing because experts have told you already!!)



All things being even, I am still VERY happy with my painting results on this, my first "traditional" rocket... I actually like the little bit of orange overspray in the LL (the drinking straw I was using as a mask slid out and I didn't realise) - the orange internal and blue exterior kinda reminds me of a Kraken!)



Now, next steps:
1) The NC fit is too tight - I think the small amount of CA I added to strengthen the tube end has made it a little thicker.. so I will be sanding the shoulder of the NC to thin it a little - I am a little worried about weakening the chute attachment section on the NC, it is a little thin already.. (inputs welcome here from others if they have hit this before) I was just going to mask the attachment section to prevent inadvertent sanding..
2) Assemble and glue the standard shock cord and mount (looks like 6mm elastic strap like you get on cheap kids swim goggles) , and attach the parachute... (chute is a slight mod with 4cm of 6mm elastic and a fishing swivel)
3) weigh the whole thing to adjust the values in OR
4) check the CG is still where it should be and adjust OR as appropriate.
5) Re-profile flights with actual weight and ensure I have the motors I want for small field launch on the weekend with the kids.
6) FLY...
7) Either SMILE or CRY..

I would sand the interior of the BT a little with some 320 grit before I sanded the shoulder on the NC. If you CA'd the BT as you said, a light sanding there won't hurt.

A little late now, but I would have used some Kevlar cord tied to the motor mount with some 1/8" elastic (treated for the heat), rather than the typical Estes "tea bag" shock cord attachment with the often too short rubber band! But that being said, I would still replace the Estes shock cord with 1/8" elastic. I order mine from https://www.apogeerockets.com/Build...t/Shock_Cord?zenid=i9rbh7u0hkvto9ntuc5fdn2rs4, but seeing as you're in Australia, perhaps there's another supplier closer to home for you.

Lastly, you haven't made any outrageous modifications to a proven design, so weighing it and doing simulations in OR aren't necessary at all, unless you just really want to do it. I think all this simulation stuff gets a little out of hand at times, especially on LPR models of proven design. But that's just me, who was around and flying model rockets long before computers became household appliances. :wink:

TangoJuliet said:

I would sand the interior of the BT a little with some 320 grit before I sanded the shoulder on the NC. If you CA'd the BT as you said, a light sanding there won't hurt.

Click to expand...

I'll give that a try first once the paint is fully dry...

A little late now, but I would have used some Kevlar cord tied to the motor mount with some 1/8" elastic (treated for the heat), rather than the typical Estes "tea bag" shock cord attachment with the often too short rubber band! But that being said, I would still replace the Estes shock cord with 1/8" elastic. I order mine from https://www.apogeerockets.com/Build...t/Shock_Cord?zenid=i9rbh7u0hkvto9ntuc5fdn2rs4, but seeing as you're in Australia, perhaps there's another supplier closer to home for you.

Click to expand...

I will definitely look at moving to kevlar cord on the MT for future builds...

Lastly, you haven't made any outrageous modifications to a proven design, so weighing it and doing simulations in OR aren't necessary at all, unless you just really want to do it. I think all this simulation stuff gets a little out of hand at times, especially on LPR models of proven design. But that's just me, who was around and flying model rockets long before computers became household appliances. :wink:

Click to expand...

This is mostly for three reasons:
1) My edification, It's a learning exercise.
2) Keeping it legal - the 400ft ceiling for local playing field launches - I would hate to lose it as a launch site because of complaints or rockets ending up on roads etc...
3) Motor selection - I am keen to keep costs under control - if I can get away with a smaller motor, I get to launch it more!!

last 2 bertha kits I have built have had a snug nose cone fit. if you used ca on the bt then a bit of sanding there (320 grit) will help...likewise on the shoulder. the good news is that you shouldn't need to remove much material, the bad news is you will want to check the fit fairly often while you're sanding to avoid removing too much. attach the chute about 2 - 6" below the nose cone so the loop on the cone doesn't need to take the weight of the rocket.
Rex

snrkl said:

2) Keeping it legal - the 400ft ceiling for local playing field launches - I would hate to lose it as a launch site because of complaints or rockets ending up on roads etc...

Click to expand...

Is this an Australian law? And how can it be enforced? No one I know can stand at ground level and tell me exactly how high my rocket flew.

Rex R said:

attach the chute about 2 - 6" below the nose cone so the loop on the cone doesn't need to take the weight of the rocket.
Rex

Click to expand...

Thanks - I'll do that...

TangoJuliet said:

Is this an Australian law? And how can it be enforced? No one I know can stand at ground level and tell me exactly how high my rocket flew.

Click to expand...

https://www.casa.gov.au/modelaircraft

"In controlled airspace, which covers most Australian cities, you must not fly higher than 120 metres (400 feet) above the ground."

Mostly, I don't want to bring the sport into disrepute - If people start complaining to the local council, I imagine their default response will be to simply ban the use of flight craft at the playing fields..

I figure if there is ever any problems, I can always show the lengths I go to to ensure I don't go over 400ft and that we are following internationally recognised safety protocols...

As for launch days, the sky is literally the limit. The QRS in BNE can get clearance to 70,000ft at their main launch site at Jimboomba and 120,000 at their secondary site... I don't think I will be hitting any of their ceilings any time soon...

You need a better understanding of "controlled airspace". If you're 5 miles (8 Km) away from any airport, you've got a lot more than 400' (120 m) of safe ceiling to launch your rockets in. I'm not faulting you for wanting to be a safe, law-abiding citizen, and not draw unwarranted attention to your/our hobby, but don't limit yourself beyond what is necessary. Controlled airspace looks like an inverted cone, the point being at the airport. The further you are from an airport/airfield, the higher the available ceiling is to you.

On the little plastic loop - I don't use it anymore. I drill a couple of holes in the shoulder of the NC and put a loop of Kevlar through that I use to attach the shock cord and the swivel for the parachute. That way I can add a Chute Release and/or AltimeterThree and not worry about the thing breaking. See the picture below.

On the shock cord: I have had perfectly acceptable results using an "Estes teabag" style mount to mount some of the same Kevlar (100 lb. braided) inside the body tube. Then I can tie the supplied shock cord (recent ones are quite a bit longer than they used to be - Estes does listen) to it. The other end can then be tied to the Kevlar loop.

TangoJuliet said:

You need a better understanding of "controlled airspace". If you're 5 miles (8 Km) away from any airport, you've got a lot more than 400' (120 m) of safe ceiling to launch your rockets in. I'm not faulting you for wanting to be a safe, law-abiding citizen, and not draw unwarranted attention to your/our hobby, but don't limit yourself beyond what is necessary. Controlled airspace looks like an inverted cone, the point being at the airport. The further you are from an airport/airfield, the higher the available ceiling is to you.

Click to expand...

Ok - so after some reading and a bunch of research, I'm definitely in an area limited to 400ft ceiling. We have an aerodrome 5km from the playing field where we launch. We're right on the edge but definitely in the zone and the language is clear - nothing over 400ft...

Whether the language I used (controlled vs restricted vs pick a name) was correct or not, the 400ft limit is.

I'm not so bothered - I'm think I'm quite happy with launches and recovery events we can see! 😁

BEC said:

On the little plastic loop - I don't use it anymore. I drill a couple of holes in the shoulder of the NC and put a loop of Kevlar through that I use to attach the shock cord and the swivel for the parachute. That way I can add a Chute Release and/or AltimeterThree and not worry about the thing breaking. See the picture below.

On the shock cord: I have had perfectly acceptable results using an "Estes teabag" style mount to mount some of the same Kevlar (100 lb. braided) inside the body tube. Then I can tie the supplied shock cord (recent ones are quite a bit longer than they used to be - Estes does listen) to it. The other end can then be tied to the Kevlar loop.

Click to expand...

I like that idea - I have some Kevlar and I'm planning on investing in an altimeter3 when funds allow.

I'm planning on doing nose cone and recovery install tomorrow night.

As it happens, a little light sanding of the NC shoulder with 400grit left the NC really tight. I was planning on sanding the inside of the BT the next day, but an overnight stay with the NC in the BT, it all seems to fit nicely now.

I'm wondering if leaving them together overnight has stretched the BT a little and made them fit better together...

Finishing touches today..

Shock cord - decided to follow BEC's advice and installed kevlar through the NC in lieu of using the built in plastic ring. Holes were created using the tip of the soon to be ejected hobby knife blade. Super easy and will definitely become a standard part of my builds where the NC shape/size suits.




Given it was too late to look at an MT shock cord mount by the time it was suggested, I have opted to use the ESTES teabag method, but with a kevlar loop.


I think in the future, rather than the tea-bag method, I will look at using a rectangle of stock card with holes to thread the kevlar in/out of.

To prevent the kevlar ends from fraying etc, I dabbed a super small bit of CA on the knots. This obviously makes them super hard and I was a little worried about the loop on the BT snagging recovery devices, so I added a little wrap of blue masking tape on the knot.

I have used a little 6mm nylon elastic with a swivel as a standard addition to parachutes lately - so these are added also.

I am planning on attaching the rubber shock cord to the BT kevlar loop with a swivel as well. Failing this, a clove hitch with the rubber shock cord on the kevlar loop.

I will also be wrapping the bottom of the chute with a wadding nappy (US folks call this a diaper �&#56860 along with a few wads below... (I can see this rocket chewing wadding much faster than the last ones I have built!)

Once the BT shock cord mounting loop is dry, I will weigh and finalise motor selections.. looking for a maiden flight on the weekend... I am thinking a B6-4 for playing field flights and an SCR C6-5 for the next launch day...

So there we are: finished build! I'd like to thank all those who have added their inputs - with your help, I have achieved exactly what I wanted to in this build: learned and established some solid construction techniques and had a lot of fun learning/doing it all... (and yes, I will be using wood glue over epoxy on the next builds... )



And best of all, this one is finished just in time - my Estes Designer Special gets delivered tomorrow... I've got some ideas, and I am planning on running a rocket camp with all four of the kids weekend after next...

And I have a v2 en route the week after that...

<cheesy grin>
I figure it is easier to be patient with paint jobs when you have 3-4 builds on the go at once...
</cheesy grin>

I use fabric medical tape to tidy down my cord ends as it remains quite flexible.

Flew this one for the first time today - two park flights on SCR B6-4s.

Flew straight and true.

First flight came in ballistic - parachute got caught on a piece of tape I put in the shock cord to stop the parachute from snagging. Irony abounds.

Only a small ding.

Second flight was picture perfect.

My son ran off to retrieve it.

And ran all the way back with the parachute flailing and spinning

Parachute is now tangled so badly it's likely going to be a cut and replace job.

Didn't fly my new AltimeterThree - we had 25-30km winds and I was worried about a long recovery drift would leave my shiny new altimeter in a tree or the pond 100m from the pad.

(We lost an 18mm MD in the trees/pond on an a8-3 on the first flight of the day as it veered suddenly 50ft up - fin failure is the operating diagnosis)

Are you using a fishing swivel on your parachutes? They work well to all but eliminate tangled 'chute lines (risers).

I do use fishing swivels.

I have a loop of Kevlar through the nose cone.

I have a loop of Kevlar on the BT.

Shock cord elastic has a loop on one end and a swivel to attach to the NC Kevlar.

Parachute has an elastic loop off the parachute cords and a swivel on the other end to attach to the NC.

Parachute was rescued.

The swivels were the saving grace. It meant I could disconnect everything and I untangle the parachute strings.

Long story short: my 11yo has been asked not to run with the parachute held, spinning behind him... &#128540;

snrkl said:

The swivels were the saving grace. It meant I could disconnect everything and I untangle the parachute strings.

Long story short: my 11yo has been asked not to run with the parachute held, spinning behind him... &#55357;&#56860;

Click to expand...

I have an 11 year old, too. I've asked her several times not to run with the parachute spinning behind her, but she gets excited and caught up in the moment. It's a small price to pay.