Bertha IV Heavy with fall away boosters flys

So since it was a nice day out today its pushing 60 degrees I decided to swing test and fly the Bertha IV Heavy with fall away boosters.Loaded it up with A8-3's in the boosters and a B6-4 in the sustainer wired it up on the clip whip and let her rip.The flight was ok it arced a bit not sure it it hung up a bit on the rod or clip whip( I think I need to make my clip whip a bit longer) but all 3 engines fired up and off she went like I said she arced a bit.She swung stable she needed a bit of clay which I put into the NC's of the boosters not sure if this is the right spot for them but I figured that once they fell off the Bertha would fall back to being a stable Bertha.The 4 second delay on the B might have been a bit on the long side it was nose over when the cone popped I think next time I will try it with with a C6-3 in the sustainer and B6-2's in the boosters.
Andy

Great! I haven't seen a forecast that gives me flying window for mine for a long time.

I wanted to send it up again with the B boosters and C sustainer but I didn't want it to get any more snow into it then what it got from its first flight there was a bit of scorch on one of the fins dunno if this is what gave it its arc or now I am leaning towards hanging on the rod.
Andy

My only question that I have about this is should I have added the weight to the nose cone or to the boosters nose cones when I balanced it?Any input will be good thanks in advance.
Andy

I put the weight in the main nose cone, so I could get by with less, but as you know mine stays in one piece.

Did you swing test it with engines in?

luv2launch said:

My only question that I have about this is should I have added the weight to the nose cone or to the boosters nose cones when I balanced it?Any input will be good thanks in advance.
Andy

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Nose weight should go into the sustainer nose cone. Partly because, unless you have really large boosters, the sustainer's nose will be further forward, meaning you'll need less additional mass to achieve the same shift of CG. And partly because, having used a lot of motor power to give momentum to that mass, you may as well keep it and use that momentum during the coast phase.

Very cool!!! I'm curious how you implemented the fall away boosters. How does the force from the boosters' ejection charges cause them to drop off.

BTW, if I was building, I would use BT-20s rather than BT-60s in the boosters to reduce the drag significantly.

Great stuff,

Jim

The boosters fall away when the motors burn out. They are only held on with dowels and launch lugs.
And

Isn't there a chance that they could fall away at launch time if the central motor lights before the outboards? How do you get them to stay attached for the photo and on the pad?

Jim

In the photo since they have no motors in them its friction holding it together on the pad i use spent motor cases to hold the boosters up until the launch button is pressed.
Andy

jcsalem's question is valid - if one of the boosters ignites slightly late, it will drop off, ignite, and go off on an unstable trajectory. My solution to this has been to have the dowels at the nose point the other way, attached to the ejecting nose cone. That way, the booster can't fall off until the nose cone is ejected.

BT-20's instead of BT-60's for the boosters would indeed reduce drag, but then the model wouldn't look like a Goonified Delta IV.

luv2launch said:

.... I decided to swing test and fly the Bertha IV Heavy with fall away boosters.Loaded it up with A8-3's in the boosters and a B6-4 in the sustainer .....The 4 second delay on the B might have been a bit on the long side it was nose over when the cone popped I think next time I will try it with with a C6-3 in the sustainer and B6-2's in the boosters.
Andy

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Way to go on getting this drop-off booster technology developed and under control! And thanks for sharing your experiences.

Just a note/suggestion on motor selection: if the four-second delay from your earlier flight (B6-4-power in the core) was a bit too long, you might want to select a shorter delay **if** you again use A motors in the boosters and another B motor in the core. If you instead go with increased power in both the boosters and core, your rocket should be moving significantly faster at core burnout and should coast a little further and longer. Bottom line here: you may need a LONGER delay with the bigger motors, not shorter.

You would do well to run some simulation calcs, and try to model your rocket's performance with the different motor sets. That way, you might stay "ahead of the game" with a smarter motor and delay selection.

powderburner said:

Way to go on getting this drop-off booster technology developed and under control! And thanks for sharing your experiences.

Just a note/suggestion on motor selection: if the four-second delay from your earlier flight (B6-4-power in the core) was a bit too long, you might want to select a shorter delay **if** you again use A motors in the boosters and another B motor in the core. If you instead go with increased power in both the boosters and core, your rocket should be moving significantly faster at core burnout and should coast a little further and longer. Bottom line here: you may need a LONGER delay with the bigger motors, not shorter.

You would do well to run some simulation calcs, and try to model your rocket's performance with the different motor sets. That way, you might stay "ahead of the game" with a smarter motor and delay selection.

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Yeah I was thinking about that.I picked up rocksim the other day and am in the process of trying to sim it in that but I am having some difficulties setting up the motors like they say to do in the ezine which is located here https://www.apogeerockets.com/education/downloads/newsletter110.pdf
But since this howto was made for rocksim 7 I am having some troubles setting up the fake motors needed to make the sim work right.All in all I think I built the rocket itself correctly in rocsim I'll attach the file if anyone wants to play with it.I just need to figure out how to setup the motors in engedit.Its not as of yet completely built a few things here and there to do like put a rocovery system in the boosters and sim the extra weight from the nose cones since you can't put nose cones on the strap ons in rocsim.
Andy
Hmm need ti get winzip it won't let me upload a rar file.

View attachment BerthaIVHeavy.zip

adrian said:

jcsalem's question is valid - if one of the boosters ignites slightly late, it will drop off, ignite, and go off on an unstable trajectory. My solution to this has been to have the dowels at the nose point the other way, attached to the ejecting nose cone. That way, the booster can't fall off until the nose cone is ejected.

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Are you saying to invert the dowel rod and launch lugs? If so, the boosters wont have anything to push against.

I think he means to somehow use the nose cones of the boosters with the dowels going into them to hold on the boosters till the NC blows on them to let them fall away.I can understand wanting the positive retention but doing it that way would for me kinda ruin the look I was going for.I based my way of the boosters dropping off on DeltaIV's scale Delta IV Heavy and this bertha bash was basically just a test bed for a larger more scale looking version of my own.
Andy

luv2launch said:

I think he means to somehow use the nose cones of the boosters with the dowels going into them to hold on the boosters till the NC blows on them to let them fall away.

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That's right. Only the front dowels and lugs are to be inverted, the aft ones stay as they are.

I can understand wanting the positive retention but doing it that way would for me kinda ruin the look I was going for.I based my way of the boosters dropping off on DeltaIV's scale Delta IV Heavy and this bertha bash was basically just a test bed for a larger more scale looking version of my own.

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The dowels are already there! How can putting the same dowels on, but the other way round, ruin the appearance? Besides, safety outranks appearance every time.

If you're trying to get the boosters to drop off right at thrust burn-out, one solution is to use C6-0's (or B6-0's, if you can get them). For best effect, and given that you're using such wide diameter boosters anyway, I'd be inclined to do something with a cluster. A core tube leading up to the nose allows the C6-0 to eject the nose itself, with dowels attached, thus separating the booster. The booster's body tube itself is cut in half with a hollow coupler fitting over that core tube, and a streamer or parachute installed. So the C6-0 ejects the nose cone and separates the booster from the sustainer, then the second motor - perhaps a C6-3 - blows the two halves of the body apart and deploys the recovery device. I've never tried that sort of cluster with a parallel stage booster but I have used it on a two-stage rocket with a large, heavy booster.

I'm not sure we're all on the same page here. From what I can tell in the picture, the dowels are attached to the sustainer and are behind the nose cones. So if, You simply flip the dowel-launch lug positions (both vertically and horizontally) the boosters wouldn't fall away with the ejection of the nose cone. Now with that being said, if you move the dowels up so they would be attached to the nose, I believe it would/should work.

I personally like your idea, Adrian, but in the end (and I hope I don't sound like a total butt in this speech because I'm not trying to) the choice is up to Luv2launch on how he wants the boosters to fall.

If I missed something or got some of the details wrong, feel free to correct me.

I thought of another idea while I was lying in bed last night (and it's probably closer to your idea Adrian). Flip the launch lug and dowel rods (both vertically and horizontally again). This time, instead of moving it forward or attaching it strait to the tubes, have a slot made in the booster tube close to the top so that the dowel will go through the tube and attach to the shoulder of the nose cone. That way when the nose ejects, the dowel will follow the slot and detach itself from the lug. This will reduce the risk of it falling of at launch and not be visibly attached to the nose which is what Luv2launch wanted to avoid.