Big Bertha/ D10-7

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Bill Gibson

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Its simply easier to ask these question s here than to try to figure it out, as my math skills are barely average, and my computer skills are worse! A perfect example of just how bad? I cant even download Open Rocket on my home computer to even attempt to use it, because my computer has a security setting that wont allow me to open PDF files and other files as well....ive tried everything to unlock the setting, no luck! So, I wanted to find out........
About how high would the Big Bertha go on a D10-7 WITH a Jolly Logic 'chute release in it?
Has anyone used a JL 'chute release in a rocket with a 1.6" ID? According to the manual, its doable.
Is there anything else I should consider while doing this?
Is this a complete waste of time?
Many Thanks:):)!!
 
as I recall, some where around *1700' or better. don't know about the jlcr...but I wouldn't use anything bigger than a 15" chute in it, if you want it back :). one should remember that the BB was originally a 3 engine cluster...
Rex
*w/3.5 oz. payload
 
Watch out. I put an Aerotech D in a tired old Big Bertha and those paper centering Rings couldn't take it. If you want to fly it more than one time you'll need to do something about reinforcing the motor mount. Kurt
 
Watch out. I put an Aerotech D in a tired old Big Bertha and those paper centering Rings couldn't take it. If you want to fly it more than one time you'll need to do something about reinforcing the motor mount. Kurt

I discovered this fact recently as well. I launched my Big Bertha on an Aerotech 18mm D and it flew beautifully. When I got it back everything seemed fine, but the next time I launched it (on a black powder B6-4) the engine mount ended up breaking loose and shooting halfway up the rocket. Somehow it managed to lift off and have a stable flight, but since the ejection charge was pressed right up against the wadding and chute it melted everything and the rocket crashed. Luckily, the field was extremely muddy and the body tube didn't crunch after it pranged. I was able to pull out the engine mount, sand out the old glue and put it back in. It will live to fly another day, but it will never fly on a composite again lol.
 
Try thrustcurve.org, click on "motor guide". It says a 1.6" diameter, 2.5oz rocket will go 1038 feet on a D10, and recommends a -5 delay. The strength of the cardboard CRs should be fine, but the glue joints will be more important.
 
Try thrustcurve.org, click on "motor guide". It says a 1.6" diameter, 2.5oz rocket will go 1038 feet on a D10, and recommends a -5 delay. The strength of the cardboard CRs should be fine, but the glue joints will be more important.

Not to get into a peeing match but not using plywood or doing something like fiberglass cloth/epoxy lamination of those paper rings means the aft end Isn't going to last long with D motors. The three engine motor cluster of this rocket was known as the Ranger. Kurt
 
It seems to me my Magician has paper centering rings and I have countless E-Motor flights on it - whats the difference ??
Knowing the OP as well as I do - I would say with certainty its properly built :wink:
 
I had a lot of flighs on my Bertha by the time I stuck that composite D in it. It wasn't the paper rings that gave out, it was the glue. I don't really plan on beefing it up as I really enjoy flying it low and slow on BP engines. I was at an extremely large field so I threw it in on a whim. You live, you learn lol.
 
It seems to me my Magician has paper centering rings and I have countless E-Motor flights on it - whats the difference ??
Knowing the OP as well as I do - I would say with certainty its properly built :wink:

If you're talking about the 24mm BT-55 Magician, It has thicker fiber rings with more tube contact surface area for gluing, and relatively small web of material between ID and OD.

The Bertha has thinner centering rings that will be more susceptible to bending which will stress the joint differently and could reduce the fatigue tolerance.


Such is my theory at any rate which is worth exactly what you paid for it
 
Alternately, you could make new Through-The-Wall fins to replace the kit fins, and slot the body tube. (fins tabs extend through the body tube slots and are mounted to the engine mount), requires a little more work than just swapping out the centering rings on a new kit build. But also makes the fins stronger for hard landings. If your kit is already built, it may actually be easier to pop off the old fins as opposed to removing the existing engine mount. Check c.g. location of the stock build, then add some nose weight to maintain that after modding the engine mount, although probably lots of margin, but you will be adding more aft weight with any of these mods.

for example:
https://www.apogeerockets.com/Building-Supplies/Rocket-Fins/Stand-up-Shape-Plywood-Fins-with-TTW-Tab
 
I cant even download Open Rocket on my home computer to even attempt to use it, because my computer has a security setting that wont allow me to open PDF files and other files as well....ive tried everything to unlock the setting, no luck!
What kind of computer, what operating system?
 
I have flown a stock Semroc Vega (very similar in size, weight, concept to a Big Bertha) on Aerotech D10s a number of times with no ill effects. The -5 is too short, the -7 is too long, at least with the 808 camera on the side. Granted the stamped thin cardstock centering rings in the current Big Bertha kits are pretty flimsy compared to the much nicer fiberboard centering Semroc uses. So if I were planning on flying a new-build Big Bertha on D10s (or D21s or their RMS counterparts) I might want to double the rings or get some plywood 2060 centering rings from BMS but otherwise no modifications should really be necessary. At the very least I'd use better quality fiber rings....and take good care with glue joints both ring to motor tube and ring to body tube. That's really the key it would seem to me.

I've flown a Big Bertha with a 24mm motor mount in it on Estes D12s with a Chute Release aboard. Typically reported altitudes (via Altimeter3, also aboard) are 700-750 feet. It'd go a bit higher without the extra weight of the Altimeter3. I got 1296 feet with the same combo on an E9-6. The rocket survived an Aerotech F44 but I didn't get good data so I don't know how high it actually went. The model is stock except for using a 24mm motor mount big enough for E9/E12 (and so some Semroc centering rings). No glass, no TTW fins, no epoxy, no supplemental nose weight. Just built with reasonable care.
 
Yeah.....you may be right. Certainly I'd be worried about the D21 or the RMS 18/20 Blue Thunder motor if the motor mount was made with the stock thin centering rings only. I've flown a Semroc Maxi-Micron on D21s several times with no ill effects (and no beefing up). It's heavier and draggier (being made from ST-18 tubing) but as I mentioned before the Semroc centering rings are thicker and stronger.
 
I FINALLY have a chance to sit down and get back to everyone who replied to my thread....sometimes life is too DAMN BUSY!! Thank you all for the GREAT input regarding my questions! Rex, I was hoping you'd chime in as I always value your input on my lil projects!
After reading all the great input, I decided to "beef up" my motor mount by adding a 1/16th" balsa "doubler" to the outside of each ring, and then epoxy 3- 1/8th" balsa braces 120 degrees apart between the rings as this adds bonding area for the mount with very little gain in weight....ive done this before with a couple of other models, and it has worked well !! Again, MANY THANKS to everyone for helping me out!
 
probably could gain the same benefit as the balsa doublers by gluing cardstock rings to the Estes rings inside and out. big question though, which way did you orient the grain on the braces? those work best when the grain is perpendicular to the motor/ body tubes, sort of a finless fin tab :). glad I could offer some insight.
Rex
 
And this is why I so appreciate your replies! Okay....I know lottsa folks use cardstock and seem to love the stuff, including a friend of mine that I fly rockets with....so comes the stupid question(not too proud to ask though) exactly what IS cardstock, and where can I purchase the stuff??? Its too late for the BB....its BONDED in the body tube with slow set laminating epoxy! BUT I would like to use cardstock in one of my next builds for those purposes!! And......affirmative on the grain...I got that part right:)! THANKS Rex!!
 
cardstock is just thicker paper (think greeting/birthday/Christmas cards) usually found in the same general area as printer paper(office supplies*). 110# is what I use, while it can be had in various colors, I would stay away from the floro colors(the coating makes it harder to glue). one can also use 3 x 5/ 5 x 7 index cards. cardstock has a number of uses (including making your own greeting cards), handy for heavy duty fin skins, fin templates, conical transitions, shimming loose nose cones/motor mounts, and in a pinch mixing small amounts of epoxy. I am pretty sure that there are other uses :) those are a few of the common ones, one could say that it is as useful as bamboo skewers and plastic shot cups.
Rex
*Walmart/ office depot/ office max to name a few :)
 
Just wondering what am I missing on triple plywood for centering rings. After reading about the number of paper CRs ending up jammed in to the nose of the rocket I scrapped the paper CRs for wood. I just replaced my Big Daddy stock CRs with Balsa CRs that ended up several grams under the stock CRs weight and have a larger edge gluing contact surface. The balsa CRs are 1/8" sheet, cut in to 4" squares, grain turned perpendicular, wood glue spread across the surface and the sandwhich gets layed up on a piece of sheetmetal with flat bar magnets on top to apply clamping pressure. The paper CRs are 5.42g and the finished/cut balsa CRs are 3.18g. I've scuffed the inside of the BT and outside of the motor tube at the glue joint to help the glue bite. I know its not an appreciable difference upfront but for my build, three balsa CRs are 9.54g vs stock 16.26g. Does ply wick in a lot of glue? Is there some Merlin-esque alchemy taking place that gives ply an advantage for D/E engine mounts? I ask because I haven't yet tested the Big Daddy mod (too windy and fire conditions are horrific) and I'm drawing up a BT60 Bomarc along the same mods.
 
for a big daddy your CRs are way, way over built. if you wanted to save weight I would suggest 1/8" extruded polystyrene foam* :). seriously the stock CRs are fine. the centering rings in a BD aren't load carrying they do just what the name implies, center the motor mount tube, the fins carry the thrust loads.
Rex
*okay a layer of paper white glued to the forward side of the forward ring to protect it from ejection debries, plus a paper ring on the aft surface of the aft ring to protect it when painting (and back blast).
 
for a big daddy your CRs are way, way over built. if you wanted to save weight I would suggest 1/8" extruded polystyrene foam* :). seriously the stock CRs are fine. the centering rings in a BD aren't load carrying they do just what the name implies, center the motor mount tube, the fins carry the thrust loads.
Rex
*okay a layer of paper white glued to the forward side of the forward ring to protect it from ejection debries, plus a paper ring on the aft surface of the aft ring to protect it when painting (and back blast).

Great info share and I'd agree you're correct on the overbuild. The BD on the table is a TTW and rear eject. Wasn't sure if the ejection pressure would wreak havoc on the BT though there are two glue surfaces per fin, the BT fillets and the motor mount lenght. I wanted little flex when the charge punches the rear CR and chute out the back. IF it tests as anticipated, I'll post the pics.
 
About how high would the Big Bertha go on a D10-7 WITH a Jolly Logic 'chute release in it?
Has anyone used a JL 'chute release in a rocket with a 1.6" ID? According to the manual, its doable.

I just realized I actually have a measured answer to this. See AltimeterThree graph attached. This was a D10-7, with the Chute Release set to 200 feet.

I fly several BT-60 models with a Chute Release. The one that benefits the most is the Star Orbiter. But that is for another thread.

IMG_9A4A4F71A164-1.jpg

IMG_B0F403B9BFD8-1.jpg
 
I just realized I actually have a measured answer to this. See AltimeterThree graph attached. This was a D10-7, with the Chute Release set to 200 feet.

I fly several BT-60 models with a Chute Release. The one that benefits the most is the Star Orbiter. But that is for another thread.

THANKS SO MUCH BEC! MAN! This is GREAT information!! This is the BB I just built for the D10-7 and the Chute Release.....I think this is BB#7 or#8!!013.jpg
 
You can see in the A3 data that if the D10-7 had really been 7 seconds it would have been perfect....but on that one I got an Aerotech “bonus delay”.
 
004.jpg005.jpg
You can see in the A3 data that if the D10-7 had really been 7 seconds it would have been perfect....but on that one I got an Aerotech “bonus delay”.

I looked at the graph, and I happily agree! If you don't mind, please have a look at these pics of my mock up for the chute release...if you see anything that you don't like, or would do differently, PLEASE chime in!
I did the shake test, the blow test(as best I could, and the release test, and everything seemed to work as its supposed to! Im SO EXCITED about trying this gadget out at the club launch next month!
OH!......I set the altimeter for 300'.....Its a really big field that I launch out of......any opinions? Again, MANY THANKS:)!!
 
That looks great. The only thing - which I'm sure you know - is to repack the 'chute just before you fly because those plastic ones don't like to open if they've been folded for awhile (especially if it's chilly) and to turn on the Chute Release! The only failure to release I've ever had was when I forgot to turn the thing on. :eek:
 
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