Newbie doesn't quite understand Est. Max Lift Weight in Estes Rocket Engine Performance Chart

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Dotini

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Hi, sorry for the dumb question. I'm an old guy returning to rocketry after a 30 year absence. My question is, does Est. Max Lift Weight include the initial weight of the engine? Thanks for your help.
- Steve
 

rklapp

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Tim said that's something Rocksim takes into consideration in the flight path is the elimination of motor solid fuel as the rocket ascends and becomes more stable.
 

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Hi, sorry for the dumb question. I'm an old guy returning to rocketry after a 30 year absence. My question is, does Est. Max Lift Weight include the initial weight of the engine? Thanks for your help.
- Steve
Yes, Steve it absolutely does. Estes BP rockets motors are listed with maximum "recommended" weights for each--this includes propellant/delay/ejection/endcap. However, once they eject (if not boosters, they're actually a little lighter because you can estimate but Estes doesn't provide any data beyond propellant weight which you can assume is gone at burnout. And max total rocket weight is an estimate--usually relatively accurate with kits, but an estimate nonetheless. "How much thrust do I need to lift this much mass to a safe height?". Rocket designs differ a lot but their estimate is probably close to true, and you can presume that they add in a "fudge factor" to be a little conservative.

If you ever have a specific rocket that you're considering launching on a specific or variety of motors and you're just not sure...well, probably one of us has launched that combination and can provide their observations. Of course no two people build rockets identically (weight/aerodynamics) and rocket motor power and delay can vary within a single multipack (hopefully not too much; occasionally so). So it's a guide more than a rule. But if you're bending that rule, I'd aim for the lighter side than the heavier side, hah hah! Unless you've upgraded your motormount and motors used (common).

Welcome back!!!
 

Dotini

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Yes, Steve it absolutely does. Estes BP rockets motors are listed with maximum "recommended" weights for each--this includes propellant/delay/ejection/endcap. However, once they eject (if not boosters, they're actually a little lighter because you can estimate but Estes doesn't provide any data beyond propellant weight which you can assume is gone at burnout. And max total rocket weight is an estimate--usually relatively accurate with kits, but an estimate nonetheless. "How much thrust do I need to lift this much mass to a safe height?". Rocket designs differ a lot but their estimate is probably close to true, and you can presume that they add in a "fudge factor" to be a little conservative.

If you ever have a specific rocket that you're considering launching on a specific or variety of motors and you're just not sure...well, probably one of us has launched that combination and can provide their observations. Of course no two people build rockets identically (weight/aerodynamics) and rocket motor power and delay can vary within a single multipack (hopefully not too much; occasionally so). So it's a guide more than a rule. But if you're bending that rule, I'd aim for the lighter side than the heavier side, hah hah! Unless you've upgraded your motormount and motors used (common).

Welcome back!!!
Thanks for your detailed answer. I'm vey gratified to have found this forum and all the helpful and enthusiastic people here. Fed up with cabin fever and bored of re-runs, I'm back because building things in my basement shop gives me new activity. I'm building a fleet of rockets over the winter to have on hand for launch when the weather gets better.

A good example of my current perplexity is my Estes Big Bertha. According to the catalog, she is 2.5 oz. There are reports of launches in which weight is claimed at 2.2 oz. I built my model almost according the kit, right down to the colors and decals, but perhaps foolishly added a baffle. Ready to launch with B4-4 and recovery device, I get weights of 4.9 oz and 4.7 oz on my two mechanical scales. This substantially exceeds the Est. Max Lift Weight of 3.5 oz for the B4-4 engine, and indeed any other engine recommended for the Big Bertha. I don't think I used too much glue or paint, so my current takeaway is beware of baffles and/or step up to a digital scale. Any recommendations?

I'm looking forward to asking more dumb questions, so thanks in advance for all your collective experience and wisdom.
 

CPUTommy

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Hi, sorry for the dumb question.
- Steve
Steve, WELCOME!! This IS the place to have your questions answered by the correct people..

The only dumb question is the ONE NEVER ASKED.

your in good hands and any questions you have feel free to post or message me directly.

Again...welcome back !!
 

heada

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Thrustcurve.org has a "match a rocket"


You enter details about your rocket and they'll come back with what should work assuming normal rules (thrust to weight ratio, minimum speed off the rod, etc)

Which Big Bertha are you building? There is a Super Big Bertha, Big Bertha, Mini Bertha, Boosted Bertha, etc. You can also look at motors other than Estes. Quest makes composite motors in 18mm that should be able to lift more than 4.9oz
 

neil_w

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Estes doesn't always follow it's own max weight recommendations to the letter.

A B4-4 on the Bertha is certainly marginal, but doable if it's a low-wind day, unless your build is indeed heavy. Definitely invest the $15 or whatever in a digital scale, they're incredibly useful. I have this one: https://smile.amazon.com/Smart-Weigh-SWS1KG-Digital-Pocket/dp/B00GS8GJGW/
 

Antares JS

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Just wanted to add a note here not to rely completely on the maximum weight chart to determine whether a motor is safe. Per its weight, my Outlander should have been fine on a C5-3. It was not, presumably because it's so draggy.
 

Dotini

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Which Big Bertha are you building? There is a Super Big Bertha, Big Bertha, Mini Bertha, Boosted Bertha, etc. You can also look at motors other than Estes. Quest makes composite motors in 18mm that should be able to lift more than 4.9oz
I've built the basic Big Bertha, but with a baffle, making it heavy. It has filler in the balsa and two coats of paint.
But instead of getting a stronger motor, I'm simply going to build another without the baffle and try to minimize the weight to where it launches safely with B4-2. Since I live in a dense urban area I plan to keep my launches rather low until I can make a pilgrimage to the nearest approved range, whatever that is anymore.

Estes doesn't always follow it's own max weight recommendations to the letter.

A B4-4 on the Bertha is certainly marginal, but doable if it's a low-wind day, unless your build is indeed heavy. Definitely invest the $15 or whatever in a digital scale, they're incredibly useful. I have this one: https://smile.amazon.com/Smart-Weigh-SWS1KG-Digital-Pocket/dp/B00GS8GJGW/
Thanks for the advice - I just ordered one! :)
 

heada

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A standard Big Bertha is 42mm diameter and your weight of 4.9oz can be safely launched nearly anywhere on an Aerotech/Quest C18W-4. It'll go about 120m (about 400 ft) high and go about 54m/s (120mph) As an added bonus, the Quest motor is composite so it'll ROAR off the pad rather than whoosh like you get with Estes BP motors. Trust me, you'll notice the difference. Quest motors are more expensive to buy and ship but still nowhere near the costs of high power motors and I think they're worth it.

-or-
-or-
your vendor of choice

$10 for a pair of motors

But yes, do build another. Build 3 or 4. Tweak them by switching to a 24mm mount or a cluster of 18mm motors or adding side pods or make it a Goony or multi-stage or ...
 

jrap330

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Estes doesn't always follow it's own max weight recommendations to the letter.

A B4-4 on the Bertha is certainly marginal, but doable if it's a low-wind day, unless your build is indeed heavy. Definitely invest the $15 or whatever in a digital scale, they're incredibly useful. I have this one: https://smile.amazon.com/Smart-Weigh-SWS1KG-Digital-Pocket/dp/B00GS8GJGW/
A stock Big Berta...not you "slightly chubby" BB flees great on a B6-4..... never tried it on a B4-4...
 

SharkWhisperer

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A standard Big Bertha is 42mm diameter and your weight of 4.9oz can be safely launched nearly anywhere on an Aerotech/Quest C18W-4. It'll go about 120m (about 400 ft) high and go about 54m/s (120mph) As an added bonus, the Quest motor is composite so it'll ROAR off the pad rather than whoosh like you get with Estes BP motors. Trust me, you'll notice the difference. Quest motors are more expensive to buy and ship but still nowhere near the costs of high power motors and I think they're worth it.

-or-
-or-
your vendor of choice

$10 for a pair of motors

But yes, do build another. Build 3 or 4. Tweak them by switching to a 24mm mount or a cluster of 18mm motors or adding side pods or make it a Goony or multi-stage or ...
The Quest D16 is also an 18mm motor that'll fit that bird and lift that mass: https://www.rocketreviews.com/q-d16.html. Pricing's not all that different from C12s...

Like cbwho said above, the newish Estes C5-3 motors would probably work in your heavy built model--it's got a lot more initial oomph to get her off the pad at and adequate speed. Estes C6-3s are rated for 4 oz rockets max. Meh. Get an accurate weight--that just seems like a lot of additional weight just for a baffle in that sized body tube, unless you made it with thick heavy wood. If it's actually only a half ounce over (12%) I personally wouldn't have any issue trying that C6-3 motor as a first-flight motor (while waiting for your more powerful ones to arrive). I'd be leary of launching if true weight is approaching 15-20% over spec, for sure. Then just wait for your hotter composite motors. No B-motors, please. Probably will just limp off the launch rod and nose over.

It's always easier to upsize your stock motor mounts for larger/more powerful motors--you can always use lower power/smaller motors in store-bought or custom made adapters, if desired (and motor has sufficient power). Take care about using Quest composite motors in Estes plastic motor adapter kits, though--the composite motors get hotter than BP motors and risk melting plastic.

And please upgrade your scale to a cheap digital scale that measures at least 10th of grams. I have two $10 scales (Amazon, AWS brand, though there's many) for measuring rocket pieces and chems (I'm also a fireworker); one goes to 100g with 0.01g precision and another goes to 600g with 0.1g precision (a switch will allow you to use ounces instead of metric, if desired). Then I have one that goes into the Kg ranges but you likely won't be weighing anything that large for a little while. A US nickel weighs pretty close to 5g if you don't want to purchase calibration weights. Even the cheaper electronic models often provide reliable, and repeatable readings. Scales are pretty much "must have" items.

Here's an example of a budget scale up to 200g with 0.01g resolution. Precision is +/-0.03g, which makes it unsuitable for use in an analytical chemistry laboratory, but more than functional for model rocketry, for like $11. Plenty of options, but I probably wouldn't go much cheaper than this--it's on the low end of quality but might be just fine for your purposes. Other max weight ranges available, too for heavier stuff... Just an example: https://www.amazon.com/Digital-Conv...436c4&pd_rd_wg=rnpom&pd_rd_i=B087WF4PK1&psc=1
 
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BABAR

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Estes doesn't always follow it's own max weight recommendations to the letter.

A B4-4 on the Bertha is certainly marginal, but doable if it's a low-wind day, unless your build is indeed heavy. Definitely invest the $15 or whatever in a digital scale, they're incredibly useful. I have this one: https://smile.amazon.com/Smart-Weigh-SWS1KG-Digital-Pocket/dp/B00GS8GJGW/
I got one and someone, let’s just say a guest, immediately asked me if I was dealing drugs when he saw it!
 

BABAR

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I've built the basic Big Bertha, but with a baffle, making it heavy. It has filler in the balsa and two coats of paint.
But instead of getting a stronger motor, I'm simply going to build another without the baffle and try to minimize the weight to where it launches safely with B4-2. Since I live in a dense urban area I plan to keep my launches rather low until I can make a pilgrimage to the nearest approved range, whatever that is anymore.


Thanks for the advice - I just ordered one! :)
Welcome to the forum, and excellent question! I’d much rather a new rocketeer come on the forum and ask a question like that than have them have a suboptimal launch and either get hurt, hurt someone else, break something, or most likely just get frustrated and quit the hobby.

most people on this forum take their medications and are relatively friendly and helpful.

for the few who are not, well, nobody is completely useless. They can always serve as a bad example. ;)

hope you get some great flights! Check the NAR and Tripoli site and see if there is an active club nearby. Generally will have a decent field and lots of help and experience for newbies.


www.tripoli.org/Prefectures
 

dhbarr

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I got one and someone, let’s just say a guest, immediately asked me if I was dealing drugs when he saw it!
I have 3-4 different ones for pinewood derby time, and yeah -- my Amazon ads got pretty interesting for a while there.
 

BABAR

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I have 3-4 different ones for pinewood derby time, and yeah -- my Amazon ads got pretty interesting for a while there.
That’s funny and scary at the same time!
 

Dotini

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I received my new "drug user" edition of digital scale yesterday. Upon weighing my Baffled Big Bertha - and contrary to the 4.9 oz figure reported on my old mechanical scales - I now get a new figure of 4.6 oz, with B6-2 motor and 7"x100" streamer. Even though this is slightly over the Est. Max Lift Weight, I plan to risk a launch with this motor.
 

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I received my new "drug user" edition of digital scale yesterday. Upon weighing my Baffled Big Bertha - and contrary to the 4.9 oz figure reported on my old mechanical scales - I now get a new figure of 4.6 oz, with B6-2 motor and 7"x100" streamer. Even though this is slightly over the Est. Max Lift Weight, I plan to risk a launch with this motor.
Steve hey! Excellent on the launch plans! Unsure how you decided your streamer dimensions, or what it's made of, but this article on streamer design might be useful to you: https://www.apogeerockets.com/education/downloads/Newsletter244.pdf . Here's another good article on streamer use: https://www.apogeerockets.com/education/downloads/Newsletter128.pdf . Point being, longer isn't always better. That last newsletter also suggests not using streamers for rockets over 1 ounce, but I've launched bigger than that with success. But you might be pushing it a little... There's also other articles and threads available on streamer design and using multiple streamers that should be easy to locate. Bertha's kinda fat and will have a bit of drag already from the separated NC and BT, and doesn't weigh all that much, but I'd consider using two shorter streamers towards opposite sides of a long shock cord. And streamer deployment is also dependent upon how you wrap or roll them, and on their material characteristics... On that B-motor, you're not going to have a lot of leeway in terms of extra time for the streamer to unfold and start doing its thing--you want immediate action. Good you picked the B6-2 instead of the B6-4 because 4 second delay seems long for that projected altitude, and delay timing is never perfect with those motors. You probably also will want to have a few C6-3's laying nearby on first launch day!

Just did a quick calculation, estimating your rocket will weigh around 4.3 oz after ejection, and for a 7" wide streamer, Rocket Reviews' calculator indicates a 23" streamer. From: https://www.rocketreviews.com/streamer-calculator.html . Obviously this doesn't account for streamer material, but it probably assumes mylar (thickness???) or crepe paper. This seems pretty short to me, intuitively. And many companies sell streamers that have a width/length ratio of 1:10, though this ratio is debatable in terms of being "optimal". This is clear by comparing my test calculation at Rocket Reviews that gave a 1:3 ratio, which most might consider to be pretty short. It's extremely unlikely that Bertha will stray far from home on a B motor no matter what, but it's also going to be a low altitude flight with you sorting out the kinks of the recovery system (and needing to get it appropriately right so you don't lose a fin on the first flight). You might not have the luxury of time for a huge streamer to completely unfurl and do it's thing. And longer isn't necessarily better because long streamers don't whip around as much as a shorter one might. You might want to use a parachute on the first flights...
 
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rklapp

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Definitely won’t miss a 7”x100” streamer glittering in the sun...
 

SharkWhisperer

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Definitely won’t miss a 7”x100” streamer glittering in the sun...
Unless it's sky-blue and cloud-white dull crepe!

But yes, that is one monster streamer! I find it difficult to imagine it'll open fully and start doing significant real work from altitudes reached by Bertha on a B-motor, though...
 

Dotini

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Steve hey! Excellent on the launch plans! Unsure how you decided your streamer dimensions, or what it's made of, but this article on streamer design might be useful to you: https://www.apogeerockets.com/education/downloads/Newsletter244.pdf . Here's another good article on streamer use: https://www.apogeerockets.com/education/downloads/Newsletter128.pdf . Point being, longer isn't always better. That last newsletter also suggests not using streamers for rockets over 1 ounce, but I've launched bigger than that with success. But you might be pushing it a little... There's also other articles and threads available on streamer design and using multiple streamers that should be easy to locate. Bertha's kinda fat and will have a bit of drag already from the separated NC and BT, and doesn't weigh all that much, but I'd consider using two shorter streamers towards opposite sides of a long shock cord. And streamer deployment is also dependent upon how you wrap or roll them, and on their material characteristics... On that B-motor, you're not going to have a lot of leeway in terms of extra time for the streamer to unfold and start doing its thing--you want immediate action. Good you picked the B6-2 instead of the B6-4 because 4 second delay seems long for that projected altitude, and delay timing is never perfect with those motors. You probably also will want to have a few C6-3's laying nearby on first launch day!

Just did a quick calculation, estimating your rocket will weigh around 4.3 oz after ejection, and for a 7" wide streamer, Rocket Reviews' calculator indicates a 23" streamer. From: https://www.rocketreviews.com/streamer-calculator.html . Obviously this doesn't account for streamer material, but it probably assumes mylar (thickness???) or crepe paper. This seems pretty short to me, intuitively. And many companies sell streamers that have a width/length ratio of 1:10, though this ratio is debatable in terms of being "optimal". This is clear by comparing my test calculation at Rocket Reviews that gave a 1:3 ratio, which most might consider to be pretty short. It's extremely unlikely that Bertha will stray far from home on a B motor no matter what, but it's also going to be a low altitude flight with you sorting out the kinks of the recovery system (and needing to get it appropriately right so you don't lose a fin on the first flight). You might not have the luxury of time for a huge streamer to completely unfurl and do it's thing. And longer isn't necessarily better because long streamers don't whip around as much as a shorter one might. You might want to use a parachute on the first flights...
Thanks for what will be extremely valuable information for me. I will think about it all for days. The streamer is silver mylar. I wanted it as big as possible for quick easy recovery.

FYI, I have substituted my own fins for the standard Big Bertha kit fins. They are of the same material and overall area, but instead of hanging vulnerably down, the trailing edge angles somewhat forward and the leading edge is at 90 degrees to the tube. I figured these would take the landings better.
 

neil_w

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FYI, I have substituted my own fins for the standard Big Bertha kit fins. They are of the same material and overall area, but instead of hanging vulnerably down, the trailing edge angles somewhat forward and the leading edge is at 90 degrees to the tube. I figured these would take the landings better.
1614895659473.png


;)
 

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Thanks for what will be extremely valuable information for me. I will think about it all for days. The streamer is silver mylar. I wanted it as big as possible for quick easy recovery.

FYI, I have substituted my own fins for the standard Big Bertha kit fins. They are of the same material and overall area, but instead of hanging vulnerably down, the trailing edge angles somewhat forward and the leading edge is at 90 degrees to the tube. I figured these would take the landings better.
Ooh, yeah, like Neil said above--it'd be good if you could upload a pic. Hopefully you ran your design through RockSim or OpenRockets to make sure you didn't move your CP too far forward accidentally. It definitely moved forward if fin area is the same...only question is how much? And your CG probably got nudged a little with the added baffle (unless installed directly on the existing CG). Those fins extend (perilously) below the motor mount rear to keep the CP backwards for stability. I'd run a sim before launching her, particularly with such a low-impulse motor. If Bertha's burning kinetic energy trying to fly "normal" then you might not get the altitude you're expecting, which might pose new considerations/concerns.

Worst case is you might have to add some weight to the nose and use one of those C-motors for first flight. Then again, these are all guesses without running a simulation, and she might fly fine. But I probably wouldn't chance guessing at it. Spiraling horizontal and parabolic missiles are always "attention getters" but maybe not what you're wanting to risk on your first flight, specially with the kids nearby and wide-eyed.

Please upload a pic of your bird.
 

Dotini

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Ooh, yeah, like Neil said above--it'd be good if you could upload a pic. Hopefully you ran your design through RockSim or OpenRockets to make sure you didn't move your CP too far forward accidentally. It definitely moved forward if fin area is the same...only question is how much? And your CG probably got nudged a little with the added baffle (unless installed directly on the existing CG). Those fins extend (perilously) below the motor mount rear to keep the CP backwards for stability. I'd run a sim before launching her, particularly with such a low-impulse motor. If Bertha's burning kinetic energy trying to fly "normal" then you might not get the altitude you're expecting, which might pose new considerations/concerns.

Worst case is you might have to add some weight to the nose and use one of those C-motors for first flight. Then again, these are all guesses without running a simulation, and she might fly fine. But I probably wouldn't chance guessing at it. Spiraling horizontal and parabolic missiles are always "attention getters" but maybe not what you're wanting to risk on your first flight, specially with the kids nearby and wide-eyed.

Please upload a pic of your bird.
I'll get a pic up as soon as I can, which considering my age and skills, will be a while. But trust me, I'll do it.

My fin is a simple reversed clipped delta, root 2.6", leading edge 3.0", tip 1.8", and trailing edge at a 75 degree angle to the tube. My research on Big Bertha indicates overstability, but I will do a swing test just to make darn sure. I have the full range of C motors and nose weight if needed. But my goals are minimum altitude and easy recovery for my arthritic knee. I have bunch of 1/4A, 1/2A and A motor odd rocs including three ringtails to launch as well, and they will go first. I'm familiar with the swing test already. I built the Bertha mainly to get back in the groove of model building. Other than launching a 4 stage once in my youth (recovered it and launched a 2nd time), I've never done anything to violate the NAR code or endanger people, and I'm not about to start now. I'm a former NAR member and plan to renew my membership.
 

BABAR

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I'll get a pic up as soon as I can, which considering my age and skills, will be a while. But trust me, I'll do it.

My fin is a simple reversed clipped delta, root 2.6", leading edge 3.0", tip 1.8", and trailing edge at a 75 degree angle to the tube. My research on Big Bertha indicates overstability, but I will do a swing test just to make darn sure. I have the full range of C motors and nose weight if needed. But my goals are minimum altitude and easy recovery for my arthritic knee. I have bunch of 1/4A, 1/2A and A motor odd rocs including three ringtails to launch as well, and they will go first. I'm familiar with the swing test already. I built the Bertha mainly to get back in the groove of model building. Other than launching a 4 stage once in my youth (recovered it and launched a 2nd time), I've never done anything to violate the NAR code or endanger people, and I'm not about to start now. I'm a former NAR member and plan to renew my membership.
I like the way you think. The vast majority of my chute or streamer recovered birds have fins either 90 degrees or FORWARD swept precisely to avoid fin damage on landing, they generally hit motor casing first.

I also like your plan for a swing test, although I suspect you are right, the fin change probably won’t change stability much.

like others here, looking forward to a picture (maybe after balancing it on your finger you can mark on the picture with a piece of tape the CG with motor and recovery installed as if for launch?)

I do admit I am a bit sketchy on the B motor with your rocket mass, although I definitely like the short delay if you go that route.

in any case, I am sure you will be careful and launch on a very low wind day somewhere that your rocket will not venture near other launch site occupants (who may NOT be watching.). These days when I launch it’s kind of like @rklapp, I have the park pretty much to myself. That’s about the only GOOD thing about Covid.

hope you get a good straight and preferably vertical trail!
 

BABAR

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Definitely fold the streamer accordion style, do not roll it. With a b motor and that mass and short delay, a rolled streamer will never UNROLL in time.
 

Dotini

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Definitely fold the streamer accordion style, do not roll it. With a b motor and that mass and short delay, a rolled streamer will never UNROLL in time.
I shortened my streamer a bit, cut it in half to make two, one to fix at the cone, the 2nd to attach about 50" further down the cord. And I'm in the process of pleating it. This is taking me awhile, but I'm taking all of you seriously.
 
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