More Half-Baked Designs Thread

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BigMacDaddy

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Someone posted about gluing nose cone and fins to an E-engine, I modeled it in OR to see how to make it stable (not too difficult actually). Realized it went almost .5 Mach so became curious -- Is it possible to make a supersonic low-powered rocket??? Simmed an 18mm swift-esque rocket with a Quest D20-4 engine and it seems close... I had to select polished for the finish on all the surfaces so this may not be realistic and I also bet there is a good chance that the fins would sheer off since you cannot use decent tabs on a minimum diameter rocket like this.

Any thoughts on how to break the sound barrier with a low-powered setup?

1638112934996.png
 

jqavins

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Remember that the CD goes up sharply through the transonic region, roughly 0.8 to 1.2 mach, which is a huge part of what makes going supersonic, i.e. above about 1.2, so difficult. And makes simply breaking 1 mach pretty darn hard too. Is it possible in LP? I'm not saying no.
 

lakeroadster

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Someone posted about gluing nose cone and fins to an E-engine, I modeled it in OR to see how to make it stable (not too difficult actually). Realized it went almost .5 Mach so became curious -- Is it possible to make a supersonic low-powered rocket??? Simmed an 18mm swift-esque rocket with a Quest D20-4 engine and it seems close... I had to select polished for the finish on all the surfaces so this may not be realistic and I also bet there is a good chance that the fins would sheer off since you cannot use decent tabs on a minimum diameter rocket like this.

Any thoughts on how to break the sound barrier with a low-powered setup?

View attachment 491840

Going up isn't the issue. Coming down is the issue. Especially with that brain penetrating pointed nose cone. :haironfire:

How about going with the bottle rocket concept? But make it safe by adding a parachute. Just need an 18" long x 3/16" diameter dowel, a 6" piece of BT-50 and an 8" parachute.

.
D-12 Bottle Rocket Photo Studio.jpg
E-12 Bottle Rocket.jpg


 
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jqavins

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For recovery of a 3FNC flying cardboard case, one could use a piece of body tube just an inch or so long, glued to the nose cone shoulder and going over the front of the motor as a sleeve. A length of very thin kevlar line, glued to the engine and nose cone would give you plenty of drag in the separated pieces.

A potential problem I see it that gluing things to the motor could be construed as modifying it, in violation of the safety code.
 

boatgeek

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A potential problem I see it that gluing things to the motor could be construed as modifying it, in violation of the safety code.
IMHO, as long as you aren't touching the energetics or doing something to compromise the strength of the casing*, you aren't modifying the motor. Your fins would have to pull off a lot of layers of cardboard motor casing to make it burst. This opinion is worth exactly what you paid for it.

* The best example I can think of for this is welding fins to an aluminum motor casing, thereby messing with the casing's temper.
 

jqavins

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My opinion, and the worth thereof, are exactly the same as yours. But I've been told repeatedly that pouring epoxy into the top to plug a rolled paper tube BP engine is not allowed, because it is modifying the engine. Under our opinions as expressed by you, that should be OK, but more experienced and presumably more knowledgeable people than I say it's not. So I do not know where the line is.
 

boatgeek

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My opinion, and the worth thereof, are exactly the same as yours. But I've been told repeatedly that pouring epoxy into the top to plug a rolled paper tube BP engine is not allowed, because it is modifying the engine. Under our opinions as expressed by you, that should be OK, but more experienced and presumably more knowledgeable people than I say it's not. So I do not know where the line is.
That argument is precisely why I used the word “energetics”—when you plug a motor with epoxy you are touching the election charge. I don’t entirely subscribe to that idea but I recognize that it’s a valid argument.
 

jqavins

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Ah, I see. It's not the word "energetics" whose significance I misunderstood, but rather "touching". That's the word that went in one eye and out the other, leaving "affecting" in its place.
 

BigMacDaddy

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FYI -- cut and weighed the bamboo...

11.25" single-section piece weighs around 54g and a 22" two-section piece weighs around 118g. This stuff is still pretty wet and I have not drilled it out at all or anything so TIFWIW. Should be big enough for a 24mm motor after drilling. I will periodically post some updates on this low priority half-baked build...
 

bjphoenix

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Someone posted about gluing nose cone and fins to an E-engine, I modeled it in OR to see how to make it stable (not too difficult actually). Realized it went almost .5 Mach so became curious -- Is it possible to make a supersonic low-powered rocket??? Simmed an 18mm swift-esque rocket with a Quest D20-4 engine and it seems close... I had to select polished for the finish on all the surfaces so this may not be realistic and I also bet there is a good chance that the fins would sheer off since you cannot use decent tabs on a minimum diameter rocket like this.

Any thoughts on how to break the sound barrier with a low-powered setup?

I went through this years ago, with less sophisticated software. The next step above an 18mm D is a 24mm E so you gain more drag. I found that an F72 was the best choice for a small rocket so I built one. I didn't just glue pieces to a motor, I used an Estes kit similar to the Alpha. I glassed the fins and of course left out the motor mount. At launch it 100% disappeared. Mach is darned fast, most handgun bullets don't break Mach so a small rocket going that fast probably wouldn't be trackable.

I remember many years ago we built a very lightweight Estes kit called the Streak. If you go back to the 1964 catalog you can see that it weighed 1/8 ounce and the catalog predicted 2000ft altitude. And realize that there were no C motors back then, B was the largest motor sold by Estes. Build one of those, maybe with a better nose cone profile, and put an 18mm composite motor in it. You likely won't see it again.
 

dhbarr

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d-21 ought to be just barely possible, but getting it back with proof would be the tricky bit
 

bjphoenix

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d-21 ought to be just barely possible, but getting it back with proof would be the tricky bit
I posted about the catalog page of the Estes Streak and its mention of 2000' altitude with a B engine. I haven't tried a sim but this seemed extreme to me, but I think a D21 could possibly break 2000'.
 

BigMacDaddy

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It looks like the 2000' flights would be on the largest engine which seems like the C6-7 according to packaging I can find but that is just a guess...

1638243731434.png
 

BigMacDaddy

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You can make quite a reasonable little rocket and still seems to sim at supersonic (sorry, transonic) w/ D20-8...

1638245200166.png


Now what would be very cool would be if I could use a minimum diameter ring tail and rely on engine-driven dynamic stability to keep this stable...
 
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BABAR

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Going up isn't the issue. Coming down is the issue. Especially with that brain penetrating pointed nose cone. :haironfire:
actually an extremely safe and essentially “no mass added” (except for The shock cord, which is pretty minimal) would be “nose blow” recovery. Even saves you the mass of gluing in the nose cone. No chute or streamer needed. You might break some NAR rules if you drill a hole in the forward end of the motor (forward of the clay cap, of course) to attach the shock cord.

now, FINDING the sucker would be hard enough even WITH a big streamer, with Nose Blow the thing could almost hit you on the head and you’d still have a tough time finding it in tall grass.
 

lakeroadster

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actually an extremely safe and essentially “no mass added” (except for The shock cord, which is pretty minimal) would be “nose blow” recovery. Even saves you the mass of gluing in the nose cone. No chute or streamer needed. You might break some NAR rules if you drill a hole in the forward end of the motor (forward of the clay cap, of course) to attach the shock cord.

now, FINDING the sucker would be hard enough even WITH a big streamer, with Nose Blow the thing could almost hit you on the head and you’d still have a tough time finding it in tall grass.

No chute or streamer needed? What's your opinion of an acceptable ground hit velocity?

NAR rules are so vague.... one would think that there would be a maximum ground hit ft/sec. A BP or composite motor free falling can cause significant carnage, if there is no recovery device.

One thread here on TRF has an issue with a "bottle rocket" that has a parachute, in which simulations show a low ground hit velocity.... yet another thread states "No chute or streamer needed."

Surely you see the issue with stating it's "extremely safe"?

I'm not calling you out, you're experience oozes from every post you make. But not everybody has your skill set.
 

bjphoenix

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No chute or streamer needed? What's your opinion of an acceptable ground hit velocity?

NAR rules are so vague.... one would think that there would be a maximum ground hit ft/sec. A BP or composite motor free falling can cause significant carnage, if there is no recovery device.

The original Estes designs used a variety of non-parachute recovery methods. I mentioned the Streak that weighed so little that it could fall to earth and not hurt anything. It ejected its motor casing and let the motor free fall to earth so apparently that was acceptable back in those days. Then there was the Scout that tumbled for recovery. It was a heavier rocket so even coming down sideways it would probably come down at a good velocity.
 

lakeroadster

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The original Estes designs used a variety of non-parachute recovery methods. I mentioned the Streak that weighed so little that it could fall to earth and not hurt anything. It ejected its motor casing and let the motor free fall to earth so apparently that was acceptable back in those days. Then there was the Scout that tumbled for recovery. It was a heavier rocket so even coming down sideways it would probably come down at a good velocity.

Sure, I'm a huuuuuge history lover, and times were simpler back then. Let's fast forward to current times. Are there any current commercial kit designs like this, that eject a motor casing, or have no recovery devices? (glider's excluded)

Tumble recovery of a finned booster is one thing... spitting out a C, D or E motor to fall anywhere seems, well, contrary to any model rocketry code.
 

BigMacDaddy

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They still sell the Swift which ejects its motor and tumble recovers...

For the revised version of this model I did put a streamer and a minimum-diameter body tube (actually making it a bit longer lets you make it a little lighter) - likely will still get lost if it really flies up 2000' but less likely than with a parachute where it will wind up in the next county.
 

Sooner Boomer

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Sure, I'm a huuuuuge history lover, and times were simpler back then. Let's fast forward to current times. Are there any current commercial kit designs like this, that eject a motor casing, or have no recovery devices? (glider's excluded)

Tumble recovery of a finned booster is one thing... spitting out a C, D or E motor to fall anywhere seems, well, contrary to any model rocketry code.

Lots: spools, pyramids, other "odd rocks". Every CHAD staged rocket drops the booster to free fall.
 

BigMacDaddy

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Lots: spools, pyramids, other "odd rocks". Every CHAD staged rocket drops the booster to free fall.

Also a number of booster rockets use pop-pods and eject motor + nose weight... some (many?) of those have recovery attached to pop pod I think.
 

lakeroadster

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Lots: spools, pyramids, other "odd rocks". Every CHAD staged rocket drops the booster to free fall.
not tumble recovery.. designs that spit the motor out....

Tumble recovery of a finned booster is one thing... spitting out a C, D or E motor to fall anywhere seems, well, contrary to any model rocketry code.​

Also a number of booster rockets use pop-pods and eject motor + nose weight... some (many?) of those have recovery attached to pop pod I think.

Can you name a current kit that spits out a C, D or E motor?
 

BigMacDaddy

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Tried launching the arrowhead rocket today -- not successful...

The video looks like a segment of the movie Cloverfield as my wife ducks and covers. I think I need to go up to a D12-3 Engine as well as use some other tricks. I tried with a C5-3 but I think the rocket never got to a good speed where drag would have helped stabilize things. I tried a design with mock flame fins coming out the back but I did not like the look of it. Maybe a ring tail or a first stage (make this portion into a 2nd stage nose cone or something)... need some inspiration so will leave this one alone for a while...

1638651100201.jpeg


A time-lapse

1638660605933.png
 
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lakeroadster

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Tried launching the arrowhead rocket today -- not successful...

The video looks like a segment of the movie Cloverfield as my wife ducks and covers. I think I need to go up to a D12-3 Engine as well as use some other tricks. I tried with a C5-3 but I think the rocket never got to a good speed where drag would have helped stabilize things. I tried a design with mock flame fins coming out the back but I did not like the look of it. Maybe a ring tail or a first stage (make this portion into a 2nd stage nose cone or something)... need some inspiration so will leave this one alone for a while...

View attachment 492614

A time-lapse

View attachment 492635
Is your test pilot skilled in such experimental odd roc flights? ;) It looks cool up there skywriting... not so cool if you were in the line of fire though I bet.

You could always retrofit some rear tubes... that would make it fly straight. It's the perfect design for that.

Please excuse my amateur photo hack..

Arrowhead.jpeg
 
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