Never Been Done In Model Rocketry !...(?)

How have I missed this? This thing is beautiful!!!

Gus said:

Great work, but I think you are still 6 ounces too heavy. I honestly believe your limit, with three canted D12's, is about 15 ounces. That said, with all the work you've put into this rebuild, I'd just go out an fly it at this point and see what happens. I honestly don't think cutting another half ounce or ounce will matter. If it flies, great. If not, then reduce the scale by 1/4 to 1/3, and do whatever you have to to get to 15 ounces.

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I agree, after this rebuild it's *easy to see* that achieving 20 oz is completely unfeasible at this scale, as for 15..no way. There's absolutely nothing left that I could cut out to make it lighter. The capsule outer skin is now little more than single ply card stock and has a single foam board structural brace, the tower, connecting rings, locking plate is all balsa, I've eliminated all the screws except the three tiny ones that hold the push rods to the servo (and they are very small). I think in total I will have cut around 14 oz off.

I have learned alot about materials and weight with this rebuild. Several times I cut material out of certain parts just to find out it didn't make any difference. The comparable weight's between paper, balsa, foam board, birch. The comparable weights between these same materials and their thicknesses, preformed card board tubes and card stock. Like the bracing in the heat shield, the difference between four and eight and several other like areas.

The goal is 22 oz, this gives me 1.3 oz left to complete both tower and capsule chutes, it's going to be a challenge.

Woo Hoo!! Let's light this candle!


TA

This is quite the build I cant wait for the your next video.

closet astronaut said:

I just found this video, seems the trajectory of my last Merc launch is standard flight pattern, I have a sinking feeling what I saw last time will be a repeat.

[YOUTUBE]V9R3bYXXJuE[/YOUTUBE]

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That flight was caused by an error in the simulation. The "Mercury Joe" was a GI Joe capsule with a large-scale HPR Redstone designed to carry the GI Joe toy capsule to altitude, complete with a GI Joe astronaut inside. The rocket was equipped with cameras in the tower and capsule. It wasn't designed to simulate the tower flight as your rocket is, so don't compare it too closely-- it's apples and oranges...

I used to follow the "Mercury Joe" project pretty closely. IIRC, the flight you linked the video to went unstable due to an error in simulating the flight. A previous flight had gone off without a hitch using a smaller, lighter weight motor. This particular flight used a larger, heavier motor, which pushed the CG further aft... As it turned out, at or behind the CP... It was caused, IIRC, by a problem that periodically catches people unawares in Rocksim, especially with rockets equipped with small escape towers... The simulation has several choices for calculating the location of the CP, and several choices for defining the "calibers of stability"... one of those choices, and the default IIRC, is to use the "first tube diameter"... which in the case of a rocket with a small LES tower motor, usually tends to be the small LES tube. If one doesn't catch it, but instead merely looks at the "calibers of stability" number to ensure it's more than 1, which describes a stable rocket, without considering the DIAMETER of the tube used to calculate the calibers of stability, the CP can be practically on top of the CG... that was the error... They read something like 1.5 calibers of stability, assuming that meant 1.5 times the diameter of the main body of the rocket, which was something like 12 inches in diameter... That would have put the CP about 18 inches behind the CG, which is plenty of stability margin for even a much heavier motor, which would move the CG back several inches at least. The error was that the 1.5 calibers of stability was described in terms of the VERY SMALL LES motor tube, which was maybe say a BT-50 (say for arguments sake, about an inch in diameter). That would make the actual stability margin 1.5 INCHES, NOT 18 inches if the same stability margin was using the MAIN body tube diameter! Thus, when the larger motor was installed, it moved the CG back several inches, which put it completely behind the CP, making the rocket unstable. It lifted off normally, graddually drifted off course, and ended up flying sideways... IIRC the electronic altimeter read apogee and then ejected the capsule from the rocket, which then streamlined in and impacted, destroying the rocket and capsule...

So, don't worry too much... this was a completely different rocket with a completely different flight regime...

Later! OL JR

Ooh, that hurts to watch and I wasn't even involved. I can't imagine what you felt. But I was happy to see the last message at the end of the video!! I've been VERY impressed with all these builds so far. Hopefully the next one will work. Good luck with it, and I'll be watching.

That was awesome.....really......

The short flight looks impressive and is flying like it should, just needs more altitude. This is a very ambitious project and very difficult to accomplish within the given parameters.

The weight was better but the drag was the same resulting in a bigger crash. More power!

awesome project keep us updated !!!!!

Sorry about the result but the video is helpful.

First, the video indicates the rocket is horizontal at 1 second which confirms, again, that the thrust to weight ratio is inadequate and the rocket is unstable. Changing to an E motor will just worsen the problem off the pad as the liftoff weight will be heavier and the thrust will be either the same, or less, than the D12s. Remember that it if you launch an unstable rocket 100 times it is probable that a couple of the flights will end up going straight up, although most won't. The instability just means the direction of travel will be the result of a lot of other forces on the rocket and the direction of travel will not be predictable.

As you've mentioned previously, you've reduced the weight of this particular model as much as possible. Time to downscale.

Second interesting element the tower cam reveals is that this rocket was rapidly spinning around it's horizontal axis. Either your motor mounts were misaligned or you had one engine thrusting at an angle. My suspicion is the former. The spinning and lack of adequate thrust contributed to the tail-wagging liftoff. The video shows that the rocket actually changed direction just shortly after leaving the launch pad. Starts out leaning to the left, ends up going to the right. Much faster moving rockets with an external camera pod often precess due to minor drag force differences, but I doubt your capsule was moving fast enough for that to have been the reason. And I can't see anything about the capsule or tower which would have caused the spin. So I presume it was misaligned motor thrust. Spin stabilization can help a faster moving rocket but in this case I think it just robbed you of a little bit of upward force. More importantly, though, it put a differential sideways pressure on an unstable rocket, contributing to the likelihood it would not go straight up.

Final interesting video find is the ball of flame that appears once the rocket was on the ground (pic below). What caused that? Was the tower on fire after the crash?

Some other thoughts. The total flight was long enough, ~5 seconds, that if your capsule release mechanism was going to work, it should have. What I don't know, though, is whether once the servos fire, do they only act for an instant or do they keep firing? The reason this is important is that if you set them to fire while the motors are still thrusting there is a huge pinching pressure on the release tabs caused by the motors trying to pull the tower away from the draggy capsule. If the servos only fire for an instant they are probably not strong enough to overcome the pinching pressure on the release tabs during motor thrust. If, as I suspect, the servos fire once and then quit, they would have a much better chance of retracting after motor thrust ends, but then there is nothing to pull the tower away other than drag separation. That may actually work since the capsule is so draggy and the tower isn't. I really doubt the fact the capsule was horizontal at the time the release should have fired had much to do with the failure.

Final thoughts. After three flights you've proven two things; first, this sized model is still too heavy/draggy, and second, your capsule release mechanism hasn't yet worked.

You still don't know what is the maximum weight/drag that three D or E engines can reliably lift.
You still don't know what scale capsule will give you a good chance of meeting that weight/drag target.
You still don't know what you need to do to get your capsule release mechanism to work under thrust.

The answer to all three questions is to test using boilerplates.

Again, I'm sorry to see this flight didn't work, and I do believe it is possible to make it work, but you will need the answers to those questions.

Hope this helps,

Steve

closet,

Have you considered using 3 x AT RMS E28's? Since the propellant is Blue Thunder, there is a great likelihood that they will all light off, providing you have good igniters and a 12v launch system. A single E28 has more max launch weight than 3 x D12s (33.8 oz vis-a-vis 29.0 oz) albeit with a shorter burn time (1.16 seconds vs. 1.60 seconds). That solves your thrust problem. The downside is the cost.

But the other problem is getting your system stable. The flight article had a lot of mass in it, so the CG is somewhere in the belly of the bell.

Here is some NASA data on a 5.37-percent-scale model used in hypersonic wind tunnel tests. Might help to get it to these locations per your scale.

Don't give up. I believe you can make this work.

Greg

View attachment 19670022687_1967022687 10.pdf

View attachment 19670022687_1967022687 11.pdf

Gus said:

Sorry about the result but the video is helpful.


As you've mentioned previously, you've reduced the weight of this particular model as much as possible. Time to downscale.

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Hey Steve, good to hear from you again. I still have one more tower to trash, so I just can't hang this one up yet untill I try the E-12's, if I do then I'll always wonder.

Gus said:

Final interesting video find is the ball of flame that appears once the rocket was on the ground (pic below). What caused that? Was the tower on fire after the crash?

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The flames are due to the upper cross member of the tower being on fire, remember I built this tower from balsa, and I also reduced the cant as much as absolutely possible. Now on every other tower there was burn marks on the same spot, but I used pine dowels so they didn't burn through. Luckily we had a tropical storm come through last week and it rained for two days, plus it rained the night before so every thing was wet. I'll get some pics of the tower damage and post them.

Gus said:

Some other thoughts. The total flight was long enough, ~5 seconds, that if your capsule release mechanism was going to work, it should have. What I don't know, though, is whether once the servos fire, do they only act for an instant or do they keep firing? The reason this is important is that if you set them to fire while the motors are still thrusting there is a huge pinching pressure on the release tabs caused by the motors trying to pull the tower away from the draggy capsule. If the servos only fire for an instant they are probably not strong enough to overcome the pinching pressure on the release tabs during motor thrust. If, as I suspect, the servos fire once and then quit, they would have a much better chance of retracting after motor thrust ends, but then there is nothing to pull the tower away other than drag separation. That may actually work since the capsule is so draggy and the tower isn't. I really doubt the fact the capsule was horizontal at the time the release should have fired had much to do with the failure.

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I didn't think about it untill you mentioned it here, but this was the first use of the new smaller servo, it may well not have had enough power to retract the tabs, I will look into that. The timer fires once retracting the tabs, I know there is damage to the locking plate, I found pieces of it inside the capsule and on the ground. Having not checked any of this yet, it may have been broken on take off, preventing release. I had alot of other things needing to be done yesterday so when we got home I just unloaded it all and went to work on other business

Gus said:

Final thoughts. After three flights you've proven two things; first, second, your capsule release mechanism hasn't yet worked.
You still don't know what you need to do to get your capsule release mechanism to work under thrust.

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I will have to differ with you on this one though, in the video of the second launch, watching the tower cam view, you can actually see the capsule deploy from the tower a fraction of a second before impact, and the capsule detaches clean from the tower. On yesterdays launch, the capsule never came loose from the tower, it only detached after picking it up, but again the locking plate is in pieces.

Gus said:

Again, I'm sorry to see this flight didn't work, and I do believe it is possible to make it work, but you will need the answers to those questions.

Hope this helps,

Steve

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I appreciate the sentiment, but there's no need to be sorry, I really appreciate your input, believe me when I say, on every lunch your words are ringing in my ears, and I have a vision of Guss Grissom's face in my head. This has been a lot of fun for me and I haven't lost any thing of value, on the contrary, I have learned more about rocketry with this than any thing else I've built and flown.

One more try, then the scale down.

Mark

GregGleason said:

closet,

Have you considered using 3 x AT RMS E28's? Since the propellant is Blue Thunder, there is a great likelihood that they will all light off, providing you have good igniters and a 12v launch system. A single E28 has more max launch weight than 3 x D12s (33.8 oz vis-a-vis 29.0 oz) albeit with a shorter burn time (1.16 seconds vs. 1.60 seconds). That solves your thrust problem. The downside is the cost.

But the other problem is getting your system stable. The flight article had a lot of mass in it, so the CG is somewhere in the belly of the bell.

Here is some NASA data on the genuine flight article. Might help to get it to these locations per your scale.

Don't give up. I believe you can make this work.

Greg

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These engines I'm not familiar with, I have heard of blue thunder propellant though. The files are deffinantly interesting, although according to the measurements seem quite small, four inch diameter base is quite tiny. These remind me of the declassified Mercury files I have, highly detailed files on every inch of the capsule, from tip of the tower to the base of the heat shield. Every nut, bolt, wire connection, switch, all of it, inside and out.

Never fear, this isn't over yet.

closet astronaut said:

These engines I'm not familiar with, I have heard of blue thunder propellant though. The files are deffinantly interesting, although according to the measurements seem quite small, four inch diameter base is quite tiny. These remind me of the declassified Mercury files I have, highly detailed files on every inch of the capsule, from tip of the tower to the base of the heat shield. Every nut, bolt, wire connection, switch, all of it, inside and out.

Never fear, this isn't over yet.

Click to expand...

AeroTech 24/40 RMS hardware (save size as an Estes D12, not counting the forward closure): https://www.hobbylinc.com/htm/aro/aro91241.htm

AeroTech E28-4T propellant: https://www.hobbylinc.com/htm/aro/aro52804.htm

Greg

GregGleason said:

AeroTech 24/40 RMS hardware (save size as an Estes D12, not counting the forward closure): https://www.hobbylinc.com/htm/aro/aro91241.htm

AeroTech E28-4T propellant: https://www.hobbylinc.com/htm/aro/aro52804.htm

Greg

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You know the crazy thing I have found with these relaodables, the shipping cost. I was looking to start dabbling in these a while back, I have a Leviathan and wanted to go to these, when I went to check out of HL they say there's a 46 dollar charge hazardous material shipping, so unless I can find these W/O shipping it will be a while before I dabble.

closet astronaut said:

... The files are deffinantly interesting, although according to the measurements seem quite small, four inch diameter base is quite tiny...

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The files are from a model used at Langley for wind-tunnel testing (not from actual flight article values, as I said above) from Mach 3.0 to 6.8, September 1960. To get to the flight artifact scale, multiply by 18.625.

Greg

closet astronaut said:

You know the crazy thing I have found with these relaodables, the shipping cost. I was looking to start dabbling in these a while back, I have a Leviathan and wanted to go to these, when I went to check out of HL they say there's a 46 dollar charge hazardous material shipping, so unless I can find these W/O shipping it will be a while before I dabble.

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If you have a rocket club near you, they may have a motor vendor on-site that will likely sell it to you without the Hazmat. If they do have a motor vendor, sometimes motor purchases can be made in advance of the meet so that you can take delivery at the launch.

I ordered 2 sets of E18 reloads and a set of E28 reloads from HobbyLinc, that came to a total of $50.07, with Hazmat 3rd class ground shipping & handling of $8.34.

So "Yes", the step-up to these motors does indeed have a cost, but it does indeed gives you thrust options that BP motors are incapable of producing.

It's just an option if you want to go with the size Mercury you have developed so far.

Greg

Tower damage...not as bad as I thought really..

Tower and locking plate, the only damage to the plate was where the battery and timer mount.

Not sure what a scale down would do, i'm sure eliminating all of the unnecessary parts of the rocket and just working out stability may be the idea, I just fail to see how that helps you make this particular rocket fly with the set up you want to fly it with.

Sooner or later you got to make this fly with all the mechanical workings included and it has shown and incredible resistance to major damage. So I would just keep working with what you have. The only thing that I can see from the videos is you may need to consider is the black powder motors just aren't going to cut it. While they are ample to the task of moving the weight they are not capable of moving something with that much drag. Moving to a composite motor may be the key.

Any way still a great flight and still one of the best threads around. Keep up the good work, nothing ever worth doing was easy.


TA

FIRST OBSERVATION from the video: Before the rocket even gets half way up the launch rail, it's completely crooked already. This is the main reason why your launch failed, but it's a problem that is easily fixed.
SECOND OBSERVATION: Had the flight gone vertical and not horizontal, I believe you would have had sufficient altitude for a deployment. It looks to me like the motors did not all ignite at the same time, and that contributed to instability, since thrust rates fluctuate during burn time. While more power would help, it would also add weight to the nose; this rocket won't stay at apogee for even a second, so you'd better time the deployment just right. I think you have sufficient power for a successful flight, but you'll need to make some modifications. Let me know if you want to see design modification suggestions. Good luck to you.

closet astronaut said:

Third attempt.

[YOUTUBE]TS7oMJ3U0gI[/YOUTUBE]

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Ow !! That sort of stuff hurts

All I can say is keep at it, failure cannot live with persistence. Its an amazing project and I really wish you the very best of luck.