Nice job with the nose cone, that isn't easy!
Extreme Airmail! Mailing Tube Rocket
- Thread starter Weldo
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Nytrunner
Pop lugs, not drugs
Thats REally slow. How long is your launch rod?
Stability occurs when you have airflow over the fins, and at under 30ft/s, youve got very little of that. Plus youve got a very fat rocket for a D flight, and itll be fighting drag the whole way.
Example, my 3" school rocket (11.5oz empty) is fattest/heaviest rocket I'll fly on a D12 (its a tad heavier than the stock school rocket, but thats because i fly it on 24mm G's)
Stability occurs when you have airflow over the fins, and at under 30ft/s, youve got very little of that. Plus youve got a very fat rocket for a D flight, and itll be fighting drag the whole way.
Example, my 3" school rocket (11.5oz empty) is fattest/heaviest rocket I'll fly on a D12 (its a tad heavier than the stock school rocket, but thats because i fly it on 24mm G's)
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You need 50 ft/sec at the point where the first launch lug or rail button leaves the rod/rail, not the last LL or rail button. Anything less than that is really not safe. You likely need a 4' rod as well, not a 3 footer. You're not going to be able to fly this on a D. You're going to have to go to a composite E motor. Sim is out with an Aerotech composite motor. It may require an E30. Also, I can't tell if you glued a engine stop into the motor mount. If it's at 70mm, you're pretty limited in how many engines you can use. If it's at 95mm, you have a lot more Aerotech single use engine choices. You also have more choice at 70mm if you do Aerotech reloads.
Can you post the OR file you drew up?
Also, have you run a simulation with the D12 engine?
Also, have you run a simulation with the D12 engine?
Weldo
Washing Hands
Thanks! It took two tries to get it right!
I was gonna do a 36" rod but I can certainly go longer. Also I sized the launch lugs for a 1/4" diameter rod. I could probably got up to 5 feet before it got too noodly.
I did glue in the engine stop. It's sized to allow a 70mm motor to stick out past the end of the motor mount by 1/2". My plan was to simply tape the motor. I don't think this will be a problem since the motor goes into the tube pretty tight.
I've run a few more simulations in OpenRocket. I'm limiting myself to choosing 24 x 70mm motors. With an Aerotech E30-4 my launch speed is 40.9 ft/s. Up sizing to an F39-6 gives 45.6 ft/s. Although the F36 is a reloadable and represents more investment than I probably want to put into this model. Also the estimated apogee for the F39 is almost 800 ft and my launch area is not quite big enough to ensure recovery.
I can post up the file, but how do I do so?
After typing up your post, click on "Upload a File" in the lower right of the posting window. A window will pop up, go to the directory where the file is located and highlight the .ork (Open Rocket) file. Then click on "Open". The file will appear on the bottom of your posting window. Done.
I'm curious why there are no flags on a D12 simulation.
Cheers.
Weldo
Washing Hands
Wait, I think I got it...
Weldo
Washing Hands
I don't know. I'm not super well versed in OpenRocket so I may have missed some critical parameter...
Weldo
Washing Hands
One thing I had to do was add about 1 ounce of weight to the file. Openrocket estimated the weight to be 17.1 ounces but when I weighed it, the rocket was 18 ounces. So I added 1 ounce to the body tube.
I am not an OR guru either.
Looks like OR doesn't flag for insufficient speed off the rod. Got a green light for a D12-3, even though the speed off a 35" rod is only 24 fps. Ran one for a C11-3, which is clearly an unsuitable motor. Apogee of 31 ft., ejection on the ground. Sim shows a green light and no warnings.
Instead of using a 35" rod, I would go with a 6 ft. 1/4" rod or rail.
Check out Home Depot or Lowes, I got my 4 ft. 1/8" and 3/16" rods from HD real cheap.
Sims with an E20 and E30 and a 72" rod show speed off the rod of 46 and 58 fps respectively, and apogees of 460 and 570 ft.
When I switch it to a 35" rod I get marginal speed off the rod. (i.e. marginal stability).
Good luck and have fun!
Looks like OR doesn't flag for insufficient speed off the rod. Got a green light for a D12-3, even though the speed off a 35" rod is only 24 fps. Ran one for a C11-3, which is clearly an unsuitable motor. Apogee of 31 ft., ejection on the ground. Sim shows a green light and no warnings.
Instead of using a 35" rod, I would go with a 6 ft. 1/4" rod or rail.
Check out Home Depot or Lowes, I got my 4 ft. 1/8" and 3/16" rods from HD real cheap.
Sims with an E20 and E30 and a 72" rod show speed off the rod of 46 and 58 fps respectively, and apogees of 460 and 570 ft.
When I switch it to a 35" rod I get marginal speed off the rod. (i.e. marginal stability).
Good luck and have fun!
Weldo
Washing Hands
That's great! Thanks a lot for checking that out!
Is a 6 foot rod OK? 1/4" is pretty stout but at 6 feet should I be concerned about rod whip?
Is a 6 foot rod OK? 1/4" is pretty stout but at 6 feet should I be concerned about rod whip?
Nytrunner
Pop lugs, not drugs
There will be a little rod whip, but heavier rockets than that have been launched on 1/4" rods for a long time before rails came on the scene
Weldo
Washing Hands
Right on.
I also want to ask about the thing I mentioned before about NAR recommendations on launch rod speed. Is it true that lower speeds off the rod can be tolerated when wind speed is low or negligible?
Say hypothetically, the best I could configure is 40 ft/s off the rod. I would be forced to wait for perfectly calm conditions to launch, not tolerating any wind what-so-ever. Could I guarantee a launch in those conditions with just as much safety factor as, say, a 50 ft/s launch speed in a 5mph wind?
I also want to ask about the thing I mentioned before about NAR recommendations on launch rod speed. Is it true that lower speeds off the rod can be tolerated when wind speed is low or negligible?
Say hypothetically, the best I could configure is 40 ft/s off the rod. I would be forced to wait for perfectly calm conditions to launch, not tolerating any wind what-so-ever. Could I guarantee a launch in those conditions with just as much safety factor as, say, a 50 ft/s launch speed in a 5mph wind?
Can you link to the article where you read that? It's the first time I've heard of wind speed affecting speed off the rod. I've heard of wind speed causing weather vaning (windcocking). I believe NAR rules state not to launch in anything over 20mph, but I'm only going by memory.
Weldo
Washing Hands
I found that info here:
https://www.nar.org/pdf/launchsafe.pdf
Scroll down to page 31, second paragraph. It begins talking about launch conditions. I confess that I haven't read the whole article... I was just looking for information on launch velocities and stability.
Let it be known that I am not an aerospace engineer so it's entirely possible that I have misunderstood and misinterpreted the information from the article. Also since I didn't read the whole thing I may be taking some things out of context.
https://www.nar.org/pdf/launchsafe.pdf
Scroll down to page 31, second paragraph. It begins talking about launch conditions. I confess that I haven't read the whole article... I was just looking for information on launch velocities and stability.
Let it be known that I am not an aerospace engineer so it's entirely possible that I have misunderstood and misinterpreted the information from the article. Also since I didn't read the whole thing I may be taking some things out of context.
Weldo
Washing Hands
Found this too: bottom of page 37
7.4.1 Improving Static Stability
All sport rockets should have adequate static stability margins at an angle of attack of 15 degrees angle of attack.
A maximum static stability margin of 3 calibers measured at an AOA of 15 degrees and an airspeed corresponding to the lowest forward velocity at which the rocket is expected to leave the launcher guidance (4 calibers as predicted by Barrowman analysis) should be used to protect against weathercocking.
These two stability margins are essential to safe flight in any conditions except complete calm.
7.4.1 Improving Static Stability
All sport rockets should have adequate static stability margins at an angle of attack of 15 degrees angle of attack.
A maximum static stability margin of 3 calibers measured at an AOA of 15 degrees and an airspeed corresponding to the lowest forward velocity at which the rocket is expected to leave the launcher guidance (4 calibers as predicted by Barrowman analysis) should be used to protect against weathercocking.
These two stability margins are essential to safe flight in any conditions except complete calm.
Weldo, I read the paragraph. My take is that it is saying that if it is a breezy day, e.g. say 15 mph, then a 45 fps speed off the rod may not be enough for a safe flight, and windcocking may occur. It is recommending 4X 15 or 60 mph as a minimum safe speed off the rod. If it is a calm day the 4X rule of thumb would not apply, in my opinion. Personally, I wouldn't launch in anything more than 10mph. Lost too many rockets to wind drift and windcocking.
Anyhoo, give us a flight report when you light it up.
Cheers.
Anyhoo, give us a flight report when you light it up.
Cheers.
Weldo
Washing Hands
That was my take on it as well. That in dead calm conditions it's not as critical to have a high launch speed. Of course the safety factor must be figured in because it's almost never dead calm.
I agree with not launching in winds over 10mph. My launch area is relatively small with trees all around so last few times I went out I had everything set up on the launch pad but still waited for a lull in the winds before hitting the button.
Here's something else I wanted to ask. I made an OR file for the Estes Nike-X after I built one. The package says you can first flight that model with an A8-3. But the launch rod speed with that motor is only 40.1ft/s off a 35" rod.
I'm also curious what is the launch speed of the Estes Mercury Redstone model since on the package it claims to offer a "Slow and realistic flight". The model is listed at 3.7 ounces and the recommended C6-3 has a max vehicle weight of 4 ounces. That tells me that since the Mercury is very nearly the max weight for that engine, that it also offers the lowest safe launch speed.
I agree with not launching in winds over 10mph. My launch area is relatively small with trees all around so last few times I went out I had everything set up on the launch pad but still waited for a lull in the winds before hitting the button.
Here's something else I wanted to ask. I made an OR file for the Estes Nike-X after I built one. The package says you can first flight that model with an A8-3. But the launch rod speed with that motor is only 40.1ft/s off a 35" rod.
I'm also curious what is the launch speed of the Estes Mercury Redstone model since on the package it claims to offer a "Slow and realistic flight". The model is listed at 3.7 ounces and the recommended C6-3 has a max vehicle weight of 4 ounces. That tells me that since the Mercury is very nearly the max weight for that engine, that it also offers the lowest safe launch speed.
Well, I would put it as there is a minimum safe launch speed in calm conditions, and that safe minimum goes up (to mitigate windcocking) as the wind speed goes up. Also rocket design affects windcocking. Doesn't mean that if the wind speed is 2 mph you can launch with a rod speed of 8 mph (!).
As for the Nike X, 40 fps sounds OK.
A Rocksim simulation of the Mercury Redstone on a C6 shows very low speed off a 36" rod (26 fps).
But most simulators tend to err on the side of caution. I have launched a MR on a 3 ft. rod and got a very nice flight on a calm day.
Weldo
Washing Hands
That slow launch speed on the mercury is surprising! I also launched a mercury twice and noticed that it took off slower than some other smaller and lighter models did.
50% of me wants to try my rocket on a D12 to see what happens and 80% of me is kind of afraid to try!
50% of me wants to try my rocket on a D12 to see what happens and 80% of me is kind of afraid to try!
nelie61
Krazy Kit Kollector
Sounds like you're trying to build a rocket around a motor that you found or came across. I suggest buying a kit that requires your "D" size motor and see how things go from there. For $20 or so you can safely check things out and go from there. It sounds like you're interested and have the skills and knowledge but give a kit a try
Weldo
Washing Hands
Thanks for the compliment!
It's finally complete, ready to fly. I did not paint it, probably won't until it survives at least once.
I do plan on trying it with a D12. I picked up a 72" piece of 5/16" round bar to use as a launch rod for this one. It gives me a few extra FPS off the rod versus a 36" rod. I also got a 100' roll of 18ga speaker wire to use for the ignition system, so I can be well far away. I'm also working on a more powerful launch controller so I don't have to rely on the four AA batteries of my Estes Electron Beam.
I plan to launch in the early morning before people filter into the park where I launch and wait for absolute calm wind. I know this rocket will fly well with an E20 or better yet E30 from Aerotech but I want to run this experiment with a D12. I just have to make sure that no one or no property will be in danger, except possibly myself...
It's finally complete, ready to fly. I did not paint it, probably won't until it survives at least once.
I do plan on trying it with a D12. I picked up a 72" piece of 5/16" round bar to use as a launch rod for this one. It gives me a few extra FPS off the rod versus a 36" rod. I also got a 100' roll of 18ga speaker wire to use for the ignition system, so I can be well far away. I'm also working on a more powerful launch controller so I don't have to rely on the four AA batteries of my Estes Electron Beam.
I plan to launch in the early morning before people filter into the park where I launch and wait for absolute calm wind. I know this rocket will fly well with an E20 or better yet E30 from Aerotech but I want to run this experiment with a D12. I just have to make sure that no one or no property will be in danger, except possibly myself...
Off Grid Gecko
Well-Known Member
The goal is that the fins can stabilize it when it leaves the pad. Try this. Tie a string to the CG, let out a measured length, and spin the rocket around your body. Once it's stable (turning as it goes around you and always facing forward), start a timer and count say 10 full rotations. Figure up the velocity with some maths, and set that as your baseline. I.e. a 1m string does 10 revs in 3 seconds.
2(pi)r is about 6.3 meters
times 10 revolutions = 63meters
divide by time 3s = 21m/s
Whatever you come up with should be your MINIMUM velocity in still conditions, but it doesn't hurt to add a safety factor (the example above is a little fast). Then go whichever is higher, the number you calculated or 4x the wind speed.
Using this method will prove (at least to you) that the rocket does orient itself at the speed you observed it without needing a wind tunnel for testing.
2(pi)r is about 6.3 meters
times 10 revolutions = 63meters
divide by time 3s = 21m/s
Whatever you come up with should be your MINIMUM velocity in still conditions, but it doesn't hurt to add a safety factor (the example above is a little fast). Then go whichever is higher, the number you calculated or 4x the wind speed.
Using this method will prove (at least to you) that the rocket does orient itself at the speed you observed it without needing a wind tunnel for testing.
I ran some simulations in OR using your initial D12 and then some using Aerotech single use motors. It looks like the E30 with a 4 second delay would give it a nice ride. 
Nytrunner
Pop lugs, not drugs
Ooph, all but the last two are sluggish off the rod, and even tbose two are a little anemic.
Well, you won't run the risk of losing sight of it at any rate!
Well, you won't run the risk of losing sight of it at any rate!
@Nytrunner I ran another sim with a F44W-4. 32.5 MPH off the rod, apogee 615', 26 MPH at deployment. The Optimum Delay is 5.61 s. Do you know if one can shorten the delay time on the 24mm single use Aerotech's?
Also, Weldo is limiting himself to the 70mm length motors as he has the engine block in there. If he could drill it out and put a screw-on motor retainer (looks like he has plenty of room) then he could use the longer E & F engines.
Nytrunner
Pop lugs, not drugs
Composite delays "can" be modified by drilling 1/32" depth to remove 1 second of delay (3/32 for 3 seconds, etc). BUT you should not drill so that there is less than 4 seconds of delay remaining. That makes the delay grain web too thin to containn chamber pressure.
For single use that are all sealed up, that requires temporarily unloading the ejection charge and drilling through the top port. It is tricky and not recommended for beginners
Funniest mailing tube rocket I ever witnessed was a guy who made a rocket out off a cardboard triangular mailing tube. Had a triangular nosecone and triangular fins. Had a 54mm motor hole too. Electronic dual-deployment. Well, the guy decided it was time to fly the thing on a K motor. Did every other motor but time to step up to the biggest motor the rocket could take. Had flown 13 other times successfully.
Well........... Funniest flight I ever witnessed. Pushed the launch button and the rocket disappeared. That is until we saw a "puff" way up there and it was evident that confetti was coming down!!! The cardboard disintegrated! Nothing but bits of cardboard and the fins were immediately found. The rest of the rocket was nowhere seen. Except, while the flier was feeling dejected and we were commiserating with him, several minutes later a bystander shouts out a parachute is coming in. Low and beholden there were the remains. The interior motor tube, ebay and nosecone were coming in under chute. The cardboard skin was gone and the tube had some of the triangular centering rings still attached.
After the cardboard blew off the rocket, it apparently was going so fast it continued flying nominally like a spool and had a successful recovery. The flier was extremely happy to get his electronics, chute and motor hardware back. Needless to say, we were very happy for him too and we all had a grand laugh over it.
The "Confetti Rocket". I wished we had a video of it. The flier didn't feel so bad as the rockets skin didn't cost him anything. Kurt
Well........... Funniest flight I ever witnessed. Pushed the launch button and the rocket disappeared. That is until we saw a "puff" way up there and it was evident that confetti was coming down!!! The cardboard disintegrated! Nothing but bits of cardboard and the fins were immediately found. The rest of the rocket was nowhere seen. Except, while the flier was feeling dejected and we were commiserating with him, several minutes later a bystander shouts out a parachute is coming in. Low and beholden there were the remains. The interior motor tube, ebay and nosecone were coming in under chute. The cardboard skin was gone and the tube had some of the triangular centering rings still attached.
After the cardboard blew off the rocket, it apparently was going so fast it continued flying nominally like a spool and had a successful recovery. The flier was extremely happy to get his electronics, chute and motor hardware back. Needless to say, we were very happy for him too and we all had a grand laugh over it.
The "Confetti Rocket". I wished we had a video of it. The flier didn't feel so bad as the rockets skin didn't cost him anything. Kurt
I think that if you can get to within 2 seconds of the recommended delay, that is pretty good. The actual delays have a great deal of variability (apparently the burn 30% faster at sea level, compared to ~5000 ft) in their burn rate, and if your rocket weather cocks at all, that will shorten the ideal delay.
