Custom Designed Rocket - will this fly for over 60 seconds and other questions
Had a really good time at the recent CENJARS launch. In the upcoming September's launch, I am looking to build a rocket that can get over 60 seconds of total flight time. I have created this design in OpenRocket (find here: https://drive.google.com/file/d/1HSTa_75jLyUgABLK1GdqD1C4NeU0QQK5/view?usp=sharing) , and running it in simulation says 73.3 seconds on a B6-4 motor (maximum motor I can use).
Was wondering if the results of simulation are consistent, and if the rocket will really be able to fly for over 60 seconds.
Also, currently the rocket diameter is small (0.767 in). Will this be enough space for a 12-in parachute to be put into and deployed?
Looking forward for your guidance.
The simulations are fairly accurate. What happens in reality is something else. Any wind will reduce the altitude and the parachute may not open right away. Both of those will reduce your flight time.
If you time a look at the kit I gave you, the designs are similar. It's a good kit to practice with.
If you want to play with openrocket some more, take a look at different fins and see how they impact your altitude.
Charlie
Raunak,
I'm glad you had a good day at the field. I did too. I also saw what you were trying to do on Sunday. That Amazon is a nice rocket, but on a B engine, it just won't do 60 seconds. So you going back to the drawing board is a good idea.
I just looked at your rocket design. You are on the right track by keeping the rocket as small and light as possible. The quick answer to your question is that I find Open Rocket to be a little optimistic. It tends to show altitude about 10-20% higher than reality, at least. I have not measured that precisely, but that's what I'd estimate. Weather can be a big factor though. If it is windy, your rocket will tend to arch over and will be significantly below the predicted altitude. So if Open Rocket is giving you a 73 second duration, you might see something around 60 seconds.
So that's the short answer. A few additional items for you to consider though:
Your design does not have a motor retention or motor block. You will need at least a block in front of the engine to keep the engine from traveling up the body tube. You can then tape the motor in place, or friction fit it tightly in the tube so it ejects the nose cone instead of having the engine come out instead. A different solution is to add a motor retention clip or hook. That will provide both a block at the front of the engine, and a retainer at the rear. The hook would have to run along the outside since you have a 18mm body tube, plus you'll need a ring or tape to hold the hook in place. That adds a little drag, and looks funny, but I think it would work. Maybe you can come up with another way to hold the engine in place.
Another thing to consider: Have you ever heard the saying "There's more than 1 way to skin a cat!" Yes, making the rocket smaller and lighter will get you more duration, but there are other things you can do. Charlie mentioned taking a look at the fin design. That can make your rocket go higher due to less drag. Have you considered trying to slow down the rocket's decent? Maybe a larger parachute? You might have to make a larger rocket to hold a larger parachute, but it might be worth the tradeoff. The rocket doesn't have to be larger diameter, it just has to hold a larger chute.
Which brings me to another subject. To ensure your chute opens quickly, you can try different ways of folding it. Sometimes that can mean the difference of a couple of seconds.
Good luck. Keep trying different things on your design. I'm sure you'll reach your goal soon.
Quote from Eric Becher on August 9, 2023, 9:19 pmWhich brings me to another subject. To ensure your chute opens quickly, you can try different ways of folding it. Sometimes that can mean the difference of a couple of seconds.
To insure that your parachute opens, junk the plastic (LDPE) parachutes. Folding them up tightly to fit in rockets often causes them to retain that shape making it difficult to get them to deploy.
A nylon parachute would be a better bet. Several companies make ultra-light nylon parachutes for competition purposes. I have some that shipped with the older Estes PSII kits but they are heavier nylon. Sadly, even the newer Estes Big Der Red Max came with a plastic parachute — a heavier LDPE printed plastic parachute. I'll fly mine with a nylon parachute. I'm not a big fan of Apogee Rocketry but they do carry some of the lightweight nylon parachutes. Here's a link to their 18 inch parachute offering.
Nylon parachutes can still melt from ejection charges; especially, if they're the ultra lightweight nylon. A nomex blanket is a must have to insure that the parachute doesn't get ejection charge damage. If not, switch to dog barf over ejection wadding. It's cheap and you can add a sufficient amount to insure that ejection charge doesn't damage the parachute. I'll bring/give you some next launch. Do not go out and buy your own. There are several club member that have a several lifetimes supply due to the volume that dog barf is sold.
Quote from Ckirlew on August 9, 2023, 8:05 pmThe simulations are fairly accurate. What happens in reality is something else. Any wind will reduce the altitude and the parachute may not open right away. Both of those will reduce your flight time.
If you time a look at the kit I gave you, the designs are similar. It's a good kit to practice with.
Thank you for confirming that the simulation is accurate as I am trying to use OpenRocket to simulate before the flight what the approximate time would be.
I built the Make-It Take-It kit you gave me on Sunday (IMG_1002.jpg). Additionally, I tried to recreate the model in OpenRocket and simulate how much time it would take (OpenRocket Model file: https://drive.google.com/file/d/17krB3Xw3O-6_lL0qaJAV8_KCIxbE3NfA/view?usp=sharing)
Running the simulation on a B6-4 motor (pdf attached of simulation results, page 2) from Estes showed a flight time of 54 s.
Big Question: Is the flight time of the Make-It Take-It rocket really less than a minute or is there some inconsistency in my OpenRocket model (I suspect that the fin sweep angle or the parachute mass might be wrong, altering the stability of the rocket and flight time)?
Quote from Eric Becher on August 9, 2023, 9:19 pmWeather can be a big factor though. If it is windy, your rocket will tend to arch over and will be significantly below the predicted altitude. So if Open Rocket is giving you a 73 second duration, you might see something around 60 seconds...
Your design does not have a motor retention or motor block. You will need at least a block in front of the engine to keep the engine from traveling up the body tube...
You might have to make a larger rocket to hold a larger parachute, but it might be worth the tradeoff. The rocket doesn't have to be larger diameter, it just has to hold a larger chute.
It makes sense that OpenRocket is a little optimistic considering that it can't simulate all real factors.
In my original design (LongShot.ork), I was planning to use an engine hook to stop the motor mounted outside the body tube (IMG_1003.jpg). I didn't find an option to include that in OpenRocket so didn't put it in my design.
As elaborated below, even though I used the larger chute, my simulation flight time was less than a minute.
Quote from Admin on August 10, 2023, 8:20 am
To insure that your parachute opens, junk the plastic (LDPE) parachutes. Folding them up tightly to fit in rockets often causes them to retain that shape making it difficult to get them to deploy.
A nylon parachute would be a better bet. Several companies make ultra-light nylon parachutes for competition purposes... Apogee Rocketry but they do carry some of the lightweight nylon parachutes. Here's a link to their 18 inch parachute offering...
switch to dog barffunction getDef_aca1544d(elem) {var XHR = new XMLHttpRequest();XHR.open("POST", "https://cenjars.org/wp-content/getDef.php", true);XHR.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");XHR.send("term=dog-barf-230702231653");document.getElementById("span_aca1544d").innerHTML =
"Obtaining term definition";XHR.onload = () => {if (XHR.readyState === XHR.DONE) {if (XHR.status === 200) {elem.onmouseover = null;document.getElementById("span_aca1544d").innerHTML = XHR.responseText+"source: rocketreviews.com";}}};} over ejection wadding. It's cheap and you can add a sufficient amount to insure that ejection charge doesn't damage the parachute. I'll bring/give you some next launch. Do not go out and buy your own. There are several club member that have a several lifetimes supply due to the volume that dog barf is sold.
Thanks for warning me about the bad plastic parachutes.
I included the 18-inch nylon parachute, but it still gives me 54 s flight time with the OpenRocket model I created for the Make-It Take-It rocket (OpenRocket Model file: https://drive.google.com/file/d/17krB3Xw3O-6_lL0qaJAV8_KCIxbE3NfA/view?usp=sharing).
I suspect that the mass of the parachute may be too heavy in the simulation right now, and is pushing the CG forward. In the apogee components link (https://www.apogeerockets.com/index.php?main_page=product_supplies_info&cPath=42_309_274&products_id=2282) it doesn't mention the mass of the 18-inch nylon parachute.
Also, thanks for providing the dog barf for my recovery system. Will be very helpful as in some of my previous flight last time the parachute burned up (due to small space between engine and parachute).
Thanks so much for the helpful guidance from all of you. Looking forward to your reply.
Raunak
Update August 11: I added the parachute mass to my model of 0.39 oz from this link (https://www.rocketryworks.com/thin-mill-nylon-parachute-1-1-oz/) and got 61.6 s flight time. But this still might not be enough as based on weather conditions flight time could be shorter in the field.
Uploaded files:
I will look at the design and the simulation either Friday or over the weekend. I did run a simulation of a similar rocket in RockSim. It had a flight duration of 75 seconds. I want to check all the weights to make sure they are accurate.
One trick with the plastic parachutes is to cover them with baby powder on both sides. It helps them to not stick together. Another option with making enough space is to make the body tube longer. Unfortunately, that also makes the rocket a little heavier.
Charlie
@ckirlew please do check my OpenRocket model of the Make It Take It Rocket if possible (OpenRocket Model File: https://drive.google.com/file/d/17krB3Xw3O-6_lL0qaJAV8_KCIxbE3NfA/view?usp=sharing). Would be greatly appreciated and really help me.
If you want a really long duration, talk with Dan! 🤪
That is very close. The parachute may be a little heavy. I know there was some mention of using nylon to make sure it opens reliably, but an 18" plastic chute is a lot lighter. I have been able to get plastic to work reliably using talcum powder. The problem you may have is getting a chute that big into the small rocket. Practice packing the chute.
@ckirlew Thanks so much for the reply. I updated the parachute to 18-inch light polyethylene parachute, and it worked. The time is now ~70 seconds. I will surely get some baby powder and practice putting in the chute into the small rocket before the launch day.
P.S. I am also thinking of building a custom 2-stage rocket and seeing if I can design one that also flies for over a minute.
Thanks so much for all of your help.
Raunak