In Need of Help Problem Solving First Model Rocket

[Mohi]

No inverted fins. They look cool as hell, but you'll have stability problems due to the CP moving too far forward. Keep them normal, and as long as they don't protrude below the bodytube, you'll be fine.

Stuff the egg in the nosecone since it's the heaviest payload. Put the altimeter below that.

Good choice on the 1/8 balsa, but I would paper them or use self adhesive shelf paper over them. They will be smoother and stronger that way.


Do you need some help designing this?

I'd appreciate any and all time and money saving help.
But I'd rather not be spoon fed how to do what is suppose to be my project--I learn nothing this way. My group member did the papering of our current rocket fins and did them all wrong, but ill do them right, what kind of glue do you recommend for the papering, ive seen some really nice finishes using notebook paper slightly smaller than fins.
So, 3 fins, 1/8 balsa, since I'll be using the E28's and this rocket will be much lighter, should I spend the time aerofoiling them? I think I'd rather focus on the getting the internals packed correctly. Should I section my rocket into a 3 piece system again (lower body tube with fins, upper body tube with altimeter, and nosecone) or just make it two sections, nosecone and body tube. I feel as though I should keep the 3 sections because the top part makes the altimeter housing a lot easier.
With dimensions for the fins and appropriate length given to me, I should be able to do the rest.

 

[GDJ]

Don't worry, I have no intention of spoonfeeding you or your team, but I would be willing to knudge you in a direction that I think would work better for you time wise, material wise (recycling is possible in this hobby) and maybe a different way of looking at things.

Papering is easy. I once did a set of balsa fins with nothing more than the gluesticks that my youngest daughter uses, then press the paper into the wood (heavy books) and after an hour they turned out nice.

At 1/8" you can get away with rounding all the edges. 1/8" is pretty thin, and you might get 1 or 2% more apogee with aerofoiling. Save your energy.

Keep the bodytube in as few sections as possible (split in half for example). Top half can hold your egg, the protective cover for the egg, and the altimeter. Lower half is the fins and motor mount.


Here's an idea that I've played around with. Hopefully you can view the .rkt file alright (used OpenRocket to make it). It's based on a very similar nose cone and body tube.

View attachment Proposed Eggy Rocket-1.ork

View attachment Proposed Eggy rocket.rkt

 

[Mohi]

Don't worry, I have no intention of spoonfeeding you or your team, but I would be willing to knudge you in a direction that I think would work better for you time wise, material wise (recycling is possible in this hobby) and maybe a different way of looking at things.

Papering is easy. I once did a set of balsa fins with nothing more than the gluesticks that my youngest daughter uses, then press the paper into the wood (heavy books) and after an hour they turned out nice.

At 1/8" you can get away with rounding all the edges. 1/8" is pretty thin, and you might get 1 or 2% more apogee with aerofoiling. Save your energy.

Keep the bodytube in as few sections as possible (split in half for example). Top half can hold your egg, the protective cover for the egg, and the altimeter. Lower half is the fins and motor mount.


Here's an idea that I've played around with. Hopefully you can view the .rkt file alright (used OpenRocket to make it). It's based on a very similar nose cone and body tube.

I'll only be able to view those tomorrow morning in class. Thanks a bunch.

 

[bill_s]

As I mentioned earlier, partial aerofoiling is the best deal. Just slightly rounding the leading edge corners cuts drag to 40% or so of perfectly squared edges. A full rounding only takes that to 30% (from looking at drag coefficients of diff. shapes). Cutting drag at the trailing edge takes more work to get much and weakens them, although a little rounding or a minute of sanding won't hurt.

1/8" basswood wouldn't be bad. Half the thickness times half the area would be 1/4 the weight of the old ones. Less if not papered.

 

[Mohi]

As I mentioned earlier, partial aerofoiling is the best deal. Just slightly rounding the leading edge corners cuts drag to 40% or so of perfectly squared edges. A full rounding only takes that to 30% (from looking at drag coefficients of diff. shapes). Cutting drag at the trailing edge takes more work to get much and weakens them, although a little rounding or a minute of sanding won't hurt.

1/8" basswood wouldn't be bad. Half the thickness times half the area would be 1/4 the weight of the old ones. Less if not papered.

I understand what you're saying, but priority wise, the rest of the rocket actually being made > aerofoiling.
Also, now I have the dilemma of not trusting 1/8in balsa wood (I have had horrible strength issues with balsa wood before). Can I get a third tie breaking opinion over 1/8in balsa vs basswood fins.
Keep in mind ill be using the E28's and the goal is 700-800 feet, nothing more or less.


Also i am extremely stressed for time so I would prefer to just make 3 fins instead of 4. And again i can't decide between balsa and basswood now. I GDJ I appreciate the new design and I am getting a rocksim number of low 900's so accounting for wind and my input to rocksim error, 700-800 is very achievable. Why may I ask is the rocket 26in long?


I have been messing around with rocksim for a little bit now.
My 22.5 inch version of the rocket with 4 basswood fins is expected to reach 911 feet
With 3 basswood fins it says 950
22.5 in 4 balsa wood fins 970 feet
22.5 in long 3 balsa wood fins 1014
And lastly, I am not use to these terms used to dimension the fins. I mean I'll go look up what each length represents but I'd appreciate it if you'd save me the time and tell me the dimensions in simpler terms.

 

[shreadvector]

Balsa fins are WAY better than basswood for TARC type rockets.

EVERY one of the teams that i interacted with that insisted on using basswood and an E motor FAILED to reach the altitude because of weight.

EVERY one of the teams that flew a non-sanded fin model and then sanded a real airfoil into the fins saw a DRAMATIC increase in altitude. Round the leading edge. Taper the trailing edge, but avoid a sharp knife edge since it will chip easy.

Use the 'strongest feeling' balsa you can select at the store. There is serious variation in density and grain direction that will affect strength.

1/8" is actaully fairly thick and draggy, but if the wood in your supply is soft or weakly grained, then go for it and airfoil. If you find strong 3/32" balsa then you will cut drag even more and it will be easier to airfoil.

And use yellow wood glue, not heavy epoxy for all balsa and cardboard gluing. Epoxy just adds a lot of weight.

Also, using a spray primer and sanding it smooth will reduce fuzzy surface drag a LOT. Again, several teams I worked with for this year's TARC learned this by launching before and after airfoiling and before and after priming and sanding. The reduction in drag resulted in a lot more altitude for the same mass rocket.

I understand what you're saying, but priority wise, the rest of the rocket actually being made > aerofoiling.
Also, now I have the dilemma of not trusting 1/8in balsa wood (I have had horrible strength issues with balsa wood before). Can I get a third tie breaking opinion over 1/8in balsa vs basswood fins.
Keep in mind ill be using the E28's and the goal is 700-800 feet, nothing more or less.


Also i am extremely stressed for time so I would prefer to just make 3 fins instead of 4. And again i can't decide between balsa and basswood now. I GDJ I appreciate the new design and I am getting a rocksim number of low 900's so accounting for wind and my input to rocksim error, 700-800 is very achievable. Why may I ask is the rocket 26in long?

 

[Mohi]

I'll take your word for it. Thanks!

4 1/8in balsa wood fins it is!
My priority list I think will be:
Making the 4 fins
Cutting the body tube to the appropriate length and adding in the coupler
aerofoiling the fins
Transferring the motor mount section to the new rocket
Putting it all together.
1st rocket was called Forward Unto Dawn and didn't live up to it's name.
This rocket shall be called Redeeming Divergence.

I am still I bit iffy on 3 vs 4 fins however. I don't know if I want to play it safe altitude wise and use only 3. And 4 would take more time to make and foil. I am starting to lean more towards the 3 side because of higher altitude and less time.

 

[273paine]

Don't forget to paper the fins after aerofoiling them.

 

[shreadvector]

I do not agree with papering the fins after airfoling them. It adds weight and thickness. If the wood is super soft (so soft you can create a depression with your fingers from handling), then it is too soft and weak for fins. Good balsa does not require papering. it just needs to be sanded to an airfoil and then sealed and sanded smooth. Heck, even adding a thin layer of enamel spary paint top coat can add a tiny bit of strength and make the sirface tougher without adding a lot od unneeded weight.


WEIGHT IS YOUR ENEMY. This is a lightweight aerospace vehicle, not a brick building.

If your approach was to build a heavy and super sturdy rocket, then you would need to start from scratch using an F motor to lift the overly heavy brick to the desired altitude.

Don't forget to paper the fins after aerofoiling them.

 

[shreadvector]

And yes, 3 fins are less drag than 4 fins. And faster to make. Make sure they are straight and that they stick out far enough into the non-turbulent airstream to guide the rocket without the rocket needing to wiggle around (which creates an obscene amount of drag).

 

[GDJ]

Why may I ask is the rocket 26in long?

Bodytube length was based on your 1st rocket. That's all. I just started with a known bodytube length and nose cone profile that was already available and in use, and a more accurate comparison between the two rockets. You can go shorter or longer if you wish. This rocket was just a rough plan and idea.

 

[Mohi]

And yes, 3 fins are less drag than 4 fins. And faster to make. Make sure they are straight and that they stick out far enough into the non-turbulent airstream to guide the rocket without the rocket needing to wiggle around (which creates an obscene amount of drag).

Well I already aerofoiled and papered them and the fins are all less than 4 grams each. I don't see this rocket weighing more than 250 to 300 grams. My only concern is would it be worth it to add primer to the rocket? I am not experienced at spray painting anything, but I want to reduce drag and I maybe forced to launch in wet conditions. I'll post pics of my progress in a little while

 

[GDJ]

You could primer it, and I'm sure the fins are fine with that, but practice on a piece of paper or wood first. Get the feel of how the primer will lay down first, then do several thin coats verses one big fat gobby coat. Your first coat should barely colour the rocket, the second one should cover more, then the third coat should finish up the colouring.

Remember, Less is more.

 

[Mohi]

Alright quick update.

It's 1:48 atm. The wood glue on the fins are drying, the shock chord is epoxy'd in, and I fixed some other issues. Aside from primer, all I have left is gluing the launch lugs and I am trouble finding a household item with a short enough diameter and long enough length to put launch lugs on. All I got its a ticonderoga pencil which fits in, but isn't as long as I'd like. Not that am I expecting an answer at nearly 2am, but if anyone is out there any suggestions?

Also the fins were glued about 9PM, even though you are suppose to wait 24 hours, could I risk launching at 3pm because I need to get at least 3 more recorded flights in, and the weather will not be too kind (i'll be launching during the breaks between rain showers, which is why I want the primer on).

On top of it all, while going to my AP chem test review session in 6 hours, I'll have to break into the lab at my school because whichever rocket group decided to leave it at school and the entire launch pad is sitting there in the lab. Great times.


EDIT: Here is a pic, this is just the body 3/4 of the body tube. Out of view is the coupler and the rest of the body tube hanging from my door.The ejection charge blows this part off, however, there are holes at the bottom which I literally filled with wood glue because that's all I had available, those have been drying for a long while. If I don't plug the holes the ejection charge will likely destroy the altimer and just about everything else. Literally all I have left is spraying on the primer tomorrow a few hours before a hopeful launch (if not, Sunday is absolute last day to get 3 full launches in). My only worry now is a safe launch and a not so rough impact considering I absolutely cannot build another rocket in time, nor do I have the supplies to do even basic repairs. (I am all out of body tubes, couplers, most wood except for the excess balsa for the fins etc.) All I have left to do tomorrow is sand off excess wood glue, and spray some primer on and pray everything else works. If not...ahh well.

 

[GDJ]

You're doing fine! The launch lugs look like they will work as is.

As for the holes filled with wood glue, that will work all right. As long as the glue grabs everything, it will work and hold up fine. You're not building a Mach-Buster, so you can get away with alot here.

Considering your time constraints, you are doing a man's job. Keep your head up!

 

[Mohi]

Alright just got home from AP review and the weather is looking great. I am about to add primer to the rocket and using a food scale of all things (measuring cup lol) I am getting a rough mass of 5oz without the motor and egg...with those I would assume it would go up to about 8.5oz (motor + egg is about 100grams). If anything, the mass may be even less. Everything glued in and fits properly so things are looking up. I am playing it safe and will be adding primer now and then waiting two hours later to launch. The ground may be a little wet so I want that primer on. My biggest impending issue is that apparently igniters and igniter clips were lost. According to my group member
"We need 1 igniter clip (reusable).
I have one copperhead igniter that should work.
So we need 3 more copperhead igniters.

IF by chance, you are able to find igniters that don't require an igniter clip that will work with our motors, that'd be awesome. They'd have to be pretty long, though."

I am using an Aerotech Reloadable E28. Could I find these at local stores because I definitely don't have time to order them. Most of the stuff that came with our motors was lost...


I am scratching the primer idea for now. I only have Rustoleum Primer which is for metal and I'd rather not go out and spend more money on a good primer and come back here and wait 2 hours for it to dry. I'll just sand whatever imperfections I can find and try to get launches in, if the goal is not reached then I'll go to the primer to reduce drag.

 

[Mohi]

Alright just got home from AP review and the weather is looking great. I am about to add primer to the rocket and using a food scale of all things (measuring cup lol) I am getting a rough mass of 5oz without the motor and egg...with those I would assume it would go up to about 8.5oz (motor + egg is about 100grams). If anything, the mass may be even less. Everything glued in and fits properly so things are looking up. I am playing it safe and will be adding primer now and then waiting two hours later to launch. The ground may be a little wet so I want that primer on. My biggest impending issue is that apparently igniters and igniter clips were lost. According to my group member
"We need 1 igniter clip (reusable).
I have one copperhead igniter that should work.
So we need 3 more copperhead igniters.

IF by chance, you are able to find igniters that don't require an igniter clip that will work with our motors, that'd be awesome. They'd have to be pretty long, though."

I am using an Aerotech Reloadable E28. Could I find these at local stores because I definitely don't have time to order them. Most of the stuff that came with our motors was lost...


I am scratching the primer idea for now. I only have Rustoleum Primer which is for metal and I'd rather not go out and spend more money on a good primer and come back here and wait 2 hours for it to dry. I'll just sand whatever imperfections I can find and try to get launches in, if the goal is not reached then I'll go to the primer to reduce drag.

We have found an igniter clip. However, only commerically available igniters I know of the basic estes, and those aren't long enough, would it be downright stupid to solder a few to the desired length? Would they work?

 

[GDJ]

I don't know if the Estes Solar Ignitors are powerful enough to do it. I've never tried this.

 

[Mohi]

I don't know if the Estes Solar Ignitors are powerful enough to do it. I've never tried this.

THEY WORKED

Results of todays launch
First flight of this rocket I built last night.
Max altitude 860 feet
Egg intact and NOTHING damaged on rocket. It drifted about a little more than a quarter mile over houses and landed TWO FEET from a busy street.

Then we tried the estes solar igniter. We weighed the rocket down with an extra 50 grams. It launched but then ejection charge somehow snapped the kevlar (probably weakened from multiple launches) and dropped the nosecone + upper body tube straight to the ground. The bottom half of the rocket along with the reloadable motor, and parachute got stuck in a 30 foot tree that was to small to climb. We even saw this coming and waited for wind to die down and moved further away from the houses but it still landed in pretty much the same spot with SIGNIFICANTLY less wind than the first launch (I blame this on the fact that the upper body tube was no longer attached). We couldn't get it down and called the non emergency fire dept. but had to leave a message and leave it there. We got a total of 4 launches in, but sadly no rocket to turn in. The first flight was only 60 feet off so I am not too upset. The problem with the second is that it flew well but only went to 300 feet according to the altimeter which is either a technical glitch OR due to the mass I added, which to me seemed small, I only added about 50 grams hoping to reduce the flight by about 100 to 160 feet and somehow ended up reducing it by 500...
Will post videos up soon.

 

[GDJ]

Well heck! 860 feet with all that payload is a pretty good flight. Glad the egg was undamaged.

Sorry about the Kevlar breaking. I sincerely hope you get the rocket back.

Weight is a funny thing. A couple of grams here and there make alot of difference.

If you do get your rocket back, add lots of elastic (the cotton elastics that goes in waistbands. Michaels has good quality ones), about 1 metre (1 yard or so) between the parachute and the nose cone.

AND NO MORE EXTRA WEIGHTS!! You are dangerous with extra weights.

 

[Mohi]

Well heck! 860 feet with all that payload is a pretty good flight. Glad the egg was undamaged.

Sorry about the Kevlar breaking. I sincerely hope you get the rocket back.

Weight is a funny thing. A couple of grams here and there make alot of difference.

If you do get your rocket back, add lots of elastic (the cotton elastics that goes in waistbands. Michaels has good quality ones), about 1 metre (1 yard or so) between the parachute and the nose cone.

AND NO MORE EXTRA WEIGHTS!! You are dangerous with extra weights.

I am happy to report that the entire rocket has been recovered. Only damage was a piece of the balsa fin chipped off (I would guess its from hitting the tree). The video isn't to good, it just shows the rocket leaving the launch pad because when it went, it WENT. Punched a hole through a cloud and drifted a quarter mile as I said before. Glad this all worked out. And I can't thank everyone ITT enough that helped all this happen through crunch time.