please rip apart my L1 design

Okay, I'm ready to let y'all see what I'm thinking for my L1 cert rocket. I want it big as can be, but I also wanna launch it on big G's to verify the build/design before I go for the cert.

Here's what I got so far, take a peek and rip it apart. Let me know what's right and what's wrong. Rocksim sez 35fps on the G64, so I think I'm right up against the edge of reasonable here.





View attachment L1.rkt

paparoof said:

Okay, I'm ready to let y'all see what I'm thinking for my L1 cert rocket. I want it big as can be, but I also wanna launch it on big G's to verify the build/design before I go for the cert.

Here's what I got so far, take a peek and rip it apart. Let me know what's right and what's wrong. Rocksim sez 35fps on the G64, so I think I'm right up against the edge of reasonable here.

Click to expand...

You have the fins and the nose cone on the wrong ends.

Stick a big enough I in it and it'll rip itself apart. Isn't there an I1299 out there?

Doesn't look bad. At 4.5lbs empty, it's not that light so you'd have to use big Gs (G77, G79, G80, etc)

-Aaron

heada said:

Doesn't look bad. At 4.5lbs empty, it's not that light so you'd have to use big Gs (G77, G79, G80, etc)

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Yup. That was one of the things I was thinking. Also - if it can be kept under 3.3 lbs loaded it could be flown without a waiver (FAR 101 notification) if the opportunity presented itself.

Nice looking rocket, but I would be afraid to fly it on a G motor.
I flew my scratch built "Thunderbird" on a G79 and it was marginal.

Remember that you have to factor in the weight of the motor and casing as well.

View attachment Thunderbird.rkt

It looks a lot like a HyperLOC 835, except it's 7 inches longer and 13 ounces heavier, and has a smaller diameter motor mount. You may want to extend the length of the motor mount tube. It looks a little short for an I motor.

DaveHein said:

It looks a lot like a HyperLOC 835...

Click to expand...

I swear that wasn't on purpose, but I noticed that too as soon as I put those colors on it.

so why is theirs so much lighter? a couple inches of BT isn't gonna make that much difference.

Forget the flights with G engines, the only ones that would be large enough, need you to be certified in order to fly them anyway (G75 black jack). The speed off the rail with a G is too slow and the altitude is to low to give you any safety margin. The delays needed would also cause potential issues. Just fly it with the H123 which sims to a reasonable 900 ft and get the short delay (six seconds) for it. Since you are dealing with a 5 lb rocket loaded, I would kick the chute size up to 48 inches.

terryg said:

Forget the flights with G engines, the only ones that would be large enough, need you to be certified in order to fly them anyway (G75 black jack). The speed off the rail with a G is too slow and the altitude is to low to give you any safety margin. The delays needed would also cause potential issues. Just fly it with the H123 which sims to a reasonable 900 ft and get the short delay (six seconds) for it. Since you are dealing with a 5 lb rocket loaded, I would kick the chute size up to 48 inches.

Click to expand...

Actually, I wouldn't only fly this on the G75. The G104 and the G339 would both kick a 5lbs rocket up with enough 'umph' to be stable and get several hundred feet below it. Problem with both of those is that you have to be certified to fly 'em.

There are ways to make a rocket like this light enough to fly on a modest G motor. Use 1/8th basswood fins that have been paper laminated. Thin walled tubes (except for maybe the MMT) 3/16th lite-ply rings, etc. Problem is, they wont stand up to a high impulse I motor so it'd be a G and H rocket only (G&H, pure cane rockets... sorry, had a song about sugar pop into my head)

Do you want to build it to survive an I (or a hard landing) or do you want to build it to fly G and cert? Both can be done on the same rocket but its hard to trade off strength for weight.

-Aaron

In my head I'd been thinking I'd fly it on I's as well, so I didn't wanna go too light in the build.

I think I'm gonna play around with shortening the top BT to try to save some weight.

Also FWIW, I was gonna go with wood glue instead of epoxy. Right idea?

In order to fly it on the G77/G79/G80 range of motors, you're shooting for a maximum of 3.5 lbs loaded.

Try reducing from 3.9in to 3.0in Just doing that shaves off nearly 0.5 lbs, shortening the forward BT to 20 inches rather than 34 brings it down to 3.8 or so. Reducing the fin thickness and coverting it to something like FG covered basswood and reducing the size would put you near the 3.3 lbs mark...and on an I it would really scream but still hold together.

-Aaron

paparoof said:

Also FWIW, I was gonna go with wood glue instead of epoxy. Right idea?

Click to expand...

Wood glue is good for attaching wood products to other wood products (paper tubes and wood fins) but not so much for plastics or composites. With this setup, you should be fine.

-Aaron

Paraproof,

It looks good so far to me. At its current size and weight, you probably won't get a safe stable flight on G motors as others have said. You could always scale the diameter down a size if you want to keep the shape and make it lighter.

DaveHein said:

... It looks a little short for an I motor.

Click to expand...

Actually, if one wanted, they could omit the motor mount all together and rely on the centering rings to hold a motor in place.

heada said:

Try reducing from 3.9in to 3.0in

Click to expand...

That's crossed my mind also, but I already have the BT's and nose cone. I suppose it wouldn't be the end of the world of I had to save these parts for a future L2 attempt, but I really wanna 4" L1.

I guess I gotta give in on something, it's either the size of the rocket or the ability to test-launch on G's.

You can do a 4in level1. I did. 4in PML AMRAAM. Flew it on an I435T dual deploy for my cert. Don't expect a 4in level 1 rocket to be able to fly MPR Gs tho. Can't have your cake and eat it too.

-Aaron

Ya know, I'm glad you mention that. I've always thought it'd be cool to cert on an I instead of the usual H.

If I give up on the idea of launching it on G's and just go for H's and I's, is there anything else about this design you would change?

For example, Dave sez the motor mount should be longer - how long should the motor mount be?

What would be the largest motor with which you would fly this design?

I would recommend a modular construction:

I modified your Roc Sim file (see L1-am.rkt). Check it out. Nothing major. I dumped the baffle, added a bulk head, and moved the parachute to the booster. This will allow you to fly Roc Sim file L1-am-short.rkt on G motors. Depending on how heavy you build, how heavy your 28 to 29 adapter is , and how much recovery harness you have, you might have to add a slight amount of temporary nose weight (easy to do). Then go back to L1-am.rkt for your L1. I moved the chute to the booster because you have a lot of airframe (almost 5 feet !!!) to pressurize with the motor ejection charge.

I did this modular construction for my L2 certification rocket (It's 2.6 x 72). The rocket in my avator is the booster (flying on a G79R), the attached photo is the L2 flight configuration. It flew on a J420R.


Alan

View attachment l1-am.rkt

View attachment l1-am-short.rkt

Now THERE'S some thinking. Modularity had also occurred to me, but not in this way. Launching a shorter version on G's would still give me some assurance that the critical parts of the rocket are solid and the fins are straight, etc. The longer version for the cert flight only adds length and a bigger motor, so I'd still have a reasonable level of confidence the day of the cert flight.

I really like this idea. Thanks!

Can't have your cake and eat it too.

-Aaron

Click to expand...

If this works, I think I'll name it "Mmmm... Cake".

paparoof said:

If this works, I think I'll name it "Mmmm... Cake".

Click to expand...

ROFLMAO! Go for it!

Aaron - I don't mean to trivialize your input and efforts here. I very much appreciate your logic, reasoning and keeping me realistic. So thank you.

But "Mmm... Cake" is prolly the best rocket name ever.

Nothing wrong with your design or the commentary. But you may consider another perspective.

I see you planning to fly on G's and H's. Why not plan to fly on H's for your L1, but build it to handle up through J's for your L2?

Build it stronger, using F-glass or C-Fiber reinforcement, put in an AvBay for Dual Deploy, and if it takes you a month or two longer to build, you will still put in less time and money and have one rocket that covers L1 and L2.

If you're looking to have your L1 this flying season, then throw out my idea. Otherwise, take the whole winter and build a more versatile bird....

paparoof said:

Ya know, I'm glad you mention that. I've always thought it'd be cool to cert on an I instead of the usual H.

If I give up on the idea of launching it on G's and just go for H's and I's, is there anything else about this design you would change?

For example, Dave sez the motor mount should be longer - how long should the motor mount be?

What would be the largest motor with which you would fly this design?

Click to expand...

For motor mount length, you don't need to have the entire length of the motor case inside a motor tube, it just needs to be held in place (hence the earlier comment that was made about leaving out the tube and putting in CR's. Decide on where you want your CR's (I usually sandwich my fin tabs then put a third one foreward of the front fin tab), and go an inch beyond the front CR.

Having two forward CRs helps with construction because you can leave the aft CR off completely when you install the motor mount (only need two CR's there to keep it straight, really) so you can do your internal fillets without having to remove the aft CR first.

Dang - that sounded confusing....I need to stop coming in to work early...

Loopy said:

Having two forward CRs helps with construction because you can leave the aft CR off completely when you install the motor mount (only need two CR's there to keep it straight, really) so you can do your internal fillets without having to remove the aft CR first.

Dang - that sounded confusing....I need to stop coming in to work early...

Click to expand...

Nothing confusing about that at all. I was planning on adding a third (foreward) CR to lengthen then motor mount, but I hadn't noticed the benefit that you just pointed out of being able to really do killer internal fillets. Cool!

dgreenapple said:

Nothing wrong with your design or the commentary. But you may consider another perspective.

I see you planning to fly on G's and H's. Why not plan to fly on H's for your L1, but build it to handle up through J's for your L2?

Build it stronger, using F-glass or C-Fiber reinforcement, put in an AvBay for Dual Deploy, and if it takes you a month or two longer to build, you will still put in less time and money and have one rocket that covers L1 and L2.

If you're looking to have your L1 this flying season, then throw out my idea. Otherwise, take the whole winter and build a more versatile bird....

Click to expand...

That occurred to me as well, but I know almost nothing about L2 requirements. Would a little fiberglass on the fins be all that's needed to beef it up enough for a future L2 flight?

Dual deploy was the first thing I thought of when looking at the modular design skip_dye suggested. And after looking at the drift of the full size rocket in Rocksim under a 48" chute, I think DD is the way to go. Of course, I haven't done DD yet, don't even own an altimeter yet, so I'd have to modify my LOC Legacy for DD to learn that art first....

I'm in absolutely NO hurry on this project (why should I be?) so taking it slow is no problem at all. Like I've said many times before, I learn more when I learn slowly. I was originally planning on making the L1 flight next summer anyway.

paparoof said:

If this works, I think I'll name it "Mmmm... Cake".

Click to expand...

Yeah ; just add another layer for the cert.:rotflol:


Al

The suggestions about using a short motor mount tube or no tube at all are interesting. However, I think it's better to use a motor mount tube that is longer than the motor. First of all, the motor mount tube provides structural support for the fin tabs in a through-wall design.

When I glue my fins in I normally put just enough 5-minute epoxy to tack them in place. I put the lower centering in place to center the motor mount tube, but I don't glue it in at this point. After the 5-minute epoxy has set I pull the lower centering off and do my internal fillets, and then glue the centering ring in place. I use 15-minute epoxy to give myself enough time to do all the internal joints.

I always put t-nuts on the lower centering ring for motor retention. To make it easier to pull off the lower centering ring I make a handle out of a loop of wire that is attached to the two t-nuts. I also make a cap for the motor mount tube out of wax paper and masking tape so I don't get epoxy on the inside of the tube.

A longer motor mount tube is good because it acts as a stuffer tube to reduce the volume of the chute compartment. Also, if you use dog barf, it would be difficult to cover the ejection charge if the motor is longer than the motor mount tube. This is not a problem if you use an ejection baffle, but you would still have a large volume between the baffle and the upper centering ring with a short motor mount.

Dave

paparoof said:

....Would a little fiberglass on the fins be all that's needed to beef it up enough for a future L2 flight?

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If you are planning on going no further than a L2 cert flight (using a "baby" J motor), then you should be OK without fiberglass. If you are thinking of flying on mid sized J's (I don't think a commercial manufacture makes a full J at 38mm - ICBW) then you would need to look at fiberglassing. Remember your original goal was to build a big rocket that could fly G's and do a level 1 cert. If you fiberglass the fins, that would will add weight to the back end. In "short" mode you are now going to have to add nose weight. All this add weight might remove the possibility of flying G's. Keep your original goal in mind.

To learn DD, you don't need to modify your LOC Legacy. With the Legacy being a 38mm airframe, you will be limited on the choice of electronics and have very little to room inside the airframe to work with. Don't get me wrong. There are several fantastic altimeters available that will fit inside a 38mm airframe, but some of the larger ones have more features.etc. Do all your DD trials with your new rocket. Build the "short" rocket. Get a couple of G flights under your belt. Then put a H in it to do your L1. While this is happening, you can research electronics, E-bay designs, and start construction of the items needed for the "full rocket". Do some H flights, maybe a "baby" I with the "full" rocket. When your are ready, try out DD. Then take the test and do the L2 cert.

You have now done L1, L2, and mastered DD all with one rocket and saved a bunch on money (or had more money to spend on motors!!!).

I wish I had done this. When I built my L1 rocket (PML AMRAAM 2) I never thought I would do a L2. After my L1 cert and building a couple more rockets, the L2 bug got me. So I laid out a plan to build a rocket that could fly G's to baby J's and learn DD. The modular design works great. I also have a short payload bay so I can fly motor ejection with the altimeter (I have a recording altimeter). I plan on continuing to use the modular design concept on future projects.


Alan

skip_dye said:

If you are planning on going no further than a L2 cert flight (using a "baby" J motor), then you should be OK without fiberglass. If you are thinking of flying on mid sized J's (I don't think a commercial manufacture makes a full J at 38mm - ICBW)

Click to expand...

The "biggest" 38mm J I can think of off the top of my head is the AT J825R which is about a 50% J. Nothing to sneeze at as it punches for 250lbs dropping down to about 200lbs for a total of just over 1s burn. I don't think you'll see a full J until you go 54mm. (J415W is a 91% J I think)

There are several fantastic altimeters available that will fit inside a 38mm airframe, but some of the larger ones have more features.etc. Do all your DD trials with your new rocket.

Click to expand...

The PerfectFlite MAWD or HA45 are perfect DD alts and fit within a 24mm tube. I have the MAWD and its been very reliable.

-Aaron

EDIT: corrected. Had put in N and meant lbs.

skip_dye said:

There are several fantastic altimeters available that will fit inside a 38mm airframe, but some of the larger ones have more features.etc.

Click to expand...

I'm aware of the MAWD and HA45 - what are the "larger ones" that you refer to? Got a link handy?