Won Too Free

[McKailas Dad]

I'm sorry, I must have been really tired, I meant to post the link. It's the public missiles one blackjack linked.

No worries! Amazing read though, and it really, -really- makes me want to make a CF rocket now! My 10" paper thang is cool, but IMO carbon fiber is just...beautiful..

 

[Xrain]

This would be pretty difficult to do with a single construction. Mostly because of how much smaller an I motor is compared to an M. If it was doing your L2 and L3 on one rocket would be trivial. Just use a L2200G and a M1500G, as they are pretty much identical motors. Same case, nearly same weight, just slightly different thrust profile. There are similar L1 and L2 motors like this as well.

So there are a couple of ways to go about this. One way, which I think would be easiest would be to get an average sized rocket which would handle all of the motors. So 4" airframe, 75mm motor mount, about 6-8 feet tall. Use plywood fins, cardboard airframe. Build everything so it is nice and well alligned. Then it should be light enough to launch on an I. You could even still do dual deploy as some practice. Then once you get your L1, you peel the smooth outer layer off the cardboard, and then wrap the whole airframe in fiberglass, and also do a tip-to-tip glass job on your fins. Now you are strong enough to pretty much do most any L2 and L3 motor. You still got all your certs on one rocket, but you probibly can't go back to a L1 motor.

The second way is to make one rocket handle all three motors in one construction. The motor sequence that might work for this, would be I600R -> K780R -> M650W. To make this work you need to really do your homework and do actual calculations on your design. Make it sufficiently robust to handle the initial thrust of the M650W, but if you build it like a battleship like most people's rockets are, it might have a tough time on the I600R. But it is entirely possible. Keep in mind this thing is going to go ~30k feet+ on the M650W if it flies reasonably well on a I. So you have to have dual deploy on it.

Since I don't have to worry about my certs myself I am pretty tempted to try something like this sometime.

 

[dhbarr]

Bearing in mind that I'm just playing around to get a feel for OpenRocket: what grievous sins have I committed with the following simplified ( derived from Garbee & Garbee ) model?
View attachment g0bl1n_i600r-6.pdf
View attachment g0bl1n_1600r-6.ork

 

[RocketryBill]

Your ORK file looks fine, however you are missing a shock cord. I don't know if your rocket has one or not. It isn't the most stable, but that's just due in part of it's design. There is discontinuity in the rocket's body diameter, which basically means a part of your bodytube is bigger than another, this may play a role in the stability of the rocket, and if I am correct the Polecat Goblin's BT is completely flush.

 

[dhbarr]

Yup, the discontinuity is from the massless pi-diameter-long base drag correction mentioned by rharshberger , which sims up from ~0.5 calibers stability to above rule-of-thumb.

 

[rharshberger]

Yup, the discontinuity is from the massless pi-diameter-long base drag correction mentioned by rharshberger , which sims up from ~0.5 calibers stability to above rule-of-thumb.

That would account for the discontinuity alright, and if it wasn't there its usually the nose cone diameter is different than the airframe diameter (usually its one number to 2 decimal places and one to 3 decimal places).

 

[dhbarr]

Xrain got me thinking : RMS 38/720 for i600r & j500g, 75/6400 for m650w . That fits the original thought exercise of minimizing the number of casings and motor mount adapters, which has the side effect of making the thing relatively cost effective to fly for it's size ( not counting a bunch of electronics ).

These would all be low-and-slow, relatively speaking; each about 12m/s off the rail, same 350cm chute for all three variants.... I see a pair of 200m flights and a 1600m, but admittedly I haven't messed with the lvl3/M much.

Have I gone completely mad?

 

[watermelonman]

Now that my L3 rocket is damaged I might try an I445 vmax in there before throwing it out. Of course it is a 4 inch airframe, not a 10 inch one, but it is still 14lbs.

Obviously there are many issues with building a single rocket to cover this much range in power, and that many construction techniques, but I am sure it could be done by someone with more experience.

 

[Xrain]

Xrain got me thinking : RMS 38/720 for i600r & j500g, 75/6400 for m650w . That fits the original thought exercise of minimizing the number of casings and motor mount adapters, which has the side effect of making the thing relatively cost effective to fly for it's size ( not counting a bunch of electronics ).

These would all be low-and-slow, relatively speaking; each about 12m/s off the rail, same 350cm chute for all three variants.... I see a pair of 200m flights and a 1600m, but admittedly I haven't messed with the lvl3/M much.

Have I gone completely mad?

That is pretty low altitude to hope for a successful chute deployment. Not impossible, but if anything is delayed in coming out that ground is coming up pretty quick. So that might not be the best choice for a cert flight.

I originally flew my ezi-65 on a j90w. The thrust was marginal enough compared to the weight, so it went off angle leaving the rail and my chute deployed late from the lower than expected altitude. I reflew it on a j570w after fixing the damage and beefing it up a bit. Much happier, the high t/w removed all the drama and it flew like an arrow.

Honestly for cert motors I'd be inclined for a high t/w, removes more variables and still keeps your altitudes reasonable. You only have to make sure you build it strong enough.

 

[RocketryBill]

Xrain got me thinking : RMS 38/720 for i600r & j500g, 75/6400 for m650w . That fits the original thought exercise of minimizing the number of casings and motor mount adapters, which has the side effect of making the thing relatively cost effective to fly for it's size ( not counting a bunch of electronics ).

These would all be low-and-slow, relatively speaking; each about 12m/s off the rail, same 350cm chute for all three variants.... I see a pair of 200m flights and a 1600m, but admittedly I haven't messed with the lvl3/M much.

Have I gone completely mad?

That is kinda on the borderline of a life vs. chute deployment death situation. Your rocket will most likely descend several hundred feet and then it's chute will deploy, having maybe a second to unfold and catch the air. Even if the rocket separates and the chute comes out, it is quite possible than the chute won't open up in time, and it'll drill into the ground, which would be a real suspense for the crowd watching your rocket. Also, if your giant 10" rocket is going only that high then I can imagine there is a huge world of possibility that many other problems that can go wrong - will go wrong.

 

[rharshberger]

Xrain got me thinking : RMS 38/720 for i600r & j500g, 75/6400 for m650w . That fits the original thought exercise of minimizing the number of casings and motor mount adapters, which has the side effect of making the thing relatively cost effective to fly for it's size ( not counting a bunch of electronics ).

These would all be low-and-slow, relatively speaking; each about 12m/s off the rail, same 350cm chute for all three variants.... I see a pair of 200m flights and a 1600m, but admittedly I haven't messed with the lvl3/M much.

Have I gone completely mad?

I would recommend electronic deployment as drilling delays that short is tough to do and the chute still make out in time, dont ask how I know.

 

[Crash-n-Burn]

Xrain got me thinking : RMS 38/720 for i600r & j500g, 75/6400 for m650w . That fits the original thought exercise of minimizing the number of casings and motor mount adapters, which has the side effect of making the thing relatively cost effective to fly for it's size ( not counting a bunch of electronics ).

These would all be low-and-slow, relatively speaking; each about 12m/s off the rail, same 350cm chute for all three variants.... I see a pair of 200m flights and a 1600m, but admittedly I haven't messed with the lvl3/M much.

Have I gone completely mad?

If your question is can a rocket be built that flies I through M motors, you haven't gone mad. Rocketry Warehouse's 75mm CF Mongoose is advertised as I-M motors. You'd surely need an adapter to fly anything I-sized, but it could be made to work. You'd also need a huge field to recover an M.

 

[dhbarr]

If, and I stress -if-, I were going to ever do this for real; I would not do it other than with fully redundant electronic deploy.

No build thread because this is all going into the corner until I'm closer to ready for it. Off to maybe try out some NARTREK stuff for a while, first.

 

[RocketryBill]

No build thread? The rocket takes like an hour to make, why not start now?

EDIT: Many hours*

 

[rharshberger]

No build thread? The rocket takes like an hour to make, why not start now?

Did you notice the diameter on the box!:y: This is a 10" diameter Goblin standing near 6' tall and weighing in excess of 25lbs when built, no hour long build here. Yah I'm poking a bit of fun.

 

[RocketryBill]

I was confused, he was talking about using a I motor so I was assuming he was talking about this, which was the first thing I looked up,

https://www.polecat-aerospace.com/cart.php?target=product&product_id=58

that's the 3", but now I found the 10" Goblin.

That thing is going nowhere on a I motor if it weighs 25 pounds.

 

[rharshberger]

I was confused, he was talking about using a I motor so I was assuming he was talking about this, which was the first thing I looked up,

https://www.polecat-aerospace.com/cart.php?target=product&product_id=58

that's the 3", but now I found the 10" Goblin.

That thing is going nowhere on a I motor if it weighs 25 pounds.

An I600R will get it a little ways up...about 600' maybe...

 

[RocketryBill]

As I've said before, 600' for a 10" rocket isn't safe and it may not be high enough for the parachute to deploy successfully. I know if it were my rocket I'd wait and certify L1 with another rocket, if you really liked the Goblin maybe a 3" one would do. But it's your rocket you can do whatever you want.

 

[Xrain]

That thing is going nowhere on a I motor if it weighs 25 pounds.

Well I threw some really rough dimensions into Rasaero, I got 383 feet out of the I600.
Pretty slim margins. Honestly the only way I think this would work is if you deployed a second or two after burnout and not wait for apogee. It would be a strange flight for sure. I probibly wouldn't fly like this. Though I like going really fast and high anyway.

The M650 sent it to 8900 feet. Seems like a pretty good motor for the goblin. Stays well subsonic the whole time too.


I think the 7.5" patriot would be way more practical to do this on. On the I600 it was simming to around 1000 feet which is very doable. The M650W was giving 12k ft, and still subsonic the whole time.

 

[RocketryBill]

If you want to get your L3, don't use your time doing the largest possible kit on a I motor for your L1, it will waste time, and run you up a few hundred dollars. Maybe a Aerotech G-Force, a Estes Leviathan, or any large medium power rocket that can be modded to fly a H motor.

 

[RocketryBill]

If your rocket takes off and deploys succesfully, I'd imagine you'd be a lot like these guys -

[video=youtube;xzcxEXHdHx0]https://www.youtube.com/watch?v=xzcxEXHdHx0[/video]

 

[dhbarr]

Good points, all.

i600, j500, m650 each sim 8-9G max. About 25mph off the rail topping out at 135mph for I & J, 400mph for M.

For our theorized I & J, you'd want to be -really- sure you could get the laundry to full extension post-haste. Same setup plus twin JLCD's makes a drogueless dual-deploy for our hypothetical L3.

I think the all-up weight could come on the near side of 20lbs rather than 25 by doing foamed & reskinned quasi-monocoque on beveled fins, thus eliminating some or most of the nose weight previously added for stability margin.

But anyhoo, back in the box in the corner this thing goes! The best part about all this is it's getting me researching and playing with different ideas for future builds.

 

[rharshberger]

Good points, all.

i600, j500, m650 each sim 8-9G max. About 25mph off the rail topping out at 135mph for I & J, 400mph for M.

For our theorized I & J, you'd want to be -really- sure you could get the laundry to full extension post-haste. Same setup plus twin JLCD's makes a drogueless dual-deploy for our hypothetical L3.

I think the all-up weight could come on the near side of 20lbs rather than 25 by doing foamed & reskinned quasi-monocoque on beveled fins, thus eliminating some or most of the nose weight previously added for stability margin.

But anyhoo, back in the box in the corner this thing goes! The best part about all this is it's getting me researching and playing with different ideas for future builds.

Composite fins could definitely save quite a bit of weight, as would making carbon or fiberglass composite bulkheads and centering rings, get rid of the plywood and you save a bunch.

 

[dhbarr]

Excellent point about centering rings especially; I was musing about lightening holes there too, but a person would be dealing with compression instead of the tension being conveyed via an integral spar.

Enter Apogee Peak of Flight 126, particularly the following figure; hey look, T-beams!

 

[llickteig1]

Good points, all.

i600, j500, m650 each sim 8-9G max. About 25mph off the rail topping out at 135mph for I & J, 400mph for M.

For our theorized I & J, you'd want to be -really- sure you could get the laundry to full extension post-haste. Same setup plus twin JLCD's makes a drogueless dual-deploy for our hypothetical L3.

I think the all-up weight could come on the near side of 20lbs rather than 25 by doing foamed & reskinned quasi-monocoque on beveled fins, thus eliminating some or most of the nose weight previously added for stability margin.

But anyhoo, back in the box in the corner this thing goes! The best part about all this is it's getting me researching and playing with different ideas for future builds.

If the rocket needs nose weight when using a larger motor, think about ways to incorporate removable nose weight to enable the lighter liftoff weight for the L1 (and probably the L2). Don't under estimate the reality of base drag in aiding stability. Come up to a KloudBusters launch and look at some of our KloudBusters kit rockets; they are short stubby rockets and I have never seen one go unstable.

I personally wouldn't recommend attempting all 3 certifications on the same rocket because it is so easy to certify L1 on a fairly small, inexpensive rocket then you can concentrate on proper build strength for the ultimately much more demanding M motor L3 flight. Understandably, it may be difficult to get a TAP on-board with your ambitious plans. I would, however, like to see I, J/K, and M motors flown in the same rocket without the added pressure of all being certification flights. I do believe that it could be done and would demand some very interesting engineering trade-offs in construction materials and techniques in order to keep the weight down while at the same time building a project that can handle an M class motor.

Good luck on your quest.

 

[jimzcatz]

I would recommend further research into the L3 processes of Tripoli Rocketry Assocation and the National Association of Rocketry as they are the two certifying organizations. I am not sure how possible it is to even attempt what you are planning, since L2 must be achieved before even starting the L3 process. Hopefully some TAPs and or L3CC members will chime in on this as they are the certifying observers/representatives of the two organizations. Welcome TRF and take the time to enjoy rocketry and soak up the huge amount of information on this forum.

This is not true. You can go through the Tripoli L3 process when ever you want. You just have to do the flights in order. I have pre-flight Tapped a few projects prior to L2.

 

[jimzcatz]

I was confused, he was talking about using a I motor so I was assuming he was talking about this, which was the first thing I looked up,

https://www.polecat-aerospace.com/cart.php?target=product&product_id=58

that's the 3", but now I found the 10" Goblin.

That thing is going nowhere on a I motor if it weighs 25 pounds.

Of course it will. This project is 100% doable. Good luck in your journey. You have already told us the journey is what your most look forward to. If you need a TAP, gimme a shout!

 

[dhbarr]

... think about ways to incorporate removable nose weight to enable the lighter liftoff weight for the L1 (and probably the L2).

It seems to me that a nose-tip-filling stack of different-diameter washers supported by a threaded rod-and-nut would be about the cheapest and most precise option which could be securely mounted as far forward as possible.

A nut epoxied into the very tip would potentially be all that remains when you want all the weight out; could easily go up from a minimum weight of "one nylon bolt" up to whichever would fail first of: nosecone tip, epoxy bond, nut threads, bolt threads, nosecone shoulder, front of body tube.

I'll keep reading, thanks for more advice!

 

[dixontj93060]

...hoping to ( eventually ) do my L1, L2, and L3 certs on the same airframe.

It can be done. Check out the latest issue of Rockets Magazine, pgs 12-15.

 

[EeebeeE]

Weighing in on this a little late...but these are my thoughts. For the L1 portion make it single deploy, but do so with electronics...not motor ejection because the high impulse I's don't burn that long. An AT I-600, which is a 38mm motor, is probably your best bet because it is a 100% I.

I quickly threw a sim together on what I thought would be a goblin (based on memory). The rocket is a typical short rocket in that stability is a challenge. Probably a .4 cal. at best. With the I-motor you have no choice. You cannot add weight. 600 avg. NS is equal to 135 ft. lbs./sec. To achieve a stable 5:1 Thrust-Weight ratio, the rocket can therefore weigh NO MORE than 27 lbs. on the I-600.

You really only have 4 motors that can do the job at the L-1 level. My preference would be the AT I-600, other choices are the Aerotech I-1299, Cesaroni I-800, and the Aerotech I-599 (the only one that is a 54mm motor - the others are 38mm).

You could use an AT I-1299, but has a lot less NS and will only get the rocket a little more than 200' off the ground, as will the CTI I-800. The I-599 gives you the thrust-weight ratio, but it does not get the rockt off the ground very high at all. You WILL need to taper your fins. YOu will increase stability, but not achieve a safe altitude if you eave them square.

My suggestion is to not paint the rocket because added weight (even the weight of the paint) is your enemy. Add base-level fillets, and design it so that more hardware can be added later. I would have the electronics located between the fins and use a chute release if you want to go DD. This will eliminate the need for bulkheads, extra eyebolts, and threaded rods.

I say all this, but your biggest challenge even after all of that is to be to get an RSO to approve it for flight. The math is there to say this s doable, but he may not like the stability even though fat rockets on skinny motors are more stable than the sims suggest they are. This rocket was not designed to fly on 38mm motors, but unfortunately, those are your best choices. You would have to make your own adapter though because there are few if any 38mm-75mm motor adapters available.

Fabricating a 38mm-75mm adapter wouldn't be that hard. Get a couple 38mm CR's for a 3" rocket. Have someone like Upscale CNC cut them as well as a 3" Plywood thrustplate out of 3/4" ply. Stick a 38mm motor tube between them. Glue in a 38mm motor retainer (it will fit inside the 75mm retainer), and you're ready to go.

Once you go to L2...don't putz around. Put a 3-grain L in it. Use a CTI L820 skidmark.

This can be done, although because you will want to add in additional items for an L2 and L3 cert, it will be very difficult to do all 3 in the same day.