2.2 tomach min dim

[bad_idea]

Never expected to see a Reddy Kilowatt reference on TRF!

 

[The_Quacken]

Ok I think I’m going to glue in the e bay coupler and the insert th electronics from the back on a string and then secure from the front. This seems like a good idea for a few reasons. A) I only have one spot it could break I don’t have to worry about the av bay falling out. B) I can lower the electronics in with the motor so that’s attacked solidly to the airframe. It reduces my overal flexibility but I think it will work

 

[The_Quacken]

So I did a tip to tip layup job on the rocket. It is a little under epoxied unfortunately but it works and I’ll probably throw on one more layer of laminating epoxy and send it.





Also I’ve gotten a hypothetical sticker scheme done. I don’t expect these to last long at like Mach 2 but it’ll look good for a little bit at least
View attachment IMG_9961.MOV

 

[OverTheTop]

I had some vinyl stickers on mine and they mostly survived M1.8. Some very fine features took a bit of a hit, but the bulk were fine.

 

[kjhambrick]

The_Quacken --

I like your Reddy Kilowatt stickers !

But don't you need one of these from the good-old days too ?

Maybe the switchblade should be a silhouette of your rocket ?

Naah ! The lawyers would never let that fly !

-- kjh( who has a sick sense of humor )

There are several styles here:

google images: Reddy Kilowatt

 

[tfish]

The_Quacken --

I like your Reddy Kilowatt stickers !

But don't you need one of these from the good-old days too ?
View attachment 592164
Maybe the switchblade should be a silhouette of your rocket ?

Naah ! The lawyers would never let that fly !

-- kjh( who has a sick sense of humor )

There are several styles here:

google images: Reddy Kilowatt

I have the t-shirt!

Tony

 

[The_Quacken]

Well I think she’s done. A little finishing but recovery is in and chosen and attached so that’s all I think. Here’s some photos of the packing process I took. Not a whole lot of space lol but it works. Now for some deployment tests

 

[kjhambrick]

The_Quacken --

That's a nice small, neat package in the left-hand photo !

I can see kinda-sorta see the Cable Cutter on the left photo but ...

Q: What do you use for a Cable Cutter ?

The reason I ask is it's time for me to learn how to use a Cable Cutter without destroying Rockets or killing Spectators.

Scott Bartel gave me a handful of Black Sky PRM and PRM II Kits ( PRM == Pyro Release Mechanism ) when I was working with him on the AltAcc.

The PRM is very nicely engineered ( as were all of Scott's Gadgets ) but it is too large for the 29mm ... 38mm Rockets I have in mind for the Blue Raven.

So anyhow ... I am looking for Cable Cutting ideas for small rockets ...( I'll open a new Thread under the Recovery sub-topic for that )...

Thanks

-- kjh

p.s. I meant to ask: Q[2]: Is the package in the photo on the right for the same 54mm Rocket ?

 

[The_Quacken]

What do youuse for a Cable Cutter ?

This is the tinder rocketry one. Same guy who makes tender descenders. They work with black powder and smokeless

Q[2]: Is the package in the photo on the right for the same 54mm Rocket ?

Yes it’s the same packing even. it shows the soft shackle I’m using for recovery attachment

 

[The_Quacken]

So update, bad news. It turns out on the loads I want to fly it on (k1103x and a k76) it’s kinda really marginally stable off the pad. I mean I’m sitting at like .89 to .98 cal and 4.7 to 5.8% body length. I’m more worried about the percent value though. I don’t know how this imbalance happened it didn’t aim at all close to this but I think the carbon tip to tip is the culprit. Solidly like 40 grams at the way back of the rocket.
This said the rocket is already at a wet weight of 5lbs with a k76 for a hypothetical hamster dance flight so nose weight isn’t an option.

Sims say the rockets static margin is just gonna climb and never drop below one cal or 8% after it passes both milestones and it passes those less than a second into the flight so I may just send it? The plan is a 10 foot tower if I can figure one out specifically how to transport it to Nevada.

I think I’ll just send it as it’s not unstable it just could be stable-er and it stays at a comfortable stability most of that flight. If anyone has thoughts let me know

 

[Neutronium95]

Significantly reduced stability can be a problem when flying shorter motors in compact minimum diameter designs intended for longer motors. With a full length motor like a L1000, a pretty significant fraction of the motor mass is ahead of the CG, and going to a smaller motor can bring it back a lot. When you add in the fact that the fins aren't swept back like on many other minimum diameter designs, you'll end up with a CP that's further forward in comparison to something like a Wildman Mach 2.

Don't play silly games with stability. If it needs noseweight, add noseweight, especially for the K1103. The CP shift at Mach 2+ is no joke. You might be able to get away without extra ballast for the K76, but I wouldn't risk it. Also, I'm not sure if this rocket would even be allowed to compete at Hamster Dance. There was some controversy last year about an Aluminum nosecone tip.

 

[Hobie1dog]

Also, I'm not sure if this rocket would even be allowed to compete at Hamster Dance. There was some controversy last year about an Aluminum nosecone tip.

Is this something with NAR? I sure see a lot of aluminum tips these days.

 

[OverTheTop]

Regarding stability, I'll check where mine was at for the flights. I did fly it on an L640DT and something else. Will get back to you.

 

[The_Quacken]

Significantly reduced stability can be a problem when flying shorter motors in compact minimum diameter designs intended for longer motors. With a full length motor like a L1000, a pretty significant fraction of the motor mass is ahead of the CG, and going to a smaller motor can bring it back a lot. When you add in the fact that the fins aren't swept back like on many other minimum diameter designs, you'll end up with a CP that's further forward in comparison to something like a Wildman Mach 2.

Don't play silly games with stability. If it needs noseweight, add noseweight, especially for the K1103. The CP shift at Mach 2+ is no joke. You might be able to get away without extra ballast for the K76, but I wouldn't risk it. Also, I'm not sure if this rocket would even be allowed to compete at Hamster Dance. There was some controversy last year about an Aluminum nosecone tip.

Yeah it’s cutting too many things too close so I’m gonna call it out for HD. Unfortunate but there’s always next year.
The k1103 I need to weigh in full built configuration because I’m using a 2800 case and a rms system which is a whole lot of aluminum ahead of the cg which I’m not sure how to weigh accurately.
Otherwise I’ll probably build a weight in a coupler that can be put in the motor tube on top of the motor which is still well ahead of the cg.

I understand not playing stupid games but my reasoning for maybe just sending it was OR said the static margin shoots well above rule of thumb levels and stays there. Also the k 76 is a very low speed flight so it doesn’t see as much cg shift due to Mach effects. I’ll send the static margin plots later but I don’t know.

If anyone has tips for simulating the longer case and the adapter system that’d be appreciated.

My current plan is to put an 8% cg mark on the rocket and not fly it if the cg is behind it feild tested lol

 

[kjhambrick]

@The_Quacken --

First of all, what @Neutronium95 said last ...

<<<snip>>>

Don't play silly games with stability. If it needs noseweight, add noseweight, especially for the K1103. The CP shift at Mach 2+ is no joke. You might be able to get away without extra ballast for the K76, but I wouldn't risk it. Also, I'm not sure if this rocket would even be allowed to compete at Hamster Dance. There was some controversy last year about an Aluminum nosecone tip.

If you're not sure about your stability, it would be a shame to waste all your time and money just to do 'a little' skywriting with a K Motor ...

And I assume you measured the CG on the physical, loaded stack to come up with the stability margin using the CP calculated by Open Rocket ?

Significantly reduced stability can be a problem when flying shorter motors in compact minimum diameter designs intended for longer motors. With a full length motor like a L1000, a pretty significant fraction of the motor mass is ahead of the CG, and going to a smaller motor can bring it back a lot. <<<snip>>>

@Neutronium95'c comment about shorter motors and your question made me wonder ...

How does one sim an RMS 54/2800 System loaded with a short stack of grains with the Aluminum RAS components at the forward end of the casing ?

Didn't Open Rocket simply stick a K1103 with a 'short' RMS 54/1706 Casing at the tail of the rocket ?

If so, wouldn't any calculated CG produced by the Sim Program be suspect ?

I don't even know for sure how one could make a new .RASP file to account for the AeroTech RAS components.

Maybe one should sim with the K1103 in the 'native' RMS 54/1706 casing and then add a virtual static cylindrical mass just forward of where the forward closure of the 54/1706 would be ?

I dunno ...

-- kjh

p.s. if you don't have an AT RMS 54/1706, I could weigh mine with the end closures and the forward seal disk ...

 

[The_Quacken]

p.s. if you don't have an AT RMS 54/1706, I could weigh mine with the end closures and the forward seal disk ...

I’d appreciate that a lot because then I could at least put a weight element in the right ish place.

But yeah OpenRocket just stuck a short 1706 case in which is why I believe the cg will be much farther forward making it safe. That’s partially why I think I may just put the “here’s 8% stability” on the rocket since the sims are sus. I also need to ensure the fins are the right shape. The weird rounded shape means I need to either free form or approximate. With sharp corners or a guess at free form. I think they are pretty accurate but still.
I don’t think it’ll sky write but it’s looking like itll be a little uhhh wiggle wiggle right off the pad

 

[The_Quacken]

And I assume you measured the CG on the physical, loaded stack to come up with the stability margin using the CP calculated by Open Rocket ?

Yeah I did that’s why I was so suprised by the stability. I wouldn’t have built it if OR had told me it was so marginal

 

[kjhambrick]

I’d appreciate that a lot because then I could at least put a weight element in the right ish place.

But yeah OpenRocket just stuck a short 1706 case in which is why I believe the cg will be much farther forward making it safe. That’s partially why I think I may just put the “here’s 8% stability” on the rocket since the sims are sus. I also need to ensure the fins are the right shape. The weird rounded shape means I need to either free form or approximate. With sharp corners or a guess at free form. I think they are pretty accurate but still.
I don’t think it’ll sky write but it’s looking like itll be a little uhhh wiggle wiggle right off the pad

@The_Quacken --

I'll get out my RMS 54/1706 tonite after work and weigh each component and post them here for you.

-- kjh

 

[ljwilley]

Very cool! I don't think that the fins are off enough to have a problem.

 

[kjhambrick]

@The_Quacken --

Below is what I have that might be helpful.

HTH.

-- kjh

Make      Component             SSN  Date   Len(in)  Mass(g)
--------  -----------           ---  -----  -------  --------
ISP       RMS-54/1706           205  04/93   15.0      268
AeroTech  RMS-54/1706           839  09/95   15.0      272
AeroTech  Std Fwd Closure       ---  -----   0.875     104
AeroTech  Plugged Fwd Closure   ---  -----   0.875     102
DrRocket  Extended Fwd Closure  ---  -----   1.375     106
DrRocket  Aft Closure           ---  -----   0.375      30

EDIT: p.s. I can't find any of my 54mm Fwd Seal Disks. I'll look in some other boxen and post them if I do

 

[The_Quacken]

I have a fwd seal disk I can weigh

 

[bad_idea]

Maybe one should sim with the K1103 in the 'native' RMS 54/1706 casing and then add a virtual static cylindrical mass just forward of where the forward closure of the 54/1706 would be ?

That's exactly what I do if I need the sim to have that level of accuracy in predicting stability. Can even add a separate mass element for the floating closure so that the cg of the phantom case section is right.

Will be interesting to know if it makes much difference in this case.

 

[The_Quacken]

That's exactly what I do if I need the sim to have that level of accuracy in predicting stability. Can even add a separate mass element for the floating closure so that the cg of the phantom case section is right.

Will be interesting to know if it makes much difference in this case.

I think it will because I had a placeholder (aluminum tube component that I just relied on OR to do the right ish mass for since it was a case thickness) and it seemed stable and then when I removed that to test the k76 it did the crazy shift but I’m about to go home so I can send real data

 

[The_Quacken]

Data Time!

first is the K1103X. a motor I own and am sure I will fly


stability, mach number, vertical orientation for the entire up section and for just the powered section.
this is with a simulated aluminum tube component that represents the rest of the motor tube. so yeah it seems to stick well above 2 cal which is about 10% even at maximum velocity. really as soon as that propellant starts burning of the stability races to something much more acceptable.

and now for the K76



the up and the boost are basically the same for this motor so ill just post one.

so again the stability seems to rush forward and as this is a much slower rocket there's no dip to be seen. that said i dont know how safe the wiggles you see in both the zenith and the stability make me feel. but this shows its not like its slipping into very high AoA



for reference I think it might be good to include a motor thats similarbut is over the 8% the whole time and is probably better for this rocket
heres the same for an L1090

ill write more in a minute but im interested to see if this is helpful or informative

 

[The_Quacken]

lazy fix. add five and a half inches.... 6 for safety. not like its optimum anyways

 

[kjhambrick]

Dang ! I've got a lot to learn here, @The_Quacken !

Especially about OR simulations.

I didn't even know that sim mode existed in OR so I can't comment.

I'll play with them a bit though.

I've only looked at CG and CP as positions on the Air Frame and the final positions look OK to me after you added six inches to 'Reddy Kilowatt'.

Q[1]: When you calculate Stability as a percentage, what are the basis elements of that percentage ?
A[1]: EDIT: never mind ... I found it here on TRF: Stability measurement as a caliber or as a percentage ... I need to ponder the usefulness of Stability Margin as a percentage of the length of the Rocket ... seems ... uhhh ... complicated ...

Q[2]: Where were the positions of the CP and CG before adding length to the rocket ?

Boy, do I have a lot to learn !

-- kjh( that reminds me that I wanted to play with @SpaceManMat's OpenRocket variable CD Plugin using Cd -vs- Mach Data that I've got )

EDIT: p.s. looking at AoA -vs- time and vertical orientation -vs- time in your plots, they sure look like typical exponential decay of a stable dynamic system to me ...

EDIT: never mind ... I 'found' the K76WN in the OR rasp.eng file ... where did you get the thrust curve for the K76 ? I see it at thrustcurve.org - K76WN but it is not in my version of OR ... VERY kool thrust profile there !

 

[The_Quacken]

So I may end up scrubbing the k76 launch but for a much lamer reason. It comes down to funding it rn. 54 parts from rcs are expensive . This will still fly on probably a k1103 or maybe something bigger if I can pick that up.

As for the pre-extension cg/cp here they are

It’s really a small shift all things considered but it’s enough to make me feel safe without tons of drag losses

 

[kjhambrick]

Thanks for the picture of your original design for Ready Kilowatt, @The_Quacken

So the fineness ratio was about 19::1 for the original, simmed 42.874 inch rocket and after adding 6-inches the fineness ratio is about 22::1 ...

The latest six-inch extension makes a little more room for the laundry and only costs 600 ft or so altitude and a tiny bit of speed.

Maybe adding six-inches was a good call ?

Going back to stability as percentages of length -vs- calibers ...

Now that I've pondered it a for little while, I am developing a 'feel' for stability as percentages of length ...

Since the aerodynamic normal force acts on the rocket at the CP and the restoring torque due to lift is ( normal force ) -times- ( distance: CP -minus- CG ) and where negative torque ( in the 'in' direction ) reduces AoA, I can see that ( stability margin percentage ) -times- ( rocket length ) is a different, maybe even more direct way, to express that lever-arm as a dimensionless stability factor ...

Opinions wanted: Are there other advantages to reporting stability as percentages instead of the old-timey calibers of stability ?

Speaking of AoA ... what was the wind speed in your sim ?

As for the K76-NW, even with the high initial thrust profile, I don''t have a rocket that I could fly it in due to low speed off the rail.

My only surviving rocket from 25-years ago with a 54mm motor mount is Nocturnal Missions, a glass, 2.8 Kg dry mass, 73mm Vulcanite Upscale.

Nocturnal Missions would depart a 10-foot rail at only 62 ft/sec -or- 42 mph on a K76.

That is way too slow where I would fly it on the Central TX prarie where the winds are almost always 10-15 mph ( 19-deg AoA off-the-rail with 15 mph winds )...

And our summer launch site -- Apache Pass, TX is in the San Gabriel River Valley at 413 ft MSL and I am pretty sure there must be a pretty significant wind-shear at 300 -or- 400 feet AGL based on the constant stiff breeze a few miles away at Walburg, TX where we go to church -- it almost always blows 20 mph or so up there in Walburg at 879 ft.

And, speaking of speed, I am being curious now, what is Ready Kilowatt's speed off the rail on the K76 at 3.54 lb / 1.61 Kg dry mass ?

Thanks @The_Quacken, I hope you don't feel like I've hijacked your thread, I am learning a lot from your build docs !

-- kjh

 

[The_Quacken]

No worries you ask interesting questions.
The main reason I use percent is it’s a little more consistent across rockets of all shapes and sizes where a cal is normalized for a rocket with a fineness of about 10:1. It’s much more flexible and is basically the only option for very short or very long rockets. I’ve seen people jam like 10lbs of nose weight into gizmos and goblins and warlocks because they were trying to hit a cal when in reality it’d be stable at .5

Realistically the extra extension is a very good call since the rocket has dropped out of being truly optiu(and I was kinda kitting myself thinking it was ever well optimized)

As for the k76 there’s a reason aerotech is in no rush to certify it. Same with the j33. They speak to a very small subset of rocketeers who make tiny lightweight rockets to send them screaming out of sight. It really just doesn’t have the initial thrust to get stuff moving. I don’t exactly know the speed my rocket would hit off the pad off the top of my head but I do know it’d wiggle quite a lot.
K76 are just hard to fly they go high in any rocket they could lift.

 

[kjhambrick]

So I may end up scrubbing the k76 launch but for a much lamer reason. It comes down to funding it rn. 54 parts from rcs are expensive <<snip>>

Thanks for the reference to '54 parts from rcs', @The_Quacken

This is another 'new' resource that I didn't know about !

It is pretty kool that a L2 certified TRA Member or .edu or .gov group is able to buy the components from RSC / AT to construct a custom motor (**) ...

Thanks again !

-- kjh

(*) - from the RCS Site: Note: Propellant grains may be sold to Tripoli Rocketry Association (TRA) L2 or L3 research flyers, bona fide businesses and educational and government customers only.