Stability for saucer rockets?

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ljwilley

I’m pretty sure it will work…
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I want to make an upscale of the art applewhite stealth saucer, that uses a 38mm engine mount. Even though they are always stable, how would I prove stability on something like this to an RSO? For my club, you typically have to have documented CP and CG information for them to let you fly it... but how is that calculated if you can't do it on a simulator? Even if I use base drag, how do you prove that a rocket has more than 1 caliber of stability, if it's not even 1 caliber long? I've seen others at my club fly large saucers... so do they just let you fly it automatically because it's a saucer? I find that unlikely.

Please help!
 
I want to make an upscale of the art applewhite stealth saucer, that uses a 38mm engine mount. Even though they are always stable, how would I prove stability on something like this to an RSO? For my club, you typically have to have documented CP and CG information for them to let you fly it... but how is that calculated if you can't do it on a simulator? Even if I use base drag, how do you prove that a rocket has more than 1 caliber of stability, if it's not even 1 caliber long? I've seen others at my club fly large saucers... so do they just let you fly it automatically because it's a saucer? I find that unlikely.

Please help!
What do you mean by documented? A computer printout. A GC and CP sticker. If your RSO is familiar with spools and saucers I would think they would know it will fly safely. We only have an RSO at our big events. Usually they want to see the stickers or they will handle the rocket and have enough experience to know what works and what doesn't. Now I'm not trying to give you a hard time. How many people in your group? Our group is small. We only have 107 members and only about 30 or 40 members that show up at launches every month. Last month there were about 20. We all know each other. When I show up with a flying chicken or my flying pumpkin it's ok because I fly some odd stuff and they fly ok. To try to answer your question. Could you show them a video of one flying from YouTube. Maybe from an LDRS or similar. I'm not trying to be nasty. I've never flown at a big event so I don't have experience with RSO's. Is it typical to have a simulation printout to fly at say LDRS? And guys take it easy on me. Remember I don't know what I don't know.:)
 
At large events they are called "Safety Check In" as they have several people checking on different shifts, working under the aspect of the main RSO.

The 'Real RSO' is only called in on something special or incident. The Large projects have already been thru the "BFR" approval process well before the launch and also an RSO inspection upon arrival.

That said, I have never seen anyone at a check in ask for a CP/CG on a Spool/Saucer. Most folks don't have a wind tunnel.

@teepot , 100+ members is a good sized club, and 40 is a real good turn out. You do have a nice desert flying site that some folks have even flown to go there. And not just me, I even ran across Bob Shultz from Michigan TRA Team-1 at your Tripoli Vegas October Fest once and was like 'Wow, imagine seeing you here Bob' to him. He was on a Vacation as well

Edit to add: I have seen RSOs called in to the safety check-in on something strange, and say "Put it out at the Away Cell"

PPS: @troj , you have manned hundreds of Safety check in shifts, what is your experience on the Saucer Issue for the OP?
 
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I want to make an upscale of the art applewhite stealth saucer, that uses a 38mm engine mount. Even though they are always stable, how would I prove stability on something like this to an RSO? For my club, you typically have to have documented CP and CG information for them to let you fly it... but how is that calculated if you can't do it on a simulator? Even if I use base drag, how do you prove that a rocket has more than 1 caliber of stability, if it's not even 1 caliber long? I've seen others at my club fly large saucers... so do they just let you fly it automatically because it's a saucer? I find that unlikely.

Please help!
Saucers are stable essentially because of the drag. When I RSO, I look at the design of a saucer and make sure it will withstand the thrust of the motor. It is not exactly science that involves odd rockets. I recommend you select a design and slowly scale it up.
 
I want to make an upscale of the art applewhite stealth saucer, that uses a 38mm engine mount. Even though they are always stable, how would I prove stability on something like this to an RSO? For my club, you typically have to have documented CP and CG information for them to let you fly it... but how is that calculated if you can't do it on a simulator? Even if I use base drag, how do you prove that a rocket has more than 1 caliber of stability, if it's not even 1 caliber long? I've seen others at my club fly large saucers... so do they just let you fly it automatically because it's a saucer? I find that unlikely.

Please help!
Art Applewhite provides the plans for a 38mm Stealth here
https://www.artapplewhite.com/free.html
He is very particular about stability and recovery so If you follow his instructions and materials I would have thought most launch officials would be happy. Note that for a while he stopped offering plans and 54mm and above versions as some builders ignored his motor recommendations and he was concerned about safety. My wife has a 54mm Stealth built from a kit and it launches and recovers safely with a nice spiralling up and down.
 
Art Applewhite provides the plans for a 38mm Stealth here
https://www.artapplewhite.com/free.html
He is very particular about stability and recovery so If you follow his instructions and materials I would have thought most launch officials would be happy. Note that for a while he stopped offering plans and 54mm and above versions as some builders ignored his motor recommendations and he was concerned about safety. My wife has a 54mm Stealth built from a kit and it launches and recovers safely with a nice spiralling up and down.
He has plans for a 29mm one. I just plan on scaling that up and probably making it from something a little stronger.
Thanks everyone!
 
I want to make an upscale of the art applewhite stealth saucer, that uses a 38mm engine mount. Even though they are always stable, how would I prove stability on something like this to an RSO? For my club, you typically have to have documented CP and CG information for them to let you fly it... but how is that calculated if you can't do it on a simulator? Even if I use base drag, how do you prove that a rocket has more than 1 caliber of stability, if it's not even 1 caliber long? I've seen others at my club fly large saucers... so do they just let you fly it automatically because it's a saucer? I find that unlikely.

Please help!
I started with a 10" on 24 mm Ds, then a 23" on 54 mm, and finally this one.
Chuck has seen my 40", 98 mm saucer on an N800. Last flown at night in 2011.
saucer_pad.JPG

 
I started with a 10" on 24 mm Ds, then a 23" on 54 mm, and finally this one.
Chuck has seen my 40", 98 mm saucer on an N800. Last flown at night in 2011.
View attachment 691920


Was this before the 1000ft TRA requirement for a N motor?

Did it really need a parachute? Looked like it was spinning down fine.

I think this is how most disk rockets behave.

 
Was this before the 1000ft TRA requirement for a N motor?

Did it really need a parachute? Looked like it was spinning down fine.

I think this is how most disk rockets behave.


The saucer was more than 1000' away at liftoff. Zoomed in video makes it look a lot closer.
No parachute on the night version. However, the extra weight of glassing, batteries, and over 200 LEDs made it needed then. With a D grain motor and cold propellant, impact was only a couple seconds after burnout.

 
The saucer was more than 1000' away at liftoff. Zoomed in video makes it look a lot closer.
No parachute on the night version. However, the extra weight of glassing, batteries, and over 200 LEDs made it needed then. With a D grain motor and cold propellant, impact was only a couple seconds after burnout.


It seemed like it slowed down a bit. What was the damage? Wasn't difficult to find I imagine with the burning flame. :)

We ended walking a quarter mile to find my rocket. Thankfully, the LED lights stayed on.

 
It seemed like it slowed down a bit. What was the damage? Wasn't difficult to find I imagine with the burning flame. :)

We ended walking a quarter mile to find my rocket. Thankfully, the LED lights stayed on.


When it hit the ground, the saucer slid down the motor and crunched both dome pods. These were LOC 4" tubes. The saucer weighed 17 lb before glassing, 30 lb. with batteries and LEDs after glassing. (Motor was another 27 lb.) See the lit on ground video.
Here's another shot showing the under side.
saucer_walk.JPG
 
A stable saucer/bowl shape on a 38mm CTI I55. Saucer/bowl has loads of drag and motor tube sticking out the top puts CG far ahead of CP.

 
For my club, you typically have to have documented CP and CG information for them to let you fly it... but how is that calculated if you can't do it on a simulator? Even if I use base drag, how do you prove that a rocket has more than 1 caliber of stability, if it's not even 1 caliber long? I've seen others at my club fly large saucers... so do they just let you fly it automatically because it's a saucer? I find that unlikely.
It's my opinion that the CP and CG relationship is for standard rockets and not necessarily applicable to saucers.

A "regular" or typical 3 or 4 fnc rocket should have enough margin between the CP and CG otherwise it may go out of control under boost at high speed and then it can act like an errant "missile".

Saucers however, have so much drag that under power they are much slower (by magnitudes) and so even if it is unstable, it's unlikely to come at you at very high speed and more likely to just tumble (standard saucers).

Additionally, saucers don't always have the CG ahead of CP, so that rule of thumb doesn't work here either. For example, my Squirrel Works Pizza Pie rocket, which I have launched and can confirm it works fine.
1739057611526.jpeg
https://www.squirrel-works.com/catalog/pie/pie.html
 
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