"Spin Doctor" - Vertical Orientation System-VOS Rocket - Scratch Build.

[MarsLander]

Let's Goooooo!

Got really interested in Jim Jarvis' Vertical Orientation System (VOS2) described here: (https://www.rocketryforum.com/threads/i-could-use-just-a-little-guidance.122042/). After a bit of back and forth with @JimJarvis50, I bought his last unit of the current run of the VOS2 system. BTW, Jim is one cool dude and I'm appreciative of his time and contributions to the hobby. Cheers Jim!

I've followed Jim a while. I have agreed with A LOT of his design precepts, sometimes only on intuition. Zipperless design, internal avbay, large fillets for T2T etc. etc....

Design objectives (5, 6, 7 and 8 are Jim Jarvis designs):

1. VOS2 integration.
2. 2000-7000' launches. (I'm in Ohio).
3. J-K motors (54 and 75mm, limited to 54/1706 and 75/2560 cases).
4. DD.
5. Zipperless design.
6. Internal Avbay (no tube break).
7. Piston Ejection on the main (you'll see why later).
8. Adjustable fins to maintain stability.
9. Motor retention without thrust plate or retainer.
10. I'm sure there are others I'm not thinking about.

Let's get going!

Here is "Version 3" of the design.

 

[311stylie]

Looks great! I too am in Jim's group of VOS testers. Originally I thought I might use the WM Argonia Cup special as a test platform but Jim reminded me it only had 3 fins (doh!). So I am looking to do something different now. Will watch your progress for sure.

 

[MarsLander]

Booster design and motor retention.

The VOS system is built on a 4" WM FG tube, so 4" rocket it is!

Jim has a spin can (a fin can that spins freely) to accompany the VOS. I decided to start with fixed fins, and can go to a spin can in the future. Jim's fin can is 17" of airframe and 4" of coupler, or 21" OAL. To make the Spin Doctor upgrade compatible to the spin can, I'll follow the design.

Motor retention is through all-thread from the zipperless bulkheads to the motor. Eliminates the need for a retainer. The 54-1706 is 15.772" long, and the 75-2560 is 15.077". Both will fit nicely.

 

[MarsLander]

Motors.

Now that we have booster design, let's talk motors. The 54-1706 and 75-2560 are the limits of the motor mount. Eliminating motors that cannot lift this above 2000', we have a variety of motors that put us into our target altitudes:

 

[SteelyEyed]

Motors.

Now that we have booster design, let's talk motors. The 54-1706 and 75-2560 are the limits of the motor mount. Eliminating motors that cannot lift this above 2000', we have a variety of motors that put us into our target altitudes:

View attachment 638661

I’m looking forward to following your project, expecting lots of details and pics.

 

[MarsLander]

Motor Selection and the Canard Connection.

Canards can significantly change the static stability of a rocket, and need to be understood during the design process to ensure stability. Additionally, off the rail speed is important with canard based active stabilization. At low velocities, the canards are not very effective at altering the direction of flight. As a results, with low velocities (and wind) the rocket will be subject to weather cocking. If the flight angle is high enough, the VOS may not be able to correct the rocket to vertical flight.

Rail Button Placement.

I normally place rail buttons at the rear of the booster, and another, 1/2 way between the rear of the booster and the CG. On this rocket, that would put the rail button at 19" up. However, the zipperless coupler is between 17 and 21" from the rear. Without using conformal rail guide glued to the outside of the airframe, it need to be placed further forward. Mounting at 22" will place it outside of the coupler zone. As a result, this removes 2' from any rail I might use.

Rail Length.

With an effective rail length less than 8', we start getting into a zone where the canards may not be effective.

Motor Selection.

Ok, here we go. First, all of the motors are 4.8:1 or greater T2W. Fine.

Let's map Off the Rail Velocity vs. Altitude (10' Rail):



This can be used for Motor Selection.

Red are not very good in almost any situation, even in low winds...they might be ok, but there are better motors to ensure canard effectiveness (it's all about the canards anyway, no?).

Yellow might be ok on a low/no wind day...but don't rive access to any altitudes I can't get with green zone motors.

Green zone are the best, and we can get to a range of altitudes from 2500 to 6200. Nice!

Finally, I ruled out the K1499 and K2050 with G loading of 16 and 23 respectively. Might be ok, but why trash equipment if we don't need to?

 

[MarsLander]

Fin design and the Motor Connection.

I decided to use a clipped delta fin, primarily for the ease of being able to add wood to the tip chord to change the CP, and secondly for drag/aerodynamics. I chose a longer chord and shorter span, also for aerodynamics.

Here was my first draft, with a 45 Degree Sweep.



I didn't like the aesthetics. I also thought (and feedback from Jim), that having a bit of sweep to the trailing edge would help with damage control on landing. Numbers are coordinates for use with Rocksim...as you will see. So I ended up here:



The base fin is the 3.0 Y, 4.0 X plan point. The other lines are glue on tip lines. You'll see how I'll use this next. The base fin design netted me a good static margin (right around 1.5) with the J540 (the smallest mass motor; if I ever decide to fly it! (Target is 1.5 to minimize weather cocking and to keep it ~>1 through the entire launch).



One of the major implications of using such a wide variety of motors is the difference in motor weight, and the resultant change in stability. The J540R is 1084g., the K1000 is 2602g, or a difference of 3.3lbs!!! With the base fin, we lose stability with the larger motors!



By adjusting the span with, glue on tips, we can fly all the motors. Static Margin with the Target Motors:

 

[MarsLander]

Avbay and Deployment.

SHAMELESS PLUG---> @JimJarvis50 GETS ALL THE CREDIT FOR THE FOLLOWING. I'm following his lead, everything he says, just makes sense. Most of the content from here:

The point of zipperless design is obvious. The point of an interior avbay is to reduce the breaks in the airframe.

AVBAY.

The Avbay will be internal to the airframe, using an 8" avbay, with a Wildman (WM) forward top-hat FG bulkhead, and a rear FG top-hat bulkhead, then an Always Ready Rocketry 9mm and 6mm plywood bulkhead, followed by another WM FB bulkhead...creating a sandwich at the aft end of the airframe.



The resulting, internal Avbay will look like this (Thanks Jim!)



The internal avbay will be "pinned" to the airframe with socket cap screws into the aft plywood bulkheads, like this:


Finally, for the Avbay, I'll be using Jim's recommended Aerocon switches for altimeters/tracking:


More to come on this later.

Again, see Jim's video I linked above. I'm going with a piston deploy for the main.



Next up...VOS UNBOXING!

 

[MarsLander]

@WILDMANRS order on file for fins, airframe, couplers, CRs, motor casings. Build forthcoming!

 

[bad_idea]

Avbay and Deployment.

SHAMELESS PLUG---> @JimJarvis50 GETS ALL THE CREDIT FOR THE FOLLOWING. I'm following his lead, everything he says, just makes sense. Most of the content from here:

The point of zipperless design is obvious. The point of an interior avbay is to reduce the breaks in the airframe.

AVBAY.

The Avbay will be internal to the airframe, using an 8" avbay, with a Wildman (WM) forward top-hat FG bulkhead, and a rear FG top-hat bulkhead, then an Always Ready Rocketry 9mm and 6mm plywood bulkhead, followed by another WM FB bulkhead...creating a sandwich at the aft end of the airframe.

View attachment 638777

The resulting, internal Avbay will look like this (Thanks Jim!)

View attachment 638778

The internal avbay will be "pinned" to the airframe with socket cap screws into the aft plywood bulkheads, like this:
View attachment 638779

Finally, for the Avbay, I'll be using Jim's recommended Aerocon switches for altimeters/tracking:
View attachment 638782

More to come on this later.

Again, see Jim's video I linked above. I'm going with a piston deploy for the main.

View attachment 638783

Next up...VOS UNBOXING!

That video hit YouTube a month or so before I went to my first high power launch, and I watched it two or three times in that month. Mid-morning on the first day of that first launch, who should pull up and set up next to the folks I was sitting with but Jim and his lovely wife Gloria. I attached myself to Jim's side like a barnacle at that launch and at nearly every launch where I've seen him flying since and rarely allow him an opportunity to decline to let me jinx help with his flights. You can learn a ton simply by jinxing assisting the man.

Both that video and Jim in person have heavily influenced my better rockets in the subsequent three years. Zipperless? Check. Single all-thread avbay? Check. Avbay internal to the tube? Check. Shorter drogue shock cord to the motor section than the forward section? Check. Aerocon screw switches? Check. I've even made good use of pistons when I don't end up misjudging packing volume and run out of room for them (as I do all too often).

We won't talk about my less good rockets except to say that my bad ideas are mine alone, but a whole lot of my good ideas were shamelessly copied from Jim.