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Ventris SRB

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Mr G

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The dual booster Ventris SRB had a successful maiden flight at Snow Ranch last month. Thanks to Ben Kolland for such a wicked cool snap of liftoff.
Ventris SRB.jpg
It was a fun experience using the "rule of thumb" to guesstimate how a strap-on booster could function with the least complexity. Happily, nothing less than carefully aligned rails and the cobbling together of spare parts for the boosters was enough. Main "engine" was an Estes F-15. Boosters were D12's.

If anyone is interested, I'll post a few more photos of how it went together.

This launch was the first time I can remember that people actually clapped as the boosters fell away and the Ventris continued to climb to apogee and parachute deployment!

Like most builds, this one was naked but by being successful, earned its colors. Should look good for launch No. 2.
 
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BDB

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I absolutely want to see more details. Did the boosters separate mid-flight?
 

TangoJuliet

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Kewl! Congratulations! Yes, yes, more details are in order for this one!
 

Mr G

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To answer the first question, yes, the boosters were designed to simply slip off once the thrust keeping them in place was depleated. The thought was that SRB thrust was higher than the main engine therefore applying an "up" force so they would not slide off prematurely. On release, there would be a short delay before an ejection charge blew the nosecone, letting the streamer unfurl for a recovery close to the liftoff area. Here is what that looked like -

SRB separation.jpg
 

Mr G

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Booster rail design included sections of Plaststruct 3/16 inch H column.
IMG_8572.jpg

Two pieces were epoxied to the booster with a gap wide enough to accommodate the third rail attached to the main rocket body.
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A small piece was glued on the end as a stop - at the top on the main rocket body and the bottom of the SRB as a back up if the top one failed.
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The booster then slid on the main rocket body until it hit the stop. With a bit of sanding on the inside of the rails, the boosters would just fall off when everything was upright.
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BDB

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:point: Very, very cool!!!
 

Cabernut

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Nice and simple. I love it.

Any idea what the altitude was?
 

Mr G

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Open Rocket sim indicated 1,000 feet. Looked more like 1,200 from the ground but that's just a guess.
 

TangoJuliet

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Was there any trick to connecting the initiators for the motors?
 

Mr G

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SRB boosters made from BT-60 x 12" tubing and NC-60 nosecone. 24mm x 6" motor mount had two balsa/cardboard sandwich centering rings. 1/8" x 10" Kevlar shock cord was glued to motor mount and ran through top centering ring. That was attached to another 8" of Estes elastic shock cord ending in a 3"x3" chute protector and a 20"x1" streamer.

On the bottom end, an Estes 24mm screw-on motor retainer was attached to the motor mount with JB Weld. The bell shaped nozzle came from a plastic shower head.

There was a bit of play in the rails to assure the fit was loose enough for the SRBs to fall away, so statically they sagged a bit when horizontal. Staggered placement of the retainers was chosen for looks with the hope that the main engine exhaust wouldn't burn the SRB retainers.

Rail buttons with Delrin standoffs from Dog House Rocketry replaced launch lugs. This assured there would be a long and stable initial launch path in case all engines didn't light exactly at the same time. A washer was added to keep the screws from digging into the main engine motor mount.

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TangoJuliet

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The plastic shower heads look awesome as nozzle bells! Where did you get the small chute protectors? I didn't know anybody made them that small.
 

noffie79

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This is fantastic, I love it. Very impressive. I may just have to try my best to copy this one. That lift off picture is awesome!
 

Mr G

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The decision to go with a 29mm center and 24mm outboard motor mounts with screw-on retainers was to maximize possible engine/motor options. The Estes F15-6 and two D12-3s were a good start as they were quick-lighting black powder, relatively inexpensive and obtainable at the local hobby store. A handmade tool using 1/16" steel rod was fashioned to fit in the two small holes in the 24mm retainers where fat fingers could not reach so the cap could be twisted on and off.

24mm and 29mm cardboard motor mounts were sacrificed to be sawed into retainer rings that were placed on the end of each engine with thin CA glue. When we bump up to composite motors, they will already have the ring so just slip in and go. Don't know if it will be another F15/D12 combo or Aerotech F37/F20 combo that would take it to 1,700+ feet.
IMG_7321.jpg IMG_7320.jpg

To maximize the chance of simultaneous ignition, 3" long Quest igniters were inserted into each engine nozzle and taped in place. They were attached to a 3-head igniter whip (from Dog House Rocketry - now showing discontinued) which was connected to the LUNAR launch pad system.
IMG_8573.jpg

One last shot of liftoff from the side where I was standing. The 1.7 second burn and 3-second delay on the D12s compared to the 3.5 second burn and 6-second delay of the F15 provided ideal event spacing and clearance so that there was no interference. The SRBs gracefully arced away from the rocket and landed under streamer within 20 feet of the pad so I could keep an eye out for the Ventris as it drifted from a higher apogee. One SRB had evidence of a little compression from landing as they both were very streamlined coming down under a streamer so a small parachute in each may be tried next time.
IMG_8325.jpg
 
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Mr G

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3x3 Nomex chute protecters can be found at least at Madcow Rocketry (and they are having a big sale tomorrow).
 

gwh

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I didn't think OpenRocket could sim strap on boosters? Could you use it to determine optimum delay of the boosters or was that just done as a guess?
 

Mr G

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It was a guess based on the 1.7 D12 burn, quick separation and immediate arcing as the main engine thrust pushed each SRB away. Another second or two delay may have been okay.

Early ejection helps slow down the boosters and keep them closer to the pad on landing. It's hard to keep track of three objects in the sky at once.
 
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TangoJuliet

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Mr G, I really, really want to duplicate your model for my own fleet. Do you have any problem with me plagiarizing your effort?
 

Mr G

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TJ, flattering that you ask, there is no plagiarism in being the second test dummy :wink:. All I ask is that you report on your project and share the results you have.

Now, do you all want to learn about the method used to create a dual deploy electronics/camera bay for those larger impulse launches that may go out of sight? It is an unfinished process but for now but I can show off the nosecone to reducer space and how it is all connected.
 

BDB

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Now, do you all want to learn about the method used to create a dual deploy electronics/camera bay for those larger impulse launches that may go out of sight? It is an unfinished process but for now but I can show off the nosecone to reducer space and how it is all connected.
Hell Yes!
 

Nytrunner

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I see that you've chopped portions of the transition and nosecone. I have a Ventris and Argent to build and I'm very interested in packing in an altimeter to bring them down somewhere close if I try out small H's. I've seen one transition altimeter setup on an Argent and am noodling around with how I'd do it.

Also your project is amazing. Its nice to see some unique action in the MPR section.
 

Mr G

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With the objective to do a minimum of modification to the existing airframe, the top and a part of the side of the transition was cut off to expose enough space for a small electronics sled. Using a 10-24 single threaded rod through the middle, the nosecone and transition bottom could be pulled together to make a sturdy payload bay.


IMG_8569.jpg
A hole was drilled big enough to fit a wing nut through a side of the nosecone base. The threaded rod with washer and nut an inch down was then placed through a small hole in the center of the nosecone base. A large washer and wing nut were then inserted through the side hole onto the threaded rod. The wing nut was held with a pair of needle nose pliers while the nut below the nosecone base was tightened up until all was snug.


IMG_8568.jpg
A small hole was drilled far enough off center from the base of the transition to fit a small eyebolt through with enough space for a large washer on the inside. A nut on both sides of the base were tightened for a snug fit. The larger washer on the inside helped distribute the load from the shock cord pull at ejection over a larger area of the plastic.


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The threaded rod was fitted through the hole in the transition bottom. A larger washer under the wing nut for the threaded rod distributed loads the same as the eyebolt but in the opposite direction. There was enough room left on the transition base for a small ejection charge well and terminal strip. Those won't be added for now as motor ejection plus the Jolly Logic Chute Release will be the standard procedure for high altitude flights. While the Chute Release is relatively expensive, it is way easier to set up and use, less messy, no wires and no extra battery weight than what dual deploy altimeters require. Well worth the investment - and since the Chute Release is directly attached to the parachute, it fits in almost any size rocket (down to BT-60 or 1.6") that you want to fly high - and get back.


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The payload bay is about six inches from the base of the nosecone to the base of the transition. That should be plenty of room to contain an 808 camera and a Jolly Logic AltimeterTwo. The camera has the optional lens extension that will allow just the lens to be mounted in a special very small low drag mount poking out of the transition. Never liked the thought of taping a camera to an outer body tube. There will be small holes drilled in the transition to arm the camera and altimeter just like the big boys.
 
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