7.5" LOC V-2 evolves to a BumperWAC

[Dave A]

A Little BumperWAC History
The BumperWAC program was devised to test 2 stage rocket systems and achieve high altitudes.
The updated V-2 rockets from WWII were grafted to a WAC Corporal already in the military's arsenal. The excerpt below is from and credited by Spaceline.com

The first six Bumper-Wac rockets were launched from the White Sands Missile Range in New Mexico. The first of these was launched on May 13, 1948. The vehicle flew to an altitude of 80 miles at a maximum speed of 2,740 m.p.h.

Five more test flights were conducted at White Sands with mixed results. Bumper #5, launched on February 24, 1949 was the most successful in the White Sands Bumper-Wac series. In this test, the vehicle achieved an altitude of 244 miles at a maximum speed of 5,150 m.p.h. This marked the first time a man-made object reached space.

In 1950, Bumper-Wac tests moved to Cape Canaveral. Bumper #7 was scheduled to be launched first, but its initial launch attempt on July 19, 1950 was halted due to a failure of the first stage to achieve proper liftoff thrust.

I will try to write about the assembly and tricks I learned along the way in future posts.
It's a full 2 stage and both are dual deploy. 2 Perfectflites in the V-2 & PML Timer in the V-2 nose to fire the upper stage.
The WAC Corporal uses motor eject for drougeless return, AltAcc2 for 9" main at 500'. More to follow.

 

[Dave A]

Yes, MDRA folks, that is a Lester Sherman signature launchpad. I modified it just for launching the V-2. May Lester RIP.

 

[Brent]

Where did you separate the V2 booster at and where did you put the altimeter bay?

 

[Dave A]

It was my brother's LOC V-2 kit he bought back in '99 when we were going for our Level 2s. We worked together back then and not wanting to fiberglass anything back then.
The pic at the top was supposed to be the scale BumperWAC. In order to fit the alt bay and all the chutes I made it a bit too long. Of course it has taken a beating with zippering and dings on landings. It has been repaired several times. Around 2003-2004 we began working on the BumperWAC.

 

[JohnCoker]

Nice job on a prototype not often modeled!

 

[Dave A]

V-2

Tailcone/Lower Section:
We moved the lower centering down into the plastic tailcone to make enough room for the drogue rigging. Cut the LOC paper body tube down

Middle Section:
Made an upper section out of PML tubing and coupler for the altimeter (which then I started using a unitary Giant Leap aluminum av bay) with enough room for Main chute and rigging.

Nose Section:
Kept the original, weighted LOC nose cone for flying the standard LOC V-2. This was the most difficult part of the project. I wanted it reliable but easy to load and fly. We bought a new LOC plastic nose cone to mate with the WAC Corporal and house the staging timer. I extended the nose shoulder and then added the coupler so I could have more room for the main rigging AND access to the staging timer.

I had to make a series of rings to start with a 54mm mmt & aeropak retainer to hold the timer housing. I made a timer housing out of a 5" piece of PML 54mm coupler. Once the PML timer is mounted inside, that assy would slide in the tube and locked in with the retainer.

A 16 ga wire would run through the 38mm coupler that would mate to the WAC Corporal.

(More on that in the Upper stage section.) The tip of the nose was trimmed down and slotted for the fins so a 38mm ACME fincan would slide in easily. The upper stage had its rear-most cr about 2" from the end so the 38mm coupler in the V-2 nose would slide in it. That made for a very solid mating of the upper stage with zero play during flight.

 

[Dave A]

V-2 Sections

 

[Dave A]

WAC Corporal:

I wanted to make a scale WAC Corporal but this was a test to get all the pieces to work so "to scale" it was not. For ease of construction I used the ACME 38mm fin can, which only has 3 fins, I believe the real WAC Corporal in a BumperWAC had 4.

Lower Section: ~6" piece of 38mm G-10 tubing bonded to the fincan. a 29mm piece of mmt was in the aft to fly only 29mm single-use motors. The aft ring was slid about 2" from the rear so the 38mm coupler in the V-2 nose would slide in. Once that mated along with the fins sild into the slots made for a precise fit. I trimmed the fins with a jigs saw and sander to mimic WAC fins. Motor eject was used for drogueless return.

Upper Section:

I fabricated a piece of PML 38mm coupler as an av bay with a window to house the AltAcc2. I made it so it slid in the body tube and affixed it with a 6-32 screw to keep it together. That was so I could pull it apart to load the small charge to deploy the 9" main chute.


All of this was so both vehicles utilized dual deploy.

A lot or work went in this but it always flew as designed except one below.

 

[Dave A]

Flying Configuration:

I have flown many V-2s of different sizes and as far as motors are concerned, fast is better. The V-2 is not an ideal rocket aerodynamically . I like using fast burning motors otherwise it likes to lay over prior to apogee. In the BumperWAC configuration, fast is a REAL good idea.

When it was lighter, no fiberglass, I flew it on the awesome Loki J-820 star grain. Off the pad and plenty of time for the WAC to stage. I could have flown it with Ks but you miss the fun seeing the WAC Corporal fly.

The upper stage weighed 1 pound without motor. My choice was AT F-50-9T. Blue thunder is easy to light. I flew the Bumper at the 2005 TARC in Plains, VA. I chose to use an F-25 and it did not light. TARC organizer Tripp Barber panicked when it all arced over towards the crowd.

It did what it is supposed to do. When the V-2 blew the drogue out the inertia knocked off the WAC Corporal. Its AltAcc2 deployed the 9" main, the V_2 deployed its main at the designed altitude. No worries, both vehicles drifted back to the launch area, Tripp and I started breathing again.

We got tired of cardboard and phenolic tuning zippering or chipping. The updated V-2 has all new G-10 FG tubing, still using the original tailcone, plywood fins and plastic nose cone.

I have flown the V-2 alone on 1750n K motors and it flies great.

At the 2019 MDRA Red Glare, the BumperWAC will fly again.

 

[Dave A]

The V-2 with the updated FG tubes and camo paint.
At Blacksburg on a classic, 12 yr old AMW K950, oh yeah!

 

[Dave A]

My method for staging:
1) Under 6" diameter:
I strictly use fast burning loads for the boost, Star Grains, Blue Thunder, etc. Why? Fast boost, longer coast phase, plenty of time for upper stage to come to pressure and go while the vehicles are still vertical. My timers fire only for 1 sec, I like to light the upper stage early , less likely to go sideways.
2) Over 6" diameter: Still a big fan of quick boost, lots of coast time. Larger sustainer motors can take more time to come up to pressure. My favorite for the upper stage, Blue Thunder or any fast propellant. Why? They light more often than not.
My larger rockets use the Missleworks WRCx remote firing system. Push the button not long after burnout, all will go as planned.
What if the upper stage does not light, so what, it will separate and deploy its chutes as designed.
Test all timers with the right igniters until you get consistent results.