ASP WAC Corporal w/Tiny Tim Booster 18mm to 18mm build

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Skp

Skp

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This may be a bit of a slow paced build, I am not feeling motivated to rush through it. I did want to do a build thread though, because there is not too much out there on this rocket. The part that most interested me is the open air gap staging. The kit comes with a removable vented body tube to close the gap, but I have seen a photo or two of open air gap staging that does seem to show it works. Results of my mindsim tell me that the upper stage is no less likely to light with the gap tube removed than when it is in place. I believe the gap tube is more of an assistance for jettisoning the booster by allowing more pressure to be able to build between the stages.

If anyone has experience or thoughts please jump in.
ASP WAC Parts.jpg
 
I've seen the ASP 18mm Open gap staged Wac-Corporal & Tiny Tim Booster fly a couple times. Seems to work very well, the Club member who owns the rocket fly's it often at our sport launches. I don't recall a single upper stage mis-fire.

I only have the ASP Micro Maxx version which is not staged but does work very well also:)
Look forward to seeing your progress. Take your time it is a bit of an involved build, makes a great looking addition to any fleet:)

MM 399_Wac Corporal 41.81495 Scale Compete_02-16-14.jpg

MM 399Lp01_Wac-Corporal on pad for (1st Flt)_06-21-14.jpg
 
I have spent most of my time on this in computersim land and mindsim land. I built the complete rocket 2 different ways in the computer. One way I built the rocket as if there were no strut gap and the other way with as close to having a gap as I could get with openrocket. The disappointing thing is the gap seems to make no difference in the CP. The instructions provided a calculated CP and my computer models match fairly closely to it. My mindsim makes me think that the CP would move further aft with the gap than without, because the gap is ahead of the CP. I also built just the Tiny Tim booster without the sustainer. I am most interested in it's CP and CG due to wanting it to tumble properly. The struts on the front would be susceptible to damage from stable free fall. I do plan to do test drops onto a soft surface to get a good tumble going.
 
I typically start with fins on a rocket, due to the fact that if they go well the rest of the rocket is a breeze. If they go badly, I am still early enough in the project to have the motivation to redo them. The Tiny Tim Booster fins are FAT, I mean really fat for the size of this model. I suspect it is to give them surface area for a good root bond and durability for the tumble recovery. The instructions encourage you to sand all edges to a somewhat sharp shape for the scale model appearance. I tried to talk myself into just rounding them for the sake of durability, but they are fat. Did I mention they are fat. I had to sand them to profile, despite the fact they are going to get dinged badly on landing. It is a far better thing to have looked good once and lost it, than to have never looked good at all.
Wac Tim fat fins.jpgWac Tim LE fin profile.jpgWac Tim Root profile.jpg
 
Just don't let anyone know about the silly mindsiming. Always go with the computer because folks trust computer results, not mere thought gaming or speculation. If the gap is in front of CP it will bring it up a bit and vise versa. Most of the airflow will be going right over the gap so it will probably not have a huge impact on CP. Oh MY! Now you have me mindsiming again which they tell me is very, very bad. Nothing a modicum of no good, stinking, performance robbing nose weight won't solve on a conservative first flight. Nose weight and power will solve all your problems, but again, do not say that out loud anywhere near the men of science.

It is a proven kit from a reliable manufacturer so you should meet all Pad Fuhrer requirements at the RSO table. I would make the first stage just tight enough to support its loaded weight when held up, just enough to avoid drag separation. Make it look marvelous and all the old dudes will be unable to resist seeing it fly. Try it first with a peppy and light Estes B6 -0, then high flying C6-0. Later on I have a bunch of Quest C6-0s we can try for a real slow take off and hot, long burning excitement. A slow, NASA style liftoff with that old time scale model will warm the Pad Fuhrer's heart. And who can resist telling the kids we are about to launch a Tiny Tim booster! So cute!
 
Skp said:
I typically start with fins on a rocket, due to the fact that if they go well the rest of the rocket is a breeze. If they go badly, I am still early enough in the project to have the motivation to redo them. The Tiny Tim Booster fins are FAT, I mean really fat for the size of this model. I suspect it is to give them surface area for a good root bond and durability for the tumble recovery. The instructions encourage you to sand all edges to a somewhat sharp shape for the scale model appearance. I tried to talk myself into just rounding them for the sake of durability, but they are fat. Did I mention they are fat. I had to sand them to profile, despite the fact they are going to get dinged badly on landing. It is a far better thing to have looked good once and lost it, than to have never looked good at all.
View attachment 291418View attachment 291419View attachment 291420
Click to expand...

YES! None of the old farts will be able to resist those plump, yet perfectly foiled and shaped fins. Finished to perfection with old school techniques and the big kids will follow you like you were the Pied Piper of Hamelin, all the way to the launch rod!
 
Nice job on the fins! What technique did you use to get them to come out so good?

Best regards,
Brian
 
BRS Hobbies said:
Nice job on the fins! What technique did you use to get them to come out so good?

Best regards,
Brian
Click to expand...

Thank you, for the compliment. I actually took the "I am so disgusted with myself for not just being able to round the edges and call it done" method. The "This is a fragile booster that is going to fall out of the sky without a parachute and get messed up edges" method. The "If I airfoil the fins, I might introduce unbalanced lift that will prevent me from exploring the open air gap staging reliability that I am really interested in" method. I attacked it aggressively with 60 git sandpaper with aluminum sanding block and steel ruler to apply even pressure across the fin span to quickly rip it up. I finished it up with some fine grit paper and a more organic free form approach and it turned out pretty much as good as when I use my supper cautious, anal retentive method. You would not believe how much respect I have for those individuals that can bring a square finned, spiral glaring, paint orange peeling rocket to the pad and have a wonderful time launching it. It is ridiculous how many pictures of WAC Corporals I have looked at lately and the scale aspect of the build is not even what interests me. Oh well, it is my hobby and it keeps me sane. I did mention that I am sane, right?
 
Daddyisabar said:
Just don't let anyone know about the silly mindsiming. Always go with the computer because folks trust computer results, not mere thought gaming or speculation. If the gap is in front of CP it will bring it up a bit and vise versa. Most of the airflow will be going right over the gap so it will probably not have a huge impact on CP. Oh MY! Now you have me mindsiming again which they tell me is very, very bad. Nothing a modicum of no good, stinking, performance robbing nose weight won't solve on a conservative first flight. Nose weight and power will solve all your problems, but again, do not say that out loud anywhere near the men of science.

It is a proven kit from a reliable manufacturer so you should meet all Pad Fuhrer requirements at the RSO table. I would make the first stage just tight enough to support its loaded weight when held up, just enough to avoid drag separation. Make it look marvelous and all the old dudes will be unable to resist seeing it fly. Try it first with a peppy and light Estes B6 -0, then high flying C6-0. Later on I have a bunch of Quest C6-0s we can try for a real slow take off and hot, long burning excitement. A slow, NASA style liftoff with that old time scale model will warm the Pad Fuhrer's heart. And who can resist telling the kids we are about to launch a Tiny Tim booster! So cute!
Click to expand...

Is your mindsim giving you different results than my mindsim? Oh, this is serious business. We need to get our mindsims together, make sure they are updated with the latest patches and lubricated with beer.
 
WAC Corporal Steel Bands.jpgWAC Corporal Bands in Place.jpg
The kit comes with styrene bands to go around the booster, it also comes with rubber bands to hold the styrene bands in place while CA glue is applied.
That seemed an odd choice to me, so I opted to cut bands from index an index card and use an Elmer's glue stick. You can also see how I have ruffed up the tube surface and even made some holes for rivets.
 
WAC Corporal Engine hook.jpgWAC Corporal 1st Strut.jpgWAC Corporal Booster Guts.jpg
The kit was designed for friction fit of both the sustainer and the booster. The sustainer and booster connect to each other via the sustainer motor tube, so it would have to be redesigned entirely to add a hook. The booster on the other hand can still sit level on it's fins and have a motor hook added. The struts take a long time of placing, gluing and sitting.
 
You know they way to the Pad Fuhrer's warm heart at the RSO table is showing him Positive Motor Retention! Motor hooks = good technique and science, Friction fit = more of an art then science. We all know how much better Science is than the Arts! All the old guys will just love this one. Put it on the rod and lets see it fly! Great expectations abound.
 
With one motor friction fit and one motor positively retained we have a meeting of science and art. The open gap staging will require a bit of religious faith. I may dub this rocket the Grand Unification Theory.
 
WAC Corporal Sustainer MM.jpgWAC Corporal Sustainer Fin Alignment.jpg

The booster forward ring hugs the sustainer motor mount tube, so both the forward ring and the motor mount tube have been soaked in thin CA and sanded so that they slip smoothly and easily. I score horizontal marks in the motor mount tube due to the fact that if the mating surfaces are hyper smooth then even if they are properly sized they will have a static bond that is impressive. Also the instructions have you mount the shock line Kevlar to the forward motor mount ring. I opted not to mount the cord that way.

A couple of rulers and clips make fin alignment easy enough.
 
Skp said:
The booster forward ring hugs the sustainer motor mount tube, so both the forward ring and the motor mount tube have been soaked in thin CA and sanded so that they slip smoothly and easily.
Click to expand...

Neat! I've been meaning to ask the forum sometime, what people do to ensure the booster doesn't get scorched by the sustainer's motor. My recollection back from circa 1979 was that the one time I flew my old Centuri Lance Corporal, the booster didn't look like it would survive more than 3 flights.

It seems that soaking in thin CA would definitely help booster longevity!
 
Soaking with CA also stabilizes the cardboard so that it does not swell with temperature and humidity.
 
skp,

What is your general assessment of the quality of the balsa parts in this kit? Soft? Hard? Just right?

I recently finished the 38mm Wac Corporal kit, and my balsa parts were softsoftsoft!

Thanks.
 
LW Bercini said:
skp,

What is your general assessment of the quality of the balsa parts in this kit? Soft? Hard? Just right?

I recently finished the 38mm Wac Corporal kit, and my balsa parts were softsoftsoft!

Thanks.
Click to expand...

The balsa parts on this kit are some of the nicest I have worked with. The Booster balsa was hard enough that I broke out rough sand paper to get it to shape, it has a slight flex to it along the grain. The sustainer fin balsa was softer, but for the size of the fin and the fact that it comes in under parachute, plenty strong. The Balsa nose cone it the nicest of all. I have never managed to work with a balsa nose cone without messing up the tip at some point in the build. Even though this is conical and comes to a sharp point it is durable. I did give it a drenching with thin CA for extra protection and finishing smoothness.
 
LW Bercini said:
skp,

What is your general assessment of the quality of the balsa parts in this kit? Soft? Hard? Just right?

I recently finished the 38mm Wac Corporal kit, and my balsa parts were softsoftsoft!

Thanks.
Click to expand...

The fins bruise easily. I have two of the 38mm versions though I lost one. One was yellow color based the other one I lost was white. I flew both of them
with a Galejs MAD unit: https://www.aeroconsystems.com/electronics/mad.htm. After a rebuild on my yellow WAC, it will be flying with a Zeptobit unit which is
inherently safer: https://www.zeptobit.com/zeptomag/ as it uses an accelerometer to activate the circuit. Will be using a Jolly Logic Chute release to
do pseudo dual deploy.

That coupler the 38mm motored WAC nosecone is perfect to hack for an ebay. Use four screws to attach to the nosecone base. Sorry to hijack the thread but
the big brother of this build subject is also a nice flier on H123's and research H160's. Kurt
 
WAC Corporal Shock Cord Mount Hole.jpgWAC Corporal Shock Mount.jpgWAC Corporal Fuel Line Conduit Carving.jpgWAC Corporal Fuel Line Mounting.jpg
The conduit line cover makes an excellent shock cord mount concealer. Just put a small hole in the body tube. Thread the Kevlar cord through the hole. Attach the elastic cord to the Kevlar cord and pull back through the body tube far enough that the Kevlar does not reach the edge of the body tube. Tie a knot in the Kevlar outside the body tube. Carve a hole on the underside of the conduit cover so that it sits flush on the body tube and glue it down.
 
WAC Corporal Full Stack.jpgWAC Corporal Horizontal.jpg

Ready for finishing. As mentioned earlier i drenched the nose cone in thin CA for finishing purposes. In the horizontal picture you can see Tiny Tim's fins are coated with something. I have never tried it before, but had some oil based polyurethane laying around. It seems to make the fins very hard. Hopefully they will withstand tumbling well.
 
[YOUTUBE]pPDVqt0xy9Q[/YOUTUBE]
Did not get the paint finished prior to maiden flight. This is on B6-0 to A8-5. This is the smallest 2 stage rocket I have and it scoots up there fast. I am tempted to try boosting on an A8-0 so that I can get a better look at the staging, but the fully loaded liftoff weight would be 6.45oz and that seems a little heavy for an A.
WAC Corporal lift off.jpgWAC Corporal Staging.pngWAC Corporal Results.jpg
The struts take a bit of a beating from the booster charge.
 
Skp said:
I have spent most of my time on this in computersim land and mindsim land. I built the complete rocket 2 different ways in the computer. One way I built the rocket as if there were no strut gap and the other way with as close to having a gap as I could get with openrocket. The disappointing thing is the gap seems to make no difference in the CP. The instructions provided a calculated CP and my computer models match fairly closely to it. My mindsim makes me think that the CP would move further aft with the gap than without, because the gap is ahead of the CP. I also built just the Tiny Tim booster without the sustainer. I am most interested in it's CP and CG due to wanting it to tumble properly. The struts on the front would be susceptible to damage from stable free fall. I do plan to do test drops onto a soft surface to get a good tumble going.
Click to expand...

Hit the leading and trailing edges with thin CA, it will toughen them up significantly. Used this trick on VERY thin trailing edges on an RC sailplane. It works great,

JR
 
Thank you for the tip JRobinsonUSAF, I applied oil based polyurethane to the booster fins. I did not treat the sustainer fins with anything and they are pretty sharp. So I hope they hold up. after my first flight there was no damage to anything except a little scorching to the booster struts. She earned her paint job.
WAC Corporal finished1.jpg
 
Very nice! Would love to see video showing the staging working. I've never seen this gap staging done before.
 

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