A Saab Story

I haven't posted a thread in a while, and Saab's seem to be the coming trend of 2015, so here's my story.

I'll be building four RB-05A (or something like that) Saab vehicular devices. All semi-scale: as in close enough to look like a Saab from a distance, and good enough to serve as motor holders. Another trend that emerged in the last flying season around here was alphabet flying. Sabrina is an alphabet flying princess, I flew a scrambled alphabet at LDRS, and most recently, my dad Tom is working on completing his fleet of Tomahawks so he can fly the alphabet with that particular model. Never original, but always willing to borrow the wisdom of others, I thought this was a good idea...so the initial plan was to build two Saabs that could fly the high power alphabet. That original plan has evolved and expanded, largely due to the recent offerings by Wildman and Badazz.

Current plan

-1.2" Badazz mid power PVC: E-G
-2.1" Wildman: G-I
-4" Wildman: J-M
-5.5" scratch: L-N

Got a new job:grin:, and part of the benefits of said job is reduced free time:sad:. I'm not sure at what pace this thread will traverse; I have no slated target dates for completion, nor any upcoming launch that I "need" new airframes for. That said, I do NEED some time at the workbench to preserve my sanity and I haven't built anything significant since October, so things should progress at the hare's pace.

-Eric-

Never have I been so intimidated by such a tiny rocket! Eric's mini offerings are unique; kind of cute little things, but totally foreign to me in terms of airframe material. PVC: we all know it and love? it, yet as a rocket airframe...its just different, maybe less than ideal. Let's "build" this thing, shall we?

The kit came in a little clear plastic bag. PVC :eyepop: airframe, G-10 fins, aluminum centering rings, wood nosecone, little stainless screws, Top Flight 12" thin mil, and lots of noseweight! Had to go buy "PVC Cleaner"...man what a buzz from that stuff:cyclops: and plastic epoxy. Not sure about the plastic epoxy stuff, but I figure that Loctite makes a decent product and this is *only* a mid power kit, so it'll be fine.



I started construction on this tiny critter last night. Loop the cord through the forward centering ring, tie a knot. Clean the airframe with PVC cleaner.:eyepop:



Push the ring into the airframe, align holes, and use those little threaded things to secure the ring in place. Clean the airframe with PVC cleaner. Work quick or melt the airframe. :eyepop:

Install the aft ring in place using four screws. Clean the airframe with PVC cleaner. Work quick or melt your nostrils. :eyepop:



Test fit a motor. Confirm Eric's note that SU motors need their thrust ring turned down in order to slide fully into the rocket. Grumble and make a mental note. Go to bed after washing my face with PVC cleaner. Why am I seeing double? The stairs are moving. The Christmas tree grew arms and is chasing me. Good grief. :eyepop:

Next step: scuff and glue fins....and rinse stuff with PVC cleaner. :eyepop:

-Eric-

On the other end of the spectrum, we have a 5.5" Saab. Largely inspired by the Dynacom 5" Saab from long ago, this thing is pieced together primarily with leftovers and scraps.

A few years back I picked up a Rocketry Warehouse Sublime from Gary Pletzer. No offense to RW or Sublime owners, but I find the rocket rather fugly. I did however find the array of parts, the price, and the lovely lime color attractive! The 4" tubes got used for some minimum diameter stuff, the nosecone was sold, and that left me a few 5.5" fiberglass parts: namely a 14" section of airframe and a 5.5" to 4" transition. The Wildman had a odd length (~43") of airframe, and I had some off spec (undersized OD) G-12 coupler material. Put it all together and we get a gnarly looking semi scale Saab.

Taking measurements and doing some scaling, a fin template was created on the backside of a foam sign abandoned following a GB Packer game. Measure twice, cut once, trace perimeters, and determine that I need a McMaster worth of 3/16" G-10.



Duct tape, a placeholder nosecone, and a Mt. Dew for scale and my drinking pleasure:



No the actual missile does not have a boat tail. Yes, this incarnation will. Totally scale: no. Looks neat: yes.

5.5" diameter, 4" motor mount, should be fun!

More to come....

-Eric-

Subscribed!

Are you going to slide all the fins back onto the fincan , because that would look friggen awsome . It will look like a saab cross breed with a hawk missle .

Eric

Glad to see you doing anoter thread.
I will be patiently watching. Congrats on the new job but the free time reduction sucks.
op:

Congrats on the new job!

I'll be looking in on this build op:

I'll be on the SAAB assembly line too, having ordered the -98 from Wildman. Looking forward to all the build threads.

I'm curious as to why putting some screws through the airframe into an aluminum ring required using the PVC cleaner at all, let alone such a liberal application?

Thanks Chris, Tom, and K'Tesh!

Eric: I think the aft fins will fall on the boat tail, but the forward fins will be forward of the reduced section...time will tell. I did order the fin stock from McMaster...will be doing lots of cutting and beveling following Christmas!

Matthew: good point; I wondered the same thing. I may have exaggerated the amount of cleaner used just a bit, but I did end up using it far more than anticipated. The only real necessary time to use it was prior to bonding the fins, and I think alcohol would probably work just as well. Oh well! :eyepop:. I don't have the Wildman offerings in hand yet, we're planning a pick up at an upcoming launch, though I'm certainly looking forward to getting my hands on them!

-Eric-

Back to the little critter. You know, I was pondering the thought if this mini missile is a high power rocket. Don't really want a debate, but it has several aluminum components, and metal nose weight, so despite the 24mm mount, I'm thinking it is. To eliminate any doubt, I vow to fly the bird on a 24-6G load. More specifically, the G100 skid. >80 N of average thrust, and spits sparks to remove any subjectivity! Plus I like that little motor....flew a 4" rocket on one once...ironic to fly a 4" rocket on a 24mm motor. I digress.

The G-10 were scuffed. I gave an honest effort at trying to follow the instructions which requested I scuff the fin roots with 60 grit paper. I did one side of one fin that way which brought me to the point of *screw this*! I regressed to my normal method of scuffing G-10 which uses a Dremel and the course sanding drum; one has to be somewhat careful not to severely modify the shape of the fins with this method, but suits my level of impatience.

Clean the fins with tack cloth, wipe the airframe with some solvent type stinky stuff and tack fins in place with medium Zap CA. I've used lots of CA in my life, and they're not all created equal. Thin and Medium Zap are my friends. One of the fins was not to my liking, so I tore it off after curing...this was an intentional step to test the bond strength of the G-10 to PVC:wink:. Pretty impressive, I must say; no doubt that this mating along would be sufficient to survive any motor that fits in the pipe.

Tack:


Aft fins cured (a hearty 20 second cure time!). So we tack the forward fins. Plastic clamps and mixing sticks make for "close 'nuff" alignment.

Tack^2:



Man this thing is tiny...about the size of an average low power rocket that typically flies on 18mm B-C engines. Cute little devil:



Part III of the mini assembly coming later this week if I can sneak away from the Holiday Hubbub. Should be able to complete construction this week.

-Eric-

Lovely bird. I am terribly missing Eric here....

I ordered one of the Wildman Saab Sports too. I'm looking forward to the build. I haven't built a FG rocket in about 14 years.

I think the fins should move back and the aft fins should be inline with the front ones, not canted with the tailcone if that makes sense. it may make things a little more difficult to build but it will look awesome and the CP will be much better without the mass of the motor hanging out behind the fins.

Holy Cats, thanks for the wakeup call, Dan!

Where were we? Who knows.

Where are we now? Not quite sure, but somewhere around here:

Finished up the little Badazz critter….haven’t flown it yet. Was going to in mid-January but the wind talked me out of it! Did fly the pair of F44W’s and 1 of the 2 went poof, so I’m happy that I kept that motor out of the lil’ Saab. Hopefully I’ll add some jazzy paint and stickers once the winter thaw is over and get it airborn.

In the meantime, the first two local (Tripoli Wisconsin) launches of the year were cancelled due to cold and wind…now this is a hardy group…truly cold and harsh winds caused cancellation. Dad (Tom) did run down to a Woosh launch in February to pick up a load of goods from the Wildman. Following inspection of the sport Saab, 4” Saab (and of course a Punisher), everything was set aside until I could regain a bit of focus on this Saab story. While planning out the 2015 calendar year (a bit OCD, but I’m busy darnit!), we put together plans of attending this month’s QCRS launch in Princeton, IL. Love flying at Princeton, and my wife loves to tell you how she absolutely hates that I “have to” have a new rocket for every “significant” launch I attend! Anytime I go to Princeton, it’s a significant launch....so I might as well build a Saab quick!

So on to the 4” dia, 3” hole Saab-er. True, the new 4” nosecones aren’t in my hands yet, but I happen to have a 4” Jart DD and a CTI K740 fully prepped…if I borrow that nosecone from the Jart and pull the K740 from No Thunder, this thing is darn near ready to fly already! So here we go!

But first, here’s the basic parts layout of the Sport in the foreground and the 4” bird in the background. No phancy photography here, just a collection of parts following unboxing…and a pair of Aeropacks (not included in kits).



...to be continued...today, not two months from now!...

-Eric-

Step 1: ogle at parts, figure out where stuff goes, and take several breaths of fresh air in anticipation of sniffing, snorting, eating, and wearing fiberglass dust in the very near future. The 4” kit (and the 2.2” too I believe) came with 6 centering rings. Not 2 or 3, but 6! You may certainly choose to use all 6; I’m going to go with 4, though 2 is probably sufficient.

Step 2: Grind stuff. Let’s start with the motor mount. As a start, the motor mounts gets into a fight with the dremel and a 60 grit sanding drum. If only they made a 36 grit drum… Anyway, grind where the Aeropack and fin tabs go, I’ll get to the centering ring bands later. Clean up the ID and scuff four centering rings while we’re dremel drumming.



Remove dust and JB weld the 3” retainer in place. Slide the aft CR into place, tack the forward side with medium CA, and blend the excess JB on the forward end of the retainer into a nice little fillet with the ring. Set aside to dry overnight. Work on other projects in the meantime.

Measure fin slot locations on the airframe and match that to the desired position of the progressing motor mount assembly. I marked the forward edge of each of the fin tabs every 90 degrees about the circumference with a metal file. As can be seen below, the motor tube heads back out to the garage for another fight with the Dremel. While I’m at it, an area on the forward end of the motor mount tube gets scuffed for Kevlar harness anchoring. Since we're having so much fun, went ahead and scuffed the OD of the main airframe where the fins will go and the ID where the rings will contact.



The dust is once again rinsed, wiped, licked, and slurped off the surfaces to be bonded, then the remaining three centering rings get tacked into place on the forward side of the file notches using medium CA (Zap Med. green is da bomb). Knock off the forward-most centering ring with a hammer after you remember that you have to epoxy the Kevlar strap in place and notch the ring accordingly before tacking in place…doh!

Pretend you don’t see darkened color of the filleted forward side and this step looks excitingly like this!



20 grams of RocketPoxy is mixed for strap attachment and filleting purposes…an intentionally small batch! Strap is attached, forward ring is tacked with medium CA (suddenly there is a recovery strap notch in there!), and SMALL fillets are applied to only the forward side of the centering rings. The fin tabs meet up with the aft side of the centering rings, so the tab-to-ring joint will be bonded with slight filleting involved.



Quick explanation of intent here: the Saab is like those other crazy missiles with lots of forward fin surface that are semi-stable and intended to be guided with steerable fins in the rear…ie: they need a lot of noseweight, a really light rear end, or both in order to fly in a predictable and stable model-rocketry intended fashion! Thus my omission of two centering rings and a serious rationing of epoxy fillets. As many others have pointed out, the rocketry community tends to overbuild. In the case of the Saab, it’s clearly not a performance based model, but I’m still going to try to keep it light in the rear and minimize the required nose weight. Plus, assuming I’m borrowing the nose from the 4” Jart for the first flight, I’d rather not add more mass to that nose which is already properly ballasted for that model. Enough babble, moral of the story is to keep added mass in the rear to a minimum.

…to be continued…in the fairly near future!

-Eric-

I've been waffling on this project! I’ve had plenty of other distractions that have made these builds an “on again/off again" occurrence. I regressed into “off” mode after the motor mount assembly until this past Saturday when the highly anticipated 4” poly cone showed up from Wildman. I took that as an omen to hurry up and finish the 4” Saab before this coming Saturday’s QCRS launch! So, here we go again, this time in fast forward motion!

Aforementioned super new plastic pointy thingy (along with a myriad of other distractions on the bench):



The motor mount was installed into the airframe by sparingly adding Rocketpoxy to the centering ring-airframe ID joints. No photos of this non-photo producing step.

Then on to fins! Rough up anything to be bonded. In prior photos, the scuffed areas of the airframe are visible…I like to scuff airframes before installing the motor mount because otherwise you trap all that fiber dust which inhibits good clean bonding! Rough up the fins well…again anywhere the ‘poxy touches.

Almost forgot...sunny skies and temps above freezing coerced me into beveling the supplied fins a bit more...just 'cause! The aft fins are pretty tiny, had to be really careful to not bevel fingers. Beveled the leading and trailing edges of the aft fins and added bevels to the trailing edge of the forward fins while I was at it.



Check the stash of fin alignment guides…plenty of 4 fin slotted guides of different diameters; even a 4” guide, but with 3 fins. Quick make a new guide out of foam using a fresh #11. Mix up a few grams of Rocketpoxy, tack cloth the fins, epoxy things in place. Align with the guide and tape in place to make sure nothing shifts around. Ponder life for a while....hey I just saw the first robin of the season (a big deal for us eskimos up here). Go Wisconsin, yeah Michigan St., Wichita St. just messed up my bracket!:eyepop:



Early in the morning, rising to the street, light me up that AP motor, and I strap shoes on my feet, deee de de de deet. (love Sublime and did have a little rocket launch on Saturday morning). Aft fins tacked, destroy the shiny surface of the forward fin bonding areas. 'Nother batch of poxy, 'nother set of tacking. The fin tabs were a bit long….could’ve sanded them down but I opted toward speed, laziness, and a slightly greater fin span, and simply added enough epoxy to fill the slight gap between the fin root and the OD of the airframe…no biggie. Aligned using the foam guide and secured in place by mummifying the fins with masking tape.



Clean up that mess on the bench from Saturday's local launch while letting things cure for a while, then on to fillets. Though Rocketpoxy stays mostly where you put it, it will sag thanks to gravity. Thus, one side at a time allowing for a few hours of gel time in between sides. I took this opportunity to play with some of the variety of pigments supplied with the Black Saturday Rocketpoxy (great) deal!

Yellow!



Doing two opposite sides yellow and the remaining sides orange. Kind of a roll pattern to see this thing twist and tumble across the sky until I get paint on it.



CP: Oh nelly, figured out where I think the CP is on this critter. It ain’t pretty, but I figured that in advance. In short, she’s gonna need quite a bit of nose weight! While waiting for fillets to set up, I stole a K740 C-star and the 75-54mm adapter out of No Thunder, put a chute, nomex, and some ¾” tubular nylon in the nose to start figuring out how much ballast is needed up front. To reiterate: keep it as light as possible in the rear and plan for to add some weight up front! Will let y’all know how much I end up adding after all the filleting and e-bay work are done.

That’s about all for now. Will update as I get a chance! First planned flight this Saturday, March 28th.

-Eric-

ECayemberg said:

First planned flight this Saturday, March 28th.

Click to expand...

:clap:

rfjustin said:

:clap:

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Looking forward to seeing you in Princeton, Justin!!!!

Worked on the e-bay last night; nose weight determination on deck for this evening!

-Eric-

For all the lurkers out there, I put the av bay together over the last night or two. Installed recovery system, took a deep breath and duct taped the empty Red Solo Cup near the tip of the nose cone. Ballast was added until the CG was .75 calibers ahead of my normally fairly conservative (compared to others' and an unnamed *evil* design program) CP.

I will not tell the masses how much mass to add; that would be irresponsible on my part, as everyone builds differently, and even calculates CP’s differently. I will say this:

A) It is significant!

B) It took up roughly 5.5” of valuable space in the nose…cone is 19.125” long with the phenolic tip and bulkhead, I have 11” leftover, 3.375” of that is reserved for the coupler sliding into the cone. So, I’m down to 7.625” of useable space for harness, nomex, and chute…yikes!

C) I have 4” and 5.5” rockets (loaded) that weigh 1 lb less than the ballast added!

D) I could not fly just the ballast without an FAA waiver

E) The chute I had planned for the entire rocket is provides a safe descent rate for just the ballast alone.

F) There’s only one other rocket that I’ve ever built the came close to this much ballast. Not a flying pumpkin, nor a flying tree, nor even a 20 motor cluster 3 stager.

G) Once again: keep the rear end light to minimize the (significant) amount of noseweight needed up front….I know I’ve said this before and I’ll continue saying it! Where I calculated the CP, mostly anything other than the nosecone is aft of the CG!

Ponder this: on a typical rocket, where does the CP lie? Forward of the fins somewhere, yes? How long are the fins on the Saab? If the CP is forward, or even near the forward ends of the forward fins, where does that place the desired CP; then the desired CG? Yep, it’s way far forward. Semi stable missiles intended to be guided by the moving aft fins countered with heavy warheads, turned into model rockets with fixed fins and lacking the warhead equals a lot of noseweight. Suffice it to say, I added an inert warhead worth of ballast! Not a rant, just something to keep in mind with this and similar models!

I do have some concerns about the new cone collapsing under thrust with all that mass in the tip...we shall see on Saturday if all goes as planned...

I’ll throw up uke:some photos sometime in the future in case anyone is listening.:wink:

-Eric-

ECayemberg said:

I’ll throw up uke:some photos sometime in the future in case anyone is listening.:wink:

Click to expand...

Damn, that be a lot of weight...

If all goes according to plan, I will see you Saturday morning. Get your brows interview ready... :lol:



Justin

Eric, it is a cool looking rocket. That being said, it is a missile designed for active guidance. These sort of rockets are poor things to model for the reasons you mentioned.

That being said, the Cp should be about the mid-point of the forward fins. So, my guess is that you have so much nose weight that you cannot fit an adequate chute and harness.

Maybe it is time to reverse the deployment scheme. Put the drogue in the nose, shear pin the coupler bay to the body, and put the main in the body.

Do you really need a 4" x 8" alt bay? I was thinking that maybe you could glue a bulkhead in the middle of the coupler and use the extra 4" for the chute in the nose. I've already considered this for my 3" version.

Best thread of 2015.

Thanks Mark and Chris for the responses. I'm on the road but will respond more fully when I get a chance. In the meantime, yes I am considering options for recovery...I'm using a pre-existing alt sled for now which limits creativity a bit, but I'll see what I can do. Regarding cp, my calculated location is somewhere in the root of the forward fins, but is definitely forward of the root chord mid point. I'm sure my figures disagree with Rocksim but that's just the way I roll.:wink:

blackbrandt said:

Best thread of 2015.

Click to expand...

Why thanks Matt! More to come...

Eric

Now if only you would bring all of these to LDRS.

Hi Eric, Nice thread on the SAAB. I just finished mine and also will be launching DA SAAB at QCRS this Saturday Match 28th as well. I like your cool florescent Rocketpoxy fillets. I mixed the Flo yellow and Flo green together with Rocketpoxy to get a Flo Alien green for my fillets. Hey wasn't the ballast on this design lot's of fun, I also had to triple check all my sims of the CP and painfully added a hellova lot of ballast weight to get the CG correct, even then I didn't believe it, so checked again and yeah it is exactly like that. Cool looking rocket but quite a challenge to build correctly, definitely not for the faint of heart.

jolevich said:

Hi Eric, Nice thread on the SAAB. I just finished mine and also will be launching DA SAAB at QCRS this Saturday Match 28th as well. I like your cool florescent Rocketpoxy fillets. I mixed the Flo yellow and Flo green together with Rocketpoxy to get a Flo Alien green for my fillets. Hey wasn't the ballast on this design lot's of fun, I also had to triple check all my sims of the CP and painfully added a hellova lot of ballast weight to get the CG correct, even then I didn't believe it, so checked again and yeah it is exactly like that. Cool looking rocket but quite a challenge to build correctly, definitely not for the faint of heart.

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John; that's awesome! Looking forward to both our flights! Love your fillets and thanks for all the neat pigments and great deal at black sat. Just got home from your neighborhood a few minutes ago. Gonna be 4 days in a row driving back and forth to Illinois...sheesh.

Eric

So does someone want to actually say how much nose weight they had to use incase I see one of these at the field this year?

Sounds terrifying.