A Saab Story

Dan , my SIM is showing about 7.75 pounds. I'm sure those who have them will be more exact.

Eric

ECayemberg said:

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:

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Eric, it all depends on whether you use Barrowman or Rocksim method. Either way, the Cp is really far forward- uncomfortably so.

I think it is nothing a foot or two of additional tube would not fix. Either that or a few depleted uranium slugs for the nosecone.

So spill it- how much nose weight did you actually use?

Letters c and d in my ballast post give a pretty good indication. Just finished prepping her for the maiden voyage tomorrow. I am without decent camera this weekend but hope someone can get photos and/or video of the flight whether "nominal" or not!

Eric

markkoelsch said:

Eric, it all depends on whether you use Barrowman or Rocksim method. Either way, the Cp is really far forward- uncomfortably so.

I think it is nothing a foot or two of additional tube would not fix. Either that or a few depleted uranium slugs for the nosecone.

So spill it- how much nose weight did you actually use?

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Will spill my beans post flight tomorrow. Want to see how johns and mine perform so I can hopefully intelligently say "x" amount did or did not work well in my case.

Eric

ECayemberg said:

Letters c and d in my ballast post give a pretty good indication. Just finished prepping her for the maiden voyage tomorrow. I am without decent camera this weekend but hope someone can get photos and/or video of the flight whether "nominal" or not!

Eric

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Okay, so more than 3.3#, and a loaded Magnum is at least 8-9#, no glass. An EZi is probably 6 loaded, so I am somewhere between 3.3 and 7 lbs.

So, steel 4-40 shear pins?

patelldp said:

Okay, so more than 3.3#, and a loaded Magnum is at least 8-9#, no glass. An EZi is probably 6 loaded, so I am somewhere between 3.3 and 7 lbs.

So, steel 4-40 shear pins?

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If this is the case I really think fitting a large enough chute into the nose is very doubtful.

So, how'd it go? I'm pretty curious to see what the nose weight was.

Eric's rocket was first off the pad and it went straight as an arrow. I'll let Eric, provide the details. Totally awesome flight.

Will post a full recap on Monday...

In the meantime John flew his on a 54-4G K550W with 1.5 lbs in the nose. I flew mine with a 54-4G K740 C-Star with 4 lbs. Both flew and recovered safely; they did fly differently.

Though I'm not thrilled that I have 4lbs in the nose, I am pleased with how it flew! 7000'-ish.

Eric

It was a great flight... Loved the nose first descent under drogue

4lbs is significantly less than I anticipated. Does the sim get worse if you use the 76mm mount?

And looked something like this

3stoogesrocketry said:

Dan , my SIM is showing about 7.75 pounds. I'm sure those who have them will be more exact.

Eric

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Hey Eric, clear out your PM box.

Done and thanks for the heads up.


Eric

Thanks for the Thread, will be taking my SAAB-98 to LUNAR HP launch next weekend.

Where did this day go? I intended to post a big debrief, but I'm short on time, so here's the brief debrief!

The 4” Saab turned in its first flight at the QCRS launch in Princeton, IL on Saturday, March 28th. The end.








:wink:

A few more specifics

Motor: CTI 54-4G K740 C-star. The rocket was balanced with the K740; requiring 4 lbs of noseweight in order to reach a CG location I was satisfied with.

Electronics: Two Adept 22’s were along for the ride, controlling apogee and main deployments at 900’, 600’ AGL respectively. They rode on a glassed plywood sled that I made years ago and has housed a pair of Adept 22’s and corresponding 9V batts for a while now.

Recovery: Apogee/Drogue Section: There was plenty of room in the main airframe for 30’+ of 1” Kevlar strap harness and a drogue…I used a Top Flight 18” Ultra X for a drogue. A Com-Spec tracker affixed to the harness was housed in this section also.

Recovery: Low Alt/Main Section: The nose could be classified as a confined space, but I will say that careful packing had the 15’ of 9/16” tubular nylon, nomex cord and chute protectors, Top Flight 58” standard chute, a pair of ejection charges, and a partridge in a pear tree had everything in there comfortably on the first try without having to put the nose and body tube into a hydraulic press for closure. Being a glutton for punishment, I might just try to fit a 70” chute in there in the future (though the 58” did just fine).

Launch: Though Bong is my home HPR field, I run down to Princeton every chance I get. The home of the infamous Midwest Power and in Tim “Wildman” Lehr’s backyard, the QCRS launches are just about the most fun….you can finish the sentence. With temps in the mid 30’s to low 40’s, clear skies, and winds topping out at 5mph, it made for a perfect day of flying. Always a blast! Anyway, a good crowd was on hand for the monthly launch, with all the rockets prepped, I selected the Saab as my first flight of the day, which happened to be the first flight of the day at the launch.

Poised for Action:



4" Saab met 8' 1010 rail, 200' of cord, and away she went! A slight tilt off the pad into the slight wind, but arrow straight after that. See Dennis's very swell photos in his post above Thanks Dennis! ...And a quick crappy cell phone vid here:

https://s49.photobucket.com/user/ECayemberg/media/Winter%202015/042_zpsb8kbarzv.mp4.html

The nosey Saab coasted for quite a while to her apogee of 7000' where the tiny 18" drogue deployed. As semi-expected, the mass of the nose outweighed the air-snatching ability of the little chute and she descended nose first in a safe, controlled, yet quick descent. At 900', the tightly packed (not rolled) chute blossomed, and the Miss Ile settled gently to the ground. I was genuinely surprised at the descent rate... so much so that I took vid of the descent....it was significantly slower than anticipated. I would guesstimate around 23 feet per second under main. Here's a super clear still::wink:



No damage, happy endings, here she is resting after her flight.



For reference, here is John's version on a K550W. Both Saabs flew with noseweight without doing loops....I'm impressed!

https://s49.photobucket.com/user/ECayemberg/media/Winter%202015/051_zpsqa3btehc.mp4.html

More to come...

That looks great David. I'm looking forward to seeing it on Saturday.

robbdm said:

Thanks for the Thread, will be taking my SAAB-98 to LUNAR HP launch next weekend.

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robbdm said:

Thanks for the Thread, will be taking my SAAB-98 to LUNAR HP launch next weekend.

View attachment 259520

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Seconded what Chris says! David, that looks great! What's the motor of choice for your maiden?

Good luck, sir!

-Eric-

Hey Eric,

Did you attempt to keep the nose tip removable or did you just dump in the ballast? I'm going to have to add an extension onto the eyebolt on mine otherwise the eye will be buried in the ballast.


Chris

patelldp said:

4lbs is significantly less than I anticipated. Does the sim get worse if you use the 76mm mount?

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According to my mental (in)capabilities, Yes. The majority of the airframe is aft of the CP, thus any additional mass (increased propellant diameter going from 54 -> 75) is going to hurt the cause. In the case of more conventional rockets, usually longer motors place a grain or two above the CP, helping the cause slightly...in this case I think longer motors will run into the nose cone shoulder before helping the CG!

Not trying to discourage anyone from this model...but like John O stated earlier, this one is not for the faint of heart. Keep her light in the rear and shift everything as far forward as it goes! Quick note: I recessed the motor into the airframe until I could barely get the retainer off...shifting the motor as far forward as possible.



-Eric-

ChrisAttebery said:

Hey Eric,

Did you attempt to keep the nose tip removable or did you just dump in the ballast? I'm going to have to add an extension onto the eyebolt on mine otherwise the eye will be buried in the ballast.

Chris

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Hey Chris,

Tied the tubular nylon onto the eyebolt, sheathed in a nomex cord protector, installed the eyebolt (epoxied the tip in place to provide a seal), then dumped and poured around it. The nomex provides protection for the cord so it doesn't get brittle (if that actually happens?). I thought of doing a removable/changeable weight system but opted for simplicity. If I went to something like a 75-3G motor, I'd probably have to add more mass to the nose.:eyepop:.

-Eric-

What's the motor of choice for your maiden?

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Low slow flight with Aerotech J401FJ, 3.000 ft. Added 1 lb of ballast to nose cone tip.

Wow, I'm surprised you can get away with that little ballast. I'm looking at 18-24oz. on my 3" version.

Just add a couple feet of airframe- things will look much better.

ECayemberg said:

No damage, happy endings, here she is resting after her flight.

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Eric- what's the little black FG rocket above the Saab in the picture? The one with the tailcone.

Your thread is making me really want a large saab rocket for my collection

markkoelsch said:

Just add a couple feet of airframe- things will look much better.

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Except that it won't look like a semi-scale Saab anymore. I know, everything is a balance...literally!

djs said:

Eric- what's the little black FG rocket above the Saab in the picture? The one with the tailcone.

Your thread is making me really want a large saab rocket for my collection

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'Tis a 4" Jart with an Aeropack 98-54mm tailcone. Dual deploy (head end ejection), built last year on the eve of the Thunderstruck J115 moon Skid drag race. :dark:

I copied the tail cone idea from another flyer in our area...Griffin maybe?!?! That bird looks a lot nicer with a cone in my opinion. Flew well on an AMW J365 Skidmark on Saturday to 5858'. It also shows that I've been lazy and need to start painting rockets sooner rather than later!!!

-Eric-

Hi Eric
Nice looking chute in the picture, what size is it? The rocket looks great also. Yes I am finding myself going to rockets I don't need to paint. Never was no good at painting. I did do all yellow fillets.

See Ya

Top Flight 58” standard chute

See post #46

Eric,
Awesome to see and beyond what I want to take on. Wish I was at some of the launches this year but the new job is a launch killer. Not to derail this thread, so message me, but every time I see top flight I for some reason thin RC plane. Seem to remember a P51 being built as hinted to in a rocket build photo. Any progress?