"LowBotomy" --- a MPR Parkflyer

er, something to keep in mind, the NAR certified delay time for the F39-6 is only 3 seconds*, while I haven't timed it I have seen that, an F39 - 6 works nicely in my Big Daddy's (which need about a 4 - 5 second delay).
*according to the AT instructions/data sheet visable w/o opening the package.
rex

Rex R said:

er, something to keep in mind, the NAR certified delay time for the F39-6 is only 3 seconds*, while I haven't timed it I have seen that, an F39 - 6 works nicely in my Big Daddy's (which need about a 4 - 5 second delay).
*according to the AT instructions/data sheet visable w/o opening the package.
rex

Click to expand...

TY Rex as I really need 4 - 5. I would hate to cut down a 6 second by 1-2 seconds and end up w/ a 2 second delay.

thought maybe I ought to mention that before folks started drilling delays...and then complaining about short delays . hope it works out as planned.
rex

Rex R said:

er, something to keep in mind, the NAR certified delay time for the F39-6 is only 3 seconds*, while I haven't timed it I have seen that, an F39 - 6 works nicely in my Big Daddy's (which need about a 4 - 5 second delay).
*according to the AT instructions/data sheet visable w/o opening the package.
rex

Click to expand...

The datasheet is not showing that, however it does show a 3 sec. version, which is not in the AT catalog.
https://nar.org/SandT/pdf/Aerotech/F39.pdf

bill_s said:

The datasheet is not showing that, however it does show a 3 sec. version, which is not in the AT catalog.
https://nar.org/SandT/pdf/Aerotech/F39.pdf

Click to expand...

Will Research this out more carefully as I really need a 4-5 second delay (not a 3 or 6 second).

Working on the Fin Fillets tonight. Since I made the internal BT fin fillets really strong I figured I only need aerodynamic, decorative outer BT fin fillets.

I loaded LowBotomy into my fin jig and placed a 1/8 x 1/8 balsa strip into the fillet area as a spacer. I used this to align the masking tape along the fins and BT.

After the 4 strips of masking tape were in place I load the fillets with a liberal amount Tite Bond.

I 1st used my index finger to remove the bulk of excess Tite Bond. I then used my pinky finger to obtain the final fillet shape being careful along the forward and aft ends of the fins.

After both fillets were shaped, I immediately pulled the masking tape off. This left a very precise fin fillet requiring minimal sanding. I left the BT sitting in that position for 30 mins or so until the Tite Bond skimmed over substantially. After that I rotated the BT 1/4 turn and worked on the next set of fillets.

I'm very happy with how this came out and a larger fillet could be obtained using a 1/4 x 1/4 balsa spacer. I would use something other then my fingers to do the molding in this case.

Installed the 2 launch Lugs /w stand offs, using 30 min epoxy.

Lug stand off detail.

Tonight it was time to start finishing LowBotomy. I used the following rattle cans:

Dupli-Color Filler Primer FP101 -- A high build primer for filling in small scratches.
Dupli-Color MetalCast Ground Coat MC100 -- Needed if shooting a Metalcast paint on something other then chrome (Grey w/ chrome flakes.)
Dupli-Color MetalCast Red Anodized MC200 -- Shinny red -- name says it all.
Dupli-Color Perfect Match Universal Black Metallic BUN0090 -- A black metal flake.

Sanded heavily w/ 240 paper.
I started with 1 light coat and 1 medium coat of Filler Primer.
Sanded fairly heavily w/ 240 paper.
2 light coats and 1 medium coat of Filler Primer.
Sanded w/ 320 paper followed by lightly sanding w/ 400 paper.
3 light coats of Metalcast Ground Coat.

This is where I am tonight. Tomorrow I will shoot the nose cone with Black Metallic and parts of the BT with Red Anodized.

Pictured is the MetalCast Ground Coat. It is a grey primer w/ chrome flakes. (If you want a grey metal flake this might be for you.)

Almost finished. Today I shot the black on the NC and the red on the BT. In both cases I did 3 light coats followed by 1 medium coat. They are both awesome metal flake type colors and came out looking great.

I really like the red but you must use the ground coat 1st. Also w/ the red when you start to paint you have 1 hour to complete all your coats as you must finish spraying within a 1 hour time frame. You need to wait 10 minutes between coats so have a timer going and be prepared our you won't finish in the 1 hour time frame.

I originally planned on shooting some black on the BT but the more I look at LowBotomy the more I like the grey metal flake middle. Either way if I decide to shoot another color on the BT I have to wait 7 days for the red to be fully cured before proceeding.

This was the 1st time using Dupli-Color and I love it. My days of Krylon are officially over

Great finish, I use Duplicolor primers & metalspecs, I always wondered about how metalcast would come out on none chrome, thanks for the info. One question, did you use JB Weld exclusively as an epoxy?

TALON said:

........ One question, did you use JB Weld exclusively as an epoxy?

Click to expand...

Basically yes except on fin fillets. I might have saved a smige on the weight using something different (probably not noticeable on this sized rocket.) Another positive using Metalcast is that it is rated for 500 degrees so I used it to paint the inside of the BT Bottom where the motor exhaust would be.

It is really hard to get a good pic of the metal flake. It looks much better in person then the pictures show.

Now that LowBotomy is basically finished I took some accurate weight measurements. I then loaded the different weights into the simm to get accurate flight data. Posted below is some flight scenarios using different weight pellets and a F39-5 motor.

The file name says what number of weight pellets are used in that particular simm.

View attachment LowBotomy-F39-5--0pellets.pdf

View attachment LowBotomy-F39-5--2pellets.pdf

View attachment LowBotomy-F39-5--4pellets.pdf

View attachment LowBotomy-F39-5--6pellets.pdf

View attachment LowBotomy-F39-5--8pellets.pdf

It is really hard to get a good pic of the metal flake. It looks much better in person then the pictures show.

View attachment 118355[/QUOTE]

Yeh, it is hard to get a good pix of metalspecs, good luck, & thanks

LowBotomy was sitting on a launch pad in my game room. I went to clean the game room tonight and bumped into the rocket. Ahhh crap I broke one of the launch lugs off at the lug standoff area. I had made the lug standoff out of balsa stock --- what was I thinking :bang:

To rectify this I purposely broke the other lug off. I then glued both back on using medium CA. Tomorrow I will carefully sand along the BT/lug areas and then add a fillet of JB Weld to both sides of both lugs/standoffs.

Here is my launch lug fix. I carefully sanded the area where the Lug, Standoff, BT meet. I then added a fillet of JB Weld in that area (I tried to be as neat as possible.) This sort of sucks that it happened after the paint was applied but better now then when it's scootin off the rod. That would have been a disaster. Lesson learned.

Also I configured what I will use as a flight log. This is to track how accurate OpenRocket is compared to actual flight data. Of course I will load the different flight simms I used for that flight and fill in the rest of the data off the Altimeter 2. The PDF I posted is the basic format with 3 weight pellets simulation loaded.



View attachment FlightLog.pdf

I forgot to drill the Altimeter holes before I painted -- :sad: -- since the holes looked like crap after painting I went another route.

Per the instructions, I wanted three 1/8" holes in my BT. I looked around the house and picked out 3 aluminum "pop" rivets that had the correct hole size. I then used a Dremel cutoff wheel to cut the "head" off leaving a little flange. With a bit of sanding they looked right. I drilled the appropriate sized holes in the BT and used a tiny amount of medium CA to permanently install them.

My Jolly Logic Altimeter 2 came this week so I made a foam sleeve to protect it. I used 1/4" latex foam and some heavy duty packing tape. I would rather have used 1/8" latex foam but all I had laying around was 1/4". Not an issue as there is plenty of room in the 3" BT. The sleeve has 4 slits by the USB end so I can charge it without removing the sleeve. You can press just front of the screen to get to the on/off/menu button. You can still easily see the red/green LED light when charging.

I'm looking forward to hearing about the maiden flight! Your goals with this design are really interesting to me.

Yay the motors finally arrived today 3 paks of F39-6 (9 motors) and a extra 24/40 case so I can take 2 motors prepped and ready to go to the field. She is ready to go and will maiden soon :clap:

My initial flight will be using 4 weight pellets which should give me:

Altitude 378'
Stability 1.77
T/W 4.49:1
Velocity off 55" of rod 40.48 f/s

Keep your fingers crossed.

ckreef said:

Yay the motors finally arrived today 3 paks of F39-6 (9 motors) and a extra 24/40 case so I can take 2 motors prepped and ready to go to the field. She is ready to go and will maiden soon :clap:

My initial flight will be using 4 weight pellets which should give me:

Altitude 378'
Stability 1.77
T/W 4.49:1
Velocity off 55" of rod 40.48 f/s

Keep your fingers crossed.


View attachment 119583

Click to expand...

When is this maiden flight happening? I want to hear about it!

Not yet unfortunately. It's sitting ready to go. Winter was about to miss us completely up until LowBotomy was completed then winter finally decided to rear it's ugly head. I had one last good weekend but the motors didn't arrive in time. Since then it's been crappy weather.

The very first weekend of decent weather (that I don't have to work), I will hit the go button. I'm very excited and this weather is killin me.

Will post pics, video and a report no matter what the outcome of the maiden is.

I finally had a nice evening (sunny w/ 0mph winds) and got in 2 successful flights on F39-6's with the delay cut down. She definitely stuck to her name LowBotomy

Flight 1: Four weight pellets, F39-5, Apogee 250'

I hit the "Go" button and she spit out the ignitor. A few seconds later a small blue flame appeared. A second or so after that she got full ignition and Whooooooosh. Flight was straight and true. She came over at apogee and looked like she was going to lawn dart. :y: A few seconds of me yelling "pop, pop, pop ........" and ejection finally occurred at 144'. Parachute deployed without a hitch and she touched down without incident. Wiped the sweat off my brow :eyepop: I need to cut down the delay a little more for next flight.

Flight 2: One weight pellet, F39-4, Apogee 325'

I cut an additional second off the delay. Ignition occurred immediately. Flight was uneventful Ejection was still a little late. Parachute deployed and she landed without incident. I need to cut another 1/2 second off the delay.


It seems there is an art to cutting down the delay but I think I have a handle on it. I have two F39-3.5's loaded and ready for tomorrow. She does hold true to being a decent sized rocket on a MPR motor that can easily be launched in the middle of a baseball or football field without worry. The bright green 30" chute looks good coming down. I believe she's going to put on a good show time and time again.

I have some flight videos and should have some pics I can post. Unfortunately I left the launch video camera rolling so I have about 40 mins of video I need to sort through to get the few seconds of usable launch video separated out. The actual full flight videos was rerecorded by someone else but he will get me those tomorrow.

Here is a raw video of the Maiden launch.

The 1st part is full speed -- it happens quick -- you can see it spit out the ignitor and then the blue flame before full ignition. When I start saying "pop, pop, pop ...." watch the upper left corner of the video and you can see the last few feet of decent. This is only 250' (with a really late ejection so it comes down quick) and you can tell how close to the launch pad it touches down. You can almost hear me wiping my brow.

The second half is slow motion of the launch.

Once I get the full flight video I will compile/post a more proper video of both the 1st and 2nd flights. Just wanted to give you a sneak preview (of the Maiden launch). I will say the 2nd flight was a better show.

[YOUTUBE]cyjOr2p5k30[/YOUTUBE]

I flew two more times today on F39-3.5, I used no weight pellets to get the maximum altitude possible. It was a nice day but a little windy at around 10mph. No issues as low altitude means little drift even in windy conditions.

The 1st launch I forgot to start the altimeter It weather cocked a little into the wind but was a nice smooth flight.

The 2nd flight I got an apogee at 402'. So in my preliminary tests it looks like I have a usable range of around 250'-400'. More launches should confirm this. All launches so far have shown it is possible to do low altitude in a small park flyer field with a bigger rocket on a MPR motor

I did get the flight videos from yesterday but haven't had a chance to check them out. I also did some launch videos today with the camera directly below the launch pad looking up. Will post more videos soon.

Yea! Maiden flight a success! I'm glad you finally got a chance to fly this baby! And it looks like you've succeeded in meeting your design goals as well.

The videos are cool and I'm looking forward to the full-flight video and the others. That first flight looked like a nail-biter toward the end.

Congratulations!

ThirstyBarbarian said:

Yea! Maiden flight a success! I'm glad you finally got a chance to fly this baby! And it looks like you've succeeded in meeting your design goals as well.

The videos are cool and I'm looking forward to the full-flight video and the others. That first flight looked like a nail-biter toward the end.

Congratulations!

Click to expand...

Yea the 1st flight with the low altitude and long delay, I no longer have any nails That's what all the laughter in the end is all about. Me and a friend both thought she was toast for a few seconds.

I'm surprised she didn't zipper a bit on that one. She was coming down hard and fast when the ejection finally occurred.

Another sneak preview video. This is a full flight video of flight #2. F39-4 w/ 1 weight pellet, Apogee at 325' w/ ejection at 301'.

[YOUTUBE]0AG9aKwWR4o[/YOUTUBE]

This is the 3rd flight. F39-3.5 w/ 10 mph winds. About 400' apogee using zero weight pellets. Camera below the launch pad, looking up. In full speed, looking at the launch rod movement and the final parachute angle you can tell just how windy it was. That's what happens in 10 mph winds. She still touched down within 200'-250' of the launch pad.


In the slow motion part you can see her weather cock into the wind just as the motor burn ends.

HD video best viewed in full screen mode.

[YOUTUBE]Hk6wC7a7m-4[/YOUTUBE]

Wow, that's one really cool bird!!:headbang::headbang::headbang::w::w::w::w:

Will post more pics, videos and flight reports as they come but for now (after 4 launches) I wanted to sum up my thoughts on how this build went.


The goals as posted in the beginning:

1) Low altitude MPR capable of launching in local ball parks (altitude range of 250' - 750')
2) Based on the low cost AT 24/40 E & F reloads
3) Stable, sturdy and easy to use (multiple back to back launches)


How well did I accomplish my goals:

1) I came close. I got the 250' but short of the 750' (250'-400'). It does come down fast and doesn't drift far even with a decent 10mph wind so definitely launch-able in small ball parks. I'll give my self a "B+" on this goal.
2) Yup uses low cost 24/40 F reloads. I'll give myself an "B+" since it can't use E reloads to get the minimum altitude and thus the F reloads don't get me the maximum altitude.
3) She is big, bold and stable. With the Aeropack retainer, baffle's/nomex blanket, and sturdy design she is good to go for multiple launches without worry about rebuilding or breaking a fin. This is the best part of the build, I will give myself an "A+" on this goal.

Overall I guess this works out to a "A" or "A-" on obtaining the overall goals. I believe I could do a new rebuild with a few modifications to truly obtain all my original goals. It has been a great learning experience. Building from scratch like this is not much more difficult then kit building. You basically do the same work but you do have to design the rocket and you do have to source out your parts. Sourcing the parts was one of the harder aspects of this build. Cost I believe would be similar to kit building w/ a high quality kit.

I'm very happy with LowBotomy overall and expect her to have a long and entertaining life.

So the F39-6 is acting like a "6" for you? I just got some and see how they're marked "-6(3)* *NAR certified time" ... how confusing & noncommital. Googled and saw one person saying they tend to be in between, -6 being about -5 and -9 being about -7. The delay grain on the -9 is about 1/32" SHORTER than a F24-4W -- this would point to both expected to burn delay faster when the motor is thrusting, but the 39 no faster than the 24 (same pressure).

Your rocket is kind of similar to a Leviathan specs-wise but looks better, I prefer the pointier nose cones, there's always something lacking with the easy, econo route isn't there?