My Madcow 2.6 Bomarc build thread

[Wally Ferrer]

Back to it, I added rail buttons instead of the lugs. I used Scott Binder's method of drilling, CA glue, sand and re- drill. A dab of epoxy just for grins.

 

[Wally Ferrer]

Added the parachute, with a swivel, so now I need to start finishing. I haven't glued the ramjet parts in, as I may eventually figure out the 3D print files for those. Hit a small problem, I thought I had another tub of CWF, but I only had a wee bit left. I am resisting going out for some, and it seems it will take a week or so to get some shipped. No worries, I have a lot of other kits to work on, but this build is on a break until I get that filler. I dilute it with a bit of water until thin enough to brush on. I find I can sand it within a couple of hours and generally get good results, but if I leave it at least overnight, I get much better results so I am no longer in a hurry when I hit this stage. Usually one very light sanding with a fine grit leave me with a very smooth surface ready for primer/paint. These balsa cones make me think I'll need a second application. I am going to just set it aside for a week, maybe I'll get lucky and the extra time will work for those.

 

[Nytrunner]

I haven't glued the ramjet parts in, as I may eventually figure out the 3D print files for those

Do you need .stl files made for those?

Send me the dimensions and I can whip them up in no time

 

[Wally Ferrer]

Do you need .stl files made for those?

Send me the dimensions and I can whip them up in no time

Thanks Nytrunner, earlier in this thread KevinM was kind enough to provide a zip file with some sldprt files and a dxf file. He said he made these for his Bomarc, the photo he included really makes me want to get these printed, see upthread. I really don't know anything about 3D printing. I was trying to confirm the files he sent before I try to find someone to print them- my niece isn't going to be able to. I'm having trouble seeing them as I would expect to- maybe it's me, or my viewer. I was going to try installing one of the recommended free CAD programs to see if I can see the parts correctly- what I don't see is the center cone and want to confirm it's there before I bother asking anyone to print it for me.

 

[Wally Ferrer]

The online Autodesk viewer reports an error on the .dxf file:

AutoCAD-InvalidFile Sorry, the drawing file is invalid and cannot be viewed. - Please try to recover the file in AutoCAD, and upload it again to view.

TranslationWorker-InternalFailure Unrecoverable exit code from extractor: -1073741831

It does open the sldprt files, and it does show the ramjet intake, woot!

 

[Wally Ferrer]

Do you need .stl files made for those?

Send me the dimensions and I can whip them up in no time

The ramjet is in two parts, without the 'webs' to connect the inner and outer parts- that's what's in the .dxf file. Do you think you could perhaps re-create those, or make a file that would print as a single model adding the webs, as Kevin called them?

 

[Nytrunner]

The ramjet is in two parts, without the 'webs' to connect the inner and outer parts- that's what's in the .dxf file. Do you think you could perhaps re-create those, or make a file that would print as a single model adding the webs, as Kevin called them?

Take a couple pics and some measurements. I can certainly try!

 

[Wally Ferrer]

Take a couple pics and some measurements. I can certainly try!

Are you able to use/modify the files provided by Kevin? I didn't re-post them but I can if you need me to. I'm not entirely sure what I would measure for spacers between the inner and outer cones. Are you asking for the tube diameter and pics of the balsa part? I certainly appreciate anything you might do to help me get these done...

 

[Nytrunner]

I'll pm you my email so we don't further clutter your proper build thread

 

[KevinM]

Would it help if I posted a screen grab of the .DXF file? If you're willing to go to the trouble of making use of the files I'll do what ever I can to help you out with that. Or feel free to shoot me a PM. I've benefited from others here who've gone out of their way to help me on my past projects, and I'm happy to do the same to pay it forward.

 

[Wally Ferrer]

Would it help if I posted a screen grab of the .DXF file? If you're willing to go to the trouble of making use of the files I'll do what ever I can to help you out with that. Or feel free to shoot me a PM. I've benefited from others here who've gone out of their way to help me on my past projects, and I'm happy to do the same to pay it forward.

Hi Kevin- Nytrunner was amazing and updated the file to be a single part, I am attaching it here. I thank you both so very much!

 

[Jim Hinton]

Hi Folks, Hi Wally;
I hope nobody minds too much if I jump in with a question here. I am finishing a MadCow Bomarc right now as well. I am at the point where I need to get serious about the CP/CG. There has been some discussion on this in the forum, I haven't seen a definitive resolution to the issue. MadCow states that with a weight in the motor mount simulating the largest engine to be used, the CG should be 23.5 " from the nose tip. Allowing 1 BT diameter of stability, that puts the CP at 26.1 " back from the nose. Rocksim says that the CP is at 30.9" back from the nose. That's a difference of about 4.8 ". That is going to make a big difference in the amount of nose weight required. I know that wing will definitely push the CP forward, the CG as suggested by MadCow is right at the LE of the wing. I don't want to put the anvil from the RoadRunner and Coyote cartoons in the NC. Has anyone out there balanced one of these in a manner other than what the kit instructions specify? Thanks for your help folks. I'll go away and leave this thread alone now.

Jim

 

[Wally Ferrer]

Hi Folks, Hi Wally;
I hope nobody minds too much if I jump in with a question here. I am finishing a MadCow Bomarc right now as well. I am at the point where I need to get serious about the CP/CG. There has been some discussion on this in the forum, I haven't seen a definitive resolution to the issue. MadCow states that with a weight in the motor mount simulating the largest engine to be used, the CG should be 23.5 " from the nose tip. Allowing 1 BT diameter of stability, that puts the CP at 26.1 " back from the nose. Rocksim says that the CP is at 30.9" back from the nose. That's a difference of about 4.8 ". That is going to make a big difference in the amount of nose weight required. I know that wing will definitely push the CP forward, the CG as suggested by MadCow is right at the LE of the wing. I don't want to put the anvil from the RoadRunner and Coyote cartoons in the NC. Has anyone out there balanced one of these in a manner other than what the kit instructions specify? Thanks for your help folks. I'll go away and leave this thread alone now.

Jim

I certainly don't mind, I have been thinking about this as well. As I have yet to complete the build, I haven't checked the CG yet, but I was going to follow what is in the kit instructions. I generally trust that unless I am going way extreme on the motor sizing, a designed kit will usually be stable for flight. As I go up in rocket size I recognize that it starts to become more of my responsibility to ensure the stability as the consequences of it NOT being stable grow. Now, looking at what you stated, rocksim puts the CP even further back than 1 BT diameter if your CG is actually at 23.5" from the nose tip which would be more than adequate for stability. You want a minimum of one BT, but more is not a real issue other than perhaps making it over-stable? Unless I am missing something, with a CG at 23.5 inches form nose tip and CP at 30.9 inches from nose tip, there would be no need to add any nose weight.

 

[AfterBurners]

Added the parachute, with a swivel, so now I need to start finishing. I haven't glued the ramjet parts in, as I may eventually figure out the 3D print files for those. Hit a small problem, I thought I had another tub of CWF, but I only had a wee bit left. I am resisting going out for some, and it seems it will take a week or so to get some shipped. No worries, I have a lot of other kits to work on, but this build is on a break until I get that filler. I dilute it with a bit of water until thin enough to brush on. I find I can sand it within a couple of hours and generally get good results, but if I leave it at least overnight, I get much better results so I am no longer in a hurry when I hit this stage. Usually one very light sanding with a fine grit leave me with a very smooth surface ready for primer/paint. These balsa cones make me think I'll need a second application. I am going to just set it aside for a week, maybe I'll get lucky and the extra time will work for those.

View attachment 412960 View attachment 412961 View attachment 412962 View attachment 412963I id

I didn't know you could still buy CWF? All I see now is the purple stuff that changes color when it dries. I have seen people use water on the purple stuff to thin it down and it seems to work fine. I'm not and never tried it.

 

[Jim Hinton]

I certainly don't mind, I have been thinking about this as well. As I have yet to complete the build, I haven't checked the CG yet, but I was going to follow what is in the kit instructions. I generally trust that unless I am going way extreme on the motor sizing, a designed kit will usually be stable for flight. As I go up in rocket size I recognize that it starts to become more of my responsibility to ensure the stability as the consequences of it NOT being stable grow. Now, looking at what you stated, rocksim puts the CP even further back than 1 BT diameter if your CG is actually at 23.5" from the nose tip which would be more than adequate for stability. You want a minimum of one BT, but more is not a real issue other than perhaps making it over-stable? Unless I am missing something, with a CG at 23.5 inches form nose tip and CP at 30.9 inches from nose tip, there would be no need to add any nose weight.

Nose weight in fairly large amounts will be required with either set of CP/CG. It's just a matter of degrees. With the 23.5 " CG, mine will require copious nose weight to balance with no motor. I was hoping that maybe somebody had built and flown one based on the RockSim CP. Being a bold explorer makes me nervous. I'll stay in touch and post anything that I find out.

Jim

 

[Wally Ferrer]

I didn't know you could still buy CWF? All I see now is the purple stuff that changes color when it dries. I have seen people use water on the purple stuff to thin it down and it seems to work fine. I'm not and never tried it.

I use DAP Plastic Latex Based Wood Filler...

 

[Wally Ferrer]

Nose weight in fairly large amounts will be required with either set of CP/CG. It's just a matter of degrees. With the 23.5 " CG, mine will require copious nose weight to balance with no motor. I was hoping that maybe somebody had built and flown one based on the RockSim CP. Being a bold explorer makes me nervous. I'll stay in touch and post anything that I find out.

Jim

Oh ok, I see what you are saying. I haven't gotten to that point yet, I will post what I come up with.

 

[KevinM]

Nose weight in fairly large amounts will be required with either set of CP/CG. It's just a matter of degrees. With the 23.5 " CG, mine will require copious nose weight to balance with no motor. I was hoping that maybe somebody had built and flown one based on the RockSim CP. Being a bold explorer makes me nervous. I'll stay in touch and post anything that I find out.

Jim

I hope Wally doesn't feel like I'm "crashing the thread again", but hopefully this will bound the areas for your bold exploration. I've attached the OpenRocket file I built up around my BOMARC. It's been tweaked to be accurate for weight and CG location that I flew with, has buried notes for what motors I used and how the flights went, what delay settings worked, etc... Feel free to PM any questions.

We now end this public service announcement and return you to your regularly scheduled build thread!

 

[Jim Hinton]

I hope Wally doesn't feel like I'm "crashing the thread again", but hopefully this will bound the areas for your bold exploration. I've attached the OpenRocket file I built up around my BOMARC. It's been tweaked to be accurate for weight and CG location that I flew with, has buried notes for what motors I used and how the flights went, what delay settings worked, etc... Feel free to PM any questions.

We now end this public service announcement and return you to your regularly scheduled build thread!

Wow Kevin, thank you very much, that is just the kind of information that I was hoping for. I will definitely check these out as soon as I am back to my home PC. It has Open Rocket installed. Thanks again, and thank you Wally for your patience.

Jim

 

[Wally Ferrer]

No worries, I expect to benefit from the info as well. I need to update this thread with the result of the collaboration to generate the 3D printed ramjets.



The key here is ramjets is plural, but I only ordered one. The second one has been ordered...

 

[Mhight]

Wally how much does your printed ramjet weigh? I printed one out it came out 2.6oz using petg filament
my balsa one weighs .8 oz
thanks for posting your build

 

[Wally Ferrer]

Wally how much does your printed ramjet weigh? I printed one out it came out 2.6oz using petg filament
my balsa one weighs .8 oz
thanks for posting your build

Straight out of the box 2.14 oz. I will likely be lightly sanding it to smooth out slightly, don't know yet if I'll add any material to get the tip looking better. I can't imagine the weight changing too much.

 

[Nytrunner]

Nice! Looks pretty solid (I was worried I made the ribs too thin)

 

[Wally Ferrer]

Nice! Looks pretty solid (I was worried I made the ribs too thin)

I am very pleased... thanks again!

 

[Wally Ferrer]

Ok, with wood filler in hand I continue to paint it on, will let it dry at least overnight before I start to sand.

 

[Wally Ferrer]

Got shipping notice for my other ramjet...

 

[G-Dog]

Got shipping notice for my other ramjet...

Excellent. Ive been following along, I happen to be assembling this same kit right now, although Im a little behind you. Im eager to see how your ramjets workout because Im considering changing mine as well.

 

[Wally Ferrer]

I need to start sanding, I'm sure it will surprise everyone it is my least favorite part of any build. But also one of the most satisfying, as the rockets I have taken the time to (mostly) fill spirals and wood grain are my favorites in the long run. They just look better, so obviously they fly better too! I may wait and sand tomorrow, giving most of the filler more than 24 hours to fully set.

 

[Wally Ferrer]

Couldn't put it off any longer, going slow so I don't over-sand...

 

[Nytrunner]

Now that looks like a disgusting amount of wood filler.

How much did you thin it down?