Bomarc "A" with twin tractor motors and rocket boost

[burkefj]

I'm experimenting with putting two small tractor electric motors in the tips of the ramjet pods and using the rear mounted E-6 or E-12 RC load for boost, then transition to electric powered cruise.

I've got the model built, profile in depron, waiting for the receiver and second motor before I do some thrust testing. The rtf rocket will be around 13 ounces RTF and 2 ounces more with the twin motors attached. I can pop the motors off and fly it as a bg if I want.

It was a bit hard to get the white wrap/stripe to conform to the cruciform shape and still look straight from many angles, but I made the best compromise I could. Again, the top view nose looks short because it is above the centerline so needs to be a bit shorter than the side view profile.

You can see the motor mounts on the ramjet pods before painting, I just taped some spinners in place for effect if I fly it without motors.

Enjoy

Frank

 

[burkefj]

A shot from the front showing the prop clearance.

 

[T-Rex]

what about using ducted fans?

 

[burkefj]

It's possible, but the motors in edf's are typically a bit behind the intake so would put more weight toward the rear, and the duct itself would be heavier than the profile. Keep in mind since it lands on the pods now you have to reinforce a cage around the duct to support the landing load, or devise some sort of skid arrangement that transfers the load to the struts. On something with a diameter this small the thrust would probably be too low to be interesting given the AUW, Especially for 24mm, much over 16 ounces it's hard to have a motor with mild thrust needed for boost.

However, upscaled like my larger bomarc can carry a lot more weight so would be an option. It took a lot of nose weight to balance, so I could easily run enough battery to power twin edf's in a 3-4" tube size.

We'll see if this works first.

what about using ducted fans?

 

[WillMarchant]

Cool project! You could add deployable landing gear as they did with test series Navahos. Or you could pop a parachute for the final landing...

 

[burkefj]

Well, the day went sort of strange today.

Got the twin motors mounted and did current and thrust measurements, more than 1:1 on thrust, and 15.5 ounces rtf.

Got out to the site, weather not too bad. Got the Bomarc ready and realized I didnt' bring my battery adapter for the launch controller.

Back home and return and get things set up. I had set it up with an E-12 reload. Got all ready and hit the button, and it ignited and proceeded to just sit on the pad burning the propellent slowly for a minute..

Went back and looked at the remaining reloads, seems Aerotech screwed up and on the E-12 which is supposed to be a slot burner, they had just slotted the end like the E-6 reload which is an end burner, that's why it never made any thrust, a blackjack end burner doesn't work that well.

Back home, find an F-12 reload, slice off 1/16" so that the forward insulator will fit(that's what the e-12 is, a slightly shorter F-12 with a forward insulator). Back to the pad.

Now the thing won't ignite. many tries, cleaning the clips, etc, and turns out my plug adapater for the power supply has a 3 amp fuse and it blew. Now it's raining.

So, I'm thinking I can use the jump start clamps on the battery instead, except they don't close all the way, as they are set up for a car battery terminal. Turns out I can get creative and grab one of the deans connector leads with one clamp, slide in my xacto blade under the other pin and clamp on to that. Get the launch controller ready and away she goes.

Boost was toward the ramjet pods as expected, straightened it up, but it didn't go very high. Just too heavy and draggy with the windmilling props.

Go into glide trim, seems ok, so I throttle up the ramjets. They pitch the model up as expected so I take off the glide trim setting and it cruises around ok. Just doesn't seem to have much power to climb, adequate for cruise but just not what I had hoped for. Battery wears down so I throttle down, put in glide trim and make a nice landing.

I decided it just is a crappy combination of too heavy/draggy for a gentle 24mm boost, and the the twin motors are sufficient but not great, anything bigger will be too heavy and make the first problem worse.

So, off come the motors, and convert it back to just rocket glider. Rain got the inside of the motor mount making it wet, so it was a bit hard to get my reload casing out.

Take it back out on an E-6, flight is ok, it's a bit too windy so the boost is fighting the wind a bit. Glide was ok, figure a higher thrust motor will be better with this model.

Back home, grab/make another E-12 and back to the field. This time the wind is off and on, I wait 5 minutes to get a break in the wind, and the wind blows the launch pad over, right on top of the Bomarc and breaks the pods and the models spine. It is dead. That's what happens when you build extremely light, they just won't stand up to being crushed by a 2 pound tripod and launch rod.

Well, I'll never launch again without spikes in the launch pad legs.

Just one of those days.....It was worth the try though.

Frank

 

[[POW]Eagle159]

I guess you HAVE to make ANOTHER rocket!:wink:





Just think about it that way!

 

[burkefj]

Yeah, gotta get back on that horse.....and re-use the parts.....I'm already cutting.....

I guess you HAVE to make ANOTHER rocket!:wink:





Just think about it that way!

 

[aerostadt]

How do you find time to do all this stuff?

 

[burkefj]

Well, mostly 9-midnight after the kids are gone to bed.....a bit on the weekends....Less sleep than needed, etc...

How do you find time to do all this stuff?