TRF Summer Buildoff: Chimera

[BABAR]

Not good at taking pics as I go, so here are the pics of the prototype.

From Webster



Simple Definition of chimera

1 Chimera : a monster from Greek mythology that breathes fire and has a lion's head, a goat's body, and a snake's tail


2 : something that exists only in the imagination and is not possible in reality

it is pronounced ki MEER ah

I guess we'll see. Main idea is something that is made of parts of something else.

In this case playing with the less common forms of recovery.
First, no parachutes
Second, no streamers

Also two stager
Also Clustered

Recovery types:
2 Gliders (puffed off the boosters)
Booster stage recovers by horizontal spin recovery (a really cool method that nobody seems to use)
Sustainer recovers by Air Brake recovery (although it will LOOK like a helicopter, and probably rotate a bit despite my best efforts.)

 

[BABAR]

Center core booster.
BT50 with 3 BT-20s (will fly on central C6-0, outboards are permanently attached and do not drop off and will go with A8-3s to C6-3s, depending on final mass.) The sustainer BTW is only single engine probably C6-3, will light off central C6-0.) Outboards will fire off the gliders about 3 seconds after separation.

This uses a ring fin. This has "windows" cut asymmetrically (think a water wheel with only two troughs.) After separation and release of gliders, as this falls the windows will induce a rotation which will result in a spin. By some weird rules of physics, spin will be perpendicular to the fall path, so will orient horizontal to the ground.

 

[BABAR]

Gliders will function as fins for the Chimera rocket total unit at launch. Because of this, they must be attached VERY firmly to maintain a perfect orientation. the "shaft" of each glider has a strip of carbon fiber on the inferior half which should protect it somewhat from the outboard booster nozzle plume. May need to put some mylar tape on the horizontal stabilizers to protect them as well. As mentioned, C6-0 will separate the sustainer from booster, the outboard engines have a delay of three seconds (may be looking for something with a 2 second delay if that is too long), when outboard booster engines fire ejection charge, will "puff" the gliders of the core booster.

I like the more delta winged booster better, but the balance was wrong. Yes, using two slightly different boosters will result in some asymmetric drag, but so far my experience with asymmetric drag has been still flies straight so long as orientation is right. on the final version however I expect perfectly "twinned" gliders.

 

[BABAR]

I confess I wonder if many of my helicopters operate more by air brake recovery than true helicopter recovery. I simply do not have the patience (or desire) to spend time air foiling or twisting rotors to get the perfect angle of attack at every point along the length of the rotor.
In any case, for "true" air brake recovery I am hoping this won't spin, but it probably will a bit. All the "brakes" on this are nearly identical to my rotor helicopters, except there is zero angle of attack. Because the brakes still integrate the fins, however, likely will induce a little asymmetric lift or drag, so may induce a bit of rotation.

 

[BABAR]

Trying something a little different, I have used this only a few times in the past.
Most helicopters use elastic to pull the rotors up, and some other mechanism (a separate rotor stop or a tether) to stop the rotors when they reach the correct dihedral angle.

In this case I have integrate the system. The black thingies are carbon fiber tips. Threaded through the tubes is monofilament fishing line, slides easily. The upper pulley is a disk cut out with a hole punch, with a little central drill hole in it. I use the same hole punch to punch a hole in the balsa, I glue the disk into the balsa with thick CA (then have to redrill out the central hole.)

Pull mechanism is attached to the brake (I made some quick releases so easy to install and replace.) Monofilament goes from brake through carbon fiber tube through the pulley hole into the rocket. Ends in a loop to which is attached elastic (in this case 3 rubber bands.) Partway down the core dowel of the rocket is a hook from a paper clip, easily attaches all 12 rubber bands, 3 each of the 4 brakes.)

At apogee (fingers crossed), ejection charge fires, melts the rubber band brake retainers (discussed below) and shoots out the blow out chamber (also discussed below). Brakes should start to open a bit here. The elastic pulls the monofilament, the filament pulls the rotors up. The carbon fiber will slide on the filament until it hits the pulley, at which point it stop at the preselected dihedral.

 

[dixontj93060]

Wow, pretty interesting! Loving this contest!

 

[BABAR]

One of the problems with long skinny rotors is getting the rotor opening "started." When the bands are stretched straight down the length of the rocket, there is no lateral "moment" of pull to get the rotors away from the body of the rocket.

The "blow out chamber" directs the ejection gases laterally right into the inside of the rotors (or in this case air brakes.) This should (fingers crossed) provide enough force to at least get the brakes moving outward from the central dowel. The further out the rotors get, the more favorable "pull" the monofilament will have to get those brakes all the way open.

Note the rubber band air brake retainers will also run right through the blast chamber directly in front of the engine, and will get appropriately burned to release the brake when ejection charge fires. Will discuss in detail below.

 

[dhbarr]

Well neato!

 

[BABAR]

This is a method that has worked will with my helicopters as well my "Spyder" camera rockets. I have had lots of things go wrong with rockets, but this hasn't failed me yet.

I use two #16 rubber bands for air brake retention. There are holes in each air brake just forward of the engine mount. This are reinforced with pieces of hotel key card with a hole punched in the middle, as the bands would otherwise cut into the balsa. The hotel key card plastic pieces are glued on with CA, and covered with mylar to make them a little more aerodynamic.

Crochet hooks are your friends here. The crochet hook goes all the way through from one air brake through the blast chamber in front of the engine and then through the OPPOSITE air brake.
Grab the rubber band, looping it over a finger.
Now pull the band all the way through the rocket, and loop it around your thumb on the other side.
Now take both ends and pull them down over the body tube. Note the body tube sticks out a bit here. On a helicopter I would just have the engine sticking out, but since this a two stage, I extended the tube.
Also note the little toothpicks at the base of the airbrake/fins. This keeps the band from sliding back between the brakes.

 

[BABAR]

This is my first experience with rail buttons.
I had initially planned to use launch lugs (the sharp eyes will notice the soda straws on the booster, which was my first plan, but didn't figure that would be sufficient.)

But for a rocket this long and complex, and given we usually have something around 10 MPH winds at our Club launches, figured i'd try the buttons. Got some from
https://rail-buttons.com/

(little plug here)
anyway got mini and micro, got a micro rail from amazon and a mini rail from Rail Buttons.com. This is my first try, but they look pretty slick.

Put two on the one of the brakes, with some stand off room to keep from rubbing against the bands. When I looked at them, I think I got them a bit close together, so I added a third more forward. I will fix this on the final version, this is just the prototype. I will just go with two a bit further apart.

Then reality struck...... I forgot about the ring fin. As I said above ,however, better to be lucky then good. The ring fins JUST BARELY fits around the rail, so I should be good IF I can get an attachment of the rail to the pad that just runs up inside one of the grooves (currently working on building a rail pad, will be my first.)

 

[KenECoyote]

Wow! Very cool! Love all those features in one! op:

Booster stage recovers by horizontal spin recovery (a really cool method that nobody seems to use)

You know what so funny about this to me? This morning I launched my 18mm spiral rocket and it went pretty high up and on the way down I noticed that the spiral spin can was spinning on the way down at about 45 degrees and I was thinking that with a light enough nose, I may not need a streamer due to some of what you called horizontal spin recovery!

 

[Cabernut]

Wow that's amazing! Really cool. I'm going to have to read through a couple more times and absorb, just absorb.

 

[Daddyisabar]

Wow that's amazing! Really cool. I'm going to have to read through a couple more times and absorb, just absorb.

Ditto. Mind is blown yet the Chimera name invokes much fear.

 

[rstaff3]

Skill level 10...

 

[Daddyisabar]

Skill level 10...

Dude, this one could even go to 11!

 

[Amsterdam]

this is so far over the top! I like that idea, "something made from something else's parts". The impossible flying Frankenstein.

 

[jqavins]

Very cool. Very very cool. If I wore a hat, I'd take it off. I lack some of the skill and lots of the patience to do something like this.

And yet, I just can't help myself...

I do have one concern and one suggestion. My concern is with the CF tubes poking through their stops on the brake panels and upper portion. How fast are they moving when they hit? If you've tried it and thought it through then I'm sure it'll be fine; if not, then you might want to, and maybe end up reinforcing a small area of the balsa with little discs of that key card.

And the suggestion regards the sustainer's fins. While I like fins that are in-plane with the sides (tangent to an imaginary body tube) I had the thought that if they were glued to the faces of the sides (closer to normal to the imaginary tube) then they would stick up above the plane of the brake panels after deployment, and that might help reduce or eliminate spin. I see that they can't be centered on the panels or they would intersect the glider pods, but that wouldn't stop you putting them on the faces if you want to.

 

[BABAR]

First, thanks for all the comments and suggestions. U guys often see things I haven't considered.

Regarding difficulty, maybe be a 3.5. Really not that hard, just a lot of outside the box stuff.
Regarding spin on fins due to asymmetric placement of fins on the edges of the blades/brakes--- I have done it with perpendicular fins for the Spyder Series, adds to complexity, a lot more breakable, and more importantly I really like that the fins work as FINS on take off and contribute to SURFACE AREA/BRAKIng on deployment ( I did this on gyskelion at same time it came out on Jim Flis' Tiddlywink) again this is is the essence of dual use. The fact that this will rotate is a bit annoying to the "purist" in me (is it air brake or helicopter), but since if it rotates it won't rotate much, and with flat blades and no angle of attack it isn't gonna get any lift, so it is pretty much all airbrake.

Regarding the carbon fiber balsa interaction, the hotel card disk/pulleys will be enough to keep it from poking through at the hub. The brake attachments are reinforced with toothpick frags.

What I really like about using the tubes is that once fully deployed, there is no "tension" on the blades. Once deployed, the tube functions as a strut.

 

[blackbrandt]

Did this end up flying?

 

[Pem Tech]

View attachment 294477View attachment 294478View attachment 294479View attachment 294480

Center core booster.
BT50 with 3 BT-20s (will fly on central C6-0, outboards are permanently attached and do not drop off and will go with A8-3s to C6-3s, depending on final mass.) The sustainer BTW is only single engine probably C6-3, will light off central C6-0.) Outboards will fire off the gliders about 3 seconds after separation.

This uses a ring fin. This has "windows" cut asymmetrically (think a water wheel with only two troughs.) After separation and release of gliders, as this falls the windows will induce a rotation which will result in a spin. By some weird rules of physics, spin will be perpendicular to the fall path, so will orient horizontal to the ground.

A ring fin with "windows" cut asymmetrically".
I wonder how this would effect a tube fin rocket without additional fins?

 

[LW Bercini]

As far as inducing spin, it may depend on the velocity. With my Fractal, I discovered there is spin only at low speed (during parachute recovery). At boost there is very little spin. I think because the airflow is directed though different sized channels, there is so much turbulence at higher speed that it actually inhibits spin.

 

[BABAR]

Did this end up flying?

Nope, I haven't put together my mini rail launcher yet. I also looked at the competition, and figured at best I'd get an honorable mention, so I'll bow out. Hopefully I will eventually launch this with my club in Memphis.

 

[BABAR]

should not be any spin on boost due to the windows. The rocket is stabilized by it's forward CG with the other parts. After separation, this section is unstable, tumbles, and the asymmetric windows kick in and begin a spin around the longitudinal axis, which actually get more powerful as it orients the rocket perpendicular to the path of fall/descent.

I have another rocket with standard lugs I will be launching soon, relying on this. Tentative name, Magnus Opum.