Flight Report Post 73 Complete post 69 Mariposa (Spanish Butterfly) PseudoKit

[BABAR]

Estimated skill level on a scale of 1 to 5...

93

Mind officially blown.

Bummer. I was hoping for a 3 or 4

 

[BABAR]

Deviating from plan for optional motor retention.

15.5 inch BT-20 tube.

Cut masking tape wraps to fit in hub.

Holes marked by placing inside rocket and marking through the band holes.

Cut a piece of aluminum can to fit inside, will serve as motor block and protect from blast.

 

[BABAR]

Holes

 

[BABAR]

Recheck to make sure holes align

 

[BABAR]

Sides are numbered so removable body tube can easily be swapped in and out

Looks backwards in pic, numbers match ADJACENT brakes

 

[Cape Byron]

Bummer. I was hoping for a 3 or 4

Hey, it doesn't mean I don't want one! Just wondering if my skills are up to it.

 

[BABAR]

Engine block, bulkhead, aluminum shield with holes

 

[BABAR]

Came out 93 grams with an A8-3 motor. Were I to build it again I would go with 1/16" fins and cheaters.

 

[BABAR]

Launch lugs on. I use paper straws. I do put one small one forward and a larger one on the back. these are not high performance Birds so I figure it doesn't really matter.

 

[BABAR]

Completed.
Pics in launch config
Post deploy pics with and without motor retention.

Without is a bit like the Estes Meteor Masher, drops a streamer bomb at deployment, in this case the motor casing. Both configs I think would pass most RSOs, but some fields may have different rules.

 

[mooffle]

Such a cool build, I love seeing innovative stuff like this!

 

[mooffle]

Have you ever tried a flexible joint towards the top of the tube like just a kevlar string? Everytime I recover my heli I worry that one of the blades will break.
Or do the blades still have enough flex in your design to make this a non issue?

 

[BABAR]

Have you ever tried a flexible joint towards the top of the tube like just a kevlar string? Everytime I recover my heli I worry that one of the blades will break.
Or do the blades still have enough flex in your design to make this a non issue?

I think your are suggesting a mobile joint between the anterior (nose end) of the body tube and the hub, and for Helis with motor retention that is a good thing. Most of mine HAVE no body tube or motor. So the heli comes down flat or planar, contact point is the mid Hub, and the bands actually function as shock absorbers as the tips of the rotors flex down with inertia and are pulled back up by the bands.

On those that have motor retention, usually I have a fixed tube, essentially a motor mount that runs all the way to the hub. Most of the time this isn’t a problem, but once in a while the rocket comes down vertically (good), spinning rapidly (also good), butt end of tube hits the ground (okay), Rocket whole tips over (not so good) and at least one rapidly spinning rotor hits the ground (bad).

A string, Kevlar or otherwise, especially with a swivel MAY allow the body tube to flow over WITHOUT angling the spinning blades laterally. What you give up here is strength of the body tube on boost (which is certainly do-able, as most of mine as I said have NO body tube or even a motor mount as such. The rotors themselves structurally function AS the body tube on boost phase. If you do this route, the downside is you need a stiffer rotor, at least 1/8”. If find 1/16” too flexible.

There are quite a number in this forum that reeeeeaaaallllly get uncomfortable with dropping a motor casing by itself. I have found a solution that works within I think both the letter and the spirit of the safety code, a flameproof crepe paper streamer on the casing. Actually makes it fit a bit tighter, works great, drops the casing with an easily visible locator and looks kind of cool (and since Estes made the Meteor Masher, a rocket that intentionally dropped
Streamer bombs

From
https://user.xmission.com/~huxley/rockets/meteormasher/index.htm#photos
Review
https://www.rocketreviews.com/estes-meteor-masher-donald-besaw-jr.html
It isn’t exactly uncharted territory.

I have thought about just a Kevlar string from the hub to the motor, just taped on, maybe with a swivel, but I am afraid it may tangle with the rotors on deployment.

 

[BABAR]

As @neil_w suggested, the butt joint without any overlapping reinforcement wasn't very strong and even before flying I could see that it was likely a failure point. I have to put these on the outside as there is no real good way of putting them on the inside here. So going back on this build where I could do it again it would have worked much better if I had just extended the spacers a little bit longer to cross the Gap. In addition, the motor sticks out a little bit further than it really needs to. I would make the side piece extender the tailpiece extenders 2 and 1/4 inches rather than just 2in. That would move my CG forward another quarter inch at least.

 

[neil_w]

I keep thinking about this. Although it is not taking everything into account, and might have problems that make it a dealbreaker, here is my proposal:

Essentially, eliminate the butt joint and the cheaters, replacing them with a piece of cross-grain balsa laminated on the outside. This simplifies construction enormously and eliminates the weak joint. Downsides are a bit more weight and drag (which honestly don't seem like much of an issue with a rocket like this.) Also, the fins are now partially mounted to the wood with the lengthwise grain, which might weaken them a bit, but with the reinforcement of the laminated piece I tend to doubt that's a problem either.

What do you think?

 

[mooffle]

I think your are suggesting a mobile joint between the anterior (nose end) of the body tube and the hub, and for Helis with motor retention that is a good thing. Most of mine HAVE no body tube or motor. So the heli comes down flat or planar, contact point is the mid Hub, and the bands actually function as shock absorbers as the tips of the rotors flex down with inertia and are pulled back up by the bands.

There are quite a number in this forum that reeeeeaaaallllly get uncomfortable with dropping a motor casing by itself. I have found a solution that works within I think both the letter and the spirit of the safety code, a flameproof crepe paper streamer on the casing. Actually makes it fit a bit tighter, works great, drops the casing with an easily visible locator and looks kind of cool (and since Estes made the Meteor Masher, a rocket that intentionally dropped

It isn’t exactly uncharted territory.

I have thought about just a Kevlar string from the hub to the motor, just taped on, maybe with a swivel, but I am afraid it may tangle with the rotors on deployment.

Yes that's a good description of what I was thinking. That also answers what I was going to ask next regarding how structural the central tube is vs the brakes.

As far as motor retention I like the design challenge having a rocket come down in one piece presents. Partially just to recover only one piece. The general uncomfortableness probably stems from that and fire hazards (maybe littering too?), being in Wisconsin dryness is almost never an issue for me. It's rather wet here.


Bonus points for the meteor masher, I always thought it was rad but never had one.

 

[BABAR]

I keep thinking about this. Although it is not taking everything into account, and might have problems that make it a dealbreaker, here is my proposal:
View attachment 443683
Essentially, eliminate the butt joint and the cheaters, replacing them with a piece of cross-grain balsa laminated on the outside. This simplifies construction enormously and eliminates the weak joint. Downsides are a bit more weight and drag (which honestly don't seem like much of an issue with a rocket like this.) Also, the fins are now partially mounted to the wood with the lengthwise grain, which might weaken them a bit, but with the reinforcement of the laminated piece I tend to doubt that's a problem either.

What do you think?

Would definitely work. The part you are missing is the inside spacer. It has two (and now 3) purposes.

1. My preference is for motor eject with NO DEDICATED MOTOR MOUNT. This saves a ton of weight for the helicopter, as it returns without the motor and with no body tube or engine hook or anything. I know this goes against the grain, but I have never had any problems or complaints with it. I don’t know that it is much of a fire hazard (less than an unstable rocket that does to ground while still firing thrust or delay), and aside from sod farms 18 and 24 mm motor casings IMO aren’t a big deal (I look for them and pick them up if I can find them, if not, they are biodegradable, not sure if they are a livestock hazard but I don’t launch on ranches, in fact usually I am in a park and I see much more non-biodegradable trash than the rare motor casing.). The PROBLEM is that in using the walls of the rotors as the de facto mount during boost, the inside diameter has to match the motor diameter (can add a bit for a wrap around streamer. Adding the internal 1/8” spacer allows me to make the blades 1/4” wider, which gives me more blade surface area and strength (better flyer and less likely to break.)

2. The internal spacer also sets up a kind of 1/2 of a “tongue in groove” arrangement when the rotors or air brakes are folded. It creates a much more structurally secure “box” to hold the motor in place.

Now add 3. Remember this is INTERNAL. So there is no drag penalty. If I just extend it 1/4 forward, it will overlap the butt joint on the outside and provide plenty of strength. The down side is that I will need to punch the rubber band hole through BOTH layers, but this is do-able, or I can just cut or sand out a notch in the internal spacer.

Your idea WOULD work, but not as well. If I do this again, I am going to use 1/16” for fins, these need to be on the lateral margins, and the grain direction will be prone to failure. In fact, it is the grain direction which is the ON,Y reason I use this technique for the Butterfly recovery. One of my next builds, the Typhoon Helicopter, will be a simpler build and take some lessons I learned from this one, plus using @mooffle ‘s idea (link isn’t coming up) with some modification, a short Kevlar loop, snap swivel, dowel (something straight to keep from tangling with rotors) and another Kevlar loop at the end to tape to the motor casing.). It will be completely removable (like this one) so can be flown with and without motor retention.

 

[neil_w]

My assumption was that the internal space remained as before, unaffected by the external arrangement, which is why I didn't show it or mention it. My goal was to eliminate the butt joint, and remove multiple assembly steps.

 

[BABAR]

Finally got to fly this one. Overall very pleased with it. Two videos attached. Doesn't go very high on an A8-3, but made for nice video since all components of flight are within the video.

In an attempt to please everyone (obviously a vain and foolish endeavor) this rocket is designed for both engine retention (for the more conservative RSOs) and for motor eject (still with a streamer on the motor, so I theeeeennnnk that most RSOs would pass this config as well). The A8-3 flight is without motor retention. the B6-4 flight is WITH motor retention.

First video is with handheld cell phone. Second is with "HatCam", which is nice because it is handsfree.

not sure why YouTube put an age restriction on the second video, I have appealed it.