MEGA-Gyroc - 4" dia. 5.3x Upscale

[eugenefl]

thump-thump...thump-thump...thump-thump...it's coming...

a 4" DIAMETER MASSIVE GYROC!!!

See attached MMT diagram concept. Details coming soon.

 

[eugenefl]

DAY 2: More planning. So far all of the fin dimensions have been determined. The patterns were drawn out this evening. Now that templates are available I can move into the motor mount drawing/planning phase to more accurately design something functional.

I figure I will dissect this project into different sections. Several considerations have to be made for an upscale of this nature.

First and foremost, the weight has to be way under the scale proportion. Only the lightest materials will be used. These light materials will have to be reinforced in a composite fashion. I placed this project in the HPR forum because ideally I'll fly it on a low total impulse H. Ideally, a G75J or H165R should do the trick. Of course, motor selection is complete speculation until a finished weight is determined.

The second aspect of this project will definitely have to be the motor mount & fin flap actuation method. The original Gyroc used a single piece of elastic and so did my 2.6" dia. 29mm powered version. This massive upscale will probably have the tension of elastic unevenly spread in 3-4 places along the flap-span with the strongest tension occurring closest to the motor mount. With this in mind, tabs attached to an ejectable motor mount will make a return appearance.

The third consideration will have to be the fin material design. Fin weight was the biggest obstacle on the 2.6" dia version. Ply is out for this project. At this point in the game I am thinking a balsa ply. Perhaps multiple (3) layers of balsa compressed and glassed lightly will fit the bill.

The last objective is to secure a custom nosecone that can handle the impact of such a large rocket hitting the ground. Sorry sandman, but I think a balsa cone is out. Maybe a hard/heavy wood? I'll be needing noseweight after all. Should I integrate a spring cushion or replaceable foam impact cushion just behind the cone?

These are all factors to consider. To me it's a rather complex engineering feat. Whether it succeeds or fails I *will* have fun working on it. ALL feedback is encouraged.

 

[eugenefl]

With any project, realistic goals have to be realized. With the 2.6" dia MAXI-Gyroc I went through almost FOUR revisions before I got it right. I've accepted that despite proper planning foresight a disaster is possible. I figure going through upscales of this rocket from a BT60 and BT80 version that I've learned a thing or two about the characteristics of this rocket.

Here are a few goals regarding this project:

- it will not be a high altitude performer; altitudes of 800-1000ft would be considered high for this bird
- it will not be meant for speed. High impulse/thrust motors are out...low and slow is the key
- lightweight components typical of model rocketry such as balsa, foam, and lightweight airframe will be tested to their limits, but will be necessary to minimize weight. Proper reinforcement to form a more composite piece of material will be mandatory.

Alright...time to pack my "tartar sauce" and dive right in!

 

[eugenefl]

To wrap up DAY 2 of planning, I've drawn the MMT concept on the PC. See drawing. Feedback welcomed.

(Does this sound like a Darwin type project yet? )

 

[powderburner]

Instead of the internal dowels and tubes (to hold the motor pod from rotating and releasing the flaps early), why not just notch (top and bottom) the edges of your last two CRs so as to slide over some 1/4 x 1/4 spruce strips glued to the inside of the 4 inch BT? That gets rid of a bunch of parts, complexity, and weight. If you want to reinforce the CRs a bit, build an open-sided 'C' channel that spans between the CRs and slips over the side spruce strips. Taper the strips if you are afraid the CRs might bind. Email me if you need me to sketch this out.

 

[MarkABrown]

Eugene,
First, this sounds like a really cool project. I loved the way your 29mm Maxi Gyroc flew at Whitakers.

Second, I think you should consider making your MMT 38mm. You can always adapt it down to 29mm and it will give you many more motor choices to test with. Since you want to avoid the high impulse motors, 29mm becomes really limiting as your rocket's weight goes up. With 38mm, you've got a selection of BlackJack, Ellis Mountain and Pro38 motors.

Third, you should seriously consider the Honeycomb composite material sold by Giant Leap Rocketry. Talk to PAH. He's used the stuff and can attest to it's usefulness in construction and possibly it's weight savings.

Good luck. I'll be watching this one eagerly.

 

[eugenefl]

Originally posted by powderburner
Instead of the internal dowels and tubes (to hold the motor pod from rotating and releasing the flaps early), why not just notch (top and bottom) the edges of your last two CRs so as to slide over some 1/4 x 1/4 spruce strips glued to the inside of the 4 inch BT? That gets rid of a bunch of parts, complexity, and weight. If you want to reinforce the CRs a bit, build an open-sided 'C' channel that spans between the CRs and slips over the side spruce strips. Taper the strips if you are afraid the CRs might bind. Email me if you need me to sketch this out.

The dowel and sleeve serve two functions - they replace the fore centering rings and also hold the flaps in place. The centering rings will be the *only* components on this rocket that use 1/4" ply.

 

[lalligood]

FWIW, I think powderburner's idea for the MMT is smashingly simple & effective as it definitely reduces parts & potential points of failure.

And I wonder if a balsa NC would be the best solution. And from one Florida guy to another, seeing how eugenefl's launch site surely is a grassy field & the Gyroc will have the benefit of a small chute to aid in recovery, damage to a well made (& possibly slightly reinforced) balsa NC would probably be perfect for this design. Other than that, only thing I can think of is to build a disposable scratch NC out of foam (but allow room for adjustable nose weight) and have it in mind that the foam will crunch on impact so that it can be replaced with a new one as necessary (???)

Sounds like you're on the right track though! Good luck with the project

 

[eugenefl]

Originally posted by lalligood
FWIW, I think powderburner's idea for the MMT is smashingly simple & effective as it definitely reduces parts & potential points of failure.

And I wonder if a balsa NC would be the best solution. Sounds like you're on the right track though! Good luck with the project

The sleeve/dowel is absolutely essential as they will replace what would normally be a centering ring on the fore section. They perform a dual purpose. However, now that it's been mentioned, I may just utilize the sleeve/dowel to serve the function of centering rings. In addition, I would add the strips and notches to prevent the MMT from rotating the flaps out of position.

Balsa for a nosecone was never an option. There was a guy who was making fiberglass cones in round and in RPG shapes. I forgot his website, but I know he used to sell them regularly on ROL auctions.

Thanks for the input thus far.

 

[wyldbill]

Fin Material Suggestions: Consider using a balsa core and multiple layers of CF tissue (or VERY light CF cloth). You could use glass, but the CF is lighter and stiffer. At the airspeeds you're shooting for, you shouldn't need anything super beefy. You may want to build it sandwich style, using mutiple layers.Rohacell makes a good, very light core as well. The 51 pound comes in lots of thicknesses. If you want to go w/ 3mm, use the 71, it'll be stiffer. These folks also sell honeycomb core in 1/8" as well.

MMT Suggestion: Consider putting slots in the end of your BT and tabs on your pod to prevent the rotation. This is less complicated than your dowel approach and on the outside, where it'll be easier to repair if there are problems. You may want a full ring (even though its heavier) farther up the MMT to keep a pressure seal until the majority of the pod has exited the BT. It's suck if the pod got half ejected because of some unforseem friction in the system and ejection gases escaped as soon as the rear coupler cleared the aft end of the BT.

Elastic suggestion: Could you use springs of some kind instead of elastic? On a gyroc this large, I'd this beefy elastic could be a drag and point of failure. My hardware store stocks lots of weird little springs, could you use one instead? What about putting springs inside the BT and using a pushrod/horn arrangement ala RC airplane surface control?


FWIW,
-bill

 

[wyldbill]

Looks like CST is offering Rohacell/CF Panels now. Could be worth a look...

 

[powderburner]

Originally posted by wyldbill
Looks like CST is offering Rohacell/CF Panels now. Could be worth a look...

Yeah, CF wings would be nice, but a 12 x 12 panel of 1/4 inch CF is $74-------EACH.

wyldbill is exactly right, "you shouldn't need anything super beefy." Could you use plain old foam-core? I have used it successfully on a ~2x Gyroc (if you only cut one skin, the other side serves as a built-in hinge) and maybe if you add a spruce insert in the leading edge for a little more strength, it might stand up to low-thrust G power?

 

[wyldbill]

Originally posted by powderburner
Yeah, CF wings would be nice, but a 12 x 12 panel of 1/4 inch CF is $74-------EACH.

Absolutely true, but you can make your own for LOTS less. These panels probably have too much CF for this application. Having worked w/ Rohacell, I strongly recommed it, but balsa, though heavier, will probably work as well. Use a few layers of .5 oz. tissue on each side. FoamCore is an option, but probably heavier, and not nearly stiff enough in the required size. But it's LOTS cheaper. The other thing to consider is mounting hinges, elastic (if used) and the outboard fins in/on the fin material. It's gotta be hard enough to take the localized stresses.

 

[lalligood]

Originally posted by eugenefl
Balsa for a nosecone was never an option. There was a guy who was making fiberglass cones in round and in RPG shapes. I forgot his website, but I know he used to sell them regularly on ROL auctions.

Maybe you were looking for these?
https://www.rgmrocket.com/html/nosecones.html

 

[eugenefl]

Originally posted by lalligood
Maybe you were looking for these?
https://www.rgmrocket.com/html/nosecones.html

BINGO! Thanks Lance. I just ordered the nosecone. BTW, I'll probably take this thing out to NEFAR for a first flight whenever it is finished.

As for materials, I already have the 4" LOC body tube, MMT tubes (29 & 38), ply, rail buttons, balsa, resins & cloths, and other misc. odds and ends. The cone is now on order. Thanks for the link.

Tonight I'll probably cut out the templates so I can use them as a reference for the MMT build. I haven't decided what I'll do for fin material, but a lot of good ideas have surfaced in the short amount of time that I posted about this project.

Thanks all!

 

[lalligood]

Originally posted by eugenefl
BINGO! Thanks Lance. I just ordered the nosecone. BTW, I'll probably take this thing out to NEFAR for a first flight whenever it is finished.

No problem. Glad I could help BTW, I've been curious to know what RGM's components are like--please share your thoughts here when it arrives!

Definitely let me know when you plan to return to NEFAR. Perhaps we can arrange a (mini-)TRF gathering...

 

[eugenefl]

BUILD NOTES:

More work was done on the MEGA Gyroc this past week. Based on advice given here on the Forum, I've re-engineered the motor mount ejection system. This new design specifically addresses several issues regarding the forces that act upon centering rings upon boost.

FORWARD MMT & CENTERING:

I've decided to abandon the tube sleeves and dowel method for centering the forward part of the MMT. The tube/sleeve & dowels were also intended to prevent the flaps from rotating the MMT while under boost. The problem with this design is that in a normal rocket the front CR it is depended on during boost to retain the MMT from shooting through the airframe. I just can't see the previous design being practical since all of the pressure will apply to two small points on a CR. The new forward centering ring will actually be functional in centering the MMT tube except it won't be glued directly to the MMT tube - just to the body tube inner wall. This forward ring will serve as a "slip" ring. It's function will be to center the MMT tube and also serve as a MMT "stop" and allow the MMT tube to reverse or "slip" out once the ejection charge fires. Glued to the outside of the MMT tube will be a thrust ring that will press against the new "slip" ring therefore aiding in distributing the positive forces of thrust. Ahead of the forward "slip" ring is the compression and ejection gas "chamber." This area will be a fairly small pocket that will pressurize and get the MMT out of the rocket in a hurry. To avoid over-pressurizing this area and possibly blowing a hole in the side of the airframe, holes will be drilled in the forward "slip" ring to assist in venting pressure into the aft chamber.

AFT MMT & CENTERING:

The very aft centering ring will feature a dowel pin that will recess into a hole drilled into a "trap" centering ring. (Think of the "trap" ring as an oversized thrust ring found in smaller kits like the Estes Wizard. The "trap" ring by design is nothing more than a large "washer" that will be glued into place to assist in distributing the lift-off load. ) The aft CR itself will sit flush inside of the rear of the airframe. Ahead of the "trap" ring will be an airframe tube coupler glued into place. The aft "trap" ring and airframe tube coupler will function as a MMT "block". The removable MMT itself will have its own centering ring. When combined, upon boost the aft MMT centering ring pushes against the "trap" ring and tube coupler to evenly distribute the positive load placed on the entire MMT assembly during liftoff.

More pictures of the build process to come. The rings, couplers, and airframe parts are cut. I'm still waiting on the nosecone which should arrive soon. After the MMT fiasco is completed I will move onto the fin construction.

 

[eugenefl]

Originally posted by wyldbill

Elastic suggestion: Could you use springs of some kind instead of elastic? FWIW,
-bill

I will be heading out to a hardware store (ie - Ace) once work on the fins starts. I absolutely love this idea as opposed to elastic. Accurately calculating how much tension is need to keep the flaps in place is another issue.

NOSECONE - I thought of something the other day that I thought would help in protecting the nosecone after each flight. What if I cut a tennis ball in half and stuffed it with an impact absorbant material and strapped onto the tip for flights? It would simulate a helmet. Basically, the 1/2 tennis ball would have 4 pieces of elastic attached. These bands would act as chin straps which would be attached to 4 anchor points on the airframe. Sound ok? Always thinking....

 

[eugenefl]

Here are the new plans for the MMT. Please feel free to comment or make suggestions. Hopefully I'll have some build pics tomorrow.

 

[jetra2]

I think I see a problem there already, Eugene. As soon as that bottom centering ring pops off, there goes all of your pressure that you are depending on to deploy the flaps.

We need to talk!

Jason

 

[eugenefl]

Originally posted by jetra2
I think I see a problem there already, Eugene. As soon as that bottom centering ring pops off, there goes all of your pressure that you are depending on to deploy the flaps.

We need to talk!

Jason

You're misunderstanding the diagram. The aft CR is flush with the rear of the airframe for a reason. The ejection charge only needs to push the aft CR a 1/4" before it is free of the rocket. Gravity will take care of the rest. You've seen my 2.6x upscale. The concept is identical to the 2.6x except the pin that keeps the MMT from twisting is internal on this new design. On my 2.6x version, the ejection charge only needs to push the locking pin free of the external lug which is coincidentally about 1/4". Once that locking pin is free of the lug the flaps press freely against the MMT tabs. Regardless of whether the MMT has left the rocket, the flaps will snap into place.

I'm sure I've lost a few people on this design, but a lot is lost when chatting in text. Jason, the next time you come over I will show you. Better yet, once I start gluing parts the pictures will tell the tale.

 

[jetra2]

OOOOHHHH....I think I gots it now...so you'll be depending on how tense the elastic is to "spin" the MMT tabs out of the way once the ejection charge has freed the MMT from the locking pins...helluva cool idea, man!



Jason

 

[powderburner]

Originally posted by eugenefl
Here are the new plans for the MMT. Please feel free to comment or make suggestions.

Well eugene, this looks pretty nice. As I understand it, the MMT tube and aft CR (with anti-rotation pin) pop out the aft end and free-fall? Any chance of packing a streamer or small chute into the volume between the 'trap' ring and the 'slip' ring, probably wrapped around the MMT tube and covered with some flat wraps of estes-style ejection tissue (or a small blanket)? It would have to be wrapped kind of tight to avoid getting snagged on anything during ejection.

Looks like you are going to need to make the CRs out of light plywood for strength. And in your drawing (very nicely done, BTW) you seem to show a solid bulkhead just below your 'tube joint' that might also need to be lite ply?

An option for keeping the motor casing attached: you could use 99 percent of your same idea and parts but assemble slightly differently, and retain the MMT with the rocket during descent (I know, that means more weight pulling the rocket back down a bit harder). If you want to use a RMS and still have a good chance of recovering the motor, you could leave the 'slip' CR solid (unperforated, that is) and glue it to the MMT central tube, not to the inside of the BT walls. That way the ejection would pressurize the same little compartment and drive the MMT assembly backwards. The same pin/trapring would unlock in the same fashion, and the fins would deploy in the same way. When the 'slip' CR moved far enough aft it would be stopped by the aft tube coupler and 'trap' ring, and the MMT would be hanging out the back of your Gyroc. You could add overboard vent holes through the main BT at a location maybe 1/2 inch behind the takeoff position of the 'slip' CR so that after it begins to move aft, and unlatches the fins, the moving CR would uncover the vents and begin to depressurize the compartment. No, I didn't invent this, DynaSoar has this idea posted currently (in a different application) in another thread:
https://www.rocketryforum.com/showthread.php?threadid=8212

 

[wyldbill]

Originally posted by eugenefl
...The ejection charge only needs to push the aft CR a 1/4" before it is free of the rocket. Gravity will take care of the rest....

What if you get a bonus delay and the nose is already pointed down when the charge goes off?

-bill

 

[powderburner]

I'll take a shot at answering for eugenefl;
if you get a 'bonus delay' or if anything else happens, regardless of the orientation of the rocket at the time, when the ejection charge goes off I think the MMT piston is pretty much guaranteed to move
it will help if the fwd pressure bulkhead is solid and does not flex, but the ejection pressurization will move the MMT back regardless and it only has to move 1/4 inch to release the main flaps
after that, the MMT can do whatever it wants, like keep on going or stop in place, because with the flaps deployed the Gyroc will start 'coptering its way back

 

[eugenefl]

Originally posted by powderburner
Well eugene, this looks pretty nice. As I understand it, the MMT tube and aft CR (with anti-rotation pin) pop out the aft end and free-fall?

Looks like you are going to need to make the CRs out of light plywood for strength. And in your drawing (very nicely done, BTW) you seem to show a solid bulkhead...

An option for keeping the motor casing attached: [/url]

Outstanding observations. A few answers to your questions all integrated - The MMT does eject and come down under parachute. This is a feature already incorporated in the 2.6x Gyroc. The 9" chute is wrapped up like a normal chute and one or two turns of the Kevlar cord hold an Estes piece of wadding securely wrapped around the chute. It kinda looks like a tamale. (Good same wavelength thinking there!) All MMT components are made of 1/4" ply. Since the MMT area will be ejected, weight isn't a concern during the boost phase. You are correct about my drawing - there is a solid ply bulkhead just before the airframe coupler. I just forgot to label it. The coupler just ahead of it aides in distributing the pressure of the ejection charge. Although I understand your idea about having the entire MMT slide back as a piston, keeping the MMT attached isn't an option. It is going to add a significant amount of weight that I'd prefer to discard. I figure the MMT will come down under a 12"-14" nylon chute that will be wrapped nicely. The edge of the aft trap ring will be rounded and smooth to avoid any snag points.

Good thinking though. Thanks for your input.

 

[eugenefl]

Originally posted by wyldbill
What if you get a bonus delay and the nose is already pointed down when the charge goes off?

-bill

Bill, powderburner is absolutely correct. Regardless of which direction the Gyroc is pointed, the MMT just needs to slide that 1/4" out so that the pin locks allow the flaps to move freely. I would consider a complete MMT ejection a success. Ideally the cone will be pointed up and gravity will assist in "dropping" the mount out of the back end.

Another good observation. Thanks for chiming in.

 

[wyldbill]

K. My only concern was the weight of the MMT. I was thinking that overall weight would be greater if it didn't clear the body (but just popped the flaps and settled back) and that the additional weight (including the casing) might cause the 'copter to come in faster than desired....

 

[jetra2]

Hey, I just thought of something. Are you going to add noseweight, Eugene, to help the rocket WANT to point down when the flaps come out?

Jason

 

[eugenefl]

Originally posted by wyldbill
K. My only concern was the weight of the MMT. I was thinking that overall weight would be greater if it didn't clear the body (but just popped the flaps and settled back) and that the additional weight (including the casing) might cause the 'copter to come in faster than desired....

Believe me, it's a huge concern of mine as well! Much like any other rocket, a major concern is *always* going to be focused on the recovery system.

Jason, noseweight (being one of the more obvious parts of this build) will likely need to be added. This is a big reason why I have to construct the fins out of something *really* light. The 2.6x Gyroc has plenty of weight on it simply because of the ply fins. For its upscaled size and the choice of materials used, I think it is marginally overweight. Exactly how much noseweight will be necessary will be determined once it's assembled.