Lakeroadster's X-Wing Alpha Build Thread

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Thanks for the heads up.

Very confident the X-wing won't be there.. but I might. Do I need any kind of blood initiation or can I just show up?

Any ideas when the event hours are?

Just show up with cool rockets. It is Tripoli's big two day event. Saturday and Sunday. Set up at 8AM when the wind is calm, fly at 9. COSROCs from Colorado Springs is there with all the LPR and MPR racks. Lots of HPR action and Sunday is research day where stuff happens that you have to be on the special part of the this forum to discuss. All the Top Men should be there. Go to Tripoli Colorado's website for more details.

Show up with you "C" motor plans and you might leave thinking of letters sliding down the back half of the alphabet!
 
Never mind then. ;)

Neil. Just get on a private jet and fly out for the weekend to party in South Park. No rocket eating trees like back East. The launch pad is already sitting at 8,800 feet above Sea Level! Like the old Mountain Man said: "Why be down in the low lands a eatin' on the hog when you can be up in the High Country a eatin' on the ELK!":)
 
Neil. Just get on a private jet and fly out for the weekend to party in South Park. No rocket eating trees like back East. The launch pad is already sitting at 8,800 feet above Sea Level! Like the old Mountain Man said: "Why be down in the low lands a eatin' on the hog when you can be up in the High Country a eatin' on the ELK!":)

OK, send over the jet in the morning. At 8800', I'll set my own personal altitude record before the launch button is pressed!
 
Did some more internal glueing of the tri-fold mount. basically covered the entire mount area with wood glue to help protect it from the engine ejection blast.

Also installed the Launch Lugs. They needed to be fairly long to cover the variation of CG due to different engine configurations. I used (2), one each side for symmetry and so they would look like 20 mm cannons borrowed from an F-16 ;)

I still need to add glue fillets to the lugs to blend them in to the body.

008.JPG

005.JPG

001.JPG
 
Last edited:
I like it!

I wouldn't worry too much about launch lug position, especially on that size of rocket. It'll stay straight pretty much wherever you put it... I just guesstimate for the length and put it so it's roughly around the CG in most configurations.
 
I like it!

I wouldn't worry too much about launch lug position, especially on that size of rocket. It'll stay straight pretty much wherever you put it... I just guesstimate for the length and put it so it's roughly around the CG in most configurations.

What? I gotta follow good engineering principals and run copious amounts of simulations so that the launch lug has to be centered on the center of gravity or Thor's hammer will hold me accountable.

Ah, the old symmetrical launch lug trick. Well played sir.

This is looking nice.

All b.s. aside.... Thanks guys.
 
Did some more internal glueing of the tri-fold mount. basically covered the entire mount area with wood glue to help protect it from the engine ejection blast.

Also installed the Launch Lugs. They needed to be fairly long to cover the variation of CG due to different engine configurations. I used (2), one each side for symmetry and so they would look like 20 mm cannons borrowed from an F-16 ;)

I still need to add glue fillets to the lugs to blend them in to the body.

I am a huge fan of dual purpose devices in Rocketry. So really like the lugs having both cosmetic and structural purposes. Bravo!
 
I'm thinking about bench testing the rocket. Today I ran some FEA, looking at stresses on the rocket if it is constrained via the nose cone.. or restrained via the front of the X-wings.

The wings (fins) seems to be the most logical approach. This would also allow testing of the ejection charge and recovery items.

The cockpit, being made from balsa, really affects deformation of the tube. Although stresses should never get to the point that it will ever be an issue... unless it goes lawn dart.

The nose cone looks wrong, and it is. Something about an ogive profile crashes the FEA program?
 

Attachments

  • Bench Test FEA Model.JPG
    Bench Test FEA Model.JPG
    68 KB · Views: 106
  • Bench Test Fins Restrained.JPG
    Bench Test Fins Restrained.JPG
    104.4 KB · Views: 96
  • Bench Test Nose Restrained.JPG
    Bench Test Nose Restrained.JPG
    106.9 KB · Views: 95
  • Bench Test Fins Restrained 2 to 1.JPG
    Bench Test Fins Restrained 2 to 1.JPG
    96.6 KB · Views: 100
  • Bench Test Nose Restrained 2 to 1.JPG
    Bench Test Nose Restrained 2 to 1.JPG
    93.6 KB · Views: 97
Last edited:
Nose is the only thing that I don't like about your model. Wondering if you could sand it down to a "wedge" like profile, flat top and flat bottom, chisel tip, to better mimic the original version.

Seems like with all that wing area in back shouldn't cause too much instability.
 
Nose is the only thing that I don't like about your model. Wondering if you could sand it down to a "wedge" like profile, flat top and flat bottom, chisel tip, to better mimic the original version.

Seems like with all that wing area in back shouldn't cause too much instability.

Great suggestion, thank you for your input.

Here's my first stab at it.... something like this?

I like it! ;)

Modified Nose Cone
X-wing Alpha 07-04-2018 .JPG
____________________________

Previous Nose Cone
X-Wing Front Three Quarter 06-08-2018.JPG
 
Last edited:
You have a weak spot combined with a concentration of load at the part of the body tube in front of the fins and behind the canopy and lugs. If you are able to install a coupler, or baffle, inside that part of the tube you can add some strength. A common damage point in rockets on landing is on the body tube right in front of the engine mount and fins. All of the ground impact is transmitted through the fins into the body and after the engine mount you have a weak spot.
 
You have a weak spot combined with a concentration of load at the part of the body tube in front of the fins and behind the canopy and lugs. If you are able to install a coupler, or baffle, inside that part of the tube you can add some strength. A common damage point in rockets on landing is on the body tube right in front of the engine mount and fins. All of the ground impact is transmitted through the fins into the body and after the engine mount you have a weak spot.

Agreed.... and thank you for your input.

It just so happens to have such reinforcement there. See post #110. The internal sleeve and tri-fold mount is glued right up against the engine thrust ring deep down inside the rocket.

The FEA models above... do not have the internal sleeve. I'll re-run the FEA tomorrow with the internal sleeve and the tri-fold mount integrally attached to the body tube.

Sheet 7 of 10 - Rev 6 - Exploded View.jpg
 
Last edited:
Here's the FEA showing the difference without the internal sleeve, and with the sleeve and tri-fold mount. Red is higher stress, blue less stress.

The internal sleeve drops the stresses significantly.


Flight Stress FEA with Internal Sleeve 07-04-2018.JPG Flight Stress FEA with Internal Sleeve Bottom View 07-04-2018.JPG Flight Stress FEA without Internal Sleeve 07-04-2018.JPG Flight Stress FEA without Internal Sleeve Bottom View 07-04-2018.JPG
 
Last edited:
Looking good. Might have a mighty tight parachute compartment.

The following idea won't change that, but might give you a better chance of a damage free recovery.

External shock cord mount.

Small loop on the ventral part of the rocket, placed at the CG of the core of the rocket POST deployment (balance point with EXPENDED engine casing and WITHOUT nose cone, chute, wadding, or shock cord.) Doesn't have to be exact, since you will likely place it before painting/finishing, might fudge a little bit tailward, since you will have more paint weight tailward than noseward.

Another option instead of a loop would be a small plastic or metal "bar" on the ventral surface, I'm sure you can actually make it look like a structural part of the fighter!

When displayed, shock cord is detached and stored in the rocket.

When prepping for flight, attach with small snap swivel, load wadding, chute, all of shock cord with a small length that runs from the attachment site to edge of body tube by nose cone (so specifically the shock cord is exposed along the ventral surface of the rocket--- still won't be seen much at launch time as it will be on the side where the launch rod is.)

On deployment, rocket dangles from the cord, cord is at CG so rocket falls roughly horizontal. Means that all the body tube and more importantly the fin surfaces will ALSO contribute to drag on descent, you'll be surprised how much that helps.

Just an idea. It's what I used on the Squirrel.

Tom
 
Looking good. Might have a mighty tight parachute compartment.

The following idea won't change that, but might give you a better chance of a damage free recovery.

External shock cord mount.

Small loop on the ventral part of the rocket, placed at the CG of the core of the rocket POST deployment (balance point with EXPENDED engine casing and WITHOUT nose cone, chute, wadding, or shock cord.) Doesn't have to be exact, since you will likely place it before painting/finishing, might fudge a little bit tailward, since you will have more paint weight tailward than noseward.

Another option instead of a loop would be a small plastic or metal "bar" on the ventral surface, I'm sure you can actually make it look like a structural part of the fighter!

When displayed, shock cord is detached and stored in the rocket.

When prepping for flight, attach with small snap swivel, load wadding, chute, all of shock cord with a small length that runs from the attachment site to edge of body tube by nose cone (so specifically the shock cord is exposed along the ventral surface of the rocket--- still won't be seen much at launch time as it will be on the side where the launch rod is.)

On deployment, rocket dangles from the cord, cord is at CG so rocket falls roughly horizontal. Means that all the body tube and more importantly the fin surfaces will ALSO contribute to drag on descent, you'll be surprised how much that helps.

Just an idea. It's what I used on the Squirrel.

Tom

oops, on the Squirrel I put it on dorsal side, it was hidden by the huge tail/dorsal fins.
 
...The internal sleeve drops the stresses significantly...

If you had already mounted the shock cord and had left that internal coupler out, you could also add strength using some external stiffeners that also fit in with the look of the rocket. For example, a strake on the ventral/dorsal fins that extends forward up to the canopy would do the trick to resist the vertical bending. The lugs could have been extended aft just past the LE of the Xwing fins for lateral bending strength also. But looks like the internal coupler you have in there should be fine. An external cardstock wrap is another option.
 
If you had already mounted the shock cord and had left that internal coupler out, you could also add strength using some external stiffeners that also fit in with the look of the rocket. For example, a strake on the ventral/dorsal fins that extends forward up to the canopy would do the trick to resist the vertical bending. The lugs could have been extended aft just past the LE of the Xwing fins for lateral bending strength also. But looks like the internal coupler you have in there should be fine. An external cardstock wrap is another option.

Having a continuous sleeve minimizes stress risers.. strakes would strengthen the fuselage but would create high stresses where they terminate.
 
Having a continuous sleeve minimizes stress risers.. strakes would strengthen the fuselage but would create high stresses where they terminate.
True. But if the strake crosses the area of weakness/concern, and also crosses the critical structures (shock cord attachment and engine mount) not sure there would be that much stress at the “edges” of the strake to fail. Couplers are used all the time, and while as you say they do “concentrate “ the stress at terminations, in routine sport Rocketry they usually don’t cause failure.
 
Having a continuous sleeve minimizes stress risers.. strakes would strengthen the fuselage but would create high stresses where they terminate.
True, it shifts the point further up the wing, but then it is not coincident with the termination point of the Xwing fins. The longer Xwing fins are most likely to hit the ground first anyway, and the potential damage site on the body tube would likely be at the leading edge of those.
 
Mylar Parachute Build.. Day 1

As you may already know from my other thread.... the 12" nylon chute I bought wouldn't fir in the short space available in the BT-50 body tube. So some folks here suggested I make my own from mylar.

So here's what I've done thus far in case others are curious.

I was headed out to buy an Emergency Blanket... my wife says "We already have a number of them" (She's a keeper :)).

DSCF4589.JPG
________________________________________________________

Basically I used the nylon chute as a template to layout out the new chute, using a Sharpie.

DSCF4590.JPG
DSCF4593.JPG
_________________________________________

Scissors won't work well for cutting the mylar, but an Exacto knife, on a cutting board, and a heavy straight edge worked great. Notice the ragged edge where I tried to cut the mylar with the scissors.

DSCF4596.JPG
__________________

When I tried to cut the mylar it seem to tear a bit. In order to help reinforce the mylar for attachment of the chords I used Scotch Clear Moving and Storage Packaging Tape.

DSCF4597.JPG
___________________________________________

I basically taped the areas on one side of the mylar, folded it over, taped the other side. Then I used the Exacto knife to trim off the excess tape.

DSCF4599.JPG

DSCF4602.JPG
___________________________________________

Next I made a template to locate attachment points for the chords. I need to buy some chord.. so I'll finish up this chute build later.

DSCF4607.JPG
DSCF4608.JPG
 

Attachments

  • DSCF4605.JPG
    DSCF4605.JPG
    165.1 KB · Views: 59
Back
Top