Lakeroadster's 2 Stage Alpha Variant

The Rocketry Forum

Help Support The Rocketry Forum:

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
It's been a while, and I forgot about your beautiful assembly drawings.:)
Thanks! I love making CAD models & drawings!

Is the long coupler, item 6 on sheet 3, for structural reinforcement? If so, I think it's overkill, unnecessary weight. As we all know, most LP rockets use stock tubes with no such reinforcement and do fine, unless they dirt dive. Will the coupler add enough strength to survive such an event? Is that your purpose?
I'm all about overkill.

The coupler ensures a tube that is about 2.5 times stronger, in regard to point loading, than a standard body tube... so, why not? Nice manicured grassy launch fields are unobtanium here. The launch sites are typically covered with rocks the size of your fist or larger.

Finally, aren't the leading end chamfers on the launch lugs backwards? Don't you want the lug profile to be a trapezoid, not a parallelogram?
The plan is to place the launch lugs against the fin / body tube and then cut to match the contour of the fin. Then once the rocket is painted... they are less visible. I'm using a 5/16" dia. launch rod... so the lugs are pretty big.
 
Last edited:

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
In order to get Open Rocket to simulate the ring fin design, to determine stability, I used Bruce S. Levison's technique as presented in issue 27 of the Apogee Peak of Flight Newsletter.

I entered the data for 6 flat fins, then adjusted the weight of those fins to adjust the CG to be exactly as the previous Open Rocket simulation calculated.

This simulation shows that 1.5 ounces of weight is needed to provide a stability caliber of 1.0, when using the 24 mm D-series motors.

The green fins in the screen shot below are the 6 flat fins that attempt to simulate the ring fin.

2021-11-17 Ahpla 24 MM Open Rocket Simulation of Ring Fin as Std Fins.jpg
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
2021-11-19 Building the ring fin.

I always like to tackle the "unknown" parts of a build 1st. For this build, it's making the ring fin.

Here's the working drawing of what I'm trying to build:
Ahpla Rocket Dwg Sht 11 of 11 Rev 0.jpg

I nosed around out in the barn looking for something to use as a mandrel. I was planning to us some PVC pipe, but I had a shipping tube that's 3.29 o.d., I needed 3.25 o.d., that's close enough. I'll simply make the fin supports a tad bit taller. The plastic ends that slide into the shipping tube are handy, they help keep the tube round and also helped me to hold the mandrel from the ends.

The plan is to form the ring by gluing strips of paper on the o.d. of the mandrel, then chuck the mandrel in my wood lathe and turn / sand the ring to the required size.

Will that work? I have no idea, but it seems logical. Using the tools available, and modifying the design as required as the build progresses. Another reason why scratch builds and scratch designs trip my trigger. :music1:

First I taped a piece of wax paper to the mandrel
000.JPG
____________________________________________
I like using photo paper, I've used it to paper fins, and to make the fins for my Shooting Star Columbine (see signature line for link). Once the paper has been glued and dried it's really amazing how sturdy it is. It also cuts easily using typical woodworking tools like a scroll saw. Only down side is the weight. Paper is about 0.474 oz/cu-in, compared to something like balsa that is 0.098 oz/cu-in.
001.JPG
____________________________________________________
I cut the paper into strips. The finished ring length is to be 1-5/8", so I used 2-1/8" strips, thus getting (4) from each sheet of paper. I pre-formed them by running them over a sharp countertop edge and then rolled them up tight. This makes gluing them much easier as they are already a rolled shell.
002.JPG004.JPG 005.JPG
______________________________________________________________________________________________________
The first strip, I taped to the wax paper previously taped to the mandrel (which looks like a baked potato).
006.JPG
__________________________________
Then I just applied white glue to the outside face of the strip, and smoothed it out with a bondo spreader. Glue is applied to each strip, after it's placed on the mandrel. I'm using Elmer's School Glue... it gives a bit more working time to position the pieces and isn't as "grabby" as other glues.
007.JPG
____________________________________
The first (3) pieces I allowed the ends of the strips to overlap themselves. For the remaining strips I started cutting them to length as I placed each one. Each strip is staggered 120 degrees from the previous.
008.JPG
______________________________________
And here's the finished, glued up, ring blank.. It's pretty gnarly, far from perfectly smooth and round, but with any luck I can smooth it all out on my wood lathe.
To everything... turn, turn, turn.
009.JPG
 
Last edited:

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
2021-11-19 Building the ring fin (cont.)

When I made the fins for the Columbine I clamped the glued ply's of paper in a fixture. The end result was no wrinkling or blistering.

So after the ring fin blank outlined in the above post had cured for about 2 hours I didn't like the way it looked. So I wrapped the outside of the glued up ring blank with wax paper. Then, using 1-1/2" 3M Green Painters Tape #2060, the outside of the blank was wrapped as tight as possible for the full length of the blank.

The thought here is the tape will help to minimize the wrinkling / buckling that occurs if the glued up blank isn't constrained on both sides.

If you've never used 3M green painters tape.. the stuff is far superior to the blue painters tape.

010.JPG
 
Last edited:

jqavins

Gone beardless since then
TRF Supporter
Joined
Sep 29, 2011
Messages
6,734
Reaction score
3,532
Location
Howard, NY
I'll be interested to see how well that comes out. I'm sure you won't get as much restraining force as you did on those fins. Will it be enough? Tune in next time to find out on Lake Roadster's Build Time.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
I'll be interested to see how well that comes out. I'm sure you won't get as much restraining force as you did on those fins. Will it be enough? Tune in next time to find out on Lake Roadster's Build Time.
2021-11-19 Building the ring fin (cont.)

Why not use green tape... and some cold rolled steel and band clamps, since I have them on hand...

011.JPG
 
Last edited:

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
2021-11-19 Building the ring fin (cont.)

I removed the outer metal mandrel & thus far pretty pleased with the results. There are only 2 troughed areas, I'm using wood glue to fill those in. The ring is about 1/8" bigger on the O.D., which will allow me to sand it to the correct diameter on my wood lathe.

001.JPG002.JPG003.JPG004.JPG
 

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
9,438
Reaction score
4,140
Looks like a great method. I tend to use materials on hand for rings, inckuding Pringles Cans, Oatmeal Canisters (Quaker Oats name brand canisters make much better rings than Walmart GreatValue cannisters, although I don’t notice Much difference in the oats!), sometimes I will splurge and use BT-80 or 100 tubes.

frequently my designs are based on the size of the parts I can find, rather than sizing the part to the design.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
Truing Up The Ring Fin On The Wood Lathe

The cardboard mandrel worked really good. I was able to leave the plastic inserts in the tube ends. Then secure the one end with the chuck and use the tail stock center on the other. Ran pretty true for something that was never intended to be used as a mandrel. See video below.

There is still a good bit of moisture in the ring from the gluing process, even after 3 days. It's really arid here, humidity in the teens.
  • Note: Allow at least 6 days before sanding a glued up ring fin.
I can physically move the ring on the cardboard mandrel, but it still has a snug slip fit.

Next up I need to make a drilling template for the holes. The plan is to actually drill the holes while the ring is still on the cardboard mandrel. I'm planning to use a Forstner Bit to minimize the torque applied to the ring.

Thus far my only regret in the process was the use of Gorilla Wood Glue to fill up the divots. It's too hard and tends to chip off.
  • Note: Use Elmer's School / White Glue for an surface repairs.

001.JPG002.JPG003.JPG

 

Attachments

Last edited:

jqavins

Gone beardless since then
TRF Supporter
Joined
Sep 29, 2011
Messages
6,734
Reaction score
3,532
Location
Howard, NY
Note: Use Elmer's School / White Glue for an surface repairs.
From the pictures in post #39, it looked like the structure was OK and you just needed to fill the divots. So maybe filler would be a better choice than any brand/type of glue.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
From the pictures in post #39, it looked like the structure was OK and you just needed to fill the divots. So maybe filler would be a better choice than any brand/type of glue.
I agree if the ring wasn't going to have holes drilled through it. I can't imagine filler holding up well though to that.

Filler tends to chip if it's messed with after it has cured.

I actually used some Elmer's also, along with the Gorilla Wood Glue. No issues with the Bull, just the Gorilla.

I thought I had some photo's... but I don't :facepalm:

1637676406782.png
 
Last edited:

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
Drilling the Ring Fin

I used a 1" dia Forstner Bit to drill the ring, and then my Dremel with a sanding drum to square off the one side.

The closeup photo's of the ring are deceptive? The ring looks rough, but it's actually smooth. I still don't think it's fully dry though. I'll be sure to keep it on the mandrel so it stays round.

Looks like this process is going to work well for building components in the future.

Time to put together a list of parts I need to buy from Balsa Machining Service.

Good times! Ya'll have a Happy Thanksgiving.

Here's a video I created...

001.JPG002.JPG003.JPG004.JPG005.JPG006.JPG007.JPG008.JPG009.JPG
 
Last edited:

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
9,438
Reaction score
4,140
Looks great. I am still going to use Pringles cans, Oatmeal Cartons, and Almond containers (the later have metal lids and bottoms, i was surprised to find the sides are paper/cardboard!)

big problem is weight——-not the rocket’s weight, but MY weight, I tend to get a bit tail heavy eating all that stuff. Plus I think SWMBO has already decided I am unstable no matter where my CG is.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
Looks great. I am still going to use Pringles cans, Oatmeal Cartons, and Almond containers (the later have metal lids and bottoms, i was surprised to find the sides are paper/cardboard!)

big problem is weight——-not the rocket’s weight, but MY weight, I tend to get a bit tail heavy eating all that stuff. Plus I think SWMBO has already decided I am unstable no matter where my CG is.
A moment on the lips, a lifetime on the hips.... Maybe strap on a tutu to move your CP?

I'm not judging.. just trying to help :music1:.
 

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,356
Reaction score
663
Clever design for a staged Alpha or Ahpla the vented ring fin is pretty cool.

Only problem is if you might have a public health scare at a public launch when the RSO announces that we have an "Alpha Variant on the field," but we are supposed to keep that topic quarantined in the existing CoVid forum here.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
Clever design for a staged Alpha or Ahpla the vented ring fin is pretty cool. Only problem is if you might have a public health scare at a public launch when the RSO announces that we have an "Alpha Variant on the field," but we are supposed to keep that topic quarantined in the existing CoVid forum here.
<----------- No worries, no RSO....
 
Last edited:

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
9,438
Reaction score
4,140
First, I think this model demonstrates you can’t make the holes too big.
F0374A35-4FEE-48D1-B7B7-33CB6062294F.jpeg
 

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
9,438
Reaction score
4,140
I am not The most scientific on my design and construction. I have RockSim and OpenRocket and have never really used them. I can claim a partial excuse because most of my designs are square or triangular cross sections or have other weirdnesses that don’t lend themselves to sims (the rest is pure laziness on my part.)

that said, I probably have more experience with scratch built gap stages than most.

tenets I subscribe to are as follows

at least two vents, equally spaced, so there is no net lateral force from the staging gas that might throw the rocket off kilter. I have no evidence it makes any difference, I just do it.

I DO believe the position of the holes relative to the sustainer IS critical, the holes should be just below the nozzle of the sustainer. Depending on how you “mate” the sections, the holes can be in the sustainer, the booster, or both. If you are not going minimum diameter, I DO believe it helps to extend the internal motor mount to “duct” or route the hot gases so they illuminate the nozzle on their way out. My sustainer ignition rate is pretty much 100%, my major failure has been when I tried to extend the gap from 53 to 72 inches. 53 worked in flight multiple times, 72 worked on a test stand but failed in flight, not sure why. I was using a D12-0 on the booster, I now have some F15-0s and hope soon to try a build with a 72” gap.

as for the size of my holes, I just use a regular Note paper size hole punch, not for any scientific reason, just because it’s convenient.
 
Last edited:

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
I am not The most scientific on my design and construction. I have RockSim and OpenRocket and have never really used them. I can claim a partial excuse because most of my designs are square or triangular cross sections or have other weirdnesses that don’t lend themselves to sims (the rest is pure laziness on my part.)

that said, I probably have more experience with scratch built gap stages than most.

tenets I subscribe to are as follows

at least two vents, equally spaced, so there is no net lateral force from the staging gas that might throw the rocket off kilter. I have no evidence it makes any difference, I just do it.

I DO believe the position of the holes relative to the sustainer IS critical, the holes should be just below the nozzle of the booster. Depending on how you “mate” the sections, the holes can be in the sustainer, the booster, or both. If you are not going minimum diameter, I DO believe it helps to extend the internal motor mount to “duct” or route the hot gases so they illuminate the nozzle on their way out. My sustainer ignition rate is pretty much 100%, my major failure has been when I tried to extend the gap from 53 to 72 inches. 53 worked in flight multiple times, 72 worked on a test stand but failed in flight, not sure why. I was using a D12-0 on the booster, I now have some F15-0s and hope soon to try a build with a 72” gap.

as for the size of my holes, I just use a regular Note paper size hole punch, not for any scientific reason, just because it’s convenient.
Thanks for the detailed response. :awesome:

"the holes should be just below the nozzle of the booster"

Is that what you meant to write? You meant sustainer, correct?
 

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,356
Reaction score
663
If you have enough room, you could vent through the centering rings out the back of the booster if you don’t want to put visible holes on the outer body tube. Then you might want the booster to have a longer motor central tube that gets closer to the sustainer nozzle.

depending on how close they are, you might not need a vent, but it does help, this 24mm stager does not appear to be vented and it has a short gap between the motors, for example:
 
Last edited:

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
9,438
Reaction score
4,140
If you have enough room, you could vent through the centering rings out the back of the booster if you don’t want to put visible holes on the outer body tube. Then you might want the booster to have a longer motor central tube that gets closer to the sustainer nozzle.

depending on how close they are, you might not need a vent, but it does help, this 24mm stager does not appear to be vented and it has a short gap between the motors, for example:
venting out the back is cosmetically and probably aerodynamically the best route for non-minimum diameter rockets, and Glen is exactly right, if you do this you need to run the motor mount of the BOOSTER (I checked, Lake!) to about 1/8 to 1/4 from the nozzle of the SUSTAINER.

there are many ways to skin this cat, one easy way is to mount the intact centering rings on the BOOSTER moto mount first (which is what you do anyway), and then use a Dremel or tool of choice to cut notches (vents) in the centering rings BFORE you insert the mount into the BOOSTER body tube. In this case, IMO, make the notches decent size, maybe 1/4” or more (allowing for structural soundness of the centering ring, but we are talking black powder motors, so a couple 1/4” holes isn’t going to weaken them much.). Put another way, as long as the remaining amount of centering ring volume is structurally sound, you can’t make the vents/notches too big.

obviously you need holes in both forward and rear rings. Lining them up isn’t critical, but since you cut the notches before you insert the mount, it isn’t hard to do.
 
Last edited:

jqavins

Gone beardless since then
TRF Supporter
Joined
Sep 29, 2011
Messages
6,734
Reaction score
3,532
Location
Howard, NY
Off the top of my head, if I had a 24 or 29 mm motor on the BOOOOOSTER, I would use the engine block as a centering to adapt down to a smaller diameter stuffer, meaning less volume for the ignition gas to fill.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
3,273
Reaction score
2,271
Location
Central Colorado
I did. Fixed.
Thanks!
Sorry but I'm still confused. Why would you want to put the holes behind the booster motor top end? If the pressure is pushing the ignition charge forward, it seems logical to have all the force going the same direction, well, logical to me anyway.
 
Last edited:

neil_w

Twaddleposter
TRF Supporter
Joined
Jul 14, 2015
Messages
12,729
Reaction score
5,691
Location
Northern NJ
I don't see the fix, post looks unchanged to me, unless I'm missing it.

In general I would assume the holes should indeed go as close to the nozzle of the *sustainer* as possible, so the cold air can escape out when staging takes place. Or rather, the holes don't necessarily need to be there, but there must be some sort of escape path for the air just below the sustainer nozzle. Could be vented out the back, as long as that path exists.
 

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
9,438
Reaction score
4,140
Sorry but I'm still confused. Why would you want to put the holes behind the booster motor top end? If the pressure is pushing the ignition charge forward, it seems logical to have all the force going the same direction, well, logical to me anyway.
I didn’t save the correction. been a bad day. They should be behind the nozzle of the SUSTAINER.

Thank you for your assistance and patience.
 
Top