Sentinel upscale 2019

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Event Horizon

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I've gone out of my mind. I decided to jump into a larger size rocket than I've done before. Years back I scratch built an Estes Starship Excalibur. A few decades later I built an Estes Sentinel and immediately felt it was the most awesome looking rocket design I'd ever seen. I packed that rocket away in a tub container and had almost forgotten it. I opened the container and found this great rocket that I knew immediately I had to build another. Low and behold, this kit is not so easy to find, and when it was found it sold for a fairly handsome sum of money. Apparently it has become a collectors item and is somewhat being hoarded these days. What to do, pay a small fortune for a Sentinel kit or kit bash another kit into a Sentinel. Ah, that's it ! Exactly what I did. I learned that an Estes Vagabond has all the correct parts except the tail fins and strake fins to clone a Sentinel from. So I did that. I cut fins from a sheet of 3/32" balsa, put it all together and painted it gloss white. Then I ordered a set of vinyl transfers from Stickershock. When the transfers arrived it was apparent to see that I had received transfers for a much larger version of the Sentinel than I was building. I contacted stickershock and he promptly sent out transfers for the correct sized Sentinel. I finished the clone. It has the Vagabond engine mount which I believe uses D and E motors. If a little thrust is good, more thrust should be better correct? The Vagabond isn't that much longer or heavier than a Sentinel. So I did it. I can always put in a motor adapter tube and use the B and C motors as well. See photo (Estes kit on left side, clone on right side).

Well, what to do with the larger transfers soon hit me as an afterthought. Easy enough answer. Build a bigger Sentinel, heck why not build two as stickershock had sent two sets of transfers. I took on the challenge without blinking another time. I contacted the guys at Erockets and they laser cut tail fins with TTW tabs and strake fins from 1/8 plywood for me. I ordered the Aerotech 11261 nose cone which has the same 5.1 ogive shape as the Estes Sentinel kit's nose cone, 2.6 inch body tubes and a coupler. An E motor mount kit seemed appropriate, I am thinking the higher thrust E motors should easily take the rocket to a sufficient altitude for spectator enjoyment. The parts arrived. The fins are absolutely awesome. The slotted lower airframe is absolutely awesome as well. The motor mount is topnotch, except I like the Estes motor retainer clip much better and may find a couple of them somewhere or bend my own from the appropriate material. That nose cone is so awesome. It's over 13 inches long and just beautifully blow molded.

Well, that didn't satisfy my building curiosity, (haven't started on the Erockets version yet but I've been drooling over it) nor my materials curiosity. I went to the Rocketarium e store and bought everything similar, or so I thought. MOre on that in a bit. I decided to cut my own fins, so bought a sheet of 1/8 basswood to cut the strake fins and will get two sheets of 1/8 Midwest Products ply from Menards to cut the tail fins from. I hope to employ the same TTW tabs as the Erocket fins. The Rocketarium 2.6 body tubes do not have the same wall thickness as the Erockets sourced body tubes. They gotta be different manufacturers or something. I was disappointed by that. I think the thin wall tubes will be more problematic to achieve a pretty paint job on because they flex so easily and will be more difficult to prep for final paint. I'll probably have to install bulkheads to stiffen it up. Which led me to thinking I better get a few ejection baffle kits as well, along with a few bulkheads I can enlarge the holes in and cord to get the connection out of the airframe where I can connect a parachute to it. The baffle kits and bulkheads should help stiffen the thin wall tubes. I cut the strake fins out of the basswood with little fan fare and am happy with the result. The plan is to get the ply from Menards this weekend and then figure out how to cut it with the home tools I have on hand, ie, no table saw, a jig saw, razor saw and coping saw. I do have a Dewalt power miter box which I may be able to use for part of the fin cutting somehow. I think the ply won't cut very efficiently with an Exacto type blade...
I could use suggestions on cutting fins from ply using stone knives and bear skins for tools. I certainly wish I could find a laser cutter locally or buy one. Wouldn't that be nice.
I hope to get a couple pictures posted soon of what the two orders of parts looks like. I think it may generate some interest from others to contact Erockets and order similar parts, especially know that Erockets has a program for laser cutting the fins.
I'll be back with more. Meanwhile feast your eyes on the pair in the photo.
Two Sentinels.jpg
 

Event Horizon

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I just got done reading a post about bending motor retainer clips from the narrow strips of stainless steel that is found with windshield wiper blades. Sounds like a very easy process now that the material source has been determined. And..... those discarded wiper blades supply free material !
 

Event Horizon

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I'm also considering that when I order baffles and bulkheads, maybe I should order a cluster mount for say two or three motors. IIRC, I saw a four motor cluster mount as well for 2.6 tube.
I'd half to re-engineer the TTW tabs, and with three motors and four fins, that might get interesting. With two or four motors it would be much less problematic I would think.

By the way, I like the Erockets single D/E motor mount a lot better than the Rocketarium single mount. The Erockets version is made of thicker wall tube, but neither of the ply mount rings had a slot for the retainer, which the Rocketarium supplied ring does. It should be pretty simple to cut in the slot to allow enough motor clip movement to ease motor install and removal.
 
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Event Horizon

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Then there's this thought. I'm not sure what motors this setup uses, but I like the looks of the mount and it's advertised strength. Includes fin lok rings for four fins. The pic shows three fins but the description says four

2.6" 29 mm Motor Mount with Baffle / 4 fin
Complete motor assembly for 2.6" rockets. Includes: 12" Motor Tube, Fin-Lok™ rings, 3 x strong Aero-Fibre™ centering rings, thrust ring, motor hook, screw eye, cooling mesh, molded ejection baffle, 2 x 1/4" launch lugs. This is the same motor mount that is supplied with all Aerotech...

What motor would this one be for??
 

Event Horizon

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Well did a little more checking, the learning curve is getting steeper for this bigger rocket, and this one isn't really THAT big. It will be about 43 inches tall bottom of airframe to tip of nose cone. I'm not sure how much height the swept tail fins will add. Anyway that motor is pretty spendy and requires an L1 certification for launching a rocket with that motor in it?
Is that what I'm reading?
 

Event Horizon

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something else I'm trying to figure out is the Erockets motor mount I bought #9 for BT80 tube has a longer motor tube that the Rocketarium motor tube. Why is that?
first pic is Erockets, 2nd is Rocketarium. The difference in length is clearly visible when comparing the tubes to the centering rings.
 

Event Horizon

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Here's pics of the motor mount parts. Erockets on the top Rocketarium on the bottom.
There is a marked difference in motor tube lengths, the stoutness of the retainer clips, differences in centering rings, the Rocketarium kit has a clip retainer, Erockets does not, See any other differences??
upscale sentinel 2.jpg



Here's a pic showing the difference in airframe thickness

upscale sentinel 3.jpg


The Erockets tube is somewhat thicker, I should use my vernier caliper to determine what the difference really is. So one rocket will be heavier right from the get go.
 

Event Horizon

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Laser cut parts rule the roost. There's no question in my mind about that.
Here's a pic of all the parts I've acquired so far. Erockets on the top, Rocketarium on the bottom.
I think sliding those tube couplers into each tube half way with glue on them is going to be very interesting.....especially with the Erockets tubes, the fit is tighter due to their wall thickness.
Again, those Aerotech nose cones are way awesome.
The basswood strake fins (bottom of pic) were fairly straight forward to cut out. I've also given them beveled edges. I think it might be prudent to coat the edges with CA to harden them, all except the mating surface of course. The edges are nearly butter knife sharp. Basswood is pretty tough though as well.
Hoping to acquire the 3mm x 4 inches wide x 12 inches long (2 of them) sheets of craft plywood from Menards this weekend for the tail fins. The tail fins are pretty big and consume a lot of material. The basswood strake fins used most of a 36 inch long x 4 inches wide sheet. The Erocket laser cut tail fins and strake fins are a thing of beauty. I'd simply buy another set of strake and tail fins from Erockets, however the build and fabricating the parts that I can is as much fun to me as any of it. I've never seen laser cut wood parts before so I was very curious what that is all about.
upscale sentinel.jpeg
 
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Event Horizon

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Just an interesting observation, technology is so amazing these days. My cheapy Canon camera takes wonderful photos, clear as bell and 10 megapixel and all. The thing is like 15 years old. however those photo files are too large to d/l onto the forum. It's just an additional hassle for me because windows 10 has a crappy program to reduce file size. Anyway taking pics with my cell phone is the cat's meow for this stuff. I'm tickled pink I'm alive during these days of amazing technology improvements. The coolest part is how much rocketry has gone high tech as well.
 

Bruiser

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This is a nice-looking rocket. Quite a difference in the thickness of the body tubes. I remember reading somewhere that "Launch Pad" kits were designed with lighter tubing so they could fly reasonably well with mid power. Did I miss what size motors you are planning to use?

-Bob
 

dr wogz

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Well did a little more checking, the learning curve is getting steeper for this bigger rocket, and this one isn't really THAT big. It will be about 43 inches tall bottom of airframe to tip of nose cone. I'm not sure how much height the swept tail fins will add. Anyway that motor is pretty spendy and requires an L1 certification for launching a rocket with that motor in it?
Is that what I'm reading?
Lets see if I can answer some of this:
29mm motors can be had for L0 people.

HPR is:
  • Uses a motor with more than 160 Newton-seconds of total impulse (an “H” motor or larger) or multiple motors that all together exceed 320 Newton-seconds;
  • Exceeds 125 grams of propellant;
  • Uses a hybrid motor or a motor designed to emit sparks;
  • Weighs more than 1,500 grams including motor(s); or
  • Includes any airframe parts of ductile metal.

You can use up to a G80, typically, for your flight and not need certification. Just check your 'ready to fly' weight to ensure you're under 1.5Kg (3.3lbs)

The difference in the tubes you got are minimal. I wouldn't worry. Supplier 'A' get his tubes from one supplier, and feel his supplied tubes are right because of [insert reason here] Supplier B get his from someone else. Longer motor mount tubes help move the forward CR forward, therefore reducing eh internal volume of the BT, therefore you'll need less of a charge to deploy the recovery gear. And inch or two won't make much of a difference. But, a 4" MMT tube vs. a 16" MMT will! This should answer your post #5 (and it looks like these parts form the Aerotech line of kits)
 

Event Horizon

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dr wogz quote "The difference in the tubes you got are minimal. I wouldn't worry. Supplier 'A' get his tubes from one supplier, and feel his supplied tubes are right because of [insert reason here] Supplier B get his from someone else. Longer motor mount tubes help move the forward CR forward, therefore reducing eh internal volume of the BT, therefore you'll need less of a charge to deploy the recovery gear. And inch or two won't make much of a difference. But, a 4" MMT tube vs. a 16" MMT will! This should answer your post #5 (and it looks like these parts form the Aerotech line of kits)" unquote

Thanks for the info on motors Paul.
I was thinking of extending a motor tube upward further into the body tube and bulk-heading it at an ejection baffle, leaving enough body tube to fit chute protector materials, a parachute and the cord and lines to be packed and still not encounter the bottom of the nose cone. Has anyone done this?
 

Event Horizon

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Measured the two airframe tubes this morning.
The Erockets 2.56 tube has an approixmately one millimeter thick wall.
The Rocketarium is approximately half of that at .5mm
IMG_5777.JPG

IMG_5778.JPG
 

Event Horizon

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Got the 3mm ply from Menards for the tail fins.
One fin per sheet. Each sheet cost $1.19 plus tax.
fin material.jpg
 

Event Horizon

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Cut the tail fins from the Midwest Products 3mm thick plywood today.
I used my power miter box and a razor saw. Not 100% accurate but pretty darn close. I think I can make them work.
Now if I could figure out how to put that awesome bevel on the leading, trailing and fin tip edges......
Belt sander?? Maybe?
How do you guys bevel plywood fins. I know a plane won't work very well across the grain of the center layer.
IMG_5782.JPG
 

Event Horizon

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Here's a pic of the fins I cut from 3mm Midwest Products plywood with two coats of Deft Lacquer sanding sealer on them.
So far I'm pretty happy with the fins.
I'm also trying to figure out a way of holding the strakes while sealing and painting them.
I've been thinking of temporarily gluing them to a piece of something so I can handle them
Got the slots for the TTW fins tabs cut in the Rocketarium tube. It was easier than I thought it would be.
Also decided to take a first evaluation of the nose cone. It's a pretty good blow mold with little mold line removal work to be done.
I'll have to use a bit of filler on it as well.
Started to put together the Rocketarium motor mount too.

Sentinel fins.jpg
 

Event Horizon

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The tail fins now have two coats of Krylon white primer over two coats of Deft Lacquer Sanding Sealer.
The strake fins have two coats of Deft.
I stuck pins in the bottom of the strake fins to provide something to hold onto and hang them from.
I'm liking the looks of the tail fins, I'm hoping the strake fins will look as good after two coats of white primer.
I ordered a
two coats primer two coats sealer.jpg
bunch of tube bulkheads, coupler bulkheads and a couple of baffles and two heavy duty BT 50 motor tubes. I've got centering rings and
a few other items coming too.
I hope I'm ordering the correct pieces, some of it I just guessed after a while. I've got some ideas I'll expand on later.
Then I ordered some kevler shock cord and forgot to order some red elastic shock cord ...sheesh, hope Walmart has some kind of elastic cord in their sewing department.
 

Event Horizon

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After the second coat of primer on the tail fins is completely dry in a day or so more, (crap the temp suddenly dropped here about 20 degrees, so my drying room, the garage, is a bit cooler and the paint takes longer to dry). I'll sand them for the last time prior to installing them.
I think I'll start with 400 grit and sand them wet. Then go to 600 wet and call it good.
 

Event Horizon

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I'm thinking of using a 12 inch long motor tube and bulkheads to reduce the volume of the body tube to an amount that hopefully will ensure the ejection charge doesn't dissipate and will blow the nose cone off so the chute comes out. I think dr. wogz kind of agreed with my thinking, but what do some of you other guys think??
 

Event Horizon

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Just checked the website for the parts I ordered a Friday evening after hours.
Says their with the carrier...sweet, a few days and I will be able to attach fins.
Meanwhile I'm going to make a fin attachment guide from a couple of hunks of 2 x 4, cut at a 45 degree bevel on one edge. One piece needs to be longer than the other, so the fin can sit on the longer piece and be clamped down. Then clamp, bolt or pin the two pieces together to form a V with a piece of fin material between them the same thickness as the fin and viola strait alignment longitudinally centered and radially passing through the centerline of the body tube. Got the system from doing a search on google for fin alignment guides. Google took me here to this forum.
The other one I may try is found on payload bay here http://www.payloadbay.com/index.php?page=Tools&action=FINGUIDES
Pop in the info and it makes a pattern for you in .pdf format, print it, glue it to something like foam board and cut it out.
Thanks guys
 

Bruiser

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I use those fin guides. I spray it with some 3m77 and stick it to cardboard. You can also stick it to foam board.

Bob
 

Event Horizon

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Bruiser,
I was thinking of using cardboard as well. I thought it might cut more accurately than foam.
I have to get the jig made too, think I'm going to use both
 

Bruiser

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I cut the circle for the body tube first, then the tip of the fins. From there I cut from the tip to the body tube. Use a sharp blade and it'll cut out pretty smoothly

Bob
 

Event Horizon

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The strake fins have two primer coats with Krylon white primer.
The nose cone was sprayed with SEM Adhesion Promoter according to the instructions on the can after roughing it up a bit with 320 grit wet and has two coats of Krylon flat white primer.
I'll probably have to fill the mold separation lines with some Squadron white putty to fill in the grooves there.
More parts and pieces for baffling and motor tube extension are supposed to arrive tomorrow.
 

Event Horizon

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The parts arrived. Apparently I ordered the wrong centering rings.
I'll have to enlarge the center hole to fit a BT50 heavy motor tube.....
A couple of baffle kits, those are pretty nice.
and some kevlar cord. That's kool stuff too.
Another motor mount and I've got several options on how to install a longer (12") heavy motor tube to bulkhead off the large (2.6") body tube and make sure the ejection charge will pop the nose cone off....
Ah the trials of hobbies...but gotta love the challenges
 
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