Semroc Orbital Transport build

The Rocketry Forum

Help Support The Rocketry Forum:

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Well, I’ve lurked here long enough. And now that I created an account to buy a rocket from another user, I should try a build thread and get official.

This is a Semroc Orbital Transport, a reproduction of the Estes original released in 1968. According to the instruction booklet, it’s based on an early NASA scramjet design for the space shuttle. It has a separate parasite glider which detaches at ejection. The booster is recovered by parachute. This kit looks to have been made before Semroc was sold to Erockets, judging by the address of Knightdale, NC on the cover of the booklet.

First off - wow that’s a lot of balsa parts. The two nearly identical sheets each have 14 separate pieces. Almost all will go on the booster. The third balsa sheet is for the glider.

I had the bright idea of filling, priming and sanding the first coat while the fins were still attached to the sheet, and that’s what you can see in the pics. That turned out to not be as great of an idea as I hoped, as I’ll explain later.

Also, eagle eyed fans will notice that the kit is missing a piece. Full internet points if you can figure out what it is.

Oh, and in case you’re wondering about my setup - I work from home and build a lot of my rockets in front of the computer. Now on to the build.
2D0D1F93-24BC-4D8F-882C-483C7FCA4E30.jpeg
F87CF95F-7BCF-4CAA-BD53-BC10F9FD563D.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
First up is assembling the booster and that means attaching all those balsa parts to the long BT-50. And this is where my idea of filling and priming in the sheet got me into a little trouble. When it came time to remove the laser cut pieces, the extra CWF and primer got in the cracks and made it difficult to detach the parts. The result was roughly cut fins that needed sanding around the edges to smooth them out.

The first parts removed were the four pieces that make up the two main wings. You can see the parts lined up poorly because of the difficulties I had in removing them from the sheet.
975CFF34-76FD-4C4D-9AFF-A6678FABC1AD.jpeg
9F91E701-99FD-4E8C-BE91-112DA7E130FC.jpeg


But with a little sanding, I was able to get them close to the original shape and glue them together with minimal gaps.
C496D605-94B0-446D-ACE3-7D6795A7CB4C.jpeg
07D94221-0527-46F2-8CDB-95A21A254027.jpeg
B8F0215D-1012-4DC1-81EB-66983A8BF6A7.jpeg
0FFF5AA3-5ABA-4D97-ACC4-99157586DA9B.jpeg
CF23B2C3-2067-4EF4-8F5B-0EFB2D4F84B5.jpeg


That process of messy cuts from the sheet followed by sanding continued, but I’m not going to show any more pics of that. Just the cleaned up parts as they go on the booster.
 

milehigh

Well-Known Member
Joined
Apr 26, 2016
Messages
290
Reaction score
24
It appears that the 4th scramjet tube is missing.

This is a fun rocket, and is well worth all of the filling/sanding.

I have one in progress on the workbench as well. Complete scratch build. Fins made the old school way with an original fin pattern sheet on blank balsa stock.

To see a very information-filled OT build thread, see Chris Michaelson's Rocket Building Blog, linked below.
The build covers 24 posts!

http://modelrocketbuilding.blogspot.com/2018/12/estes-orbital-transport-kit-k-42-part-1.html
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Next is to create the scramjet engine assembly which will be attached to each main wing. To do that, we need to glue two pairs of BT-5s (which represent the scramjet engines) together. The problem is the kit came with only 3 engines. I need a fourth! This is a good time to finally try my Estes tube cutter, which I got when I needed to add something to my last AC Supply order to qualify for free shipping.

The cutter is easy to use, as long as you have the right size. The pack comes with standard LPR size: BT5, 20, 50, 55 and 60. I grabbed an extra BT5 I had, measured the kit tube against it and attached the cutting guide. It comes in two parts that attach and hold the tube from sliding. Just put the first part on, attach the second one and it won’t move. Now just put your blade against the guide and turn the tube. You’ll get a pretty good, clean cut. Now I’ve got four engines!
20C48A22-0E5E-4DB1-8AF6-F9210284ABEA.jpeg
F6DB6313-9C04-48F3-8BF7-EBF1B603243F.jpeg
0B9AD6A3-B137-479C-931C-C359BA03A439.jpeg
6D7DC3C4-80EE-4833-A4EC-E51309604852.jpeg
9710304F-ADFC-4E13-8149-CBA33D5BAA7E.jpeg
DC77B72C-D6BA-438D-9DA8-9E0661436CC0.jpeg
802CF817-9B97-44A5-B0FA-072F1C21C9B1.jpeg
E67E5D99-2CA4-4023-89D7-0C5BE4795EE4.jpeg
D5E99B43-DD43-48FA-A71D-B9F2157F9ACE.jpeg
 
Last edited:

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
It appears that the 4th scramjet tube is missing.

This is a fun rocket, and is well worth all of the filling/sanding.

I have one in progress on the workbench as well. Complete scratch build. Fins made the old school way with an original fin pattern sheet on blank balsa stock.

To see a very information-filled OT build thread, see Chris Michaelson's Rocket Building Blog, linked below.
The build covers 24 posts!

http://modelrocketbuilding.blogspot.com/2018/12/estes-orbital-transport-kit-k-42-part-1.html
Correct, the engine was missing.

I always check Chris’s blog before I start my own builds. The amount of good information on that page is amazing.
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
After gluing each pair of scramjet engines, the next step is to glue the outboard housing flush to the trailing edge of the wing. Then the engines are attached with 0.5” overhang and against the housing.
85CFAA4E-C17A-44AE-AC7E-1DC2A6D807A2.jpeg
The intake vane goes in front of and in the middle of the engines, followed by the lower housing which goes on top of the engines (the wing is upside down).
FE6E5803-306A-486E-B949-107E22EBB2A1.jpeg
E8E1E066-B33B-421C-AF9B-9A508423893D.jpeg
Finally, the inboard housing is attached.
EAD44F8E-93C5-4493-9803-B9C9C5345D14.jpeg
3B1BA783-DF56-44EE-BBD6-45B3D27D1545.jpeg
7B807E0D-44F5-46E2-8390-D18BAE9F4C49.jpeg
4FB895A0-FAE9-43A4-A09B-0F753B71FD51.jpeg
All joints were filleted. You can see I had some fit issues. The lower housing is sticking up a bit over the side housings. This is a result is having to sand the edges after cutting the pieces from the sheet. I later went and sanded the housing smooth so pieces weren’t sticking out.
 
Last edited:

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The wingtips are next. Perpendicular and flush with the edge of the main wing.
313A0D93-B9EB-4498-9A5C-D7943EBCDE7C.jpeg
32EC6445-EA22-4FC7-B6D6-57BF75F58F00.jpeg
And the completed main wings.
EC27B8D5-3527-4180-9FFA-F178B44CC15B.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Engine mount assembly is standard. Engine hook, BT20, a retaining ring and two CRs. You have to cut a notch in the aft CR to get over the hook. Kevlar thread was passed through the forward CR and knotted at one end to keep from sliding through. Some glue was rubbed in the knot to hold it in place. The motor mount was inserted in the main body tube with 0.5” overhang.
489205E2-7310-4A7E-8745-ADC9034B6963.jpeg
BE16C951-1078-4AF8-BA92-C8D482225D3D.jpeg
98D181D2-4DC1-484D-B172-A01BC337153B.jpeg
589D45E5-D389-42FA-8C8E-626A7C7B4411.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The booster marking guide was cut from the attached card stock and taped around the main body tube. As you can see, it didn’t fit all the way around the tube.
EFF9084B-4849-4AFB-BFE3-04601C853898.jpeg
Since I scan in all my card stock parts (just in case), I decided to try and print out the guide on plain old paper instead. The fit was better. I went with the paper. Eight lines were drawn around the tube and marked with the letter on the guide.
5E9788BD-3909-4254-B829-F80AC81DF4EB.jpeg
0CE0ADEB-731E-4D0E-B124-9727EB629B20.jpeg
And now a first for my short rocket building career - the instructions have you attach the lugs before any other parts. The lugs are attached to wood dowels. I’m not sure why, though. There’s no need for a standoff. Chris’s blog says it might have been a better match for Estes’s c-rails rails at the time. I wouldn’t know. Anyway, the lugs and dowels are each cut to 5/8” first, glued together, then attached to the main tube at 0.25” and 8.5” from the aft end of the main tube.
FC097A6E-708B-42EB-9183-5C3EC89202DB.jpeg
F55B302A-0B5B-4E4B-9832-9B5E13D24BF2.jpeg
 
Last edited:

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The main wings are then glued on. Alignment of the main wings was set with the alignment guide included on the cardstock sheet. It turns out that the lines I drew with the paper marking guide were a little off from the alignment guide. Using the guide, the wings look closer to being 180 degrees, so I went with the alignment guide. Guess I should have stuck to the cardstock guide.
68A0EF0B-4DB9-4962-8127-A2BB0C3D8CB1.jpeg
B40346CA-107A-4B85-9540-80AAFEF4EBFA.jpeg
BF7C2A10-A607-41EB-880B-7E1F6421239A.jpeg
960FF6C6-AB42-4F92-89A6-03FADBBA9AAC.jpeg


The wing fairings were next, followed by the canards along the main wing line. For the fairings and canards, I used the line set by the marking guide and ignored my drawn line.
9B79A941-E4DA-4152-8256-43111BB4F0C5.jpeg
76D611F8-9988-4448-80E3-CA1EB6643A02.jpeg


The booster so far (upside down):
8AF45101-A288-46FF-877D-597D7E9E00F5.jpeg
 
Last edited:

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The ventral fins were attached to the underside of the booster flush with the aft edge of the main tube.
E267C247-AC62-44D0-BFCB-8F9D300327B6.jpeg
1F74B8F8-4EAF-46CA-98CD-EEF3BE60254B.jpeg
3CFE8F6F-5673-46C6-A21D-51CC8AF5A870.jpeg


Then the glider supports were attached to the top of the booster.
EF893995-D534-4B6A-B9E3-47E8A06DED51.jpeg
65BA6237-0616-40FC-A6F7-C887CDF245A1.jpeg
Finally, another lug was attached to the top of the booster for the glider attachment. The lug was glued directly to the tube, no dowel was used. I forgot to get a picture of it.
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The wing alignment guide was used to mark the placement of the rudders and wing fences. I marked the placement of each part in three spots along the main wing and then drew lines.
372566EC-30F5-4533-A3CF-082439F9ECBB.jpeg
25E3EC2B-137F-4733-BD32-89AB266AE4CB.jpeg
A19C0367-B5AB-4417-BDDF-051C0196BE27.jpeg
B5C05AF0-10A8-4BF7-94A0-E2B36934FE53.jpeg


The rudders first, then the wing fences:
D2D12A3E-DBCB-460D-8BCE-32160FFB9335.jpeg
ABD9AF0E-AB86-44A5-AC13-8CF83F1537F9.jpeg
0C546C4D-5849-4386-9D9E-4967A1D7C6CF.jpeg
9C10D53D-2418-4F80-BC9D-6299338042CB.jpeg
3B8BDD76-CD7E-4732-8762-CE110B294BCE.jpeg


A screw eye was attached to the balsa nose cone and the elastic shock cord was tied to it. The Kevlar thread was pulled through the tube and tied to the shock cord. (No pictures). Here is the completed booster (minus a parachute which still needs to be assembled), and here is where I stop for now. I’ll start work on the glider next week. Titebond no-run no-drip for scale. My favorite glue for fillets.
E6732F5A-CAEA-4E1D-84AD-778321CF2711.jpeg
 
Last edited:

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Methodical! I like your detail to capturing step-by step construction
Thanks! I’ll try and keep that up for future builds. It is time consuming as I have to keep reminding myself to take a picture.
 
Last edited:

neil_w

Hunkered down
TRF Supporter
Joined
Jul 14, 2015
Messages
8,280
Reaction score
1,887
Location
Northern NJ
Nice work and nice documentation! I love builds with lots of balsa construction.
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Back to work means back to building. I’m starting (and maybe finishing) the glider today. The wings are cleaned up and placed next to the bt20 they’ll be attached to.
D11D28A7-A6CB-4AF6-AB80-FABCF2AA8A76.jpeg


I took a cue from Chris’s blog and sanded a slight bevel in both wings for better contact when gluing then together. Not sure if you can see it.
6802C2E2-1CF8-4D7D-A5B4-D4FF6942937A.jpeg


The wings are glued together and placed over the body tube to get the correct angle. Wax paper is placed in between to prevent the wings from being glued to the tube. Looks like I sanded too steep of an angle in the wings. That just leaves more room for fillets!
DE37B194-861E-45B9-B566-19AD8C5890A8.jpeg
1865E008-F7B7-47A7-8873-8789BE09F2D8.jpeg


09AFC5D1-578E-467F-9CF2-C4A70834CF6A.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
While waiting for the glue on the wings to dry, I’ll mark the glider tube. Again, the marking guide doesn’t really fit all the way around the tube. But that’s okay, because it’s only two lines that are 180 degrees apart. I’ll use my Estes tube marking guide (also bought from AC Supply as an add on).
9545ED41-111C-4DC6-B0D5-11ED304AAE16.jpeg
7B2927CF-B06C-4FE3-912B-05734F1DBDF8.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The wing is glued to the tube along one of the marked lines and flush with the trailing edge of the tube.
4F0ABD84-B620-4869-B617-1CD5F8D59B11.jpeg
5CDF3F48-96FC-41E5-9C4C-296CF0329ECF.jpeg
B052A27E-F4BD-4B5E-B594-190FF11820DD.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
The thick dowel, which serves as the hook to attach the glider to the booster, is shaped to the same angle as the hold down support and the two are glued together.
4F3DAE1A-F903-4B87-8B70-6EE95943BAB3.jpeg


The hold down assembly is then glued to the wing line just above and touching the wing.
image.jpg


I’ll test the fit in the booster when it dries. I’m trying not to go heavy with fillets. Trying to keep the glider light. I’m already thinking ahead to finishing and whether I want to put a light coat of primer or go straight to paint.

Looking at these pictures has really made me realize I need a new cutting mat.:D
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Time to curl some paper. The glider’s nozzle shroud is cut from the cardstock sheet. I curl my paper transitions in my hand with an appropriate sized round tool. In this case, my hobby knife worked just fine.
1BE54067-6CEF-4885-9EB4-BC621FE8B295.jpeg

Curl it enough and the paper will want you to glue its ends together.
96FB2F99-CA16-4029-BD59-8A5C28802082.jpeg
Here’s the glued nozzle.
image.jpg
 

T-Rex

Ordinary Average Guy
Joined
Jul 22, 2011
Messages
2,939
Reaction score
21
Another of the many in my build pile that is waiting for when I feel I have the skill to do it justice..... Thanks you for sharing your build. Watching yours makes it not so intimidating.
 

Mugs914

"We got both kinds, country AND western!!"
Joined
Oct 1, 2012
Messages
1,007
Reaction score
459
Location
Temple TEXAS
Great thread! I have wanted to do an OT since I was a kid. Gonna have to pull the trigger on one soon.

Keep up the good work!
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
A paper block is glued to the end of the tube and the glider rudder is attached to to the top.
1D562527-3E52-40E8-A9DD-60AC824FDDD4.jpeg
E0925FEC-8960-467A-9D7D-BEEBF9084CF2.jpeg
A182E167-5211-47FB-ADF1-1DC74859BDBC.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Getting towards the end of the build. The ends of the paper nozzle were sanded lightly to smooth the edges. The nozzle was then glued to the end of the tube, but I forgot to get a pic.

The elevons are the last parts to attach. You use the included cardstock elevon guide to set the angle. I tried to sand the angle into the elevon for better attachment with the main wing. I think I did a better job here than when I sanded the main wing attachments. It was hard to hold my phone and the pieces so the pictures aren’t great.

Here I’m trying to show the sanded angle of the elevon and how it attaches to the wing:
992FD622-42C6-4808-9EBF-1844B27E6BFD.jpeg
AC37F70A-3001-4B7F-9711-64F077C2AB54.jpeg


This is with the glue still a little wet and checking the angle (took the second picture in the wrong orientation):
B4A6008A-9242-4683-9E0F-17EEF4429163.jpeg
D88D80E2-5AFF-493B-8D21-77064FE9D865.jpeg


And some pics after the glue dried:
1E82EDF4-C830-47AE-A7FE-2501990D8456.jpeg
BA28DFC3-0AA9-4970-B2D2-30AAD255A12E.jpeg
D19CB581-62A7-4949-8D52-E192B2A5D107.jpeg
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Finished gluing the second elevon. Here is the completed glider followed by some pictures of the glider on the booster.
854F8F6E-7BFD-49B8-9989-06BDF4442BB1.jpeg
EA8D00E4-CEBF-4100-B480-A1EA656D974F.jpeg
7827E00B-78FC-4414-8B06-C486FA309871.jpeg
FA321705-E424-426A-B40D-CD2B62E36E55.jpeg
4B36810A-CB92-4797-9358-6C172A273300.jpeg
0CA4D10E-F906-47CF-A123-71ABF0D964FA.jpeg


I still have to make and attach the chute for the booster, trim the glider, paint and decal. The instructions say to trim after finishing by softening the glue with a little heat. I’m going to give it a test flight when the glue on the elevons dries just to see where I’m at. If it’s good, I’ll apply paint and decals, and then test again.

I’m not sure how well I should finish the glider. I don’t want to make it too heavy, but it’s safe to say I can be liberal with the paint. o_O The instructions list the glider weight at 14.2g. I’m at 12g right now. I’d like to have it smooth enough to apply decals, but I don’t need every grain line filled. I want it to fly well. I was thinking a very light coat of primer, sand with 400 grit to smooth it out, and then light mist coats of white until I have complete coverage. Thoughts?
 

SecondRow

Well-Known Member
Joined
Jan 29, 2019
Messages
349
Reaction score
173
Finally back to it. I’ve been out of commission studying for a professional exam. They come up every six months and rocketry has to get put to the side for a bit.

I test flew the glider and it did not fly well at first. It stalled badly - I must have glued the elevons too steep. The instructions say to apply heat (in my case, my wife’s hair dryer) to the joint until the glue softens and try and adjust the angle. This did not work for me. So I added weight to the nose. I used the Estes clay that sometimes comes in their kits. I didn’t really have a place to put it, so I tried to shape it around the nose. It’s pretty ugly as you can see.
71C3874C-E722-4F1D-B757-71D7FB777E3E.jpeg


I wish I hadn’t glued the nose cone in already. I could have put the clay inside, but I didn’t think about it during the build. Oh well. Next time. On the plus side, the test flights of the glider from my deck have been great. So I’m going to move on to painting and stick with the ugly nose. Hopefully, the clay will stay on.
 
Top