Resurrecting my X-15 with my scratch STRETCH X-15

Back when I used to launch rockets with my kids, I built a model from scratch of an Estes X-15 (here's my old fleet).  It flew great the first time, but on the second flight, the shock cord must have burned through because all I ever recovered was the nose cone and parachute.  I always like the looks of that rocket, partly because of its role in getting astronauts ready for spaceflight, and kept going back to look at the plans on Jim Z‘s site.  I finally decided to build a new one, starting from the nose cone I recovered. 

I printed the plans, cut fins from 3/8" balsa wood (more on that in a moment), cut the body tube (BT-60, 1.637" diameter), glued the fins together on wax paper, brushed them with wood filler and sanded them to get ready for assembly. I decided to use some epoxy putty to make a "cockpit" on the nose cone and plan to use Kevlar to avoid having the next shock cord burn through.

After gluing the fins together on wax paper, I coated them with DAP Plastic Wood thinned with a little water using a paint brush.  When dry, I sanded the fins with sand paper.  I also added a second centering ring at the top of the engine mount, glued and clamped together to give more strength when I add the Kevlar shock cord.

It was at that point that I discovered I had printed the fins too big!  

The online plans printed as an 8 1/2 x 11 sheet but if I open that particular page of the plans in Preview on my Mac and check the properties of that page they were supposed to be printed as 4.03 × 8.5 inches.

I had already cut the body tube to 7 1/4 inches, based on the dimensions on the plans, but it clearly was too short by about 2 inches.  Luckily, this also shows what size I will need to print the decal sheets included on JimZ's site.  As an aside, my earlier scratch built X-15 may also have been a “stretch” version, since I built that from the same plans.  However, I just found an old copy of the plans that printed correctly (at work on a PC) so it may have been a change in the way Mac's Preview handles old PDFs (the PDF of the plans was created in June 1999).

At this point, I decided to explore some different options using OpenRocket. I couldn’t locate a simulation that anyone has designed for the X-15 so I had to do mine from scratch. It took a while to simulate the three parts of the fins but I think I finally got it (including the paper shrouds). 

Using a 9 1/4 inch body tube the rocket is predicted to be stable and fly to 355 feet on an C6-3 engine.  I added 1 oz on the side of the nose cone to account for extra weight from the canopy.

I also explored upgrading to a BT-80 (2.600" diameter) but that would have led to the need to use 24 mm engines (C11, D12,  E12 from Estes) but I decided against it because of fears it might weathercock and disappear.  I’ll recut the BT-60 body tube, attach a Kevlar anti-zipper shock cord and weigh the finished rocket to see how close it comes to these calculations.

Stay tuned...

Oct. 28 update:

After going back and forth I decided to go ahead with making the BT-60 "stretch" version.  I test fitted the engine mount and measured the distance to the top of the 9.25" body tube (6").  Based on the diameter of 1.6", the Kevlar formula was 6" + (1.5 X 1.6") X 4 = 33.6".  I cut 36" just to be safe, then drilled holes in the top of the engine mount and threaded the Kevlar through the holes.

I glued the engine mount, being careful to extend the Kevlar so it didn't get caught in the glue, then used my Estes fin guide to attach the two wings and two vertical fins with Titebond II Wood Glue.

Unable to wait, I even test fit the nose cone and it's starting to look like an X-15!

Now I have to wait for the glue to dry, reinforce the fins and wings with fillets, add the cardboard wing shrouds, prime, sand and paint.  I'll try again to print the decals like I tried to do with my Leviathan clone, though these will be smaller decals and easier to position without losing all the ink (hopefully!).  To be continued...

October 31st update:

I've attached the wing shrouds, applied some extra glue to hold them in place, attached the launch lug and applied some undiluted DAP Plastic Wood to fill in gaps.  I ended up having to free cut some of the wing shrouds to get them to fit (printed at 135%).  After one more quick sanding with smooth sandpaper I'll be ready to prime, sand and paint (when it warms up outside!).

November 4th update:

I've painted with primer, sanded and painted with the final coat of black paint.  It's starting to look like an X-15.  Now it's time to start printing and trimming the decals!

November 6th update:

I spent several hours trying to print the decals using waterslide decal paper as previously described.  The first attempt yielded green background, since that was the way it was scanned.  After several attempts to trim around the green (since I couldn't figure out how to remove it using Gimp) I finally found a better image (.TIFF) from JimZ's site and was able to remove the background and make it transparent.  Here are the two attempts printed side by side for comparison.

However, when I cut out the yellow NASA insignia from the sheet with the white background and placed it on the black tail fin it practically disappeared because there wasn't enough color to show.  The white US AIR FORCE logo similarly vanished on the wings.  Giving up in frustration, I started to write to Estes to see if by any chance they had any decals on a shelf somewhere because I couldn't find the X-15 reproduced on StickerShock23.com.  In searching my notes, I came across another site, CMR PRODUCTS, a railroad hobby store, with decal reproductions for ~300 different Estes rockets!  I ordered a set for the X-15 for a mere $10 (free shipping), deciding I'd already wasted enough printer ink and photo paper.  I'll know in a couple of days if I can use them or not.

My Stretch X-15 is ready to fly (naked) and weighs 2 1/2 ounces (75 gm).  Adjusting the weight in my simulation, the prediction is still for a stable rocket (1.83 cal) that should fly to 436 feet on a C6-3 engine.

Name	Configuration	Velocity off rod (ft/s)	Apogee (ft)	Velocity at deployment (ft/s)	Optimum delay (s)	Max. velocity (ft/s)	Max. acceleration (ft/s²)	Time to apogee (s)	Flight time (s)	Ground hit velocity (ft/s)	Simulation Warnings
B6-2	[B6-2]	39.997	159.885	20.696	2.618	94.977	314.091	3.242	12.467	18.136	Too many parallel fins
STRETCH X-15 C6-3	[C6-3]	40.709	435.876	32.167	3.791	164.206	342.549	5.32	29.706	18.11	Too many parallel fins

*NB-The OpenRocket team just released version 23.09 with the ability to export simulation tables so I can include the text instead of a screen shot.  They also now provide tutorials, including how to export parts from OpenRocket for 3D printing and the ability to render your simulation with a transparent background: 

Flying Naked no more:  Decals came (thanks, TangoPapaDecals.com):

Next to build ... I'm contemplating try to convert (hack/kit bash) the Red Nova seen in the background of a couple of the above pictures of my work desk into a two stage rocket.