Special Hobby X-15A-2 Tweak List
By Thierry Laurent
- TYPE: North American X-15-A2
- SCALE: 1/32
- COMPANY: Special Hobby
- KIT Number:
- 32022 (initial A2 release)
- 32031 (second A2 release with tanks and ground handling dolly)
- 32081 (third A2 release with tanks, ground handling dolly and dummy scram jet)
- MOLD CREATION DATE: 2007 (initial plastic parts)
TWEAKS LIST VERSION 1.0 (publication date: January 2021)
Compiled by Thierry Laurent
The following list is intended to help modelers in improving scale accuracy of an airplane model replica. In no way it is intended to support or be offensive towards a scale model company.
As such, it is only the result of a progressive process and is in no way intended to be absolute or even comprehensive. Hence, it is intended to focus on commonly admitted discrepancies and will probably not cover some errors. It is up to the modeler to decide whether correcting the listed issues is worth the time and money he will have to invest in the quest for accuracy process.
No aftermarket correction or detail set is mentioned in this document as the availability of such items may be very variable. Hence, refer to other LSP sections to find relevant information. Moreover, aftermarket sets do not necessarily correct all listed issues. Please refer accordingly to relevant documentation.
- The first, third and fourth Special Hobby X-15 releases cover various schemes of the X-15A2 56-6671 airframe. The first A2 kit release has the black scheme without external propellant tanks, dummy scramjet or ground handling dolly. In practice this means the kit may only be built as a replica of a post-landing configuration. The second A2 release has the same scheme but got the tanks and dolly. And, finally, another one added the dummy scram jet but only has the 1967 mission’s white ablative coat markings.
- The kit is made of short run injection-molded medium grey plastic parts, a clear-molded canopy part, more than 100 cast resin yellow/grey parts (in the two last releases), one etched fret with close to 50 parts and one photo film sheet (with 2 instrument panels). The initial release had resin/vacform optional parts for the canopy rather than the injected one.
- Many kits still have a thin layer of mold release agent on the parts. This gives a greasy/glossy look to the parts. It is highly recommended to clean the sprues with warm soapy water before starting any assembly.
- There are no locating pins. The plastic surface is a little bit rough on some parts. So, be prepared to sand, buff and polish the plastic as the plane surface was far smoother. There are also some molding sink marks and blemishes here and there. So, look closely to fill and sand them.
- Various small holes need to be drilled to add small parts. Double-check closely the angle of such full-scale details to drill with a correct angle as this should not always be perpendicular to the surface.
- The kit surfaces are nicely detailed with finely scribed panel lines and restrained rivet details. However, panel lines are not always consistent and are often inaccurate. Actually, it looks Special Hobby mixed rivet and panel lines. So, have a close look at walkaround pictures as a major effort is required to fill a lot of panel lines and recreate some new ones and relevant rivet lines. Even if time-consuming that step is recommended as such lines are quite visible on the full-scale black airframes. The improvement will be particularly noticeable on the nose and front top fuselage area.
- The reproduction of the Inconel X corrugated surfaces of the fuselage is excellent. Take care of not damaging it.
- General dimensions are globally correct. Fit is generally good but assembly is sometimes challenging. However, this stays very acceptable for a short-run kit.
FUSELAGE (from front to rear)
- The fuselage length is a little bit too long because of the nose shape. Glue the Q-Ball (A6 part) and remove a 2,5mm slice of plastic at the nose edge. Reshape the nose and glue a new Q-Ball (a lead pellet, a sinker or a steel ball is perfect). The detail lovers will use extra fine drills to add the differential pressure port holes in the Q-Ball.
- Drill further the Reaction Control System holes around the nose as they are too shallow. Ideally three drills should be used. Use first a drill with a diameter slightly smaller than the one of the holes you want to get. Then use a slightly larger one but stop at more or less half of the depth as there is a visible step in each hole. Last, the RCS hole itself has a far lower diameter and shall be drilled with a thin drill in the middle of the initially drilled hole.
- Do not use the P22 sensor probe part as it was only deployed during the flights.
- The “Skylight” compartment door scribed on the rear bulge just aft of the canopy is too short and far too narrow. Fill the engraved rectangle and scribe new panel lines 4 mm outboard of the existing ones for the width and another one 2,5 mm further on the aft end of the compartment.
- There is a nasty seam to hide between the rear upper and lower fuselage pieces. Take care of not damaging the surface details that are very close to that seam. According to the instructions, the upper and lower fuselage parts should be assembled separately before mating together the top and the bottom to assemble the full fuselage. This is a logical approach but this results in misaligned panel lines between the upper and lower halves. To avoid being forced to correct that annoying issue, assemble together the full top fuselage (A1 & B1). Then, add separately the lower front and rear fuselage sections A2 and B2). That way, you will get a single and not too visible gap issue to solve across the bottom of the fuselage. Last, it is recommended to use a putty that does not bite into plastic and/or use masking tape to avoid damaging the very nice surface details.
- For some flights, the airframe had more than a single probe (P34 part). This option is missing on the instruction sheet. It should be located on the belly central axis, right after the fourth panel line molded behind the P34 location showed on the step 15 instruction drawing. Drill a small hole in the belly and in each resin probe to use a section of wire in order to get a stronger assembly. In some cases, an identical probe was located on the top of the fuselage, behind the Skylight compartment. Note it looks the airframe had always a minimum of two probes (one on top and one on the bottom, one on top and two on the bottom or only two on the bottom). However, the kit has only two resin P34 parts.
- Thin the edges of the P12 resin parts.
- The camera bay door fairing is incorrectly located and too small whereas it should be further aft (between the tanks) and its edges should be protruding from the surface. Seen from the bottom, the fairing had a short H shape and should be created with thin plasticard sanded to get the correct profile. Last, the frames of the optical port should be scribed with a circular template. Take care while looking at pictures as many ones show the longer Hycon Maurer camera bay door fairing used on the X-15A1. That one had a fairing with longer and pointier edges.
- The kit second and third A2 releases have the huge external tanks. Plastic parts must be combined with resin details and copper wire intended to reproduce all the fuel lines plumbing. This is a very detailed assembly but there are some issues to avoid:
- The shape of the P47 squared parts to be added on the tank rear end is incorrect. The part front flat face should be perpendicular to the tank axis. Add a little wedge of plastic to the rear in order to lengthen each part and sand it to correct the parts angle. The side profiles of the decal schemes show the correct angle.
- The location of the fuel lines entry point in each tank is incorrect. Look closely at the instruction sketch as the three dimples indicating where the plumbing is going in the top of the tank are not correctly located.
- Similarly, check closely the alignment of holes in P54 and notches in P50 as they do not look correctly designed to ensure the plumbing lines are perfectly parallel as they should be.
- Last, as the plumbing system is raw metal whereas the tank is painted in white, orange and black, it is easier to assemble the full system with numerous dry assembly checks on the tank but keep it separate for painting before final assembly.
- The front and aft tank ejectors and their doors are missing on both sides between the tanks and the fuselage. The four doors must be cautiously scratchbuilt with beveled edges as they were added over the fuselage skin. The front ones were located close to the front of each tank. Similarly, the rear ejection arm with its door is missing between the fuselage and each tank. If you look at the length of the tank, it was located close to the level of F3 part but lower, where the space between the tank and the fuselage was very small. They look identical to the front ones with the door hinge at the front whereas the rear edge was rounded. For each one, a round hole should be drilled and a bare metal ejector (similar to F3 part) must go out of the tank through that hole (covered by the door when it was closed).
- The instructions ask for drilling out the 3.2mm diameter mounting holes for the horizontal stabilizers. Do this carefully to set the correct anhedral on these parts and check that you get a 29mm distance between the stab leading edge and the wing trailing edge (after having corrected the wing location). Note that the horizontal stabilizers are approximately 4,8 mm too short. Special Hobby seemingly did not take into account the pronounced anhedral of such flying surfaces. Extend their tip with plastic card or replace them with aftermarket parts.
- The horizontal stabilizer hinge fairings (P18 & P19 resin parts) are not correctly shaped. Moreover, they were only added in March 1965. So, look closely at the mission era you want to depict before possibly improving them.
- There are errors in the fin parts number in the instruction sheets. D11, D12 and D13 are the correct dorsal fin parts whereas D5, D6 and D15 are the deep ventral fin.
- The L15 parts should be located further back on the fin (in the panel ahead of the ridged one) and not used on the ventral fin.
- The two initial A2 kit releases do not include the modified ventral fin option that was used to carry the dummy scramjet amongst various payloads. Only that last release is including that option with three parts depicting a resin dummy scramjet (P83, 84 & 85). In that configuration, the dimensions of the ventral fin are a length of 70mm and a 14 to 18mm front to rear height.
- The leading edge of the ventral fin got a variable number of pitot tubes according to the specific test mission. Six of them were used during the speed record run but a maximum of ten of them could be mounted on the modified fin. The last release (32081) has a small photoetched part (L28) to reproduce them. They are so fine that replacing them with extra-fine tube would be a true challenge.
- Check closely the configuration you want to reproduce as you may need to add test panels used for specific flights. One was for instance added on the side of the ventral fin.
- The parts closing the bottom side of the ventral fin are too small. 3mm should be added at the end of part D14. When this is done, add thin strips on each edge of part D16 to get a correct width. Last, do not put L15 parts on the ventral fin.
- The ventral and dorsal fin airbrakes are missing some internal elements. SH just provides their actuating pistons as resin parts. As it is opened at the rear, add the missing dump pipes and multiple bare metal hydraulic lines in the ventral fin. Take your time as the assembly of the airbrakes parts is really tricky.
- The helium tank configuration located at the rear of the dorsal fin evolved noticeably. According to the considered mission era, the spherical helium tank was secured by a strap (up to 1965) or two mounting brackets (later). SH does not give any of both options. So please add the relevant details. Last, the B3 & B4 support parts assembly is too narrow as the width should be similar to the fin one.
- The rear side of the dorsal fin tail needs a thin section of plasticard to have clean and correctly sized edges.
- There is a nicely resin cast Thiokol XLR-99 rocket engine nozzle. However, the holes located around the exhaust nozzles need more depth. Drill them accordingly.
- The dummy scramjet in kit 32081 is only useful if you intend to use the stand to show the plane in flight. The other option asks for making oneself a small stand to show the dummy scramjet on the ground, close to the airframe. And the final one, for the very brave modelers, requires scratchbuilding at least a section of the NB-52A intended to carry the X-15!
- The wings are located about 2,5 mm too far back. To solve this noticeable issue, simply cut a new mounting slot in the fuselage sides and move each wing part forward. Alternately, you can cut 2.5mm out of the front of the wing locating tab. This option is easier but will result in a weaker assembly as the tab is very narrow.
- Drill slightly the Reaction Control System holes into each wing upper and lower surface of as they are too shallow. Us the process recommended for the fuselage RCS.
- The outlines of the flaps are too small and slightly mislocated. The flap leading edge span was 43mm inches long; its wing root chord was 24.5mm and 10mm at its outside edge. Fill and re-scribe accordingly.
- The A2 right wing outer half was removable. So, there was a visible panel line that starts close to the aileron external edge and is going through the “A” of the USAF white lettering. That line suddenly turns at 45° towards the wing tip when it crosses the rear of the wing leading edge section.
- The kit cockpit has some highly detailed areas whereas most others are rather plain. Be prepared for a serious amount of time and research to get an acceptable level of detail. Take care with NASA pictures as there were many differences between the three airframes and each one evolved as well. So, there are very noticeable differences such as fully different instrument panels, different colors of components, etc.
- Many small details are missing on the sidewalls (stiffeners, riveted plates, wiring, hoses, etc.). A large rectangular instrument white box with knobs is missing on the port sidewall.
- Some instrument panels and details are missing on the side consoles E14 & 15. Moreover, they have plain vertical sides whereas there was a large hole with a protruding edge strip in the rear of the actual ones to give access to some control components when the seat was removed. However, that discrepancy is not very visible when the seat is positioned.
- P23 and P24 resin parts are reversed and P17 is not correctly positioned on the instruction sheet. Refer to NASA cockpit pictures to position the parts correctly.
- This is fortunately not very visible but some equipment is missing between the bulkhead and the seat. The canopy actuating mechanism is also missing.
- The single photoetched part is correct but flat whereas the full-scale front instrument panel had many protruding elements. T-handles (like the canopy emergency jettison one) are missing and shall be added but the detail lovers will also add all the missing switches as well as the knobs and protruding oblong warning lights.
- The seat is very visible but far too basic in spite of the close to 20 parts required to build it:
- A very large number of small details are lacking or are too simplified from the bottom spurs to the top of the head set (oxygen tube and connector, T-handle, strengthening plates, etc.).
- The E7 cushion is rough and needs to be somewhat reshaped.
- Many rivet lines are missing on each side of the seat (parts E20 and E21).
- Prominent rivet and screw heads are missing on the external side of the two stabilization wings protecting the top of the seat (E29 & E30). Their massive hinges are also missing between their lower edge and the seat sides.
- Note photoetched seat belts are nicely reproduced but are unfortunately too narrow. Replace them fully or at least cut cleanly the buckles and put them on new ones made of lead foil.
- Note the resin eyelid windscreen heat shield fitted to the left-hand windscreen (P44) was normally closed on the ground (it only opened during the landing phase). It was installed before the 1967 high Mach number flights that requested the use of the ablative coating (protecting the airframe from the high heat air friction). Its internal actuator arms are missing. If you ever want to open the eyelid, this will ask for reconstruction and the arms should be added at the middle of the length, behind the two shutters.
- The canopy has no internal detail. This is unfortunate as this area was quite busy on the full-scale airframe. Many items should be added such as a head cushion, structural strengtheners, windows frames, seals, plates, piping/wiring, spotlights, cameras and many rivets and screw heads.
- The original release has two options for the canopy: vacform and resin whereas injected plastic was the only option in the later kits.
- The kit does not have the two sticks intended to support the canopy when it was opened.
- The nose gear leg A7 part has very basic details. There are very visible shrink lock missing elements on the front of the leg. They really deserve to be added. Scratch them and add 6mm to the front strut to decrease the excessive nose down attitude. Last, resin part P25 has a more than 1mm too large width. Cut it in the center and sand the two edges before re-mating both halves together. The P25 part is actually far more simplified than the actual connectors linking the gear leg and the door. They had strengtheners, bolt heads and other details that should ideally be added.
- The forward edge of the nose gear bay is a little bit too far aft of the correct position but this is not really noticeable (1,5mm). The front wheel well and its door are 2,5mm too long. Here are the correctly scaled door dimensions: length: 30.5 mm and width: 11,2 mm at the forward edge and 12,7 mm at the aft one.
- After having solved the dimension/location issue, correct the location of the landing gear leg anchor point. Actually, it should be at least 4.5mm closer to the aft edge than it is on parts E4 and E5.
- There is a noticeable lack of internal details in the well. The full scale one had various elements such as the large retraction piston, some structural details, wiring, heat insulation and other gizmology that are unfortunately fully missing in the kit. The insulation may be reproduced with a rectangular section of heavily crushed aluminum foil.
- The nose gear door rear end (top of part A8) should be actually rounded rather than squared. Moreover, part P43 should be offset to the port side of the door.
- Only the instructions of the first A2 release (32022) give the deployed position of the landing skids. If you want to choose such a post-flight configuration for the two other kits, the instructions are available on the Internet and the parts are available in both other boxes (E6, E9, E12, E26, P35, P36, P39 & P40).
- The way the main landing gear is secured on the fuselage is quite weak. With the additional tanks and other details, there is some probability this will not sustain the load for long. To avoid a LG break, it is recommended to reinforce it with brass wire going from one side to the other one. Drill holes in the leg end (through E11 & E26) and glue everything with CA gel or epoxy glue. Replacing the resin shock absorbers and retracting legs with polished aluminum tubing is also a way to strengthen the full assembly.
- The rear landing gear is made of a front skid pad and a rear support strut intended to attach it to the aircraft. Oddly, the kit pads corresponding to the flying and landing configurations have different lengths. The rear support strut is also not the same length in both configurations in the kit. The correction you may want to make will depend on which configuration you are modeling.
- The flying configuration has a correct ski pad part. Cut to separate the front skid pad and rear support strut at the scribed line level. Then, add 6mm to the front end of the rear support strut section. Mate both parts back together with glue and scribe again the line to simulate the separate parts. The final overall length of the assembly should be around 60mm.
- The landing configuration pad part is too long. Remove 33mm from the aft end of the part. Take care as that correction is weakening the full landing gear assembly.
- Drill out the rear pivot points and insert a 1 mm diameter length of plastic tube to simulate the pivot itself. If you do not have a tube of the correct diameter, use a rod and drill a hole in the end to simulate the end of the full-scale hollow tube.
- The skids have a correct U section but the full-scale airframe part shows a quite thinner cross section. Try to restore the correct profile. There are also multiple sink marks to fill in the skids external surface as well as mold ejection tabs to remove on the other side of E6. Take your time and possibly do that cleaning work in various steps as this is a quite tedious task.
- The second and third A2 releases have the ground handling dolly. This is a very complex assembly made of more than 70 resin, photo-etched and wire parts. Use reference pictures to build the hydraulic hoses and connectors. Take you time to build cautiously that subassembly as it is very complex and rather fragile. Last, the full-scale item had some very visible large black with white lettering service labels. Unfortunately, they are not given by SH.
- The speed brakes may be opened. Landing skids are supplied in both the landing and flying configurations. However, the kit has no pilot and if the interior is close to invisible when the canopy is closed, the pilot white helmet was very visible under the canopy. Note a 3D printed aftermarket seated pilot is available.
- Note the second kit release (kit 32029) is the shorter X-15A1 with the two XLR-11 engines and the nose test probe. No kit of the first airframe with the XLR-99 or the third and final airframe have been released up to now.
- The kit has the later type of canopy with the oval windows commonly used during the mid-sixties era. The airframe used trapeze-shaped windows at the beginning of her life. To depict that era of use, you can cross-kit that model with the X-15A1 kit (32029) to make a late X-15A-1 and an early X-15A-2.
- The kit does not give the bug-shaped bulging cameras option. Two of them were installed behind the canopy for some early flights.
- The kit has the helium tank fairing configuration used during the mid-sixties. Initially, the airframe had none behind the dorsal fin (1961-1962 era).
- The Inconel black scheme was actually everything but plain black. Pictures of the full-scale airframe show a lot of differences of color variations and shine intensity between the various panels. Please refer to them and use various satin hues of extra dark greys, metallic dark brown and very dark blues to get a more realistic scale replica. Last, a light grey wash will replicate nicely the standing out rivet and panel lines.
- The Q-ball should actually be painted with a dark metal color.
- Before the use of the final full white scheme, some test flights used the Martin MA-25S brick red ablative coat, white and/or dark green thermal paint to cover some specific areas such as part of the fins, the stabilators, the wings, the lower nose area or some belly panels close to the ventral fin. Again, this varied from one mission to another. So, check closely beforehand what you want to reproduce.
- Some X-15A-2 flights used tanks with a bare metal rear (chrome color) and silver painted front finish. So, again, check the period and configuration you want to reproduce.
- If you want to reproduce the speed record plane with the white ablative paint coat, there are two very different options:
- If you choose to put the plane on the ground handling dolly with her tanks before the flight, the finish was totally pristine. This is what the kit is proposing in the marking schemes (before and after installation under the NB-52A wing). Nonetheless, note a light beige color was visible around the panel seams.
- If you rather choose the landing configuration, you cannot use the droppable tanks or the dummy scramjet as it had been lost during the flight. Moreover, the plane was badly damaged during the flight and her surface was severely burnt when she landed. Accordingly, be prepared to reproduce paint burns and brown to black traces on the paint (typically on panel lines and the fins). The detail lovers will also try to reproduce the orange peel finish as well as cracked paint areas on the nose. Moreover, the fins revetment surface was heavily damaged. This was very visible on the ventral one leading edge and sides; the areas being literally pierced with edges torn by the heat.
- The decals are quite fine but they are multiple small errors on the black schemes: black rather than royal blue NASA logo markings, too large stencil lettering on the nose, incorrect serial number digit and NASA font use, mix of mission markings, use of outdated markings on the belly, etc. Moreover, look closely at the mission you want to reproduce as the markings evolved a little bit along the airframe life. Fortunately, most of the marking errors are not that noticeable and can be solved quite easily. Alas, for some others the only solution relies on the use of aftermarket markings.
The following sources were used to build this list.
- Modelling essentials:
- Guenther, B, Miller, J., Panopalis, T, North American X-15/X-15A2, Aerofax Datagraph 2, 1986.
- Colour pictures photofiles:
- Jenkins, D.R., Landis, T.R., X-15 Photo Scrapbook, Specialty press, 2003.
- Jenkins, D.R., Landis, T.R., Hypersonic: The Story of the North American X-15, Specialty press, 2003.
- Other references:
- Baker, David, North American X-15 Owner’s Workshop Manual: All types and models 1959-1968, Owner’s workshop manual, Haynes, 2016.
- Godwin, Robert (Ed.), X-15: The NASA Mission Reports, Space Series 13, Apogee book, 2001.
- Landis, Tony., X-15 photo reference, CD-Rom, 2007.
- Some magazines articles (more particularly from Wingmasters & SAM)
- Some web pages (more particularly NASA, Hyperscale & LSP)
© Thierry Laurent 2021
This article was published on Saturday, February 13 2021; Last modified on Saturday, February 13 2021