by Tommy H. Thomason

Tuesday, April 23, 2013

A Note on Rotor Blade Droop

Most helicopter rotor blades droop when the rotor is not turning, some more than others depending on the type and design of the rotor hub and the stiffness of the blade. However, as a general rule:

1. Most rotors have a "droop stop" at the hub. This keeps the blade from hitting the fuselage when the rotor first starts turning. That means the blade will extend straight out or at a small downward angle from the hub with little bend for the most inboard portion of the blade.

2. The outboard end of the blade doesn't curve as much as the middle. That is because there is less weight outboard to cause bending as you move outboard on the blade.

3. The most curve is very roughly somewhere between 20% and 50% of rotor diameter. The inboard end doesn't curve as much because of 1 and the outboard end because of 2.

This is an illustration from a discussion of the shear and deflection of cantilever beams (http://www.codecogs.com/reference/engineering/materials/beams/cantilever_beams.php) that illustrates the general rule:
 An example from the Emil Buehler Library at the National Museum of Naval Aviation:
Note that the root of the blade that extends aft angles upward because the rotor mast of the Sikorsky H-3 is tilted forward relative to the fuselage waterline.

Saturday, April 20, 2013

Cyber-Hobby SH-3D Build by Jodie Peeler


8 June 2015 update from Jodie Peeler: Cyber-Hobby subsequently released its SH-3H kit that includes some components left out of its SH-3D and SH-3G kits (which were identical in content except for decals). It includes both types of sponsons among other details and is a better starting point than the SH-3D kit I used for this build. For an inbox review, see http://tailspintopics.blogspot.com/2014/11/cyber-hobby-sh-3h-in-box-review-by.html

Although it would have become clear soon enough from the breadth and depth of the content and the number of excellent pictures, the following post was provided in its entirety by a guest modeler and fellow author, Jodie Peeler. (For background on the U.S. Navy ASW Sea Kings, see http://tailhooktopics.blogspot.com/2013/02/us-navy-asw-sh-3-sea-king-variations.html )

Cyber-Hobby's announcement of a 1:72 SH-3 Sea King kit got my attention fairly quickly. I've loved the SH-3 for a long time and always welcome new kits of the Sea King. I've built several of the trusty old Fujimi kits over the years, but it's due for replacement. As much as I looked forward to this kit, I felt uneasy when I saw Cyber-Hobby's box art. What was an SH-3D doing with all those goofy sensors, antennas and fittings? I hoped it was just box art being box art, but photos of the completed kit (http://tanooma.blog75.fc2.com/blog-entry-822.html) made my heart sink. Once the kit got to market, though, I couldn't help myself, and in the interest of science I set out to find if the Cyber-Hobby kit could be salvaged. It...was an odyssey.

OVERVIEW: The kit has five trees of gray plastic parts and one clear tree. The breakdown reminds me of Hasegawa's magnificent 1:48 Sea King: two fuselage sides, a separate hull bottom, and a tail assembly that attaches at the fold line. Main rotor blades come in two styles: curved up as in flight, or sagging as if at rest. You can depict port and starboard doors open or closed, the tail extended or folded, and the main rotors deployed or stowed. There's a ton of parts you won't use, and your spares box will be grateful. A closer look starts to reveal problems. The fuselage has several sensors and mounts meant for other variants, and those must be removed and filled. Some are difficult to fix because of close tolerances. The most bothersome area is on the starboard side, below and behind the cargo door: you must not only fill the mounting slot and tab for the boarding steps (while preserving the door track), but you must backfill and then grind off the electronics fairing left over from this kit's origins in the AEW.2 Sea King issue. (Detail-oriented modelers will also want to add the little rectangular recess beneath the cargo door, easily done by cutting out a little rectangular opening and backing it with sheet styrene.)

The most puzzling omission is atop the fuselage. There's a shallow curved recess for the little doghouse aft of the transmission housing, but the kit gives you no part for the doghouse. Without it, the model will look incomplete. (You'll also notice that while there are tiny little mounting holes in the grab handle recesses on the engine compartment, you don't get any grab handles to put there.)

Fortunately, the Westland-style hump on the port side of the transmission housing is a separate piece, and can just be left off. There are grill recesses on various parts of the airframe; while their shapes are accurate, they have no grill detail in them, and no photoetch is supplied. It looks funny. Elsewhere on the fuselage, the forward cabin window on the port side is appropriate for an SH-3H, but wasn't there on SH-3Ds of this vintage. Scribed outlines for observer windows on the aft fuselage must be filled too. The tracks for the starboard side cargo door have an extra set of mounting rails for the door part, and it looks clumsy. Even if you display the door open, your model will look infinitely better if you shave those extra mounting rails off.

You get a sonar housing and a really nice sonar probe to fit in it, but must cut out a hole in the cabin floor to make it all fit.

The sponsons look decent and have very nice separate wheel wells. Comparison to outline drawings convinced me the wheel wells needed to be moved aft about 3 mm or so, and that the sponsons themselves needed a little more rounded upper shape. There's also a very prominent access panel molded on the outboard half of the port sponson; it needs to go. The stub wings that attach the sponsons to the fuselage fit flush against the fuselage; on real Sea Kings, there's a very small gap between the stub wings and the fuselage, with two round struts are just visible. (Both Fujimi and Revell-Germany depict this gap and the twin struts on their kits.)

The cabin interior is a vast array of severely underscale sling seats for tiny troops, with no representation of ASW equipment at all. The cockpit looks okay, though the mounting hole for the port-side collective is on the wrong side of the seat. The exquisite pilots' seats are the revised crashworthy variants, which didn't come along until the mid-'80s. Clear parts look good; the cockpit cab is especially nice. You get open and closed side windows for the cockpit, but they're incredibly thick moldings. Windshield wipers aren't molded on the greenhouse, but are separate parts (albeit very thick ones) on the gray trees.

The Cartograf-printed decal sheet gives you three bright, colorful options for high-visibility SH-3s: an HS-3 aircraft off Forrestal in 1974, an HC-1 aircraft off Coral Sea during the 1970s, and an HS-75 aircraft from the early '80s. Some elements of these decals look nice and the colors look good, but others have accuracy issues and look a little clunky, and some appear to use modern fonts instead of more period-appropriate lettering or stenciling.

RESEARCH SOURCES: There's no way around it: you must do your homework before you begin. As Tommy's research has shown, SH-3s had numerous configuration changes through their lives, and what's accurate for one build may not be accurate for another. It's best to choose a specific aircraft at a specific point, one for which you have good references, and build from there. If you have to imagineer a bit, at least you'll have the fundamentals correct. There's a lot of Sea King pictures on the Internet, and an afternoon's searching helped me find good interior and exterior detail pictures. So far as printed sources, "Famous Aircraft of the World No. 15" is an absolute must for constructing an accurate Sea King model. In addition, Tommy supplied me with many marvelous documents, drawings and photos that helped in countless ways throughout this project. Read his post about the Sea King, and use the material he posted there. It will definitely help you. As for this build, I deliberately chose an aircraft that was close to the kit's intended configuration, would let me construct an appropriate interior for a properly-equipped SH-3D of the period, and had markings that interested me. I then conducted my research, and the build, accordingly.

BUILDING THE KIT: Before we begin, I must warn you: Test-fit most everything before committing glue. This is especially true here. Some parts I expected to fit one way were keyed the opposite (and would have seriously messed up the build if I hadn't caught that in time). Also, be aware the kit's fit tolerances are sometimes so tight a layer of paint will mess up the fit. Trust me: test-fitting will save you a ton of grief.

I like making heavy modifications first thing; it not only gets the most severe angst out of the way up front, but minimizes damage to complex assemblies later on. I started with the fuselage, removing some unneeded lumps and bumps and filling various holes and slots. This is also a good time to plug the extra cabin window opening on the port side. On the interior side, I used styrene strip to fill out the incomplete structural framing, and also removed the clunky window mounts inside the cockpit. Some of the exterior step recesses are molded so deep that daylight can get into the fuselage; little bits of styrene on the inside half will take care of that.

The instructions have you drill all manner of holes for mounting various things, some of which you don't need. I'd rather trim off pins and locate things myself later on, so I didn't bother with any of that.

Now is a good time to modify the sponsons, if you want. My references convinced me the sponsons would look better with the gear wells moved aft about 3 mm. The mounting tabs had to be removed and I had to sand the outside edges of the well box to make everything fit. I also recontoured the upper edges of the sponsons, inserting corrected outlines made of thin sheet plastic into slots down the centerline of each sponson. All gaps were sealed, and everything was faired in with epoxy putty and sanded to shape. Lost detail was later rescribed.



INTERIOR: I mostly built the cockpit as-is, though I moved the port-side collective lever to the proper side and built older-style seats for both pilots. The new seats are modified Fujimi units sanded to shape, enhanced with frames made from 28-gauge craft wire and seat belts made from Tamiya tape, and mounted on the modified Cyber-Hobby seat brackets. Seat cushions in SH-3s were usually orange during this time frame.

Everything aft of the cockpit was rebuilt. I laid down a new floor of .010" sheet and built up from there, cutting the hole in the floor for the sonar housing. (If you're building an Apollo recovery helicopter with its sonar equipment temporarily removed, or an SH-3G, you can skip cutting that hole; instead, put a thin circular plate where the well hole would be.) I used the kit's "broom closet" as a guide for a new one. I also built a simple framework over where the AQS-13 cable/motor installation would be, covered it with a shroud made from Tamiya tape, and added a few cables running to the electronics racks.

There should be a second crew seat in the cabin, but I only installed one; fortunately, on the completed model, you can't tell there's a seat missing. I didn't install the sling bench seat in the aft cabin until later.



 SH-3s usually had the cabin blanked off with canvas just aft of the starboard side door, and I represented that with sheet plastic covered with painted tape and detailed with ink. It's simple, but it works. You'll also need to make a ceiling for the cabin, but that's easy enough with .005 sheet cut to shape. The overall interior color is Dark Gull Gray, with details brush-painted as appropriate.



MAJOR ASSEMBLY: If you've done plenty of test-fitting (and you have, right?), everything should fit fine and joining the fuselage should be easy. Cyber-Hobby's fuselage breakdown means minimal seams and easy clean-up. Be sure to install the sonar well inside the hull bottom (or the plug, for a -3G with the hole plugged) before you close everything up. For a helicopter with its sonar temporarily removed or for an SH-3G that still has the well opening, cut the sonar well insert so its top sits flush against the bottom of the cabin floor.






If you don't want to fold the tail, now is a good time to install it. I had some minor problems getting mine to fit flush, and had to fill a small gap at the driveshaft housing. If I build another I'll probably join the tail halves to the fuselage halves before assembling the fuselage.

The Cyber-Hobby instructions have you install a lot of delicate parts - air data probes, antennae, mirrors, etc. - at various points when they'd be easy to damage or lose forever. Save all that for the very end. Right now, think in terms of painting strategy. I install the cockpit greenhouse before painting, as I wanted to reshape the nose a little and take care of any seams. Unfortunately, the fit tolerances are so tight that installing the greenhouse was a struggle, requiring lots of precise filing and sanding. It still isn't perfect, but the black anti-glare paint helps hide some flaws. By the way, if you install the greenhouse at this point, it's best to paint the overhead windows from the inside before you install it. Most SH-3s had clear blue overhead windows in the late '60s (green and smoke tints came along later, and occasionally a Sea King operated with windows of two different colors depending on what was on hand). Tamiya's transparent acrylics are ideal for this task.

There have been complaints the Cyber Hobby kit has nose shape problems, and I spent a lot of time looking at pictures of the real thing. To me, the Cyber-Hobby nose looked a little flat across the "bridge" beneath the cockpit windows. I tried to improve the shape with a little putty, and that did help a little.
 On top, install the (nice) exhaust tubes and the engine cover - but make sure the exhaust tubes are keyed the right way. Mine weren't, and I had to do some drilling to orient them properly. Don't install the (exquisite) intakes just yet; paint them separately and install them during final assembly. As with the cockpit cab, you'll probably need to do some fine file work to get the engine cover in place.

The Cyber-Hobby kit doesn't give you the SH-3's prominent teardrop-shaped ADF fairing on the lower edge of the aft fuselage. You can steal one from a Fujimi kit or make your own (just laminate some plastic and sand it to shape). Either way, the model really looks naked if you don't add one.

You'll also need to make that little doghouse aft of the transmission hump. Though easy to cut from sheet plastic, getting the right shape for it to sit against that groove was the devil itself. The Eduard photo-etch for the Westland variants has a doghouse part, and I used it as a guide; I'm hoping a similar set for the SH-3 will be forthcoming.

The intake shield is the later two-part variant with the dished base. It wouldn't work for the aircraft I wanted to build, so I had to extensively modify it with sheet plastic, using the Fujimi kit's intake shield as a guide. I didn't install the sponsons yet. It's best to leave them off until final assembly.


PAINT AND DECALS: Tamiya spray primers formed the base for airbrushed Model Master acrylics: Flat White for the upperworks and Gull Gray for the lower fuselage and sponsons. The warning band on the tail is Insignia Yellow, and the red trim is Chevy Engine Red (chosen because it's warmer than Insignia Red). The anti-glare cockpit surround, intakes, exhaust hide area and stub wing non-skid areas are Aircraft Interior Black, and the exhausts are a custom-mixed dark aluminum. Main rotor blades were first sprayed Tamiya Chrome Yellow; with tips and stripes masked off, I painted them Gull Gray on top and Interior Black on the bottom. Everything got a coat of Future before decals and weathering. I wanted to depict an SH-3D of HS-3 in 1969, assigned to CVSG-56 aboard USS Yorktown. With period references to guide me, I created artwork in Illustrator and printed my own laser and ink-jet decals. Standard airframe markings came from the kit decal sheet and the Apollo Decals "Old 66" sheet. After the decals had set, I applied some very mild weathering with watercolors and pencil, and finished everything off with a custom-mixed semi-gloss clear coat. Sea Kings got sooty and I'm aware my model is too pristine, but I'm wary of overkill and thus keep my methods restrained.

FINAL ASSEMBLY: The sponsons went on very easily, and the model had the correct "sit" even after the sponson modifications. I also added blade and wire antennas at this point, and installed the doors and windows. The cockpit side windows looked much too thick, so before painting their frames I cut them into separate pieces and used a multi-grit nail polishing stick to reduce their thickness and polish them out. The separate "nested" pieces look much better this way. G-S Hypo Cement holds the windows in place. Up front, I ditched the clunky injection-molded windshield wipers in favor of new ones made from stretched sprue.

I also detailed the crew door on the port side with some stretched sprue, too. All doors benefit from being thinned down to a more in-scale appearance. I think I used the wrong door on the starboard side, but it's too late to worry about now. I ran a mooring line made from stretched sprue from the bottom of the hull to the port side of the cockpit, and added a tiny cover over the end below the cockpit window. (Not that stricken SH-3s tended to stay afloat long enough to moor, but it's nice to know it's there.)

The winch assembly looked a little clunky, so I modified it to mimic the Hasegawa parts. I added a length of thin stretched sprue to represent the cable and attached the hook end to a winch strut, commonly done to make it easier to reach from the doorway.

As with all 1:72 Sea King kits, you don't get weapons shackles. I made some from bits of styrene and circles punched with a Waldron set. Photos taken aboard Yorktown in 1969 showed full shackles on all four stations, but I was feeling lazy and only put mounting stubs on the aft stations.

Up top, I'd decided some time ago to fold the main rotor and save some display space. I modified the folded blade mounts to make them look less clunky, and added a little plumbing to the rotor head. I couldn't get the outer blades to sit to my liking using the kit parts as-is, so I modified them to taste. My efforts to make tie-downs for all five blades came up short, so I just tied down the outboard blades, as was sometimes done. This was done with painted Tamiya tape, fine brass wire and smoke-colored "invisible thread."

After last touch-ups, the little SH-3D was all done:


And it was ready to meet the other 1:72 Sea Kings in my collection. Here it is with a Fujimi kit I converted to an SH-3G a few years back:







And here it is with a Revell-Germany kit I converted to an SH-3H a few months ago:


Here's a family portrait. Fujimi to the left, Revell-Germany in the middle, Cyber-Hobby to the right.



CONCLUSIONS: The good news is that, properly built, the Cyber-Hobby SH-3 kit can give you a very nice model. For my money, a corrected Cyber-Hobby kit gives you the sharpest-looking Sea King in 1:72 scale. The bad news is, you really have to work for it. You must deal with mismatched features, fit tolerances that are sometimes too tight for comfort, and a few toylike details. It's funny, because some parts of this kit are downright gorgeous. Yet you're left thinking about what it could have been. As an example of modern computer-assisted kit design, it's a marvel. As an accurate representation of an SH-3, it falls far short. While the needed modifications are within the skill set of most modelers, errors that could be forgiven in a $15 kit are very difficult to pardon in a $40 kit, especially when some homework and some input from informed sources would have prevented those errors. The mismatched features, the inaccurate inclusion of some parts and the absence of others (missing the prominent ADF fairing on the tail is especially inexcusable, for one thing, and I'm not even going to comment about the interior problems) just should not have happened in a modern kit release, certainly not on a subject for which so much information is available from so many sources. This kit left me incredibly torn. The finished result has the best look of any Sea King I've built in 1:72, and looks more like the real thing than the Fujimi or Revell-Germany kits I've built. The end result made me very happy. At the same time, I'm aware of how much work I put into making it look this way, and left regretting the potential that was left on the table.

In spite of my feelings, I'll probably build another, and the lessons learned on this build will guide me on the next. Unless Hasegawa sees the light and scales down its magnificent 1:48 Sea King, at least.

Thursday, April 18, 2013

AJ-2 Savage Cockpit

When I was working with Anigrand to provide the data for their excellent resin 1/72 AJ-2 Savage kit, I didn't have much on the cockpit. This is my crude sketch from memory and notes from when I was in the cockpit of the Lycoming AJ-2 at Stratford.

It turns out that it actually looks more like this:


Since then, I've had the opportunity to photograph the cockpit of the same AJ-2 now at the National Museum of Naval Aviation at Pensacola. It was a former civil fire bomber used by Lycoming to test a jet engine suspended from the bomb bay so the AN/ASB-1 equipment had been removed, but otherwise I would guess that it was stock although the seat headrests have been removed. My drawing was pretty close except I had three indented steps leading up to the flight deck instead of two...

Note that the cockpit changed notably between the AJ-1 and the AJ-2. The pilot's control stick was replaced by a control wheel and the engine controls being moved from the left console to the center console. The crew chief was moved up from the lower compartment to the flight deck and the big circuit breaker panel was moved from the pilot's left back to the crew chief station. This is a picture of a North American flight test AJ-1 that is also missing the AN/ASB-1 and probably some other stuff. However, it shows the control stick and the throttle quadrant on the left console:

On to the tour of the NMNA AJ-2.

Most of the cabin door could be jettisoned for bailout with a small section remaining on the hinges as a wind break.
The ladder to the cabin folded so it could be stowed in the airplane.
The view from the cabin door directly into the area under the flight deck.

The view from the cabin door up to the flight deck. Note that there is a passageway under the flight deck on the left side of airplane for maintenance access.
The steps up to the flight deck also functioned as a slide down to the cabin door. (The pilot and bombardier seat backs could be collapsed aft for less impeded access to the slide.)
The pilot's instrument panel and center console:

For a description of the bombardier's position, see http://tailhooktopics.blogspot.com/2013/01/aj-savage-bombardier-station.html

The left console (yes, that is an ash tray painted red on the left):
The crew chief's panel. On the other side of that bulkhead is a fuel tank with a V-shape bottom in cross section:
The view aft, down, and to the left from the flight deck (the door to the bomb bay is open). Note that the flight deck angles to the left side of the airplane at the crew chief's station:
The door to the bomb bay when closed:

Wednesday, April 10, 2013

Things Under Wings: VA-25 A-1 Skyraider Toilet Bomber

In October 1965, VA-25, which was flying A-1 Skyraiders from Midway, famously dropped a toilet during a close-air-support mission over South Vietnam. For more, see http://www.midwaysailor.com/midwayva25bomb/
From the Midway Sailor web site

I was recently asked to identify one of the bombs carried on the mission that cannot be seen in the picture taken from the side. I naturally turned to my go-to guy for things under wings, Jim Rotramel. He recognized it at a glance, of course, as a 250-lb AN-M57A1. He also reported that the generally accepted identification of the other stores is incorrect. The two big bombs on the outboard pylons are not M117s but the similar looking, smaller, and somewhat lighter 500-lb AN-M64A1 with a conical tail. The store on the main wing pylon is generally identified as a cluster bomb dispenser, specifically an SUU-30 of some sort; Jim was sure that it wasn't but couldn't identify what it really was.

I looked more closely at the pictures available and did some analysis using Illustrator and the excellent drawings of the stores that Jim provided and finally came to the conclusion that it was actually another AN-M64A1 with the shape of the afterbody obscured by the red edge on the lower side of the inboard main landing gear door. No wonder Jim couldn't match it up with any CBU that he was aware of.

Mr. Skyraider, Ed Barthelmes, came through with a color slide that positively demonstrates that:

Note that Ed's Squadron/Signal Walk Around No. 27 on the A-1 Skyraider, written with Richard Dann, is one of best references for this venerable airplane.

The load out on the left side is presumably a mirror image of the one on the right side except for the toilet, of course.
 From the Midway Sailor web site

Based on drawings provided by Jim:
Note that the bombs in the illustration above have the fins in the + orientation; the tail cones of the bombs on the airplane have been rotated to the x position.

There are a few different kits and aftermarket toilets available for this particular aircraft; see http://www.midwaysailor.com/midwayva25bomb/. As far as I can tell, none have the correct stores configuration depicted, much less included, and none include the red tail on the toilet.
From the Midway Sailor web site
 A side view of the store showing its position on the pylon and the size of the tail: