Lessons Learned building the Mustang II
a.k.a.: "I wish someone told me that 8,000 rivets ago..."
This information is compiled from various sources intending to help present and future builders of the Mustang II.
Submit your "Lessons Learned"

Use of this information for Your aircraft is obviously AT YOUR OWN RISK.

To slew ahead, click on the sections below:
General Time management / psychology Safety Tools / Hardware Sheet Metal
Riveting Systems Center Section Flap Forward Fuselage
Wet Wing Tailcone Landing Gear Fiberglass Canopy / Plexiglas®
Paint Flying / Flight Testing Cleanup Corrections "ADs" & Service Bulletins

Updated February 12, 2016

Time management / psychology
  • Rick's Law: "Everything [done correctly] takes a lot more time than you'd expect."
  • If you start to get "builder block", work on another assembly or system for a while.
    (Or spend some time reading one of the above references.)
  • Make a list of everything you can think of that you need to do to build this plane. Date each item on the list as it is completed, but leave it on the list. When a roadblock interferes with the current task at hand, a quick reference to the "To Do" list will get the project moving again, because the list can be used to pull yourself away from the task at hand. Kirk Harrell
  • Keep a daily log of time on task. Just a short note of what was being done. Then when frustration sets in or it feels like you aren't getting anywhere, a look at the log and "To Do" list will give reassurance that there is progress being made. Kirk Harrell
  • Try to do something on the project every day - even if it's only for a few minutes.
  • If people come to visit, after a few minute "tour", get back to work while talking to them. Maybe even put them to work.
    Deburring is a good job for visitors...
  • Smooth all sheet metal edges, and [at least slightly] round exposed corners.
  • Use eye protection! A graphic close-up photo of the doctor removing a piece of grinding grit from my right eye (while I was wide awake) would make a believer of anyone.
    The fuller story: I was wearing eye protection, but I transferred a piece of grit from my dirty hands to my eye when the grinding job was done.
    The lesson learned: Cleanliness!
  • Use a cartridge style respirator when spraying any zinc chromate, solvent or paint; or when sanding fiberglass or mixing microballoons for filling fiberglass. Kirk Harrell
    Change cartridges if you ever smell solvent through them. (Or sooner...)
  • If spraying polyurethane, invest in a separate air source hood / mask. A cartridge style respirator is just not safe enough for this paint.
  • Incompleted items: At any given point in the project, but especially when systems are being installed in the airframe, there are a number of unfinished tasks going on at one time. Keep a "To Do" list and don't mark anything off of it until that task is torqued, safety wired, double checked,... etc. Keep the full list and date the item when it is complete. If you have to remove a bolt or take off a safety wire, take the date off of the completed task. Kirk Harrell
Tools / Hardware
  • "Use the right tool for the right job". My high school shop teacher...
  • A pneumatic squeezer is a "must" for a metal airplane project.
    ("Would you build a house with only a hand saw?!")
    A pneumatic squeezer can be used for a large percentage of dimpling operations as well.
    I would suggest not even buying a hand squeezer - spend the extra $300 now and get a pneumatic squeezer. RH
  • A frame riveter can speed dimpling operations and is very helpful on long rivets, such as for the control tubes.
    (Rivet head down, shop head pointing up.)
  • Rivet shop head gauges and a Rivet length gauge are a "must".
  • "Oil-less" air compressors (typically a lot larger for less money) are painfully too loud. Get an "Oil-lubed" compressor instead.
  • An angle drill and a snake drill with #30 and #40 threaded drill bits are useful in tough-to-get-to areas.
  • Drill Bit / Size / Application / Fastener size (to post on your shop wall):
    #11 .191 #10 screw , AN3 bolt (.186 -.189)
    #19 .166 # 8 screw (.164) (I usually use #18 .169 for access panels, etc.)
    #21 .159 -5 rivet (.156)
    #28 .140 # 6 screw (.138)
    #30 .128 -4 rivet (.125)
    #40 .098 -3 rivet (.094)
  • 6 inch and 12 inch drill bits are also helpful in ways you'll discover as the project advances. Start with: 1/8", 3/32", #30, #40 in both 6" and 12".
  • Buy a deburring wheel for your shop grinder. They are fantastic for deburring aluminum and steel. Avery Tools recommends the 3M scotchbrite 7A-MED wheel. I purchased a Shur-Brite convolute wheel thru Wholesale tool. Bill Lamb MII-254
  • Bucking bar #751 is recommended. Jack Phillabaum Other favorites: #723, #736 and a very narrow bar (1/2 inch wide) such as #646.
  • Reamers: Always, always, ALWAYS mike a reamer!! Never use ANY reamer that you don't first mic! Always (did I mention, always?), have a mic in your hand. Fresh new 1/4" reamers from the certified tool crib vary all of .010". I've taken my micrometer to the tool store (gotta couple of sideways looks) but there is a BIG difference in reamers. Look for one in the .2485 - .249 range. Mic at least twice, down by the end. The flutes should have a slight 'back taper' so mic at the tip. Larry.Schurr@Wichita.BOEING.com
  • Bolt fit: A close fit fastener - of about any dia - should be tough to push in with your thumb but not require more than a very light hammer (4oz) to insert. Larry.Schurr@Wichita.BOEING.com
  • A set of inexpensive reamers (cheap) can be had from Harbor Freight, and Enco Tools. Enco has a wider selection of machine shop equipment including some of the "aircraft stuff" we pay through the nose for. I've had a set of cheap reamers for some 25+ yrs. If used judiciously, they're just fine. They are not shop quality. Torello Tacchi
  • Standard size drills are not the size they claim to be, i.e. 1/4" will make a .250 hole +.003-.001 assuming the bit is new, and sharp, and most importantly drilled in the proper manner. Standard bolts, Grade 5 and up including AN are under sized. This undersizing would be detrimental on a stressed fitting such as a spar attachment. No matter how tight, it will move, and in a shear motion. Once the movement starts, the shear is not far behind. A close tolerance bolt is no stronger than a standard bolt. It's strength lies in the "close" fitting of bolt in relation to the hole.
    The Bible, "Standard Machinery Handbook" will answer such questions. Yes, when making spar mounts, it must be close tolerance. We've already spent a lot money on ancillaries, don't skimp on this. Torello Tacchi
Sheet metal
  • Smooth all edges and round protruding corners with a fine mill file or Swiss needle file. The tapered half round works well, especially for the inside of curves, instrument holes, etc.
  • "Break", "Brake" or slightly bend (approx. 3°) the edges of overlapping pieces that will be exposed, so that when riveted, they will seat tightly.
  • When drilling rivet holes, never drill in separate pieces of metal by measuring, always "match drill" (drill through all the pieces of metal at the same time.)
    When drilling, use lots of clecoes to keep the pieces of metal matched and flat.
    Try wide masking tape or duct tape to initially align pieces prior to drilling.
  • "Ultra Fine Point Sharpies" are good for laying out rivet holes, either on masking tape or the metal itself.
    The mark is about 1/32 of an inch (~.032) which I found to be a reasonable "tolerance" frequently used in the sheet metal work.
  • Using a 6 inch rule marked in 32nds of an inch, I started "thinking in 32nds".
    e.g.: An edge distance for -4 rivets that works well in many cases is 10/32", (the minimum being 8/32").
  • Drilling "from inside out" such as skin to rib rivet holes will help keep rivet holes in the center of the rib flange.
    You may mark and drill the end ones this way, then after confirming that the rib is straight, drill the remaining holes "from the outside in" (normally).
    When drilling "from the inside out", have a helper hold a block of wood against the skin to hold it against the rib while drilling.
    This is a good place for those 6 inch and 12 inch drill bits.
  • Practice a lot on scrap before the real thing.
  • Collect "all" sizes of rivets. "Half" sizes are especially helpful.
    e.g.: AN426AD 3-3.5s are great for many skin to structure applications if using -3's instead of -4's.
    The use of rivets that are [even slightly] too long may result in more "tipped over" and bad rivets.
  • Learn the significant differences in pressure, feel and timing between riveting -4 and -3 rivets.
    Also notice timing and pressure differences on light weight versus more massive structures, and light versus heavier bucking bars.
  • On flush rivets, have the less experienced person drive. Using a swivel-head, rubber edged flush rivet set, most anyone can be taught to drive in a short time. Have them stabilize the set against the metal with their thumb and forefinger.
  • On Universal head rivets, it is especially important to keep the rivet set firmly against the rivet and to stay perpendicular. With shiny aluminum, you can use the reflection of the set to stay straight.
  • Keep the bucking bar perpendicular! Sometimes, putting your forefinger and thumb on both sides of the bucking bar between it and the metal, you can feel it approach the metal as it's setting. In tough to reach places, this may be the only way you can keep the bucking bar perpendicular.
  • Drilling out rivets: For a -4, use a 1/8 inch drill, not a #30.
    For a -3, use a 3/32 inch drill, not a #40.
    Center punch and slowly, maybe by hand, start the drill to get a solid, centered hole in the rivet to be drilled out.
  • Many folks like countersinking marginally thick skin - e.g.: .032 skin for a -3 flush rivet.
    I DON'T. I believe a dimpled hole will be stronger and look virtually as good (or better than over-countersunk), and may actually be as quick.
  • Tip for dimpled holes: very slightly countersink dimpled holes - by hand (only two or three "half turns") to get a real nice, flush seat of the flush rivet.
    "Spring back" dimple dies will reduce or eliminate the need to do this.
    As with most of these techniques, experiment to find the best results.
  • Drilling out rivets: Creating a good sized cavity in the center of the rivet head with a Dremel tool helps in getting the drill started and centered. I use a spherical carbide engraving burr of either 0.090" or 0.107" depending whether it's a -3 or -4 rivet. Works well for both flush and universal heads. A large magnifier can help. Tom Note
  • Keep it simple.
  • Study the Bingelis books for numerous ideas and answers.
    Refer to FAA AC 43-13B for specifics on riveting specs, wire sizes, etc.
  • Try to imitate certified aircraft systems when possible. Piper or Cessna Service and parts manuals can relieve a lot of the guess work regarding many systems installation questions.
Center Section
  • If you are working on the CS, you may discover that installing the flap hinge reinforcement isn't quite like the plans. Chris referred to the reinforcement looking like "Swiss cheese" once I would be through with it. It does have a few holes in it to clear Universal head rivets, and the ends tapered. So don't become discouraged the first time you hold it up to the spar, and it doesn't fit. It will, eventually. Roger Allen, Flushing, Michigan
  • Flap reinforcement: Unlike the manual, I'd recommend fitting the flap reinforcement, but not riveting it to the rear spar yet. Rivet the bottom skin to the rear spar (can be done by squeezer), THEN rivet flap the reinforcement to the rear spar (some Cherry Max rivets may be required in the hard-to-reach areas, then rivet the bottom skin to the flap reinforcement (again, may all be done by squeezer).
  • When building the flap, pre-drill small pilot holes in the upper flange of the flap spar (where the top skin attaches). These can be drilled fairly quickly using a drill press. When you have the flap ribs clecoed into place, lay the trailing edge extrusion onto the bottom skin, and tape or clamp the top skin into place, being sure to tape the skin down to the trailing edge extrusion. Then drill upward through the pilot holes in the spar using the drill bit called for in the construction manual, clecoing every 2nd or 3rd hole from the top side as you go. This will allow accurate edge distances and a straight rivet line on the top skin/spar join. Dean Casey
  • When building the flap, measure and drill the forward-most row of rivets in the flap nose ribs after you have drilled and clecoed the top skin/spar join, then cleco the nose rib holes. This will allow you to more accurately locate the 2nd and 3rd flap nose rib rivets. Dean Casey
Forward Fuselage
  • Side Skins - Be sure to follow the construction manual, step by step when doing the forward fuselage. Don't rivet anything to anything, just use lots of clecos. I have had the side skins off and on I'll bet 20 or 30 times. I'm attaching the belly skin with nut plates and #8 screws. Jack Pillabaum
  • Jig security - Be sure you are very accurate with the lines drawn on the floor. I thought I had my jig secured to the floor but it moved. It is now bolted to the garage cement floor. I spent about 3 days getting the center section level in all directions. I would think I would have it correct and then the next day re measure and find it was off. Jack Pillabaum
    I bolted the 4x4 to my garage roof rafters and epoxied the bottoms to the cement floor. Wayne Sweet
  • Firewall Sealant - There are several products that will meet the FAR and Mil spec for firewall sealants. I feel the best product is Desoto ProSeal 700. It will give you the best service and protection if you have a firewall forward fire.   Ed Glinsky
  • Seats that are quickly removable will be appreciated later when you have to do maintenance behind the instrument panel.
  • Be sure to incorporate forward and aft seat track limit locks. A #10 screw through a 3/4 inch high bushing into a tapped hole in the seat track is a quickly removable, solution - one track per seat works OK.
Sealing the Wet Wing
  • The wing structure: spars, ribs, spacers (under ribs) all riveted in place, in the vertical jig as per plans. (The wing is pointed up as in vertical flight).
  • The wing skins and leading edge skins are all aligned, fitted, drilled, deburred, dimpled.
  • For the leading edge skins / tank I used 1" spacing and -3 (3/32") rivets EXCEPT for the bottom aft 6 inches where I used three -4 (1/8") Cherry Max rivets on 2" spacing at each rib (except the tip and root ribs).
  • Confirm alignment with Profile boards and a digital level that should show 90° along the top of the tip and root profile boards. This plane is parallel to the wing reference line.
  • Do NOT rivet the main skins on until AFTER the leading edge (wet wing tank) skins are riveted on. (To allow access to rivet the aft edges of the leading edge skins to the spar which can be squeezed.)
  • Seal the tip and root ribs leading edge filler pieces, and any alignment holes and doublers and patches with Pro-Seal and rivet.
  • I will only list this once, but should be repeated at each line: USE PLENTY OF PRO-SEAL! Don't scrimp or attempt to "conserve" sealer.
  • With the leading edge skin removed, seal the spar - except where the skin will attach to the spar. Do seal the edges of the cap strips well against the spar web just below / above where the skin will attach to the spar. Also seal the rib spacers and their rivets. Seal the connections for the vent at the tip. Don't get sealer in the vent tube! Let this set. When dry, inspect for missed areas.

    DAY TWO - Upper Section:

  • At least one Helper is needed from this point on: Two (one just for mixing and cleaning sealer) would be optimal.
  • Put Pro-Seal on the upper edge of the spar and place the skin on, clecoing it to the spar upper flange. Rivet this edge of the skin to the spar.
  • Put Pro-Seal on the upper edge of the ribs. Rivet all the upper flanges of the ribs to the skin. Note: full access to the interior is still available because the lower part of the skin is not clecoed to the ribs. Bend the skin up and out of the way as necessary for access.
  • Apply more sealer to all shop heads of the rivets installed, along both sides of the upper rib flanges to the skin. Root and tip rib rivets (upper halves only!) can be squeezed.
  • At this point the upper half of the tank should be completely sealed, but completely visible. Seal any areas or rivets missed. All rivet heads must be sealed. Any mating surfaces of two pieces of metal must be sealed. Let this set. When dry, inspect for missed areas.

    DAY THREE - Lower Section:

  • "Practice" this procedure (without sealer) with a comfortable bucking bar ( I like # TP-723) and plenty of clecoing / unclecoing to make sure the flow of access will work:
  • Starting with the rib one inboard from the tip, seal and rivet the first (forward) half of the rib - again applying plenty of sealer to both the rivets and BOTH flanges of the ribs after riveting.
  • Access is more difficult for the bucker now: Proceed with starting to rivet the first few rivets of the next rib inboard from the tip - "working down" the skin and riveting as access allows. Delay inserting the Cherry Max rivets until the skin must be laid down due to progressing inboard. A long reach under the skin that can be bent up will be necessary to buck and then apply sealer to the rib flanges and finished rivets. Before Cherry Max rivets are put in, a fairly thick bed of sealer is put on both flanges of the rib, the skin where the rib will make contact and the spar. Don't forget to seal the spar!
    The Cherry Max Rivet is dipped in sealer, then inserted. You will probably not be able to reach in far enough to seal the last 6 inches, so "pre-lay" the sealer.
  • The process should flow inboard with the skin being bent up for access and rivets applied as the skin can smoothly lay down. In other words, you will be working on a couple ribs simultaneously, with the most outboard rib riveted with Cherry Max the last three holes and the skin riveted to the spar at that rib, the next rib inboard will be down to the last 6 inches and the next rib inboard only half-way back, etc.
  • As you progress inboard access gets easier since the rib lightening holes are larger.
  • As the last (root) bay is riveted, make one last check that drain and quantity probe doublers are sealed before closing. (All bucking bars and other items removed?!?)
  • Seal and squeeze the root rib rivets.
  • After removing from jig (some time later) fill with avgas and check (hope!) for no leaks.
  • Spend a lot of time carefully aligning bulkheads before fitting the skins.
Landing Gear
  • Slightly loose tailwheel chains and springs makes the M-II handle much nicer than when tight.
  • When sanding fiberglass or mixing microballoons for filling fiberglass, ALWAY wear a respirator. Kirk Harrell
Canopy and Plexiglas®
  • Go slowly.
  • Temperature of the Plexiglas® should be at least 70° F / 21° C to cut or drill to reduce chances of cracking. Wear good eye protection! This can not be emphasized enough.
  • Get a sheet from the hardware store to practice on - much cheaper than the canopy itself, and will be a real confidence builder.
  • Drills / Holes: Invest in specially made drills for plastics. Drilling should be done with a drill ground to a zero rake angle to prevent digging in. A 60-90°-tip drill would be best, but a standard drill bit ground with no cutting edge would work. "Plexiglas drills" are available from aircraft materials suppliers and are highly recommended. Recommended drill speeds: 1500-4500 RPM for holes to .187" and 1500-2000 RPM up to .375".
  • Make holes slightly oversize to allow for expansion and contraction. Deburr all holes with a countersink. Do not tighten any hardware beyond making slight contact. Loosen screws a half turn after bottoming.
  • Smooth all edges and round corners with a mill or Swiss file, followed by 400 grit sandpaper. Smoothing of the edges is important to reduce the chances of stress cracks in the future.
  • The Plexiglas® may be marked with a fine "Sharpie™" type marker. Cutting and trimming is best performed with an abrasive disc such as a three inch cut-off wheel powered by a die grinder, high speed drill or Dremel tool. These cut-off wheels are available at most hardware stores. Saber saws are not recommended - cracking would almost be guaranteed. The grinding action of the cut-off wheel will actually melt the Plexiglas® as you cut. A feel for the proper speed to progress will be quickly found. The molten Plexiglas® on the edges can be broken or picked off immediately after cutting, and then filing, followed by fine sandpaper can smooth the edges further.
  • Clean with plenty of water and dry with a clean chamois or soft cloth. Light dust can be removed with an air blast or a damp soft cloth. As convenient as paper towels are do not use them because of their cellulose content. Never use any abrasive cleaners and be very cautious about using any form of solvent on Plexiglas®. "Mirror Glaze™" is recommended for cleaning and small scratch removal. A "Micro Mesh kit" will remove deeper scratches. Automotive paste wax may be applied but be sure it's NOT a "cleaner / wax". Most of those products one grabs off the shelf at the local store are "cleaner/waxes" and have varying degrees of rubbing compound in them which of course would create fine scratches or swirls. Rick Clarke
  • A "Micro-mesh" Plastic restoration kit does an amazing job at removing scratches. (But does take time.)
    I follow this with Mirror Glaze™ #10, (which curiously, the Micro-mesh makers don't like).
  • I made the mistake of getting a clear canopy - some form of tint would make flying in the sunshine much more bearable. "Stick-on" plastic sunshades of different sizes are "no-go" items in the summer. They stick by static to the interior of the canopy and fold up when not being used. Even with blasts of fresh air coming in, the cabin temperature runs 20-30° hotter than the OAT when in the sunshine.
  • For cleaning, I now prefer "Plexus" spray, which I have found far superior to Mirror Glaze that I used for decades. R.H.
  • A HVLP system (Graco / Croix) is GREAT! Much less overspray and wasted material. Much less orange peel. "Makes an amateur look like a Pro."
    A different technique from a conventional spray gun is required, but easily learned. You can learn while spraying the primer.
    Gun is held much closer for example.
  • If spraying polyurethane, invest in a separate air source hood / mask. A cartridge style respirator is just not safe enough for this paint.
Flying / Flight Testing
  • The Mustang II is a wonderful airplane, but some "high performance" time and tail wheel experience is a must to fly it safely.
  • I tell all pilots that fly with me: "Lock your wrist to your leg, and NEVER move the stick more than this much"
    [showing a 1 1/2 inch circle with my thumb and forefinger].
  • Exhaust residue can be easily removed after flight with "Scrubbing Bubbles", R.H.; A rag dampened with fuel from the gascolator followed with waterless cleaner/wax, Kirk Harrell; or "Turtle Wax Bug and Tar Remover" Ray Gearhart
Corrections and improvements to the drawings
The information below is intended to help others. These items are not necessarily endorsed by Mustang Aeronautics.

If you see any corrections to these corrections, please notify me! Thanks. 
Note: comments ending with "RH" are from my 20+ year old drawing set. Some of these changes may be incorporated on newer drawings.
I have just ordered a new, current drawing set (2/12/16) and will update after receiving and reviewing them.
  • Mustang Aeronautic's Main Revision list: [Here]
  • Mustang Aeronautic's list: [Here]
  • 220.003 Leading edge skins: Gear access hole needs to be larger and extend more toward the leading edge in order to remove the gear tube assembly (if necessary in the future). [Specific recommendation requested]. (RH)
  • 230.001 Add note: "Rivet spacing with -3 rivets = 1.5"" (Newsletter May, 1995) (RH)
  • 230.005 Upper left drawing - wing skins: Newsletter from July 1992 mentions new dimensions, however I strongly recommend that skins be cut oversize to fit the structure and later carefully trimmed to size when in place. Do not attempt to cut skins to size before laying on the structure! (RH)
  • 240.015 Items 3, 4, Belly Skins: Newsletter Vol. 1, #2 recommends "cut belly skins longer so as to extend 3/4" beyond Sta. 209.5" (RH)
  • 240.018 Items 6, 7, 8, 9 Bellcrank support angles: Dimension 3.406" should be 3.750" and dimension 2.344" should be 2.675" (RH)
  • 240.023 Item 14: Add note: "Plate nuts need to go on Horizontal Bulkhead (Item 7), not on Station 209.5 bulkhead" (RH)
  • 250.002 Items 11, 12: Add note: "Not to scale!" (RH)
  • 250.009 Item 3: Dimension 1.562" should be 1.312". Dimension from upper edge to bolt centerline is 1.562" (1.312 + .250). Additional note: "Make slightly larger to increase edge distance for .250" bushing" (optional) (RH)
  • 260.004 Add note: "See Newsletter #10 for alternate flap control design" (RH)
  • 260.006 (Upper left hand item) "Aileron tubes are .600" too short." [My drawings are too faded to provide any more info. Specific correction info appreciated.] (RH)
  • [Your suggestion here ...]
"Airworthiness Directives" & Service Bulletins
Although Airworthiness Directives are not actually applicable to Experimental Amateur-Built aircraft, appropriate similar advisories will be listed here
  • Mustang Aeronautic's Main Revision list: [Here]
  • Elevator bellcrank support gussets to be added. [Newsletter #, additional reference(?) to be added.] (RH)
  • Older Wing attach fittings to be hardness tested. (circa mid-1980's) [Newsletter #, additional reference(?) to be added.] (RH)
  • [Your suggestion here ...]
  • [Your suggestion here ...]

If you have any Mustang building "Lessons Learned" that could be added, feel free to submit them.
If you wish to remain anonymous, please advise. Otherwise, I'll list your name after the entry. (e.g.: "Rick H., TN")
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Thank you in advance!

Updated 12 February 2016