March 26, 2016 - I have started to update and complete the instrument panel with some instruments my father had laying about. We've added a full engine monitor, fuel flow/totalizer, and a Aiti Mach II Air Data Computer (that is altimeter, airspeed, vsi, and encoder all in one).
April 9, 2016 - Took off the Sterba propeller and found a mud dauber nest!
April 10, 2016 - Removing the engine baffling to get at and remove the engine. The black material on the aluminum sheet baffling is odd in that it seems to corrode any metal it touches! It is supposed to form an air dam agains the cowl so that incoming air is forced through the cooling fins of the engine. We'll replace it with a silicone rubber sealing material.
April 25, 2016 - Day 2 of Revealing the Engine! Today I have finished removing the baffling around the engine. Unfortunately, I have found more and more corrosion. You can see in the second picture the intake ports on the Scat Racing cylinder heads are much larger than standard VW's. Also note that most airplane engine use two spark plugs per cylinder to increase reliability. The engine is now almost ready to remove from the airplane. I will be taking out the engine and replacing some critical part - putting in newer, better ones so that I know I'm safe when up in the clouds.
Aug 12, 2016 - OSHKOSH Airventure Trip
Flew to Oshkosh, WI from Davis, CA for the Experimental Aircraft Association's (EAA) annual gathering. It was fantastic. We got to meet a few other KR-2 builders and flyers. While I did not get to fly a KR-2, I did go to the KR Forum where experiences, lessons, and advice on the building and flying of the KR-2 were discussed. Additionally, I got to meet members of the KR community and actually sat in Mark's Lanford's KR-2.
While Oshkosh has pretty much EVERYTHING aviation, we were a little disappointed at the representation of VW aircraft engine information/companies. There were no forums? AeroCoversions was represented (as part of the SONEX display) with their new turbocharged engine:
Additionally, there was this engine on display in the ultralight area (perhaps a Great Plains? - notice Force One Hub):
January 2017 -
Yikes! Time is marching on. I've been busy with school and some activities. I've joined our school's Speech and Debate team, and really love it.
I'll begin on-line ground school this spring and hopefully flight training this summer - if I can afford it from after school and summer jobs.
We have made some progress on the airplane, and hopefully by the time I have my pilot's license, my KR2S will be ready to fly.
Engine Decision
After considering engine options, I think I'll stick with the HAPI engine the plane came with. But here's the issue:
The Continental O-200 engine is clearly a more reliable and "real" airplane engine. Additionally, it is much more powerful, giving the KR2 fantastic performance of ~175mph cruise and 1200 feet per minute climb. This compares to about 135 mph cruise and 700ft/min climb with a VW engine.
The advantages of the Continental O-200 engine are many - with reliability being perhaps the greatest, followed closely by the fantastic performance. If I was starting this project from scratch, I think I'd go with the O-200 engine. My dad even considered buying a different KR2S that became available and has an O-200. It was a blast to fly.
Check out my video of an Continental O-200 engine powered KR2S:
However, the Continental O-200 engine has some significant disadvantages. These include: extra weight (another 75-100lbs - a significant amount on a 500 lb airplane), higher stall speed (extra weight results in ~20% higher stall speed), greater fuel burn (~4 gallons/hour autogas for VW and 6 gallons/hour avgas for O-200) thus greater operating costs, cost (~$700 to get my HAPI up to snuff, and >$3000 to install an O-200), and significant rework of the airplane to adapt for the O-200 adding at least another year before completion of the airplane. I think these seem to tip the balance against the Continental O-200 engine, at least for me.
There is something about the KR2 cries out for the home-spun VW conversion. I think I am going with the VW.
Sticking with a VW engine, I have to figure out how to make it most reliable.
Fixes to the HAPI VW engine: I keep getting advise to replace the Scat split head with conventional heads for better cooling. Additionally, I'll re-enforce the Diehl alternator flywheel (a known trouble spot).
Engine issue are among the most important in building an airplane. You'll see later on down this page I re-vist my worries about the VW engine and work on options to improve it.
March 21, 2017
Wow! Its almost been a year - and I've made less progress on the plane than hoped . We were held up trying to decide what to do about the engine. We've decided to stick with the VW - but still unsure about sticking with the SCAT individual heads, or moving back to conventional heads that are supposed to cool better.
In the mean time, my dad and I put new bench and flooring (pulled from a lab my dad just shut down) in the garage. It should make for a great space to work in - now we just need to get some work in...
Finished the garage re-do (how cool is this place to work!)
Now I'm starting in on the engine again.
Ceramic Thermal Barrier Coatings
There is a growing recognition that high temperatures are the major cause of engine reliability issues - and the VW has a particular issue with over heating when trying to get more than 60hp out of it. Ceramics have a number of remarkable properties, including very very low heat conductance. Thats why external ceramic tiles were used on the Space Shuttle to insulate its metal airframe from the heat of re-entry. We'll try the ceramic thermal barrier coatings of the pistons, valves, and cylinders in the hope of decreasing the temperatures enough to get decent reliability out of the engine. I want to make sure I don't see cylinder temperatures above 400C, above which aluminum starts to deform and reliability is dramatically reduced. To monitor temperatures I will have temperature probes on each cylinder.
Techline
I ordered ceramic thermal barrier engine coatings from Techline. I'll be coating the tops of the combustion chambers, the piston tops, the valve faces, the exhaust valve stem up to where it meets the stem guide, and the exhaust port with Techline CBC-1. CBC-1 is a ceramic thermal barrier coating. I don't know how well it will work in practice, but the theory is that by significantly reducing heat transfer, it will keep more of the waste heat in the exhaust that dumps out to the air rather than having to remove that heat from the engine via air cooling. A lot of sources agree that the VW engine is heat limited, and hopefully this will help improve reliability. These are the instructions for coating CBC-1. Basically, I will clean and degrease parts, blast with 100 grit aluminum oxide, clean again, bake to cure the ceramic coating, and then reassemble the engine. Sounds simple - I hope it doesn't take the rest of the summer.
My next step is to remove the cylinders and pistons in order to check the internals of the engine (crank, connecting rods, etc), and in order to coat the pistons and head, and valves with a ceramic thermal barrier coating (CTB). The CTB should help reduce the damaging effects of high temperatures often encountered with air-cooled aircraft engines.
Removing the Pistons and Cylinders
I watched YouTube videos on how to remove the cylinders and pistons - and then started in on it. (I know it sounds sketchy, but YouTube is an excellent "how to" resource!) First I marked each cylinder, piston, and head with 1, 2, 3, or 4 small dots (using a drill) to denote its location on the engine.
Here's a pretty good animation of the ignition firing made by Darryl Deppe:
For orientation, the propeller would be at the bottom of the picture above (about where the muffler and Darryl Deppe attribution is in the picture).
Using a rubber mallet and pulling by hand, I loosened and removed each cylinder (carefully laying the pistons on a cloth). Then I removed the piston wrist pin clips with needle nose pliers. Then pushed out the piston wrist pins (with the rubber coated end of players) and removed the pistons.
Here's the plane with the cylinders, pistons and heads removed from the engine:
You can see that even with the small amount of test run time on the engine, the cylinders, pistons and heads are heavily coated with carbon.
Additionally, you can see blow-by at the cylinder/head interface. I don't know how significant this is - but the engine only has a few hours of test run on it. I think this blow-bycan be reduced with a thin copper ring. (Note the small dot marking denoting which cylinder each is from. ) Interestingly, the blow-by is almost all on an axis parallel to the crank (front or back of the engine but not to the top or bottom).
Preparation for Ceramic Coating:
Cleaned the pistons and cylinder heads in preparation for ceramic coating. There was a very heavy layer of carbon (as you can see in the pictures above). Just scrubbing didn't have much effect, so I "painted" on some Berryman Chem-Dip, let it sit, scrub, and then repeated. Worked pretty well. They are not perfectly clean, but the abrasive blasting should take care of the rest. I still have to dis-assemble the heads and remove the valves. But soon the parts should be ready for the abrasive blasting and degreasing preparation for ceramic coating.
Progress!!
The airplane is really starting to come together - even though I spend almost as much time taking it apart as I do building it.
VW Engine #2: Great Plains TOP BUG
Started working on a Type IV VW engine that was donated to Sacramento's EAA Chapter 52 some time ago. The HAPI VW I've been working on is of the Type 1 through 3 variety - which was originally designed in 1936 and powered the 30hp VW Bug. While there has been a lot of evolutionary improvement of the Type I engine, getting 75hp out of it reliably is quite a stretch. Above I've gone through some of the many issues with the magnesium cased HAPI Type I VW engine and I'm hoping that ceramic thermal barrier coating my help.
But a lot of folks suggested I should look at the Type IV VW engine used in VW vans and Porsches. The type IV is significantly redesigned, bigger, and originally designed for 80hp. But it is also a lot heavier. This particular engine has already been converted for aircraft (two spark plugs/cylinder, prop hub, etc) - but like the HAPI, I don't really know its history and condition, so I have to treat it down and start over. What I've learned so far is that it is the rare TOP BUG conversion of the Type IV engine, but made with 103mm cylinders and a 78mm stroke crank shaft giving a HUGE 2600cc displacement! It was made with a Scat forged crankshaft with the extended "Force One" prop bearing. You can read a little about it here in some newsletters from 1989. Here are some pictures of the engine:
Current plan? - I'm going to tear down my original HAPI Magnumengine and rebuild it. Replace what needs to be replaced, ceramic coat the pistons and heads, and build it up with fuel injection, electronic ignition, and a turbocharger.
This should give me a great performance boost at high altitude - and perhaps a bit more reliability than the HAPI.
Currently I plan on completing my KR2s with the original HAPI, and hope to get at least a few hundred hours out of it. (MOM - Don't read this!!) The smaller engine is a lot lighter and that weight savings will translate into a much lower stall speed (minimum flight speed) - which could be critically important as a new pilot since the energy of a crash goes up by the square of the speed. After a few hundred hours, I'll move to this "new" Type IV engine.
VW Engine #3 - Custom Turbo Conversion Type 1
Wow, ok this is getting a little (a lot?) crazy. I got yet another VW engine. The HAPI Magnum engine that came with the engine had a very interesting and "high performance" set of "individual cylinder heads" made by SCAT.
These heads have a number of performance advantages great for racing VW's, and the are similar in form to the individual cylinder heads of all certified aircraft engines (like Lycoming or Continental). However, they have very few cooling fins and in practice on aircraft conversion engines, overheat. I was thinking I could deal with that with the ceramic thermal barrier coatings, but kept getting advice to go back to conventional VW heads. Then suddenly, two opportunities arose at the same time:
First) The individual Scat Heads are coveted by builders of the 1/2VW engine (where the engine is sawed in half to reduce weight for ultralight applications - you can't make this stuff up).
Second) I found another Type I engine for sale (for almost the same price I could get just by selling the individual Scat heads), that had very very nice components that I could use. Specifically, this new engine was built by a retired Ford engine engineer and had:
So I sold the Scat individual heads and bought this very cool Type I VW.
Check out the pictures:
OK - so now what's the plan?? I think I'll assemble the best but simplest normally aspirated (not turbo charged) VW Type I engine I can from the HAPI and the above VW# 3.
Eventually, I may try to turbocharge the Type I or perhaps move to the Type IV TOP BUG.....
But or now its onwards with the Type I engine. Hope I can find some help on this.
Here's a diagram of the VW Type I engine:
The only major difference between this diagram and the engine I am using is that I will not have a magneto (#26), but rather a distributor-less electronic ignition.
Back to Airframe / Avionics !
Finally finished the electrical connections for an engine monitor. I will have cylinder and exhaust temperature probes on each cylinder to help monitor the health of the engine. Had to learn how to solder and heat shrink (the red bands in the picture below).
In this picture I'm testing each line for continuity and lack of shorting to any of the other lines:
Calibrating the Aircraft Engine Instruments: Engine reliability is a major concern - especially if I stick with the VW. One of the best ways to monitor engine health is to monitor the cylinder head temperatures (CHT) and exhaust gas temperatures (EGT). I found an almost inexpensive used JPI 701 engine monitor on eBay that will monitor CHT and EGT for each of the four cylinders. After a little bit of work fixing the connectors (probably why it was inexpensive), I set out to test the instrument and calibrate the temperature probes. Its important to test the instrument for accuracy - if a CHT probe is in 400 degree oil, does the instrument read 400 degrees?
As you can see in the picture above,I set up a pot of engine oil on top of a camping stove. Into the oil I secured the tip of each CHT or EGT probe, and a confectionary thermometer the reads up to 500 degrees. I connected the JPI Engine Monitor to the cable I made to run from the cockpit to the engine compartment (see August 11 2017 work above), and then connected the wires from that cable the the probes. After I connected the JPI to power, I could read temperature reported by the probes.
Success! I tested the CHT and EGT probes at 200 and 300 degrees. I found that the JPI Engine monitor connected to the engine temperatureprobes exactly reported the same temperatures as the thermometer. I didn't want to go higher than that for an oil bath! (It was scary enough!) I'm not sure how I'll test the EGT probes at higher temperatures (exhaust gas temperatures are commonly 900 to 1500 degrees)!
Folding Wing: I am building a wing fold assist option into each wing. This should help in storage of the airplane in the corner of a hanger or a trailer. Plans for the KR2 wing fold assist option were sold by R.W. Moore back in the 1980's and 90's. While far from a complete wing flying mechanism, it basically assists single person manipulation of the wings as they are removed or re-installed.
Paint / Finishing ?
I think I am planning to use AlexSeal paint - I think.
I am learning as much as I can about the many options out there for painting the plane, and am still thoroughly confused and will probably need a lot of help. It seems there are some folks who cheap-out and use common household latex paint. It kind of works as long as you don't look at it too closely and holds up for a few years, as long as you don't get oil, gas, or water? on it, leave the plane outside, or fly through rain (perhaps that's me being biased). While the price is appealing (~$100?), it kind of seems a shame to cover something I'm works so hard on with a subpar paint. But the motivation is clear: everything else is REALLY expensive. It is surprising how little price difference there is between the cheapest generic automotive paints (~$800), and the expensive specialty aircraft paints ($1500). (Those price estimates include a high build fairing/priming layer, a finish primer, a finish color top coat and the various reducers and solvents required).
One of the major decisions is acrylic vs urethane based paints:
Additionally - one of the better trends is towards water borne acrylic paints (such as Stewart Systems Aircraft Paints). This makes them much less toxic to spray (and the neighbors and mom's don't complain about the smell as much).
In reading about the various paints, two really stood out. Stewart Systems appeals due to the lack of toxicity and the fact that they are specifically designed for airplanes. However, I was also drawn to a new entry - AlexSeal. AlexSeal was developed by the maker of the very successful AwlGrip (Urethane) and AwlCraft (Acrylic) paints and supposedly combines the durability of the the urethane with the fixability of the acrylic. They do this by using a urethane formula that minimizes the clear coat separation while still giving a great gloss. AlexSeal has been very successful on high end yachts, but is actually a little less expensive than Stewart Systems. I believe finish and durability will be better with the AlexSeal. Does this advantage overcome the hazards of spraying a cyanide catalyzed paint?
I'm still researching paints / finishing systems. What about waterborne urethane systems? In fact, AlexSeal sells a waterborne urethane. If you have any suggestions I'd welcome the input - contact me via the contact page!
Vinyl Wrap Alternative:
There is an alternative to paint - Vinyl Wrap. A number of airplanes have been finished with vinyl wrap and the results have been pretty good.
Advantages of vinyl wrap:
Disadvantages of vinyl wrap:
Light Weight KR
Richard Fowler, the original builder of this KR, spent many of his last years finely crafting this beautiful airplane. As I work on completing it I am consistently impressed with the quality and thoughtfulness of his work. Especially the fact that he worked hard to keep the airplane as light as possible. This KR is on track to being completed at ~450lbs. That is about as light weight as the original KR2, and almost 200lbs lighter than many KR's. Weight is critical not just because its "got to fly", but because as a very light weight aircraft, any extra weight is a larger fraction of its "empty weight" and thereby has a larger effect on the flight performance of the airplane. Following the design mantra of keeping the airplane light, I have changed plans a but on completing the airplane.
Fuselage Repair
One of the last blow's to Mr. Fowler's effort to complete his airplane came after an argument with his brother. To end the argument, his brother threw a brick at the airplane Richard so cared about. The brick crashed through the thin wood side of the KR's fuselage, leaving a nasty torn hole in its side. While luckily, the brick had not damaged any of the critical framework, it had ruined a panel. The strength of the KR fuselage depends both on the framework and the skin. The bitter damage to Richard's airplane knocked the wind from his sails and he never worked on the airplane again.
I had intended to build a door into the fuselage to facilitate inspection and modifications. However, after realizing that ample access to the fuslage interior is available from both the cockpit and the inspection port at the tail, I decided to repair the hole by the lightest, most structurally sound means available.
Engine Progress - My ongoing engine dilemma
KR is a basic, light, and economical airplane designed to be powered by a VW conversion. The economical "grass-roots" VW just seems like the right engine for a KR.
The project I bought came with what was the state-of-the-art VW conversion in 1980 - the 75hp HAPI Magnum (see the HOME section of this site). However, HAPI was soon out of business as the liability crazed 1980's decimated the aviation industry. Worse, the HAPI VW did indeed have a number of problems. One of the issues had to do with heat. The SCAT split heads, while innovative, did not cool well. This was a serious problem in an engine already know to be "heat limited". Getting 75hp out of an engine continually that was originally designed to produce only 36hp transiently turns out to be a problem... Over the years, most of the "issues" with converting a VW engine to aircraft operation have been worked out - mostly. However heat, poor and mismatched manufacture tolerances, and poor metallurgy still tends to limit head life to ~ 300 to 500 hours and engine life anywhere from 300 to 1000hrs.
VW "Alternatives" - The obvious solution is to move to a "good" engine - one designed from the start for aviation. The front runners are the Continental O-200 (200lbs, 100hp, ~$7,500 used) or the Rotax 912 (190lbs, 100hp, $12,000 used). But moving to either of these engines feels like a violation of the original KR design. Worse, they are both well beyond my high school summer job budget. So...
New VW Heads - I sold the Scat Split Heads that came with the HAPI Magnum to a fellow building half VW's. For almost the same price I was able to buy another engine that had very nice heads that had been modified for two spark plug per cylinder. Here is a picture of the head and valvesafter coating with a ceramic thermal barrier:
Hopefully the ceramic thermal barrier coating will keep more of the heat in the combustion chamber and dump it out in the exhaust.
I also CC'ed the heads - a process necessary for building VW engines with a defined compression ratio (I'm shooting for 8:1). To measure the volume of the head, I cut out an acrylic disk using a hole saw (fly cutter). I then laid the disk in the head and measured the volume of water under it. If you are interested there are lots of videos on youtube detailing how you measure the head volume (CC the head) and then calculate the compression ratio.
New Cylinders - Nickies!
The VW engine is built with steel cylinders. This was a engineered choice driven by economy and the fact that aluminum in the 1930's (when the engine was designed) wasn't hard and strong enough. Unfortunately steel is both heavy, and slow to conduct heat - increasing the heat load on the heads. Modern aluminum alloys are strong enough, but not quite hard enough. To harden aluminum cylinders, they can be nikasil plated. Nikasil is short for Nickel Silicon Carbide. Silicon carbide is a very hard ceramic (much harder than steel) that can be dissolved in nickel. The silicon carbide / nickel solution can then be electroplated onto aluminum cylinder bores. The piston rings will then rub off the exposed nickel, leaving a very hard layer of silicon carbide to prevent the cast iron/steel piston rings directly contacting the aluminium cylinder.
In the very budget conscious VW aircraft conversion world, aluminum/nikasil cylinders got a very bad reputation. The makers of the AeroVee resold nikasil coated aluminum cylinders from the low cost parts manufacturer QSC. While it seems the QSC nikasil coating was ok, the aluminum was soft resulting in the "mushrooming" or deformation of the cylinders. High quality high strength cylinders should be forged rather than cast, or better yet, milled out of solid forged billet stock. Unfortunately this makes them much more expensive. Two suppliers I'm aware of make high quality aluminum/nikasil cylinders: 1) Scott Casler of Hummel Engines makes beautiful CNC'ed aluminum cylinders, and 2) LN Engineering is famous for their Nickies - CNC machined aluminum/nikasil cylinders. From the LN Engineering website:
Nickies have more surface area and up to twice the thermal conductivity of factory Mahle cast aluminum cylinders
Nickies have as much as four times the thermal conductivity of cast iron or ductile iron cylinders
Nickies have up to 50% greater tensile and ultimate yield strength than OEM Porsche cast aluminum cylinders
Nickies are stronger and more ductile than any cast iron, ductile iron, or aluminum OEM or aftermarket cylinders
The down side of CNC machined aluminum/nikasil cylinders is cost. A set of 4 cylinders from Hummel Engines cost ~$1,600, and a set of 4 from LN Engineering cost ~$3,800! Ouch! You can understand why they aren't much used in the "budget conscious" VW aircraft conversion world. However, I lucked out. I bought an engine (see section above) that was in "mid-build" and it had a brand new set of Nickies. Here's a pictures comparing the weight of the Nickie cylinder (25 ounces) to the steel Mahle (75 ounces!) That's a weight saving of ~12.5lbs!!
Aluminum vs Magnesium VW Engine Case
The HAPI Magnum engine was made with the original VW magnesium case, while the custom build engine I am scavenging has a new aluminum aftermarket case. So which to use? Aluminum cases are considerably stronger. While I haven't read of catastrophic engine case failures, it is not unusual for magnesium case threads to strip, resulting in loose cylinders and heads. Stronger sounds a lot better for aircraft use, but .... Aluminum engine cases run ~10 - 15 degrees F hotter than magnesium cases. Additionally, aluminum cases are ~18lbs heavier. Finally, the aluminum case / crank is unmodified, while the HAPI magnum has the HAPI Ultra Crank which became the Great Plains Force One crank and extended #4 bearing (HAPI was bought by Mosler which was in turn bought by Great Plains).
So - In keeping with the "Keep It Light!" mantra for my KR2s, I am going to keep the HAPI magnesium case, but incorporate the Nickies cylinders. The magnesium case may hale keep the engine cooler, as should the Nickies and the ceramic coated piston tops and heads.
Finish Body Work
To finish the airplane, I need the airplane's surface to be as smooth and aerodynamic as possible - without adding significant weight. Other builders have found that the most efficient way to achieve this is to completely cover the surface with a thick "icing" of epoxy and micro-balloons in a "epoxy wipe" process.
While the "epoxy wipe" process is perhaps the lightest and most efficient way to achieve a completely smooth surface, it still adds significant weight to the airplane. I am going to sacrifice completely smooth in the hope of eliminating ~15 lbs of epoxy and micro-balloons by minimizing the areas where micro is used. Here are a few pictures of my work so far:
March 2021
OK- yes, very slow progress as I continue the finish preparation process. In reading about painting, its often said that preparation is 99% of the work. I have slowly been filling and sanding, but as mentioned above, the focus is keeping it light weight rather than attaining a perfectly smooth surface.
And - I finally made a finishing system choice. Here I will very clearly demonstrate how I over think everything... Worse - I have learned just enough to know that I have no idea what I'm writing about so be warned - I may be entirely wrong!
Vinyl Wraps: I was considering vinyl wrap rather than paint due to the very light weight (and relative ease of application) of vinyl wraps. Unfortunately there have not been many (any?) airplanes finished this way over bare fiberglass. Questions of longevity, UV protection of the underlying fiberglass, actual finish quality, and the possibility of catastrophic in-flight un-wrapping makes me unwilling to go with a vinyl wrap finish.
Paint: After extensive research on paint choices there were a a few clear leaders in terms of the characteristics that I want.
Water Based Paints: Waterborne paints have the tremendous advantage of low toxicity. Additionally, clean-up uses just soap and water! There are a number of water based paint systems ranging from common house latex, to the Stewart System. In the automotive refinishing world, there are water based alternatives to almost any of the finishing systems, including epoxies. Unfortunately I still know little about water bourn epoxy or urethane systems. But after a bit of experience with a the Stewart System on a KitFox and a Cavalier, my impression is that the water bourn paint is too soft. It scratches/damages fairly easily, and that soft gummy nature makes it harder to get a great finish with. Additionally, I am concerned about its resistance to solvents in gasoline, solvents, oils, hydraulic fluids, etc.
Enamels: Single component (no mixing with a catalyst) enamels are now the low cost automotive refinish of choice. Modern acrylic enamels provide a fairly durable and shinny finish.
Urethanes: Two component urethane systems are the premium finishing systems available today with close to the best durability, chemical resistance, and finest finish results. All urethane paints are "polyurethanes" in that they are formed by a chemical reaction between subunit building blocks (polyols) that react with polyisocyanate subunits to form a polymer (many linked subunits). There are two main types of polyol chemistries used to create urethane paints;
Performance from each can vary widely depending on the chemical composition/structure of the polyols used and the degree of cross-linking or branching of the urethane polymer formed/catalyzed during curing. Therefore, it is very difficult to generalize performance based on the type of polyol (acrylic vs polyester) used. The actual formulation of a specific paint matters more than the type of paint. This is why not all acrylic urethane or polyurethane paints are the same and why it is best to focus on the performance data/experience and recommendations from fellow users.
AlexSeal: AlexSeal is a remarkable paint system developed for yachts that is the clear leader in terms of application, durability, finish and repair. Unfortunately, it is also very expensive. I think I would have gone with the AlexSeal system if my budget/priorities allowed. AlexSeal was developed by the formulator for AwlGrip/AwlCraft paints. AwlGrip is based on a polyester urethane resin (generically known as a polyurethane paint) and Awlcraft 2000 is based on an acrylic resin (generically known as an Acrylic Urethane paint). ... Awlgrip (the polyurethane) has more abrasion and chemical resistance than Awlcraft and is usually more rigid. Awlcraft (the acrylic urethane paint), on the other hand is easier to apply and can be fixed by buffing. AlexSeal is a happy middle - having properties of both - the durability generally associated with polyester and and the reparability (buffing) generally associate with acrylic urethane paints.
Deft/PPG Transportation Acrylic Urethane: So if I'm not using AlexSeal because of price, what am I going to use? I found a "deal" on Craigslist (again) on a batch of very high quality, very expensive but now surplussed acrylic urethane paints (PPG/Deft Acrylic Polyurethane Topcoat) and its companion Polyurethane Primer Surfacer. I got 6 gallons of each, and their matched activators, for $150. This is more than enough for 3 airplanes - which is just about right since it usually takes me 3x to get something right!
One major concern with this "surplussed" paint is the fact that it is expired by many years. The major issues with expired urethane paint is that its can either self catalyze, or no longer be catalizable/cured. A small amount of both the primer/surfacer and the topcoat were tested and found acceptable. Additionally, before spraying onto the airplane, I will spray onto test pieces, then test their cure and finish. This is something professional shops wouldn't put up with, but something I would have done anyways since I have never painted before and will be teaching myself. No sense doing my first failed attempts on the airplane itself!
Now that I have a primer/surfacer and paint - I just need to get the airplane ready for painting. Back to the sanding!
OK - so another craigslist find and now I have the trim color paint!
Another Single Stage (no additional clear coat) Acrylic Urethane. This time High Teck Charcoal Mist Metallic #1407 - Should be very very sharp!
Back to the sand and fill and sand and fill and... Well you get it.
How much longer until it looks like this?
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