3435 OCEAN PARK BOULEVARD, SUITE 206
SANTA MONICA, CALIFORNIA 90405-3311
TELEPHONE: (310) 390-8000
FACSIMILE: (310) 397-0028
Volume II Issue I January 1997
The KROnline Newsletter is intended to serve as a
conduit for information and building ideas about the KR family
of experimental aircraft. It is meant to share the knowledge that
has been hard won by those who have gone before us. Education
is the cornerstone to a quality built KR.
The article submissions each month are from KR builders
and suppliers. Opinions express are solely those of the individual
authors and not of KROnline. Any ideas or techniques discussed
are to be duplicated and used at the sole risk of the experimental
aircraft builder. KROnline does not endorse or warrant any certain
Rand Robinson Engineering is in no way affiliated
with KROnline and as such, does not formally endorse any information
published in KROnline.
Fuel tank/forward deck. My tank was scratch built using 1/4" thick 4 pound density Clark foam with two layers of 5.85 oz glass cloth wetted with Safety Poxy II sandwiched on each side.. Hexcel's Safety Poxy II is no longer in production, but 2427 is the new replacement. One 5 quart epoxy kit is all that is needed for layups and assembly. Also, vinylester resin is reputed to be fuelproof, and is very inexpensive. Given recent discussions on delamination of Hexcell products, I would use vinylester next time. I modeled my tank in 3D on a CAD system in order to maximize fuel capacity, while providing ample room for instruments, avionics, and legs. I put my avionics cutout on the left side, because with a center stick, my left hand will be free to operate GPS and radios. Given my experience with the pitch sensitivity of the KR2, I don't think it's wise to try to fly one hands off. Originally, the fuel capacity of my design was 21.5 gallons, but after reflecting on the consequences of having that much "volatility" in my CG range, I decided to reduce it to 17.5 gallons.
The first step to constructing the tank is to spray or brush a layer of PVA (polyvinyl alcohol, available from Aircraft Spruce East and others) release agent onto a quarter inch piece of glass. I picked up a 3' x 3' piece of salvaged glass for $15. This glass sheet is required so that when the resin is pulled down to the glass surface, a perfectly flat surface results. Trying this on polyethylene will result in voids and pinholes. After the PVA cures, lay up two layers of 5.85 oz fiberglass on it. Be liberal with the epoxy resin here. A little extra weight is worth the headaches of several tiny pinholes. Immediately micro one side of a large pice of Clark foam and stick it to the fiberglass. Squeegee the clean side of the foam to ensure direct contact between the microed side and the uncured epoxy/fiberglass. Then apply micro to the top of the panel and lay up two more layers of fiberglass, and squeegee again. The end result is a "plyfoam sandwich", with two layers of fiberglass on each side of the 1/4" foam.
Decide on the shape of your instrument panel and draw a template for it. This is basically a mock instrument panel, and will extend to the outside of the two longerons, and will represent the outer shape of your forward deck. I made mine 7.5 inches taller than the longerons, with a nice elliptical shape, and it extends about 2" below the top of the longerons. Use the firewall template from the plans (or design your own more pleasing shape, like I did) as the front template for the tank. Once your templates are drawn up, cut out a firewall and instrument panel contour out of 3/4 inch particle board to be used as sanding guides, and clamp them in place. The aft end of the tank will be something that looks like a cross between the firewall and the instrument panel. If you make it a little large, it will simply be sanded to contour with the rest of the top of the tank.. The aft end of my tank is 17" from the rear of the firewall, which yields around 17 gallons of fuel, 7" of space for instruments, and 14" of space for radios.
You also need two baffles for the interior. Don't forget to leave openings at top and bottom, for air and fuel to circulate through. I made the bottom of my tank slope down as it goes aft, so that in a level or nose-up attitude, the fuel pickup will always be covered with fuel. There is also a sump in the center. This ensures that in straight and level flight, only about two ounces of fuel is unusable.
Position the foward end of the tank against the firewall, and the aft
edge about 7" forward of the instrument panel. Cut out the two pieces
which will sit on the two plywood firewall shelves and one which connects
the two pieces together. Edge glue them together (with the smooth glass-like
surface facing the inside of the tank) using flox and resin, and layup
two layers of glass tape at each seam, overlapping in the corners. I used
one strip of 1" tape, and one layer of 2" tape on top of that.
The end result will be four layers of glass in each corner, with losts
of resin to ensure against pinholes.
Install the two tank sides and the two baffles along with the aft end of the tank, edge glueing all joints with flox and resin and clamp lightly together.
Here, the bottom is being temporarily installed while two more layers of glass tapes are used to create flanges between the side walls and the bottom. Peelply is used to prevent the bottom from sticking to the flanges. After curing, the bottom is removed so that the top can be constructed and sealed from the inside. Later, lots of resin is spread on the flanges, and the bottom is reinstalled permanently.
A view showing the bottom of the tank temporarily installed during flange creation. Duct tape was used during the process to hold the bottom tightly against the sides of the tank. No tapes are installed on the outside of the tank yet, but there's no reason why they can't be.
The top of the tank is constructed from two inch urethane foam, with the bottom side laid up with two layers of fiberglass on glass again, as before. It is then trimmed to fit into the top of the tank in three or four pieces. The fiberglass layer on the bottom of the foam should be a nice tight fit inside the top of the tank.
Flox them in place with a generous fillet in all corners. Then, working inside the tank from the bottom, immediately install the two fiberglass tapes around all joints again.. For mounting, I installed piano hinges between the longerons and the tank sides, where the two meet. The fuel tank is now removable by simply pulling the pins. Until these hinges are installed, the tank is actually resting on the ears of the front and rear tank walls.
Sand the top of the tank to contour using a sanding block long enough to span both instrument panel and firewall plywood templates. Cover the longerons with duct tape to prevent damage to them.
The resulting top surface is now ready to be 'glassed.
Lay up the top of the tank with one layer of 5.85 oz fiberglass cloth and one layer of fine weave 1.5 oz cloth on the outside. Squeegee on peelply over the tank top to absorb excess resin. After curing, use micro to blend the edges of the tank to the fuselage sides. Install the fuel cap either forward or aft, depending on whether your gear is conventional or tricycle, and flox into place, reinforcing from the inside with fiberglass tape. Locate the fuel cap a few inches from aft or foward edge, to ensure that the tank can't be filled completely full. This allows a small air space for expansion of fuel after it warms up. Otherwise, fuel will be expelled out of the vent tube. Install the fuel sending unit. I used a universal VDO adjustable sending unit, available for about $25.00. It has a range of from 6-24" or so. Don't forget to connect a ground to it. Ensure that there are passages at the top of the baffles on each end for air to pass through, and apply epoxy to any exposed foam. Install a 1/4" aluminum tube as a vent. It entes the tank at a high location, and should end internally at the highest point of the tank. After installing the finger strainer in the tank bottom, epoxy the bottom on, and reinforce with the now familiar two layers of 'glass tapes.
You should now pressure test your tank with about 1 psi of pressure. Too much and it'll blow! I used oxygen from my acetylene tank, because it has a very accurate pressure regulator. Yes, the area was well ventilated.
The finished product with canopy and frame installed. The canopy also needs to be at least blocked in place during the panel mockup exercise so that the front deck will conform to the canopy's natural shape. This way stresses aren't introduced into the plexiglas that could later cause cracking or crazing.
For more info on my project, visit my web site at http://fly.hiwaay.net/~langford/kmarkl.html.
I've been lurking long enough, Its about time I try to make a contribution. Hopefully this will be beneficial to someone. As the temperature in the North Country starts to plummet, I am forced to
resurrect my "cure chamber" to permit my epoxy to cure
in a thermally controlled environment. It is neither original,
complex or expensive. It is cheap, simple and provides temperature
control to +/- 3 deg F. I do both wet lay ups and vacuum bagging
depending on the part / application. I have used a plethora of
resin systems. My current favorites are manufactured by PTM&W
(Aeropoxy) I prefer to cure at a min. temp. of 95 deg F for 24
hrs. Raising the ambient temp. of my hanger is cost prohibitive
and I feel that localized heat in the form of heat lamps or space
heaters is to haphazard. The obvious solution (at least for small
and medium size parts) was a cure chamber / oven.
1) The chamber base / bottom is .125" thick X 4' x 8' aluminum.
It is supported on a wood frame. I added legs to raise it to a
convenient work height.
2) The back, top and front of the chamber are 1" x 2' x 8'
Styrofoam from the local builders supply.
3) The sides are 1" x 23" x 24" Styrofoam.
4) The sides, back and top are secured in position w/ tooth picks
5) The front is removable and is held in position by the weight
of the top and an occasional tooth pick. This "5 sided"
Styrofoam box is not secured to the aluminum base.
6) Parts are held off the base of the chamber by wooden racks
and / or hooks.
7) I inserted several thermometers at strategically located positions
to monitor temperature.
8) Conductive heat is supplied to the chamber by directing any
combination of heat lamps and / or infer red heat (Mr. Heater-propane)
at the underside of the aluminum base. (ie--aim the heat up at
the exposed aluminum from underneath)
9) Some testing is required to determin the proper combination
of heat sources.
1) I know I lose some thermal efficiency as the base is larger than the chamber, but I like the extra space for a staging area. If increased efficiency is a primary concern:
a) An internal heat source (light bulbs) could be utilized if care is exercised to avoid localized over heating
b) Styrofoam "skirts" could be added to enclose the
area between the chamber base and the hanger floor.
2) I use a smaller chamber of similar construction (internal heat)
to store my epoxy at a relative stable temp.
3) This chamber has the advantage of being a temperary structure if you are space limited.
There is a unbelievable amount of oil 'misinformation' that resides
in our collective 'knowledge'. There are all the arguments about
which break-in oil to use, whether or not to use 50 weight (auto)
oil in a V-6 converted for airplane use, which (if any) additive
is necessary, how often to change oil, etc.
There was an article in the General Aviation News & Flyer
recently authored by Kas Thomas (editor of TBO Advisor). The article
cites recent studies that show the multi-grade oils as not being
as good as plain old SAE 30.
'Now it turns out there may be solid scientific evidence that single-weight oils protect engines better than their multi-viscosity counterparts. A recent study published by the Society of Automotive Engineers (the folks whose initials adorn the top of every can of oil sold in this
country) casts doubt on the theory that multigrades are better
all-around lubricants than straight-weight oils.'
'Last March, Mercedes-Benz engineers Rudolf Thom and Karl Kollman,
along with Shell Oil engineers Wolfgang Warnecke and Mike Frend,
authored SAE technical paper 951035, which discussed recent research
results involving a variety of oils. Among the many interesting
findings presented in the paper was a graph showing cylinder-wall
wear rates versus cylinder wall temperature in an operating engine.'
'Three tests in a 2.4-liter, four-cylinder Mercedes-Benz OM 616
engine compared three kinds of oils. In one test sequence, a straight
30-weight oil was used; in another, 10W-30 multigrade; and in
the third, straight 10-weight oil. In each case, the engine was
operated at fixed speed, torque and temperature conditions until
constant wear rates were observed. Wear rates were then plotted
against cylinder wall temperature.'
'While two of the oils turned in very similar wear performance,
one oil stood out as protecting the engine against wear at the
extremes of temperature. That oil was plain SAE 30 (straight-grade
30-weight). At either extreme of temperature, the maximum wear
rate with 10W-30 was more than double that of the straight SAE
30 oil. The worst performance was turned in by straight 10-weight.'
'These finding should come as no surprise because , in general,
thicker oils make for thicker oil films and the thicker the oil
film the better the wear protection. What's surprising is that
a 10W-30 oil, which is supposed to have viscosity comparable to
an SAE 30 oil at high temperatures, does not provide wear protection
at least equal to that of a 30-weight unmodified oil. The simplest
explanation, it appears, is that the base stock from which a 10W-30
multigrade is made (namely, 10-weight oil) is fundamentally not
as good a lubricant as a 30-weight base stock. It would also appear
that viscosity-index (VI) improvers are not, in and of themselves,
It should be noted that some multigrade oils are made from base
stocks that have higher viscosity than 10W. Shell's 15W-50 starts
life as an SAE 30 and Phillips X/C starts life as a 20-weight.
The first time I saw an advertisement for this instrument (about
8 years ago), I thought to myself, "How in the world can
anyone justify paying that much for a KIT, and who needs
all that high tech, failure-prone electronic stuff anyway?"
At that time it seemed to be a matter of status to have an instrument
panel literally jam packed with radios, gauges, switches, and
lights. The more that was there, obviously, the more redundancy
you had and the more you could do with the airplane (I now refer
to these crowded panels as "eye-magnets"). Time and
experience has taught me, however, that the less there is to look
at inside the airplane, and the easier it is to assimilate the
information presented by what is there, the safer and more
enjoyable the act of flying becomes, and the more prone you are
to spend most of your time looking out the window for traffic
or sights on the ground. I resolved a few years ago that no matter
which aircraft I decided to build, the cockpit was going to be
as uncluttered and complete as possible, within the constraints
of budget and weight, and it was going to be digital. Ron Mowrer
of Rocky Mountain Instrument markets a pair of instruments designed
to do exactly what I'm looking for - make my flying experience
more enjoyable, less fatiguing, and most importantly, safer.
Let me start by showing you what data the RMI instruments present
to the pilot, the standard instruments they can replace (in VFR
applications only), and a little bit about value.
The comparison table I put together should give you a good idea
of whether the expense associated with these projects can be justified
in your personal application. As a point of reference, the prices
I used came from the 1996 AS&S catalog, and I looked for average
priced TSO'd components. In some cases I've noted the price of
a non-TSO'd component for your reference. The right hand column
of the table is my "realistic estimation" of the standard
instruments the typical KR builder/pilot would actually buy to
put in his airplane, which also helps point out the capabilities
you will get for "free". Also note that the RMI prices
I'm using are the latest prices for the kits -- if you want to
buy them preassembled, add another $300 to the price of each (or
contact me, I really enjoyed putting this thing together
;-}). Oh, and by the way, the price for the Micro Monitor (which
I haven't built yet) does not include all of the sensors and probes
needed, so I didn't include probe and sensor costs with the "standard
instrument" prices, either. Expect to spend another $200
to $500 on these items, depending on how much capability you desire
(EGT/CHT on every cylinder, carb temp, fuel flow, etc.).
Some of the features of the RMI equipment are not available in
standard instrument form (or at least I couldn't find them), most
notable of which are the many alarms that are built into the monitor
and encoder to help the pilot monitor the health of his power
plant and the accuracy of his altitude control. Without my getting
too melodramatic, let me propose that these alarms could potentially
save you from making an error that could get you violated, or
more importantly, from missing an indication of an engine problem
that could cause you to lose your airplane or your life. In the
case of the Micro Encoder, it has three altitude alert modes:
hold altitude, converge altitude, and approach altitude (check
out the web page at http://www.rkymtn.com for more details), as
well as programmable airspeed alerts and alarms for just about
every V speed. You'll have to assign your own value estimation
on these features. Ok, time to get off the soap box and on to
the details of the fun I had building this contraption.
Micro Encoder Kit Composition. RMI has been around for
a number of years, and they have done extremely well at refining
their kits to the point that just about anyone can assemble them.
The documentation is excellent, and written in such a way that
you don't have to know a thing about electronics and you will
still finish up with a working instrument. The assembly manual
starts out with a list of tools you will need, and then goes into
just the right amount of detail telling you how to make a good
solder joint. If you've never soldered before, you will learn
enough to be proficient. If you're already an expert, you'll appreciate
the review. I personally appreciated the many "piece
of mind" notes sprinkled throughout the assembly manual,
particularly the one telling you that the parts you have left
over in your anti-static box when you've finished construction
of the main unit are for the temperature probe you will construct
after the rest of the kit is complete... (ever take a carburetor
apart and have a few pieces left over after you're through putting
it back together?? You know the feeling...). Other notes let you
know that you won't be filling all of the component positions
on the printed circuit cards. Sure helped me sleep better while
I was building. After I quit and went to bed, that is....
Speaking of printed circuit cards, there are three of them in
the Micro Encoder, and all are silk screened to show both where
the components go and how they are to be oriented on the board.
The components themselves are shipped in three formats -- static-sensitive
components, such as integrated circuit chips and the display driver
circuit board, come in anti-static protective containers and bags;
large non static-sensitive parts come loose in a plastic bag;
and small resistors and capacitors come on sort cards, neatly
labeled and arranged in the order they are needed for assembly.
They really make this easy for you.
Construction Details. First of all, make sure you
have ALL the tools the manual tells you that you will need,
and heed their advice regarding a quality soldering iron. They
recommend a temperature controlled iron (which runs about $230+!!!),
but say that a professional quality 25 watt iron will work just
fine. They were right, I paid $35 for a Weller professional quality
pen-type soldering iron, and didn't have a lick of trouble with
it (NOTE: I had two other soldering pens in my shop, but both
were inexpensive [read that as CHEAP] tools I had purchased to
make some emergency repairs in the past. I bought a high quality
iron for this project, and you'll thank me for advising you to
do the same!). Make sure you get a 1/16" screwdriver tip
like they recommend, and keep it clean during the construction
process. Check out http://www.mouser.com, Mouser Electronics,
and request a catalog. They have soldering irons as well as all
(and I mean all) of the switches, lights, and electronic
components you will need for your airplane. The rest of the tools
and equipment you probably already have, with the exception of
a 4 and a half digit multimeter. This is another big dollar item,
and is best borrowed from your neighbor with the home electronics
repair shop in his basement. Don't worry if you can't get your
hands on one, the manual tells you how to work around it. More
on that later.
Figure 1. Here's everything that comes with the kit. The
black bags on the right hold the static-sensitive components.
The white cards in the front hold all of the small resistors and
capacitors, identified and sorted in the order of assembly.
Figure 2. You will be doing a lot of detail work, so make
sure your work area is well lit. Also, observe the anti-static
procedures outlined in the manual to the letter!
Figure 3. Here are the two main circuit boards with all
the components soldered in place, mounted in the chassis and ready
for the IC chips to be installed. Notice the socket pins for the
chips. The pins come on plastic strips that hold them together
in place while you solder them to the board. It's a lot easier
than it looks!
You don't need a large work space. I completed the entire assembly on a card table-size work area in my basement. Good lighting, on the other hand, is essential. The manual says to allow 15 to 20 hours for construction (it took me about 11), and all the work you will be doing is detail work, so make sure you do everything you can to avoid eye strain. I couldn't locate a pair of those flip-up magnifiers that you can wear on your head; I will DEFINITELY find a pair before I start on my Micro Monitor. I used a hand magnifier to examine my solder joints, and that slowed me down considerably. Which brings up a good point -- TAKE YOUR TIME!!!!! This kit goes together very quickly and easily, and the people who wrote the assembly instructions are experts at keeping the horse in front of the cart. I was tempted to skip ahead a few times, and work on something that seemed to make sense at the time, but fortunately that voice in the back of my head remembered the line at the beginning of the manual that said "Don't skip steps!". In hind sight, following the directions EXACTLY saved me some rework.
Gotchas. There were a couple of things in the manual (albeit
very small things) that I commented back to RMI on. Out
of all of the components in this kit, there was only one with
markings that did not exactly match the call out in the manual.
Actually, the nomenclature didn't match at all. A call to RMI
revealed that they had recently changed suppliers for this particular
part (a resistor network), and the new supplier's markings were
different from the original suppliers. No big deal, it fit where
it was supposed to go.
The other items pertained to testing the completed kit. The manual
tells you to hook your kit up to a 12 volt car battery charger
as a power source to perform the initial testing. I found that
the battery charger I had didn't have a steady voltage output,
and this caused the indications on my unit to be unstable, i.e.
the altitude wouldn't hold steady, and the VVI was jumping around
constantly. The manual tells you that if you have problems, you
should hook your unit up to a car battery and see if that stabilizes
it before you call in for technical help. I opted to use two 6
volt dry cell batteries wired in series instead, since I didn't
have a spare car battery in my basement. The steady voltage source
solved my problems.
The last gotcha (which cost me another phone call) has to do with
the 4 and a half digit multimeter I mentioned earlier. There is
a 4 volt test point on the air data PC board, and the manual says
to adjust it with the digital voltmeter to exactly 4 volts. I
assumed (and apparently a number of other folks have as well)
that the reason for using this precise voltmeter was to make sure
you got the voltage adjusted to exactly 4.000 volts. The
real reason is that the voltage adjusts from 3.997 volts
to 4.003 volts, and you can't see it unless you have a meter that
reads to the appropriate number of decimal places. The manual
doesn't tell you this (at least not yet, Ron was revising it when
I called him), and this step comes right after you adjust the
voltage on the display board, which you can take from 0 to well
above the required 3.8 volts with the variable resistor. Well,
I didn't have a $300 4 and a half digit voltmeter, I had an analog
meter that's been around for a long time. I had just set the voltage
on the display board with it, and I wanted to at least check to
make sure that I hadn't blown anything on the A/D circuit board,
so I hooked it up and started adjusting the resistor -- nothing.
No movement of the needle. I thought I had cooked the resistor.
Ron set me straight with a laugh, and said something about wishing
he had left that out of the circuit.... The bottom line is, the
manual tells you how to set the resistor to midrange without a
voltmeter, and that's what I finally did.
Figure 4. The display is very readable and intuitive. The
photo on the left shows all the display segments illuminated;
and the photo on the right shows a typical operational display.
The top of the display shows altitude information, with programmable
airspeed alarms for Vne, Vno, gear extension,
flap extension, and flap/no flap stall speeds. The middle of the
display shows altitude information, with three altitude alert
modes. The bottom of the display shows the altimeter setting,
which can be set in millibars or inches of mercury, and OAT read
from a sensor you construct, displayed in degrees Celsius or degrees
Fahrenheit. And finally, the right side of the display shows vertical
velocity both digitally and graphically. The VVI graphic presentation
sensitivity and range is programmable, and magnetic heading input
from an external compass engine can be displayed in place of the
digital VVI. Actuation of the switches at the bottom of the unit
display the indicated information, as well as provide access to
the "set" and programming modes for the alarms and indications.
Overall impressions. I can't say enough about this project.
The kit is 100% professionally done, and I don't know how they
could make it easier to put together. Customer service was great,
and Ron answered my emails all within one day. As for the finished
product, if you don't tell people you built it from a kit, they
will NEVER guess. As far as functionality in the cockpit, I can
only speculate at this point. But based on my experience with
head up displays and digital avionics, and after running my unit
in its demo mode for a couple of hours, I am extremely happy with
my choice. The display is intuitive, as are the unit controls;
it's easy to operate, and the alarm/alert modes alone will be
worth the cost of the whole unit when flying in the congested
areas here around St Louis.
Recommendations. Take a look at the cost comparison table
and make your own assessment. Don't forget to consider the benefits
in safety of flight and reduced cockpit workload. And don't shy
away from the technology just because it's electronic and you've
never built anything before -- it's really as easy to build as
I described. Weight savings over conventional instruments may
be there, but I didn't take the time to research it fully. I had
originally estimated my weight savings at about two pounds by
using both the Micro Encoder and Micro Monitor instead of conventional
instruments. But I'm planning on using the optional backup battery
for the Micro Monitor in my installation, so the weight difference
will most likely be a wash. I feel the backup battery option is
really a must, though, as we all agreed (I think?) when we were
discussing this issue a month or so ago on KRNet. A redundant
power source for instruments displaying critical engine and flight
parameters only makes sense.
On the other hand, take a look at what your personal instrument
panel plan and flying applications are, and determine if you need
what this product has to offer. If you live in Nebraska and are
planning to only fly for pleasure around the local patch, it doesn't
make sense to invest that much money in something like this, unless
you are a techno geek and just WANT one (no offense, I are one
too ;-}). At the other end of the spectrum, if you are planning
on a full IFR setup, remember that the Micro Encoder should only
be used as a replacement for only your VVI, nothing else!
The prudent aviator will still need his/her standard A/S and altimeter,
so make sure your panel layout will make sense. The utility of
this unit in IFR conditions is obvious, but panel space is limited,
and a full panel is already expensive enough.
And last, take a look at the RMI web page, http://www.rkymtn.com.
All of the information you could possibly want is available there,
including downloadable versions of all the manuals. All of the
contact information is there as well, but for completeness, here
Rocky Mountain Instrument, PO Box 683, Thermopolis WY 82443
Phone/Fax (auto detect) (307) 864-9300
Email firstname.lastname@example.org, email@example.com, firstname.lastname@example.org,
I talked to Ron about volume discounts, and he said that they
start at 5 units. You may be able to save some money if you can
get enough folks here or at your local EAA chapter interested.
I'll be buying the Micro Monitor kit sometime next fall (that's
when my engine installation is scheduled for), and will be canvassing
to get other interested folks together at that time.
I hope my insights and opinions have been of value to you. After
looking back over what I've written, I think it's important to
mention that I am NOT on the RMI payroll, and I'm not getting
any promotional fees or considerations from Ron!! I am just really
impressed with the RMI products, and truly believe they are a
the best value for the money on the market. Not only that, but
way down deep inside, I'll always be a techno geek
to infinity and beyond!!!
Hi all ,
I wrote to the list last fall regarding the plenum box cooling
system that I made for my Revmaster Q2. All the testing that I
did (CHT temperatures) was with two CHT senders. One was a bayonet
type that was secured to the left side aft cylinder head and the
other a gasket type under the spark plug of the other aft cylinder.
At one time I even tested the gasket type with boiling water,
it was accurate.
Well, a couple weeks ago I installed four new CHT senders(gasket type) and a four way switch(I haven't tested these). Today I flew(thank God for one flyable day in Minnesota during the 9 months of winter). Boy, was I ever surprised. Seems things are running very HOT. Two cylinders were hot at
around 400 the other two were closer to 500. I didn't bother to
figure out which two were the hottest(frustrated and didn't feel
like crawling under the panel). I imagine it is the front two.
Last fall I had reduced the two - three inch cool air intake tubes
to two inches. This had warmed things up quite a bit(old senders)
and I could reach 400 CHT in a climb(50-60 outside temp). I think
the front two cylinders are not seeing the necessary air flow
and are running hot. Apparently the bayonet sender (mine) was
far from accurate. I blame its placement. The other was accurate
but on the wrong cylinder.
I wanted to alert everyone/anyone that may be installing a similar
system. I plan to convert to a Subaru next winter and the last
thing that I want to do is spend the summer working on cooling
the VW. I am debating what to do, either install the old style
baffles or spend a little time trying to fix what I have. If I figure it out I will post it here. Sorry for the misleading info.
Last week I modified the cowling inlet and hot air exit. The inlets
are now back to 2" diameter and the exit is much larger and
a ramp typedesign(about 3"x21"). I flew yesterday and
temps were significantly better without any internal baffling
in the plenums over the cylinders.
Outside temp: 25F
Climb CHT: 400(high cylinder) - 350(low cylinder)
I didn't spend alot of time cruising so don't have any numbers
N54JF 1835cc VW Quickie
N90MG 2100cc Revmaster Q2
I have had this same experience with my KR-2 (2180 CC). I found
that the cylinder to cylinder temperatures to be different by
way over 100 degrees F. I now feel it is extremely important to
monitor all four cylinders with sparkplug gasket thermoucouples
during the first 40 hours or so of operation. If you don't do
this you may think you have CHT's in the 350 degree range, when
in fact one or more cylinders are really running at over 500 degrees
F. I ended up making small baffles, temporarily pop riveting them
in, and by trial and error iteratively modified the internal airflow
in my cowling by modifying these internal baffles. After about
20 test flights I finally got all the cylinders to run within
20 degrees F of one another.
Craig Sellers CFI KR2 N34SS VW 2180
Well folks that all for this issue, as mentioned before we are
just trying to kick the issues out as quickly as possible to get
caught up! I apologize for the lack of tidbits and other neat
things that are missing. But as we catch up we will have more
time to post the great ideas that have been submitted for the
Tidbits Section. I hope everyone enjoys this issue and the February
issue is soon to follow!
I also changed the text size to 12 verses 10, do you like it better
or would you prefer that I take it back down to the smaller size?
The size of the font has no relation to the size of the file,
its just easier to read. Also I have started using Adobe Acrobat
and uploading the Acrobat version of each issue to my server,
Acrobat is a great little program and I hope you are downloading
the Acrobat Reader and utilizing this awesome tool! Acrobat files
are much smaller than MS Word documents (Jan issue in Word 7.5
meg, Jan issue in Acrobat 700k!) and the reader is free, it is
available for windows 3.1 WIN 95 WIN NT and of course Apples and
MACs. What a great way to get this newsletter to anyone regardless
of their PC platform!