Larry Larkin is a very experienced CFI who specializes in Comanches. The following is a small fraction of the volumes of information that he presented in his extremely thorough course given July 6 and 7, 1995 in Vero Beach.
I do not offer this info as a substitute to Larry's course, but merely as a taste of what he has to offer. If you find any of this useful, then I urge you to call him up and sign up for his course. If you have 4 or more Comanche pilots in your area, you may be able to arrange for him to come to your location.
- Malcolm Dickinson, CFI
Larry noticed that we have just a couple of
static wicks on the airplane and suggested that we should have at least one on
every moveable control surface. He suggests adding them to flaps, ailerons, and
both sides of the stabilator trim tab.
Pin in Nosewheel Steering Linkage
See pages 2.4 to 2.5 in the Larkin
Our right turn limit stop is gone (the right
one always breaks; the left one is stronger because it is integral with the
shimmy dampener mount). It is now possible for an FBO tug to exceed the proper
turn angle, twisting the nosewheel past its acceptable turning range, putting
damaging stresses on the three bolts that are depicted at the top of figure 2-1,
connecting the steering column to the steering arm (item 5). Further damage can
be caused to the piece of metal that links the rudder cables to the rudder.
Larry recommends avoiding tows by tug
whenever possible. The way to prevent this problem is to remove the bolt that
joins the upper and lower torque links. The bolt should never be more than
finger tight (to allow for movement of the torque links) so it is easy to remove
without tools. The only change that needs to be made is to replace the cotter
pin with a safety pin for easier removal.
Then we simply remove the safety pin, bolt,
and nut, whenever parking the plane somewhere where it may get towed. This
includes any unfamiliar FBO, and also our home one if we expect the plane to be
towed in for maintenance. With the bolt removed, the tug can tow at any
excessive angle without causing any damage to the plane.
There is, however, a danger of taxiing or
even taking off without any positive steering if you forget to replace the bolt!
Therefore, Larry recommends attaching the bolt to the pilot’s yoke or door
handle whenever it is removed, so that it cannot be forgotten.
Head Temperature Gauge
Larry was shocked to see that we had EGT but
not CHT gauges. He said that particularly with the cowl flap, we need a CHT to
monitor the cooling of the cylinders, which is directly affected by the cowl
flap. He said that the EGT gauge will not help to gauge cylinder head cooling,
since exhaust gases are basically unaffected by cylinder head temperature. I
guess we should replace the existing gauge with one that displays both CHT &
Both steering columns, the pilot’s yoke
especially, are binding against the holes in the panel from which they protrude.
You can see black stuff on the right side of the pilot’s steering column—I
believe this is a result of the column wearing at the hole in the panel. Larry
noticed this, particularly how “sticky” the elevator adjustment is, and also
the amount of side-to-side “play” that you can wiggle the steering column
back and forth. He said that each column has three rollers that should be loose
enough not to bind but tight enough so that the steering column doesn’t
contact the sides of the hole through the panel. I think we need to have this
looked at. It should be a simple adjustment for a mechanic to tighten the
adjustment screws, moving the rollers towards each other a little to keep the
column centered, and also lubricate the columns for smoother control movement. I
regard this as a high priority.
I tested this at altitude and it is working.
There is no horn—just an amber light.
Tank Selector – we spent a lot of time on fuel management because
Comanches have a history of accidents caused by fuel management, particularly in
a new Comanche pilot’s first 100 hours.
I noticed that both aux tanks indicate 1/8
tank when they are empty! This should be placarded.
Larry and I noticed that one required
placard is missing. It exists somewhere in a pre-printed version similar to the
existing placard about the parking brake. It should be located directly above
the parking brake handle and should read “No braking action results when toe
brakes and parking brakes are applied simultaneously,” or words to that
effect. The complete owner’s
manual lists all placards and where they must be located.
Both Brendan and Larry confirmed my
suspicion that the large deflection of the aileron trim tabs is indicative of
misrigging. Brendan said, and Larry agreed, that both trim tabs should be just
about straight back when correctly rigged. Larry and I noticed that when you
move the yoke so that one aileron is level with the flap, the aileron on the
other side is several degrees too high! I think we should have this fixed—then
we won’t need the trim tabs to be deflected so far. Brendan said we should go
to a mechanic with a lot of Comanche experience. There are a few
Comanche-knowledgeable A&Ps listed in the ICS yearbook by state.
I received the PulseLite from Precise Flight
(via Aircraft Spruce for discounted price). It will require an entry in the
airframe logbook and a small adjustment to the weight & balance.
The technician I spoke with at Precise
Flight recommended utilizing our current two landing light switches as follows:
Rewire both landing lights to one switch for; then wire the PulseLite to the
other switch so that when it is down you get pulsing; when it is up you get
steady (normal) operation. This installation will be good because if someone
else is using the a/c (ferry flight, maintenance, etc.) they will flip up both
switches and will get steady (normal) operation just like they are used to.
This is an extremely valuable book. A large
part of Larkin’s class was built around getting the pilot extremely familiar
with all the information and charts in this little book. I would like to make
several bound copies, full-sized, one for each of us to keep at home and write
notes in. Let me know when would be a good time for me to remove this book from
the plane and take it to the office to do the xeroxing. Note that I filled in
Centigrade equivalents to all temperatures while I was in Florida. Looking at
the performance chart (ratings table) at the back you’ll note that the
standard lapse rate of 2 degrees C per 1,000 feet is evident in the ratings
Even more valuable is the FAA
approved modern POH that’s available from ___
Larry Larkin has, on his plane, a copy of
the ratings table, xeroxed onto clear plastic at 150% enlargement, taped to the
sun visor for easy reference. I suggest we do the same. I can make the clear
plastic copy at the time that I do the owner’s handbook copies.
We use two sponges (in the air intake and
cowl flap) must continue to be very diligent about removing the two sponges as
well as the three red plugs!
Larry recommends against our current
practice of lashing the yoke back with the seat belt. It prevents water from
draining out of the stabilator, causing corrosion. In the winter, water can
freeze inside the stabilator, leading to weight distribution problems,
over-gross weight condition, or damage to the skin of the stabilator.
Larry uses a bungee cord between the yokes
to keep the ailerons from moving and something that connects the yoke to the
rudder pedals, which keeps the rudder and stabilator from moving. There are
descriptions and/or plans for these homemade devices in the Tips book, and they
may be available commercially through ads in the Comanche
The best option seems to be the large
chrome-plated metal gust lock available through the Flyer.
Do not set the parking brake for long-term
Prepared disposable weight and balance
sheets based on the current weight and balance. One side is used to work your
current weight and balance; it includes a full version at the bottom as well as
two “short cut” versions at the top in case you have full tanks. On the back
make several examples to show exactly how much you can have in the plane. With
five people there should be great concern on the part of the pilot about going
over gross. With six people it is almost unavoidable unless they are all
relatively small people and there is half fuel or less. Keep a few of these at home to help
me estimate capacity when talking over a prospective trip with friends.
Our door does not close very well (difficult
to close and not flush with side of aircraft). Larry says that one little-known
adjustment on Comanches is that the door hinge has a moveable bushing with an
off-center hole that allows the door to hinge from a point closer in or farther
out as necessary to accommodate the thickness and condition of the door seal.
Larry says that part of the required preflight passenger briefing is how to open
both doors, the main one and the baggage door, even if there
aren’t passengers sitting in the back seats. The procedure is identical to
main door: “Pull up on the lock knob, then turn the handle.” Maybe we should
have this placarded on the inside of the baggage door.
The main cabin door is very difficult for the front-seat passenger to close.
Because of leverage, the pilot should close this himself.
We bought a placard that says “only the pilot may open and close this
door” which is affixed to the door to keep the right seat passenger from
not lock baggage door before flying so that someone could get in to rescue you
in case of an accident which makes the main door unopenable.
The baggage door should be easily openable from the inside regardless of whether
it is locked or not. Check it to be sure it can be opened from inside even when
The leveling panel is a piece of metal
fuselage skin located on the starboard side just behind & below the boarding
handle. To level the aircraft back out the 2 screws and place a level on top of
the resulting ledge. To level a/c from side to side, place level on the hat
Flaps are lowered with positive control by
an electric motor, but their return is dependent on a spring. If the spring is
not strong enough, or if there is too much friction, one flap may not retract
after takeoff. Since the Comanche, unlike Cherokees, does not have a rod
connecting the two flaps, it is likely that only one would fail to retract,
causing an imbalance in flight. I
have seen this happen – we were able to continue the flight safely but at
reduced power to keep us below VFE.
All three oleo struts should show 2.75” of
The left gear trunion can crack at the hole
where the bolt goes through. The bolt holds the clamp that holds the brake line
in place. For some reason this happens to most people on the left gear. Check
during preflight for red or black fluid leakage near the bolt hole, which
indicates a crack in the trunion.
When it’s time to have the 1000 hour AD
done on the landing gear, be sure that you go to a mechanic who has done this AD at least
twice before! This is a very involved process and there is a large learning
curve on how to do it properly and expediently. Many bushings have to be
measured with a micrometer and replaced if their measurements are not within
tolerances. If you are the first time for a mechanic your bill for labor will be
extremely high because it will take them forever to figure out exactly what
needs to be done.
If the gear will not retract after
takeoff, it could be that the squat switch has jammed or has gone bad.
Simply land and check the switch. The squat switch is the switch that prevents
the landing gear from retracting while the aircraft is on the ground and is
located on the left main gear only. (See Larkin materials p. 2.9)
If you don’t get a green light on
gear-down, it could be a broken wire leading to any of the three
gear-down switches. Try reducing power below 1500RPM. If the gear warning horn
does not sound, that means the nose gear is down and locked, because the horn
works off a single additional gear-down sensor located on the nose gear only.
Since all three gears are tied together mechanically, it is a very safe bet that
if the nose gear is down and locked, the mains must be also. If the position of
the manual gear extension handle confirms this (i.e., up in the air) then go
ahead and land.
When the plane is up on jacks for the annual
inspection, be sure to be present when it’s time for the mechanics to do the
required annual emergency gear extension. Get in the plane and do it yourself.
However, be warned that when you pull the red motor release arm, the gear will
fall very fast and hard - almost hard
enough to knock the plane off the jacks or to crack something - unless you have
one mechanic under each wing holding the main gear up and lowering it down
gently after you release it. Another way to lessen the sudden falling of the
gear is to extend the emergency gear lever
Larry Larkin doesn’t make videos—Maurice
Taylor does. Larry recommends Maurice’s videos and says they are advertised in
the Comanche Flyer. We bought four of them and they are excellent.
Larry Larkin suggests the following change
to our run-up procedure:
Throttle up to 1500RPM and exercise the prop three times. Move prop control
through full travel but the RPM should only drop to 1200.
Then throttle up to 2000RPM just long enough to do the mag check and to check
the engine gauges.
This causes less noise and less wear on the
engine by allowing it to warm up a bit at 1500 instead of going straight to
Maximum fuel efficiency is attained at
approximately 11,000 feet density altitude at 65% (55% would be even better) by
leaning to peak EGT. (See range chart in little owner’s manual.) Larry said
that range is drastically increased if
you run at 55% or 65% instead of 75%. At this level I was able to burn each
auxiliary fuel tank for just over an hour and a half before running dry.
I noticed that both aux tanks indicate 1/8 tank when they are empty! This should
definitely be placarded.
I flew back at 65% the whole way (9,000
pressure altitude but I calculated density altitude at over 11,000 due to the
high temperatures, using our handy OAT gauge and the little owner’s manual)
and had more than 45 minutes left in the tanks when I landed at Bridgeport.
That’s a pretty impressive range! (The empty Gatorade bottle in the back seat
is not trash; it’s my pilot relief system.)
Larry said that for true maximum range you
should have the fuel tanks filled off to the absolute top. He said many fuelers
will stop fueling the main tanks as soon as they see the fuel level reach the
bottom of the filler neck. In our airplane this is a mistake because there is an
additional five gallons of capacity if you continue to fill it all the
way to the top of the fuel neck. The fuel moves out of the neck to fill up the
big air bubble at the top of the tank. Larry has not heard of anyone ever
filling a tank so high that it dripped out of the fuel tank vents the way you
sometimes see on other airplanes.
To get even
more fuel in the tanks, park the plane so the nosewheel is pointing downhill
or in a small depression, or by loading people into the front seats and leaving
the baggage area empty until after fueling. The tanks can be filled more if the
nose is low because you can fill the parts of the tank that would normally be above the top of the filler neck, thereby making the bubble even
The tachometer will record hours equal to
real time only when the engine is running at 2310 RPM. He recommends operating
at 2300 because it makes the tachometer record less engine time (the plane might
be “worth more” compared to TBO at some future resale date) and it is also
quieter in the cabin and to people on the ground. When we operate at 2400 or
2500 RPM we are just spinning the tachometer hour meter around at a faster rate.
We should log actual
times in our pilot log books—using the time indicated as “FLT” time on the
ADF. We should continue to use tach time to figure our hourly costs. I didn’t
ask him for an estimate of hourly fuel & maintenance costs but we have found
it to be $75 - $80 on our 260 (including fuel at $2.20/gal).
For maximum range use 55% or 65% power at
2300 RPM and lean to peak EGT. The red indicator on the EGT gauge is not
“redline” per se; it is just a marker that you use to remind yourself of
where peak EGT is so that you can accurately lean to 100 degrees rich of peak if
you are aiming for best power mixture.
Larry said that our choice of 2200, 2300, or
2400 RPM should reflect our personal preference and will not affect the speed or
power setting provided we use the MP setting specified in the rating table. I
would like to get some advice on this from Maurice Taylor or Mark Giovenga to
find out what is best. Perhaps it’s better to use 2200 because it will take us
so much longer to get to TBO? Of course, LoPresti always uses 2400 or 2500 for
more speed. I guess we will want to vary it depending on whether we are trying
to save money on fuel or are in a hurry.
Flap (LoPresti cowl only)
The cowl flap is huge and we must be certain
to use it properly. The new cowling is very streamlined but provides just barely
enough cooling air to the engine during cruise. Failure to provide adequate
cooling to the engine can have terrible consequences, and we don’t have a CHT
gauge to tell us when the engine is not getting enough cooling air. Larry said
that the EGT gauge will not be of any help in this regard, since exhaust gases
are basically unaffected by cylinder head temperature.
Cowl Flap Procedures
• Before starting engine: Remove sponges from cowl flap
and from air duct underneath front of cowl. Remove bird plugs. Cowl flap
open: twist counterclockwise, push full in, then twist clockwise to lock.
Leave cowl flap open for taxi, takeoff, and climbout
When you transition to cruise climb (at 500 to 1000 feet AGL; Larry recommends
500), unlock the cowl flap and pull the knob until you see the black ink mark on
the rod, then lock in this “trailing” (half open) position. Then turn fuel
pump and landing light off, and continue climb at 130mph with gear and flaps up.
When you reach cruising altitude, close the cowl flap fully. LoPresti didn’t
provide a speed above which an open cowl flap will be damaged, but I suspect
that we could damage it by flying above 130 with it fully open.
Keep cowl flap closed for descent to avoid shock cooling. Larry recommends
reducing manifold pressure by 2” per minute when slowing down.
After landing, roll off runway onto taxiway and come to full stop. Then do
after-landing checklist: Transponder off, landing light off, fuel pump off,
flaps [not gear!] up, cowl flap full open.
After shutdown, close window and cowl flap. Install bird plugs and both
sponges. Secure cabin cover.
Cowl flap should be open for all ground operations, e.g., compass rose, repositioning, taxi, etc.
Of particular concern to me is that I tend to forget to open it right after
should add the above steps to our checklist.
Get a very wide and short screwdriver and file it down until the tip is the
exact width and length of the quarter-turn screws that secure the inspection
doors on the cowl.
Be very careful when opening and
closing the quarter-turn screws to open the cowl, as it is very easy for the
screwdriver to slip and scratch the paint.
Emergency Gear Extension Procedures (LoPresti Cowl Only)
1. Pull main gear circuit breaker
2. Pull nose gear circuit breaker (on center
3. Slow to below 100mph
3. Push silver button on the red nose gear
door lever, then while continuing to hold the silver button in, pull the red
nose gear door opening lever. Note: when you do this in flight, the enormous air
pressure that is normal inside the LoPresti cowl will blow
the doors open very violently with a loud BANG.
4. Now open floor panel and proceed with
gear extension by lifting the red motor arm lever. Gear should fall into place
and lock. (It will not fall violently like it would on the ground because the
100mph of air pressure is pushing back on the nose gear as it extends.) You
should now get a green light. If not, extend the telescoping lever that sticks
up from the floor to its full length and push it forward to be sure.
5. Once on the ground the entire cowl will
have to be removed in order to get the little pin back into the gearing that
attaches the nose gear door motor to the nose gear door push-pull rod. This
takes about ten minutes and is best done by one person with a screwdriver poking
at the pin while a second person sits in the cockpit adjusting the red
If all else fails, you can make a gear-up
landing on the grass next to the runway and cause minimal damage. Be sure to
stop the engine and feather the prop on short final. Hopefully the prop will be
motionless when you touch down.
Induction heat was required to be installed
by an AD a few years ago. We have the Webco fix, not the Piper fix, which is
good because the Piper fix can cause a fire if the engine is overprimed before
starting. Know when to use induction heat.
The weight & balance sheets in the
binder that came with our airplane show the make and model of the original Narco
radios that were once in our airplane. In looking at them Larry noticed that
they were replaced with King radios in 1992 but he didn’t see any entry
indicating that the power amplifiers and power supplies were removed from their
position behind the bulkhead. He said there is a possibility that the old heavy
power amplifiers and power supplies are still back there behind the bulkhead,
making the plane slower and reducing its useful load. It would be easy for us or
a mechanic to see if they are still there and remove them. It would require
removing part of the bulkhead to see back there.
Flap open for all ground operations. Open it before starting engine
and again after landing while rolling out on the runway.
Field Takeoff: 15 degrees flaps. Roll on to runway and set the toe brakes.
Run up to 2500rpm, check all engine gauges in the green, check RPM and MP to be
sure you’re developing full power, then release brakes.
Gear up, flaps up, climb at 105. At 500
feet, reduce power to 25/25, half cowl flap, fuel pump off, climb at 130.
On departure, climb at Vy
best rate (105) with the cowl flap fully open until you are above 500 feet
AGL and on course in approximately the right direction. At that time,
immediately transition to cruise climb
at 130mph with the cowl flap halfway open (pull handle until you see the black
ink mark in the groove of the pull rod). Be sure flaps are up. This will give
you an acceptable rate of climb and will be very efficient because you will be
moving towards your destination at 130mph while you climb.
There are four ways to cool the engine:
• Increase airspeed (descend)
• Enrichen the mixture
• Reduce power
• Open cowl flap
Use pitot heat anytime
you are in clouds, rain, or visible moisture. It prevents moisture from entering
the pitot system and ruining the altimeter. Note that our pitot tube differs
from newer Piper pitot tubes in that it doesn’t have a drain hole at the back.
We also don’t have a pitot/static system drain sump like the newer Cherokees.
This means it’s even more important to keep moisture out of the system.
When you are at cruising altitude (generally
between 6,000-10,000 on longer trips) you need to plan your descent carefully to
extract the maximum fuel efficiency from the airplane. Determine how many
thousands of feet you need to lose to get back to pattern altitude. Multiply
this by 12, then add 15. The result is the number of miles out (Loran) at which
you should start your descent at 250fpm. (180mph = 3 miles per minute; descend
at 4 minutes per 1000 feet; arrive at TPA 15 miles out from airport.)
• Do not reduce throttle during
• Do not enrichen mixture during
• Allow airspeed to build up as you push
the nose down and trim for the 250fpm descent.
• Once you get to pattern altitude /
fifteen miles from the airport, begin to slow down about six minutes out by
reducing manifold pressure by 2” every minute.
Approaches and Pattern Work
The enclosed scheme by Larry Larkin shows a
foolproof way to set up for approaches. He strongly recommends doing all
approaches at 120 knots (138mph). It is easier to fly the approach faster
and the power settings he provides accomplish the necessary approach level and
500fpm descent on the glide slope beautifully. “Gear down to go down.” It
also allows you to use the exact time (FAF to MAP) given on the approach chart
without having to guess/extrapolate for other speeds.
Once at holding altitude, reduce MP at 2” per minute to 17-18” at 2400RPM.
For a descent reduce MP to 12-13” and don’t change anything else.
This will provide a 500fpm descent.
To level off again add 5” of MP when you are 50’ above desired “approach
level” altitude. Continue flying 120 KIAS (138mph). Don’t change anything
else and the airplane will level off like magic.
At the FAF or Glide Slope intercept, put “gear down to go down.” This will
result in a perfect 500fpm descent at 120kts with 17-18” of MP.
To level off at MDA, add 5” of MP to 22-23” and put RPM full forward
preparatory to landing or missed approach.
Note that flaps are never used (the approach is flown too fast for flaps.)
Note that flying the approach at 120kts makes you a Category
B aircraft subject to Cat B minimums (generally the same as Cat A minimums
with perhaps 1/4 mile greater visibility).
Missed approach: 25/25, gear up, climb at 115 KIAS.
Larry Larkin wrote two articles for the Comanche Flyer on flying the
above-described Cruise Descent and Approach. Check in the Tips book—they might
be in there. Otherwise we can get back issues from ICS.
in landing configuration is 66mph at max gross weight; 56mph at lighter weight.
GLIDE IS 97mph
In the event of an engine failure, it is
very important to pull the prop control all the way back to “feather” the
prop as much as possible. Try this sometime at altitude with the engine at idle
and you can really feel the difference in drag particularly with the new
three-bladed prop. You can see on the VSI that your descent rate at best glide
speed (97mph) is reduced by over 200fpm, allowing you to stay aloft much longer.
If you lose one magneto, the MP and RPM will
stay the same. The power will go down noticeably and the EGT will go down
If you are losing oil pressure, your first
indication (assuming you have not been checking the oil pressure gauge) will be
that the prop will begin to rotate at higher and higher RPM, eventually going
over redline. If the prop begins to overspeed like this, bring back the prop
control and immediately check the oil pressure gauge. If oil pressure is low,
look for a place to land—fast. If not, the overspeed may indicate that the
governor has gone bad. Try pulling the prop control back. If it doesn’t slow
down the RPM, the problem is the governor, so reduce the throttle to lower RPM
below redline, then slow the airplane down to keep it below redline.
Fire: Open vents.
on fire: Keep vents closed.
Fire: Fuel selector off FIRST. Then throttle off and mixture to
Descent: Power to idle, slow to 150mph, gear down, prop full forward for max
drag, then descend at 150mph. This will yield a descent off 4,000 fpm!