Cherokee Pilots' Association
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Cherokee Pilots' Association |
Letters to the Editor
Concerned Over
Duration Discrepancy
Dear Terry,
I currently fly a 1995 Archer III.
This aircraft uses the Lycoming 0-360-A4M engine. The POH notes that fuel flow
at 75 percent best power is 13.5 gph. The Textron Lycoming operator's manual,
however, states that the 0-360-A engines at 75 percent power consume 1.5 gph.
Lycoming's figure is also used in the Piper POH for the Archer II models, where
fuel flow at 75 percent best power is stated to be 10.5 gph. The Archer II also
uses the Lycoming 0-360-A4M engine.
Usable fuel for the aircraft is 48
gallons. Based on Piper's figures at 75 percent power and 13.5 gph, endurance is
3.5 hours. Using Lycoming's and the Archer II figure of 10.5 gph, endurance is
4.5 hours. The additional hour is significant to me, as I will not land with
less than one hour fuel remaining in the tanks. Also, the additional hour at 110
knots or so provides a range increase of some 110 NM. Can you explain the
discrepancy between Lycoming's fuel flow number and Piper's, and which number
should I use?
Sincerely yours,
David Gameroff
Westmount, Quebec
Canada
Dear David,
Normally, where there is a
discrepancy between the engine handbook and Piper's, the rule is to use the
Piper numbers. Lycoming tests its engines on a test stand, while the Piper
numbers are derived on a particular plane, utilizing the accessories and exhaust
system supplied by Piper.
The 75 percent number supplied by
Piper seems suspect, however, not only because it is higher than both Lycoming's
number and that of Piper's previous model, but because it is also inconsistent
with the other numbers in the Archer III manual.
As you no doubt know, you can
approximate engine power if you know the fuel burn rate. In other words, fuel
burn rate (gph) varies nearly directly with the percentage of power which an
engine is putting out. The Archer III manual does show a higher burn rate than
did the older Archer II manual. At 55 percent power, for example, it shows a
burn of 8.2 gph. Now, if you do a proportion based on that number, you would
expect the burn rate at 65 percent power to be 9.7 gph - close to the Piper
number of 9.5 gph. Then, if you made the calculation for 75 percent power, you
would expect to get 11.2 gph - not 13.5. You would expect to burn 13.5 gallons
at 90 percent power, not 75 percent. It sounds like the 13.5 gph figure is an
error.
As to what figure should you use? I
would not suggest using either figure as an etched in stone guide. And that
applies to all figures in all tables compiled by all manufacturers. What you
should do is to carefully check fuel flow in your plane after carefully
setting power and then leaning accurately. This is the only way you will know
for sure what your airplane will consume and what duration you can expect.
My guess is that when you do so you will find you have a fuel consumption
closer to 10.5 than to 13.5 gph.
Sincerely yours,
TERRY LEE ROGERS
Be Alert to
Performance Creep
Dear Terry,
I've owned my PA-28-140 aircraft for
four years and have taken many a cross-country trip with it. At Altitude (5000
feet) it's always demanded careful attention to loading and density altitude
but I have managed to regularly fly to Lake Powell (Bull Frog) from my home in
Loveland Colorado. I was always on the lookout for proper engine performance
and was never quite satisfied with the performance figures I was getting. EGT
a little off, Static RPM check on hot days a little low, air speed off
slightly (Low).
Nothing ever checked bad enough to
warrant serious investigation (in my mind) however, I had my mechanic give it
a look see several times, he said "Yep they don't have much power and you're
operating it on the edge." So I would feel better for a while.
One day I just couldn't get the
altitude that I needed to safely get over the continental divide for a Powell
trip, I headed back home. I went to the friendly local prop shop (I boat a lot
and am constantly prop swapping). They informed me that I had a cruise prop
and a dull one at that. I had them re-work it into a climb version, (a little
better performance) and then came the Tach check, it was way off -- 250 RPM
Low at 2000 RPM. I thought, "that's it; now the numbers match better."
It was a hot summer last year and I fly back and forth to work every day,
careful about loading especially those HOT 95 Degree days. On this particular
day the figures showed I should get a ~400 FPM climb. I nearly brushed the top
of the trees at the end of 08 in Boulder showing 0 FPM climb (Down slope winds
that day, had me in a slight down draft). I thought, this is not good enough,
something is wrong, as my feet shook on the rudder pedals.
I was finally released from the down
draft and I received a blistering ~200 FPM climb.
I took it to my regular mechanic and
told him to find out why I'm off so much on my performance, otherwise, I'm
selling it for a more powerful one. I remembered a story long ago about a
similar event in the AOPA magazine and suggested "Check out the muffler". To
summarize, the muffler had come apart slowly, internally, a baffle cracked and
over time wedged it self into the exhaust port. With a new muffler, my
figures, match book figures exactly - 138 MPH top speed not 125, 600 FPM not
400 FPM exhaust temperature ~800 C. She is a different machine!
I was too complacent; I should have delved into this a long time before I did,
but it was such a slow moving problem that it got by my limits checking, as a
creeping thing. So check it out thoroughly if you have numbers that don't
match up like they should.
Sincerely yours,
Tony Cash
Loveland, CO
Source For
Stainless Plugs
Dear Terry,
In the June issue, Kent Shaw of
Gaithersburg, MD, asked for a source for the stainless steel plugs used to
cover the main landing gear strut service valves in the wings of his Warrior.
A couple of years ago, I was able to obtain these plugs from Herb Jacobs, Post
Office Box 5390, Lighthouse Point, FL 33074. The price was $15.00 per pair of
plugs. I hope that this information will be helpful.
Sincerely,
Gus Jamison
Winston-Salem, NC
Problem With
Re-plated Strut
Dear Terry,
I note in the June issue Harold
Mueller's question on strut replating. I am currently in the process of
getting the right main on my 180 redone that Industrial Plating did a little
less than two years ago. They are being cooperative and will redo it at no
cost, but I still have to lay the plane up for two weeks which also means
getting a hangar for that time since I tie the plane down. I made the original
decision to have it re-plated on the recommendation of my mechanic.
I was going to get a used one from
Wentworth ($400), but they won't yellow tag it and the mechanic didn't want to
install it without a yellow tag. (A good used one would in my mind be a better
bet so you don't have to tie the plane up.)
The strut looked great when we got it
back and installation was no problem. However, it always tended to stick and
not operate smoothly. This was no great problem and I lived with it until the
plating started to come off. The place where it has failed is where the worst
pitting was originally so they must not have removed all the rust.
I don't want to bad mouth them in
print - they are cooperative and attempting to make good on their work. But
could you pass this on to Harold Mueller for his information. I am going to
send the strut in next week and will let you know how it all comes out.
Name Withheld
Heater & Fresh
Air Cables
Dear Terry,
I have a 1966 140 and am having
trouble with my heater cable. As I run the heater at any level other than wide
open it vibrates shut. I have a condition of feast or famine but could often
use a nice light lunch. Any suggestions would be appreciated.
Also the cable that opens the fresh
air vent has managed to break at the door and naturally is too short to be
reattached. My mechanic tells me a new one runs in the $100 dollar range. Do
you know of an alternative solution with a little more reasonable price?
As always I greatly appreciate your
efforts on behalf of all us hopeless Indian lovers.
Sincerely yours,
Ed Frye
Polk, PA
Dear Ed,
I asked George Durham, of No Toro
Aircraft, for input on your problem. His reply:
"Your creeping heater control needs a
little friction. One way which this can be accomplished is with a piece of
metal about 2 x 3/8 and .090 inch thick. It should be bent down the middle 1/4
to 5/15 inch deep and about 3/4 inch wide with a worm clamp.
"It will look like a cross section of
a ten gallon hat. Lay the housing (control cable) over the flats with the
clamp in the middle and tighten the clamp just enough to get the desired
friction. About your fresh air cable, it will cost more and take longer if you
change the whole assembly. If you measure the inner wire diameter, get some
music wire and replace only the inner wire. The cost should be pennies
compared to changing the entire assembly and it will also be easier on your
mechanic."
Sincerely yours,
TERRY LEE ROGERS
Roughness After
Rebuild
Dear Terry,
This comes to you all the way from
Africa...from a tiny Kingdom called Swaziland!
I am the proud owner of a Cherokee
180 C (1965) which has spent it's whole (35 year) life in Africa.
It was originally bought new by a
tobacco farmer in Zimbabwe and shipped out in a crate from the USA. The
aircraft was little used, but meticulously maintained, and hangared. Two years
ago whilst in Zimbabwe on a flying holiday, I happened to mention at the bar
of one of the flying clubs that I was looking for an aircraft to buy.... One
thing led to another and three months later I was the owner of the most
original Cherokee I have ever seen. It had a total time of 1750 hours, and
everything was as per factory, except for a KX 175BE and a KY 195BE.
Anyway I took the plane home, and myself and a friend (who is a licenced
engineer) spent a year taking it apart and putting it back together.... there
was nothing wrong, but we renewed everything from brake systems to hoses,
oleos, windows, fuel tanks, and totally overhauled the engine....new
Millennium cylinders etc. The interior was in very good original condition,
the seats were re-stuffed, the side panels backed with aluminum, and new
carpets fitted. all the interior plastic was perfect, and was simply cleaned.
The paint work was almost polished
away, but was sound and blemish free. We simply dressed it and sprayed a coat
of fresh paint onto it. Most people wont believe it is not a bare metal
respray..... The list goes on and on including some new avionics, electronics
International instruments etc.
Now I have a lovely plane, in which
we travel all over southern Africa. Our airfields are primitive and navaids
non-existent but our skies are uncluttered the scenery breathtaking....
Imagine spotting elephants on your cross-country!
Now to the important bit.... I am an
avid reader of your Piper Owners Magazine.... In the latest issue in the
article WOE TO THE FIRST ANNUAL you refer to the incorrect fitting of Lord
engine mounts, as a reason for vibration, and engine mount wear.
Since I had the engine overhauled,
there has been a persistent vibration in the power unit. At first I thought it
might be the prop (also overhauled) but after having it dynamically balanced
three times I gave up. I have pursued every other avenue, but everything seems
normal, and the engine performs very well (140 hrs SMOH). The engine was
fitted with new Lord mounts at the time of the overhaul!
Please could you tell me if the
arrangement described in the article applies to my plane. If so please explain
in more detail how I check the mounts for correctness of installation and
explain exactly how the mount should be installed.
Thank you for a great magazine.
Sincerely yours,
Trevor Mulroney
Swaziland, Africa
Dear Mr. Mulroney,
As was stated in the article, the error was in installing the mounts
backwards, so that the weight of the engine is supported by the large, liquid
filled side. The mounts in question were installed backwards - the top ones
had the larger, liquid filled side toward the front, while the bottom ones are
reversed. The weight of the engine should not be resting on the hard, smaller
biscuit.
But that was given as an example, only. It would be very rare, indeed, to see
Lord mounts incorrectly installed. Other causes of vibration, however, are
more common. Incorrectly indexed propellers are one possible cause.
Also, some engines are just smoother than others. Although some precision
balancing might help, a little roughness might simply be something you have to
live with.
Sincerely yours,
TERRY LEE ROGERS
Erratic Vacuum
On Gauge
Dear Terry,
I have a 1968 Cherokee 140 with an intermittent vacuum problem. On some
startups, the vacuum kicks in fine. Yet on others, there is no reading on the
gauge until the tach reaches 1,500 rpm or so. One time the gauge swung around
in circles before resting on the maximum reading. At first, I thought the
gauge was defective because the instruments seemed to work fine once I got
some reading on the gauge. So, I replaced the gauge, and all was OK for a
short period. Now, I still have occasions where the tach has to get pretty
high for the gauge to "kick in". Is it time for a new vacuum pump? The current
pump has about 350 hours of service.
Thanks for a great resource in your magazine.
Larry Aull
Monroe, GA
Dear Larry,
I asked George Durham of No Toro Aircraft to comment. He said, "It sounds to
me like your vacuum regulator is sticking. This is a common problem on some of
the older regulators. you may be able to disassemble and clean it. Then
reassemble it and give it a try."
Sincerely yours,
TERRY LEE ROGERS
Wants Information
On Compression Test
Dear Terry:
Would you e-mail the proper method to perform a compression on a PA-28-140 a/c
with a Lycoming 0-320 engine. I checked the Hints & Tips manual and it only
tells what the mechanic does. I would like if possible a description starting
from the beginning.
Sincerely yours,
Jack Tedford
Dear Jack,
The differential compression test is an industry standard - it is a static
test (the propeller is not turning during the test and is normally hand-held
by the mechanic during the test to provide rigidity.) The test is performed on
an engine which has been warmed up to operating temperature.
Air is fed through a calibrated orifice (normally .040 inch) at 80 psi. The 80
psi is used because it is the highest pressure at which a propeller can be
hand-held to prevent turning. The testing requires a special unit which
consists of two pressure gauges separated by the restrictor orifice and a shut
off valve. Supply pressure is adjusted to 80 psi on one valve and the residual
pressure read off the second. Testers are not overly expensive - you can
purchase one from Aircraft Tool Supply, P O Box 370, Oscoda, MI 48750
(800-248-0638). It comes complete with spark plug adapter.
The air source is then removed and the loss of pressure noted. Some people
believe that if the pressure drop is more than 20 psi (60 psi), the cylinder
should be scrapped. But there is no such requirement by either any
manufacturer or regulation. The better view is that if pressure drops more
than 20 psi, it is one of many factors which should be taken into account in
determining what, if anything, needs to be done with that cylinder.
Unfortunately, the process requires some interpretation. It is easy, for
example, to drastically alter the results simply by bumping the propeller a
bit. Also, a cylinder which reads low today may read higher tomorrow after
flying the engine and causing the rings to realign themselves.
Nonetheless, the test is one of the most trusted barometers of engine health
today.
Sincerely yours,
TERRY LEE ROGERS
Recommends
Black Mac Prop
Dear Terry,
I am a co-owner of a 1967 Cherokee 180. I saw the letter in the June edition
of POM regarding a cruise prop for a '76 Archer 181. I don't know if my
experience with my 180 will help him but I'll pass this info on.
Last summer we needed to install a new prop. I had just assumed that we would
replace the original Sensenich prop with the same type of prop until I had
heard about the "Black Mac" by Macauley. Another Cherokee 180 owner at a
nearby airport had reported an approximate six knot speed increase after he
got the Black Mac installed.
Since there was a 30 day waiting period for a replacement Sensenich and the
cost was only about $500 more I ordered the Black Mac. Sure enough, we also
got another six knots. I hope this information helps.
Sincerely yours,
Dewey Lee Crepeau
Colombia, MO
Cause of Stall
Warning Problem
Dear Terry,
In the POM July issue, Ray Andraka has improper stall warning action. The
symptom he describes means that someone either leaned on or otherwise
distorted the stall vane.
When the stall approaches, flow separation drops along the leading edge until
it begins to blow from "under" the vane. If the vane is adjusted too low, the
stall may get there before the vane actuates. Some of the switch mounts are
slotted and can be adjusted, on others, you might have to bend the vane to get
the proper angle.
To make the warning occur earlier, move the vane up, and the converse. If
necessary to bend vane, better to pull vane and switch out and support switch
end while bending. These assemblies are quite expensive from Piper, but they
seem to be the same as I had on a 1965 Cessna 182.
I had the reverse problem from Mr. Andraka's on my Cherokee 180, and had to
adjust, fly, adjust, fly and so on until the warning/stall speed difference
was about five mph. Normally, I would expect to see light flashes in very
rough approaches or climb outs, up to 90 mph. Hint: Cherokee stalls are easier
to control with a couple notches of flap.
Sincerely yours,
Dallas Vaughn
Holliston, MA
Keeping Cabin
Moisture Free
Dear Terry,
I have a comment concerning the use of calcium chloride in removing humidity
from the cabin (May POM). A few years back I bought such a kit from a marine
store, but found the whole thing frees up in Connecticut winters.
Since then I have tried to be consistent in having the upper and lower vents
open when the plane is tied down. It really does work.
Sincerely yours,
Douglas Noiles
New Canaan, CT