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1. 07:07 AM - Emailing: pitot (Dave)
2. 11:01 AM - N17EF data update (EAFerguson@AOL.COM)
Message 1
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PitotPete,
The last part of this article proved to be interesting. It may help
in the future to eliminate a problem.
Remember a couple of months ago you called me for some axle and
brake parts that I had, which you could not get from Esqual, to help
someone get back into the air. You received them within 3 days without a
bill.
I ordered lightning gear struts at S&F and asked you no less than
5 times about them. Remember I have the shimmy problem, after asking in
private, I am now asking publicly, where are my gear struts, or who do
you get them from.
I did you a favor, sorry I has come to this, Dave McC
BUZ,
If I find sonething that does or does not work, I'll be first to admit
it. The bypass oil line proved not to perform as expected. I then
removed it and installed an air deflector from the nose strut forward 8
inches having a height of 2.5 inches. This gives me oil temps 187 at
2950 rpm and cylinder temps at 300 or less with oats of 88 degrees.
Climbing straight to 8,000 at 500 fpm it did not go over 200 oil temp..
Something so simple made a huge difference. Just passing it on Dave
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Pitot-Static System
AMONG THE MINIMUM instrumentation required for VFR (Visual Flight
Rules) flying are two flight instruments - the airspeed indicator and
the altimeter. While a small number of builders might think a rate of
climb (vertical speed) indicator is essential, it is not one of the
mandatory VFR instruments. Nevertheless, the three instruments do have
something in common - each must be vented to a source of atmospheric
(static) pressure for proper operation. In addition, the airspeed
indicator requires a source of ram air (pitot) pressure. These two air
pressure sources, and the interconnecting plastic tubing, constitute the
aircraft's pitot-static system.
Calling it a "system" when little more than a bent aluminum tube
and some plastic tubing embody the main elements may be a bit grandiose.
However, you can make your own installation of the pitot-static system
into a big deal or keep it on a modest minimum effort level.
Static Pressure Sources
Some pitot tubes contain both an inlet for the pitot or ram
pressure, and another for the static pressure. These pitot tubes are,
therefore, more correctly identified as "Pitot-Static" tubes. In such
installations the pitot-static tube is a dual-function unit providing
both ram (P) air and static (S) air for the instruments connected to it.
Although the static pressure is not always obtained at the pitot
tube head assembly, it would seem that such an arrangement where both
ram air and static air are taken from the same source area is a good
one. It could assure a higher degree of accuracy in instrument
performance than might a static air pressure source remotely located. On
the other hand, one fairly reliable source location for a static
pressure vent, remote though it might be from the pitot tube area, is
the fuselage . . . somewhere in the side of the fuselage, that is.
There you will often find one to three small vent holes, in a
flush-mounted fitting of sorts, serving as a static air inlet. Actually,
static ports are ordinarily installed on both sides of the fuselage to
minimize the effects of slipping or skidding flight resulting from
sloppy or unintentional rudder inputs. Brief transgressions from
coordinated flight will affect your instrument readings only momentarily
unless you habitually fly the airplane in a constant skid.
Both static vents, when located on opposite sides of the fuselage,
must be manifolded (connected together by a "T" or a "Y" fitting).
One advantage of a separate static source remoted from the pitot
tube is the theoretical assurance that your altimeter and vertical speed
indicator will continue to function even though the pitot tube may
become blocked by mud daubers, ice, dirt or a forgotten pitot tube cover
. . . and this is worthy of your consideration.
The remoted static pressure vents, when installed, should be
located in an area of air flow unaffected by wing junctures or fuselage
bumps and irregularities. Even though the fuselage sides may seem to be
uniform in the area selected for the static vents, a future relocation
of the vents could become necessary because of erratic or unreliable
instrument readings.
If the static source is located in an area producing higher than
true (surrounding atmosphere) static pressure, your altimeter will read
lower than it should. Conversely, a static source producing lower than
true static pressure will cause the altimeter to indicate higher than it
should.
A poor static source also affects the airspeed indicator's
readings. For example, a static source co-located with the pitot head
positioned just ahead of the wing but too close to its under surface
could be in an area of slightly higher pressure than that of the
surrounding air. This is an area of higher pressure induced by the flow
of air around the leading edge of the wing. In such a case the airspeed
indicator will be induced to read slow since the pressure differential
between the ram and static air would be less in that area.
A location too high could induce the reverse effect causing a too
fast indication by the airspeed gauge. Similar errors can occur with the
remoted fuselage static ports if they are located in a disturbed
pressure field.
Carrying this static error subject a bit further, we can see where
the same errors could result in a biplane installation where the
pitot-static tube assembly is mounted too high or too low on an
interplane strut. If too high the static port could pick up a slightly
higher pressure under the top wing and give a resultant slow reading. If
the static tube is located too low on the strut, the static source will
pick up a lower than true pressure because of the induced airflow over
the top of the bottom wing. This would result in an airspeed indication
that is too fast. Remember, the airspeed indicator measures the
differential between the ram air and the static air.
Pitot or Ram Pressure Sources
As previously stated, only one of the three VFR flight
instruments, the airspeed indicator, requires ram (pitot) pressure. Its
source of ram air pressure is a pitot tube mounted parallel to the
longitudinal axis of the aircraft and in line with the slipstream
(relative wing). The location of the pitot tube is no less important
than its orientation on the aircraft.
All this really means is that the pitot tube should not be located
inside the propeller blast area or any place where its pick-up opening
might be in air disturbed by the influence of proximate aircraft
structure. Although some airspeed error is no big thing for the weekend
aerial putt-putt, it can be a serious matter for a fast high flying
homebuilt or one used occasionally in IFR excursions.
It seems as though the only thing standardized about pitot tube
head locations is that, for some reason unknown to me, more pitot tubes
are located somewhere in the left wing than elsewhere. But you are just
as apt to see pitot tubes installed almost anywhere on the aircraft.
In a twin the fuselage nose location is quite suitable because it
is not within the propeller blast area.
The most serious boo-boo you can make in locating your pitot tube
is to place it in the leading edge of the wing. Yes, in spite of the
effectiveness of that location. It is so easy to install a pitot tube
there that it is almost irresistable for the first time builder to
ignore. Unfortunately, it is such a good location that almost anyone
walking by will notice it after he has bumped into your pitot tube or
has broken it off. Even more unfortunate - the builder himself may be
the very first one to ruin it. One builder told me his was broken off so
often that now, just before he flies, he slips a drinking straw into the
hole once occupied by the original pitot tube.
Of course, the leading edge location is not too bad in a high wing
aircraft . . . if that wing is high enough off the ground.
Maybe Molt Taylor has the solution for vulnerable pitot tubes
sticking out where they can get bent or broken. He has installed, in his
MicroIMP, a flexible pitot tube that merely gives way under impact and
twangs back good as ever. (I wonder how he does that?)
It becomes obvious then that the safest location for a pitot tube
is beneath the wing. Almost anywhere under the wing is O.K. for aircraft
utilizing the older airfoils (Clark Y, etc.), just so long as the pitot
tube opening is about 5" or more below the surface of the wing. An
aircraft with a laminar flow airfoil should have its pitot tube located
further aft to some point where the maximum camber of the wing occurs.
Pitot-Static System Installation Notes
Some pitot static tubes are made with built-in heater elements.
These are electrically powered and must be hooked to the electrical
system. The pitot heat would then be controlled by an appropriately
labeled instrument panel switch . . . but why a heated pitot-static tube
if you don't fly IFR?
When the static source is to be obtained at the pitot tube head,
you can make your own assembly using two aluminum tubes attached to a
mounting bracket.
One of the tubes in the pitot head assembly will have an open end
for ingesting ram air pressure. This tube should be connected to 1/4"
polyethelene (plastic) tubing routed to the "P" (pressure) opening in
the airspeed indicator.
The other tube (static) of the pitot head assembly must have its
end sealed (pinch, weld, insert a screw or otherwise close the opening
in the tube). In addition, it will have at least four small holes (use a
#60 drill bit) equally spaced, around its circumference to provide the
ambient (static) air pressure needed by the airspeed indicator,
altimeter and the rate of climb. This static source will also be
connected to each of the VFR flight instruments with 1/4" plastic
tubing. See Figure 1 for a few ideas and typical hook-ups.
Before completing the connections at the instruments, blow out the
tubing to assure yourself that none of the lines are plugged. Do not,
however, blow into any of the instruments as that may cause internal
damage.
Aircraft used in instrument flying should have an alternate source
for static pressure in case the primary static source becomes
inoperative. This alternate source can consist of a single valve that
opens the line to the cabin atmosphere - an unreliable source at best
but better than inoperative instruments.
A few builders of uncomplicated aircraft often don't bother with a
static source and simply leave the "S" ports of the instruments open
behind the instrument panel.
This is a poor installation if for no other reason than the abuse
the instruments will be subjected to from ingested dust and dirt
floating around in the unfiltered air. Another drawback to using the
cabin atmosphere as a static source is the wild fluctuation induced in
the instrument readings every time the cabin ventilation vents are
opened or closed.
Ever hear of adjusting your airspeed by modifying the static tube
in a pitot-static installation? Well suh, the story goes like this.
If your airspeed reading is slow, it is because the static port is
in a slight high pressure zone. This can be corrected by slipping a
small "O" ring over the end of the static tube ahead of the tiny drilled
holes (vents, that is).
Moving the "O" ring aft on the tube (in very small increments)
will increase the airspeed - on the gauge (not for the airplane, amigo .
. . sorry). Conversely, moving the "O" ring forward, away from the
ports, will decrease the indicated airspeed in much the same manner.
Very small changes in the "O" ring position make a noticeable difference
in the indications.
What happens is that you are attempting to lower the static
pressure "felt" by the static ports with the "O" ring interrupting the
airflow, thereby causing a slight lowering in air pressure behind
(downstream) the ring.
The closer the ring is to the ports, the lower the induced
pressure.
If on the other hand the static-tube port happens to be located in
an area of low pressure, moving the ring to a position behind the ports
should provide a slight increase in the pressure felt by the static
ports with results opposite to that described above.
Because a rubber "O" ring will deteriorate, it should be replaced
with a metal ring having identical dimensions after the proper location
is determined. A dab of paint or epoxy should hold it in place. One gent
who does some wild gyrations in his modified Starduster has a big ol'
set'screw securing his "scientifically" located ring.
Author unknown, I found this in my plumbing files ~ cdngoose
Message 2
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| Subject: | N17EF data update |
Listers:
I got the attached e-mail from Jeff Lachmund reminding me that I haven't
posted any performance data on N17EF for some time. There isn't much to report,
but here's the latest:
Grand Rapids had sent the wrong EFIS box, which got installed before Nick
realized that it was the "Sport" version instead of the full Horizon I. As a
result, my initial flights were without the EFIS. I did have the EIS installed,
so I hade good engine instrumentation. However - no Nav capability except the
mag compass and a clock. That lead to some minor excitement when the new mag
compass decided not to point anywhere close to north. This happened at the
southern end of a DR round robin, leaving me 35 miles south of Shelbyville.
That's called VFR partial panel, or IFRR (I Follow rail Roads). The compass
would not point between 030 and 330, period. I'll omit the details, bot I got
back to Shelbyville OK. I took Buz's handheld GPS along on subsequent
flights.
The EFIS finally arrived and got installed. Not having ever flown with one
of these boxes, I'm learning. The capabilities are huge, but the device has to
be set up, and we're in the process of doing that. I spent Friday and
Saturday of this week in Shelbyville working on the chore list. At 35 hours, it
was
time for the first oil change and re-torque the heads. The spinner was out
of balance, so we put a new one on and checked it. That took care of Friday, so
I stayed over and worked Saturday. I was supposed to call Grand Rapids from
the airplane Friday to go through some calibration stuff, but just didn't get
to that. So Sat Ben helped with the setup procedure for the EIS and EFIS.
They work together. Then I took a stab at the compass calibration procedure.
It's called magnitometer calibration in the EFIS manual, and should take about
10 minutes. After an hour +, I finally finished, or so I thought.
With an accurate compass heading I could do a wind calc with the GPS track
and GS and get accurate air speeds. We know the airspeed indicator is
inaccurate at the low end of the speed range, it isn't even marked below 40K.
Normally
not important, but I'm certifying to the Light Sport 45K stall speed. So
the plan for the Saturday flight was to get the airspeed calibration and do
stalls. No luck, I still had an obvious compass error, maybe as much as 30 deg.
Wasted flight, still no accurate stall speed. Rats! I'll talk to Grand Rapids
about the calibration procedures tomorrow and find out what I did wrong.
The airplane now has 28 hours of the 40 required before I can fly it home.
Because of the EFIS delay, I could hit the 40 hour mark before I have the
required data for the Light Sport certification. Meanwhile there is a lot to do
before it's fully operational. Mine is the first Light Sport Lightning, and
Arion wants the performance data as much as I do.
Back to Jeff's questions:
My empty weight was 806 lbs. Since the weigh-in the only change has been
the addition of the EFIS, We haven't updated the W&B for that, but the
system is only about 2 lbs. As far as reducing the empty weight, they are working
on that, and will probably find a few more pounds to trim. Check the Arion
web site at _http://www.arionaircraft.com_ (http://www.arionaircraft.com) for
details and watch this list for announcements.
Regarding stability, I indicated slightly positive stability. Properly
trimmed, it will fly straight and level until there is a disturbance, then there
will be a change in pitch and or roll which may or may not damp out by itself.
N17EF is still flying slightly out of rig, so accurate date isn't available.
We're working on that. Another factor is fuel loading, since the airplane is
light, it is very sensitive to fuel imbalance, which affects roll
stability.This is clearly a sport aircraft, very responsive, but not highly stable.
Finally, Jeff asked about the ballistic parachute. No, I don't have (or
want) one, and that adds significant weight.
Earl Ferguson
Atlanta
- - - - - - -
Jeff's e-mail:
Hi again Earl from Australia,
I trust you don't mind just some questions I missed from the previous email.
Your mention the pitch and roll as 'slightly positive'. Can you spell out
what you mean. The empty weight finished up at 806. Do you think you could
have reduced this and where? Obviously this figure will increase with
instruments to be finalised etc. Have you installed the ballistic
Parachute? Have you had any further performace details to report since
Aug.26.
Regards Jeff Lachmund
Jindabyne, Australia
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