Warbird Information Exchange

Ken, I have always heard that the cowl flaps settings are important on the A-1. Can you elaborate on this some? Also, the Oil Radiator flap is auto as well as manual. I almost never see it down on static as well as operational A-1s. Does this mean the motors have to be really hot for the flap to be lowered?

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Better is the enemy of Good.

The cowl flaps are DC electric and are controlled by a 3-position, OPEN-OFF-CLOSE toggle which is spring loaded to the OFF position. Nose petal flaps (deactivated by the USAF and on many warbirds) are manipulated with the same switch and the petal position is shown to the pilot via a mechanical rod which sticks up from the upper cowl.

From the USAF Dash One:
"Generally, the cowl flaps must be closed after takeoff
to prevent the engine from running at cooler than
desired temperatures. However, adjust cowl flaps as
necessary to maintain cylinder head temperature
below 245°C when climbing at METO power. When
operating at military power, do not exceed 260°C. A
material reduction in cylinder head and oil temperature
can be obtained by climbing at an IAS from 15
to 20 knots faster than best climbing speed. A
tendency for oil to overheat can be checked quicker
by reducing engine speed than by throttling alone."

It goes on to say:
"USE OF COWL FLAPS. It is not generally necessary to
position the cowl flaps during ground operation, as they are
automatically opened fully when the weight of the airplane
causes compression of the landing gear shock struts. This
automatic opening feature can be overriden by use of the
cowl flap switch on the left console. The cowl flaps should
not be closed during ground operation when warming up
the engine, but may be closed after shutdown when the
engine has cooled, to protect the engine from existing
weather conditions. Closing the cowl flaps in the air will
not override the automatic feature, and the cowl flaps will
open immediately after the airplane has landed. If the cowl
flaps have been closed after shutdown, any interruption of
the DC power supply will reinstate the automatic opening
feature. Therefore, the cowl flaps, if closed, should automatically
open immediately after DC power is supplied to
the secondary bus, for instance, during the engine starting
procedure."

For the local, low power flying we were doing, the cowl flaps were left open. The continuous CHT range is 150-232C, and, although the engine stayed on the low end of this, our goal was to minimize overall temp changes to the engine. The other side benefit is there was no risk of the flaps becoming stuck closed. Going cross-country would call for procedures more in line with those stated above.

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"Take care of the little things and the big things will take care of themselves."

Can any of you shed some light on the how & why of the R-3350-26WD manifold pressure regulator? In short, the book says that it A) Limits MAP to 56" B) Maintains selected MAP under all flight conditions C) resets MAP when changing blower speeds. In today's warbirds, only B would likely apply since 100LL fuel causes us to use much lower MAPs and Low blower only.

The MAP regulator operates using oil pressure, so I've been told that it is wise, before shutdown, to set the throttle position desired for the next start, as oil pressure obviously disappears upon shutdown. Yet there must be some remaining control since the Dash One goes on to add a related Caution that reads:

"If throttle is opened or left in open position
while engine is not running, sludge or congealed
oil may cause pilot valve and/or servo piston of
manifold pressure regulator to stick in full
INCREASE position. This condition may result
in runaway during the next start. This condition
is more likely to occur in cold weather."

Should the MAP regulator fail, the Dash One has this advice:

"Loss of engine oil pressure will result in failure of the
automatic feature of the manifold pressure regulator. When
the oil pressure drops below approximately 25 psi, the
spring-loaded piston in the manifold pressure regulator
drops into the full-low manual schedule, wherein the actual
throttle position is only one half the corresponding position
of the cockpit throttle control lever. Under these conditions,
the maximum attainable manifold pressure at mili -
tary RPM will be approximately 1.5 times the outside air
pressure in low blower and 2.3 in high blower. Movement
of the throttle control lever to the full OPEN position will,
in most cases, provide up to 40 inches of manifold pressure
if desired. Under certain conditions, the use of this
procedure may allow the pilot to reach a landing field prior
to complete engine failure due to lack of oil."

I spoke to the gentleman who restored the first civil AD about a MAP failure he had on an early test flight. He reported that the engine behaved just as the book predicted.

I think my question overall is: How does the MAP regulator interface with the throttle for start? Does the pilot have any direct control of the throttle linkage or is it strictly through the MAP regulator? If it is through the regulator, then does the throttle response of the engine change dramatically between the time of first rotation and once oil pressure becomes available & the regulator operates normally?

Anyone?
Ken

_________________
"Take care of the little things and the big things will take care of themselves."

Power settings are often pilot or organization technique. The following are the ones I used in my training (100LL fuel):

49"/2800 Limit
45"/2800 Normal takeoff
38"/2600 Climb
35"/2300 Max cruise and initial go-around
30"/2000 Cruise & airwork, estimate 100 gph & 170-180 KIAS
20"/2000 Min power in pattern and during practice stalls
28"/1800 Slow cruise, estimate 85-90 gph

During lunch with the owner of the first civil AD, he mentioned some great conversations he was able to have with retired engineers from Curtiss-Wright back in the early 80's - picking the brains of the experts who developed the 3350. They reported that, if power was routinely kept below 50", engine reliability skyrocketed and they would approve a 2000 hr TBO. A big contrast to this was chatting with Stew Dawson about how hard (and high RPM) they are able to run Rare Bear at Reno ...

_________________
"Take care of the little things and the big things will take care of themselves."

Ken wrote: "I have always heard that the cowl flaps settings are important on the A-1. Can you elaborate on this some?"

I believe this is the answer to the question: Some A-1's have a engine blocker inside the cowling that is part of the cowl flap switch. If the engine block is extended to cover the cylinders, the engine can be over heated and damaged. The engine blocker covers the cylinders to prevent overheating during an extended dive bomb profile.

In a way, the cowl flap switch is 3 position ( on many A-1s ). Full open: cowl flaps are open & blocker is retracted.
Middle: cowl flaps closed & blocker retracted
Full closed: cowl flaps closed & blocker extended

Not all A-1s had this, as I understand. If anyone knows more, please correct these comments. Thx. VL

That's terrific, Ken. Thanks.

It's great to hear the straight goods, in real-time, and a modern setting, from someone who is doing it.

Dave

The USAF deactivated them upon transfer and I recall a few warbirds also have them deactivated. The following text from the USAF Dash One is nearly word for word from the 1954 AD-5 NATOPS and your description seems to match the text as well:

"The cowl flaps are electrically operated and are controlled
by a three-position momentary contact switch placarded
COWL FLAP located on the left hand console. The switch
has the positions OPEN, OFF,
and CLOSE, and is spring loaded to the OFF position.
Cowl flaps position is changed by holding the switch in
either OPEN or CLOSE. Position is maintained when the
switch is released to the OFF position. Power for operation
of the cowl flaps is supplied from the DC secondary
bus.

Nose Flaps. (Deactivated. Flaps remain open at all times).

Nose flaps are installed to reduce the cooling airflow during
cold weather operations. The nose and cowl flaps are
actuated by the COWL FLAP switch in a sequence
controlled by a limit switch arrangement. The nose flaps
open first; and, at the full open position, the cowl flaps
open. Closing of the flaps is the reverse of the opening
sequence. An indicator, mechanically linked to the nose
flaps, extends upward through the antidrag ring to the right
of the top centerline when the nose flaps are closed. This
indicator may be observed from the cockpit."

A few good photos of the nose flaps (and indicator pin) are here on this modeler's resource page: http://tailspintopics.blogspot.com/2011 ... notes.html

_________________
"Take care of the little things and the big things will take care of themselves."

How did it maneuver and or fly any aerobatics?

Steve

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"Any excuse is good enough if you're willing to use it!"

So which Skyraider will you be flying on a regular basis? Cavanaugh's? Thanks for sharing the interesting info.

I don't have an airplane to fly now but I do believe that someone has to be part of the next group of custodians for these wonderful airplanes and this was a first step I was able to take to start down the path.

As far as flying goes, it's tough to put into words and, as I said earlier, I don't claim any special insight, these are just my observations. There are a lot of T-6 analogies to be made. Handling, speeds, and procedures are similar, but the A-1 obviously dominates in power, size, weight, mass, and complexity. I'll admit that, before I flew the T-6 for the first time, I thought it would be clunky and heavy. Quite the opposite, it has a light touch and is quite responsive. While it has "enough" power and does a nice job accelerating and getting into the air, once you're there you don't see homesick angel climb performance. I guess that's the rub: a responsive airplane moment to moment but one that takes planning regarding where you want to be in 10 or 20 seconds (which is a long time if you stare at a second hand). As a result, IMHO, it's a great teacher of energy management, particularly in aerobatics, since, if you don't manage well, you will lose energy (such as finishing a loop lower than where you started) and eventually have to break the sequence and climb back up to continue maneuvering. Experienced guys seem to turn it into an energy neutral platform. I've been told by several guys that they think the A-1 is easier to fly than the T-6. I'm torn - I think they both have their demands.

If you aren't familiar with the airbum.com pilot reports, you'll enjoy these:

http://www.airbum.com/pireps/PirepAD-5.html

http://www.airbum.com/pireps/PirepT-6.html

More later ... Ken

_________________
"Take care of the little things and the big things will take care of themselves."

I'm not flying this Skyraider ... but I was honored to be asked to fly formation with one by the accomplished photographer Brian Silcox. --Ken

_________________
"Take care of the little things and the big things will take care of themselves."

Thanks for sharing that Ken.
Really cool!

Andy