F-14 approach AoA, is it really 15 degrees?

Elsewhere I've read that the Tomcat flies "units" of AoA, not degrees, with
its AoA range of -10 to +40 degrees being converted to units in the 0 to +30
range. That would mean the formula for converting units to degrees in that
plane is [UnitsAoA = .6 * DegreesAoA + 6]. I've also read that approach AoA
for the F-14 is 15 units, which would be... 15 degrees! Holy crap. Is that
correct? That seems awfully high (too far nose up) to me, especially given
the Hornet's ideal 8.1degrees. Can anyone confirm or correct these values?
Or is there something weird going on with wing angle of incidence (or
something else) that throws a spoke in my assumption that 15 degrees AoA
means 12 degrees nose up on approach. (15, minus 3 for the glideslope.) Any
help appreciated. Thanks!

Scott

On Tue, 27 Jun 2006 13:45:19 -0400, "sttp"
wrote:

Elsewhere I've read that the Tomcat flies "units" of AoA, not degrees, with
its AoA range of -10 to +40 degrees being converted to units in the 0 to +30
range. That would mean the formula for converting units to degrees in that
plane is [UnitsAoA = .6 * DegreesAoA + 6]. I've also read that approach AoA
for the F-14 is 15 units, which would be... 15 degrees! Holy crap. Is that
correct? That seems awfully high (too far nose up) to me, especially given
the Hornet's ideal 8.1degrees. Can anyone confirm or correct these values?
Or is there something weird going on with wing angle of incidence (or
something else) that throws a spoke in my assumption that 15 degrees AoA
means 12 degrees nose up on approach. (15, minus 3 for the glideslope.) Any
help appreciated. Thanks!

Scott

Start by disregarding your initial assumption that the AoA "units"
equate to anything other than an index for the driver to use regarding
performance.


Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
www.thunderchief.org
www.thundertales.blogspot.com

"Ed Rasimus" wrote in message
...
On Tue, 27 Jun 2006 13:45:19 -0400, "sttp"
wrote:

Elsewhere I've read that the Tomcat flies "units" of AoA, not degrees,
with
its AoA range of -10 to +40 degrees being converted to units in the 0 to
+30
range. That would mean the formula for converting units to degrees in that
plane is [UnitsAoA = .6 * DegreesAoA + 6]. I've also read that approach
AoA
for the F-14 is 15 units, which would be... 15 degrees! Holy crap. Is that
correct? That seems awfully high (too far nose up) to me, especially given
the Hornet's ideal 8.1degrees. Can anyone confirm or correct these values?
Or is there something weird going on with wing angle of incidence (or
something else) that throws a spoke in my assumption that 15 degrees AoA
means 12 degrees nose up on approach. (15, minus 3 for the glideslope.)
Any
help appreciated. Thanks!

Scott

Start by disregarding your initial assumption that the AoA "units"
equate to anything other than an index for the driver to use regarding
performance.


Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
www.thunderchief.org
www.thundertales.blogspot.com


With all due respect Ed, that doesn't really help me. ;-) That AoA is an
"index for the driver to use regarding performance" is patently obvious to
anyone who's ever piloted, whether that value is measured in degrees or some
arbitrary "unit". My question is basically this: what is the Tomcat's
optimal approach AoA in DEGREES? (I know it's 15 units.) Is the conversion
from degrees to units linear in this particular aircraft (which helps with
the first question, if the answer is not explicitly known)? Do you have any
idea? Thanks.

Scott

Scott,

Just to add fuel to the fire, the slatted F-4E's approach AOA is at
19.2 units, and the F-15E's is at 22 units.

No idea what those numbers equate to in actual degrees.

Kirk

On 27 Jun 2006 13:08:03 -0700, wrote:

Scott,

Just to add fuel to the fire, the slatted F-4E's approach AOA is at
19.2 units, and the F-15E's is at 22 units.

No idea what those numbers equate to in actual degrees.

Kirk

My point was that those numbers don't equate to anything in actual
degrees--while you could find an AOA that equalled 19 units for an F-4
wing, you won't find a linear conversion between AOA degrees and
indexer units. (As an aside and confuser, note that the AOA units are
showing relationship to optimum whether the flaps are down or
not--further indication that the wing AOA in degrees is not related to
the indexer units.)
Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
www.thunderchief.org
www.thundertales.blogspot.com

"sttp" wrote in message
...
Elsewhere I've read that the Tomcat flies "units" of AoA, not degrees,
with its AoA range of -10 to +40 degrees being converted to units in the 0
to +30 range. That would mean the formula for converting units to degrees
in that plane is [UnitsAoA = .6 * DegreesAoA + 6]. I've also read that
approach AoA for the F-14 is 15 units, which would be... 15 degrees! Holy
crap. Is that correct? That seems awfully high (too far nose up) to me,
especially given the Hornet's ideal 8.1degrees. Can anyone confirm or
correct these values? Or is there something weird going on with wing angle
of incidence (or something else) that throws a spoke in my assumption that
15 degrees AoA means 12 degrees nose up on approach. (15, minus 3 for the
glideslope.) Any help appreciated. Thanks!

Scott

A complex question. Units are, of course, not degrees. Issue, exactly what
equates to "zero" in the calculation? Usually the armament datum line,
waterline, or whatever the manufacturer chooses to call it. In the case of
the Turkey, the aircraft's envelope exceeds the AOA display limits ... you
can be flying at pegged AOA, well sort of flying. Adverse yaw could bite
you pretty hard if you had a heavy hand. For that matter, the old Phantom
could be there too ... but not for very long. The point, your assumption
that the gauge equates to the envelope is faulty.

IIRC, aircraft attitude (as reflected on the VDI attitude indicator and
mirrored on the HUD) was about 11 degrees nose high in level flight at
optimum AOA, somewhere around 8 degrees on a 3 degree glideslope (anybody
with more recent time in the jet ... feel free to chime in with
corrections). The airplane had a pretty pronounced cocked-up attitude on
speed, but not necessarily more so than the Phantom. It also had a large
hook/eye value (which affected lens setting for the target crossdeck
pendant).

The Hornet (and its bigger friend, the Rhino) are the only USN aircraft I
know that actually display AOA in pure and simple degrees as opposed to the
artificial "units." Of course it's capable of sustaining prodigious AOA, on
the order of 55 degrees with the current control programming.

Approach speed for a carrier aircraft is a brew of several objectives. You
want to be as slow as is practical. Attitude on touchdown is critical. You
want to be comfortably faster than L/D max. You need to preserve good
visibility over the nose (a big driver in the F-8J in which the engineers
came up with one number and after a few T&E passes at the ship had it
lowered slightly for pilot vis).

R / John

"John Carrier" wrote in message
. ..

A complex question. Units are, of course, not degrees. Issue, exactly
what equates to "zero" in the calculation? Usually the armament datum
line, waterline, or whatever the manufacturer chooses to call it. In the
case of the Turkey, the aircraft's envelope exceeds the AOA display limits
... you can be flying at pegged AOA, well sort of flying. Adverse yaw
could bite you pretty hard if you had a heavy hand. For that matter, the
old Phantom could be there too ... but not for very long. The point, your
assumption that the gauge equates to the envelope is faulty.

IIRC, aircraft attitude (as reflected on the VDI attitude indicator and
mirrored on the HUD) was about 11 degrees nose high in level flight at
optimum AOA, somewhere around 8 degrees on a 3 degree glideslope (anybody
with more recent time in the jet ... feel free to chime in with
corrections). The airplane had a pretty pronounced cocked-up attitude on
speed, but not necessarily more so than the Phantom. It also had a large
hook/eye value (which affected lens setting for the target crossdeck
pendant).

The Hornet (and its bigger friend, the Rhino) are the only USN aircraft I
know that actually display AOA in pure and simple degrees as opposed to
the artificial "units." Of course it's capable of sustaining prodigious
AOA, on the order of 55 degrees with the current control programming.

Approach speed for a carrier aircraft is a brew of several objectives.
You want to be as slow as is practical. Attitude on touchdown is
critical. You want to be comfortably faster than L/D max. You need to
preserve good visibility over the nose (a big driver in the F-8J in which
the engineers came up with one number and after a few T&E passes at the
ship had it lowered slightly for pilot vis).

R / John




Thank you John. Part of my confusion stems from this post, from
rec.aviation.military:

****************
"Units are the arbitrary form used to express angle of attack on some
systems. For example, the F14 flies a typical approach at 51 thousand pounds
more or less at 130kts at 15 units AOA. The T38 flies a typical approach at
9200lbs.at 155kts plus 1kt per each 100lbs fuel remaining 1000lbs. with
the indexer on speed ( Indexer shows green donut at .6 units AOA in the
Talon.) Basically, units are expressed as a decimal on the T38 between 0 and
1. (.6 is optimum for approach ). The F14 uses aoa units from 0 to 30. This
is roughly equivalent to a range from - 10 degrees to +40 degrees of
rotation of the aoa probe. The on speed indexer in the Turkey is amber
instead of green like the 38.

Hope this helps,

Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/Certificated Flight Instructor
Retired
****************

This implies (or mayb I inferred ;-) a linear relationship between units and
degrees, but I suppose there's no reason that would be mandatory... (and it
looks like it's not linear after all). I just thought 12 degrees nose up on
approach seemed... well, wrong. Even the F-16 comes in at "only" 13 degrees
AoA. I know the F-15E uses units as well, and comes in more nose-up than
most, but I have no idea how many degrees that is either. The rationale for
unist vs. degrees... who the hell knows. (I suppose it would have something
to do with precision and/or the need for a non-linear scale?) I appreciate
the info though about attitude on approach..
Scott

Each manufacturer used his own scale for AOA 'units'. The 104's read
from 0 to 5. At 5 the auto stick kicker kicked. I never looked at the
AOA gauge in the F4 on approach - I used the 'bullseye' indicator and
if the runway was wet it ws the bullseye plus the slow chevron
together. FWIW the F102 with its 60 degree swept delta wing did make
its approach at roughly 15 degrees which happily coincided with the tip
of the pitot boom on the horizon. (Same AOA for rotation and liftoff.)
At 18 degrees you could drag the tailpipe (and P/O maintenance!) I'd
be surprised if an F14 in standard landing config reached 15 degrees
AOA.
Walt BJ

Hey Scott,

For the F-14 approach alpha, true degrees is 10.8 which is published
in various sources.


Julian.

" wrote in message
oups.com...
Hey Scott,

For the F-14 approach alpha, true degrees is 10.8 which is published
in various sources.


Julian.

That would make my 20 year old memory (11 degrees) pretty good.

R / John