Flying Blackhawk's 850 HP Caravan - Blackhawk Modifications, Inc.

Flying Blackhawk’s
Car
By LeRoy Cook
FAA approval of Blackhawk Modifications’ XP-42A engine upgrade
for the Cessna 208B Caravan was obtained in July, with European
approval following in September. The STC allows the Texas-based
company to convert standard 675-hp Caravans to a steroid-charged 850-hp
XP-42A version. We were fortunate enough to be able to fly the aircraft
used for the certification testing at AOPA’s Aviation Summit in Hartford,
Connecticut. As might be expected, it’s an eye-opening experience for
anyone acquainted with the stodgy manners of a fully-laden ‘Van.
The Walkabout
Chris Dunkin, Blackhawk’s manager of flight operations, walked us
around the familiar Cessna 208B’s exterior, just to acquaint us with the
salient features of the conversion. The most obvious change is the use
of a pair of short exhaust stacks, similar to those seen on other singleengine
turboprops that are powered by the PT6A, rather than the single
exhaust outlet, emptying into a secondary augmenter shroud, that Cessna
employs with the stock PT6A-114. Extensive testing during the 210 hours
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avan
An engine upgrade that takes a good Cessna
airplane and makes it even better.
DECEMBER 2011 TWIN & TURBINE 17

logged in Blackhawk’s recertification showed no CO
contamination in the cockpit or cabin, owing to the
precise “clocking” of the Frakes stacks installed on the
PT6A-42A engine.
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The test aircraft was fitted with a full APE (Aircraft
Payload Extender) kit, which allows a gross weight
increase to 9062 pounds (max landing weight is 9000
pounds). The standard 208B ramp weight is 8785
pounds. To take advantage of the weight increase, the
XP42A approval requires installation of the APE kit’s
minor changes, if the retrofitted aircraft is not already
equipped with it. The APE kit includes larger mainwheel
axles, an airflow fence on each wing’s outboard leading
edge and a wavy aerodynamic device added to the
inboard portion of each flap’s trailing edge.
A 100-inch four-blade Hartzell propeller is part of the
installation, replacing the 104-inch standard propeller.
Standard TBO for the new engine is 3,600 hours. Credit
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18 TWIN & TURBINE DECEMBER 2011

is given for the service-life hours remaining on the
traded-in PT6A-114. The original engine mount and
accessories are used, but new vibration isolators are
installed and the support ring’s mounts are increased
from three to four. Typical weight increase is between
20 and 40 pounds. The PT6A-42A engine is three inches
longer, requiring installation of an all-new carbon-fiber
composite cowling, which Blackhawk builds in-house at
its Morgantown, Kentucky, composites facility.
There’s ample workroom inside the cowling; someone
listened to long-suffering maintenance technicians.
Dunkin lifted the left cowling half to point out an
engine oil sight glass, used to verify proper oil level
without pulling a dipstick. A Concord RG-380E/44
lead-acid battery is on the right side. The oil cooler in
the nosecap is 40-percent larger than before and the
adjoining air intake opening is bigger as well, with its
angle changed to increase FOD dispersion.
Aft of the firewall, most of the airplane is the same as
it came from Cessna. The power quadrant in the cockpit
is unchanged, but all the power gauges are replaced by
Blackhawk’s own Digilog units that have digital vernier
readouts as well as analog needle presentations. A
new placard on the panel calls for a minimum of 130
knots airspeed to be maintained when flying in icing
conditions. Those are the only changes required.
Dunkin related his experiences when conducting
the natural icing tests. One sloppy autumn day,
meteorologists directed him to a likely area in western
Kansas, where icing was present between 5000 and
9000 feet. He flew in the accumulating ice for 50
uninterrupted minutes and never saw the airspeed
deteriorate below 145 knots, even though the bootequipped
aircraft picked up massive chunks of rime
on unprotected areas. A meteorologist viewing photos
of the flight pronounced it to be “near severe icing”.
No further testing was needed.
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20 TWIN & TURBINE DECEMBER 2011

Going Up, Fast
We climbed into the cockpit, pulled up the boarding
ladders and went through the routine PT6A starting
procedure; master on and fuel pump to normal, engage
start switch and watch rotation begin on the Ng gauge,
waiting for 15% Ng to introduce fuel. The lightoff and
rise in rpm caused no more than a 750 C. indication
on the ITT (start limit is 975 C). Once stabilized, we
confirmed that the starter had been switched into
generator mode and the avionics were flipped on.
The cooperative Hartford, Connecticut tower offered
to arrange for VFR flight following service as we exited
their airspace to the east; Dunkin’s plan was to execute
a max-performance climbout above Providence’s Class
C environment. We quickly taxied to runway 21 for a
prop governor test and advanced to high idle condition,
extended ten degrees of flap and took the inertial
separator handle out of “bypass” position. With the
APE kit, extreme short-field takeoffs are approved with
30 degrees of flap, versus 20 degrees for an unmodified
airplane.
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The propeller wound up to 2000 rpm while we held
the brakes, and we advanced the power lever to about
2150 pounds of torque on the roll. The torque built to
2200 as we lifted off at a leisurely 80 knots, halfway
down the 4400-foot runway.
Once past 95 knots, the flaps were brought up and I
quickly accelerated the aircraft to 120 knots. Dunkin
advised me to hold 115 in the climb; by doing so,
visibility over the nose was nil. The VSI read 2000
fpm initially, finally settling in at 1600 to 1700 fpm.
Blackhawk’s brochure says the XP42A has double
the climb rate of a standard Caravan, and when we
compared numbers with the standard and modified
charts, it appeared to be true; under similar conditions,
a 675-hp 208B would manage around 850 fpm.
With torque tweaked occasionally to keep 2200
pounds pulling us upward, the ITT started out at 730
degrees C. and rose to no more than 750 at the top of our
climb, 11,500 MSL. Only about 8 minutes had elapsed
since our sea-level liftoff. The -42A Pratt had kept its
2200 pounds of torque until 10,500 feet. Temperature
was about 16 degrees over standard ISA and takeoff
weight was estimated at 7700 pounds.
As we leveled off with 2100 pounds of torque and 750
degrees on the ITT, the airspeed settled at 165 knots
IAS, computing to a TAS of 202, while burning 460
PPH of Jet-A. The standard 208B’s book showed that
only 1370 pounds of torque would have been available
at 12,000 feet, providing a TAS of about 158 knots.
In all fairness, Dunkin pointed out, our TAS would
have been ten knots or so less if we had been at full
gross weight.
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DECEMBER 2011 TWIN & TURBINE 21

With power reduced to 1900
pounds torque, we lost about
10 knots of speed, cutting fuel
flow to 400 PPH. Dunkin then
demonstrated a quiet-cruise mode
by backing away a bit of torque
and slowing the propeller rpm to
1700, bringing torque back up to
2200 pounds, but in a much quieter
environment for the passengers.
Handling at cruise remained trucklike
but benign, just as the Caravan
has always been.
We experimented with slowflight
at 80 knots and full flaps, which
turned out to be a thoroughly honest
bit of flying, simply lighter on the
control feel but still ponderous in
response. We did not essay a full
stall, but Dunkin assured us that
nothing has changed over the simple
Skyhawk manners we have come
to expect in the 208. Because the
FAA insisted on duplicating the
certification criteria, a complete
spin program has been flown,
comprising some 115 spins.
Going Down, Fast
Because one of the major markets
for the XP42A mod is for skydiving
centers, we experimented with
the skydive descent at flight idle,
pushing over to reach the 180-
knot redline. With the VSI pegged
solid at 3000 fpm down, we timed
an eardrum-splitting 4000 fpm
descent, then quickly resumed a
500 fpm letdown. Combining the
improved climb rate and rapid
descent, skydive centers will be
able to take four loads per hour to
the top of the non-oxygen altitudes.
Cleared to land back at Hartford’s
Brainard airport, we slowed to 175
knots, where ten degrees flap was
permitted, which reduced speed to
150 knots so we could extend twenty
degrees of flap. The final flap limit is
125 knots. A defunct set of runways
a few miles east of the airport, the
former Rentschler Field from World
War II, tempted us, but, fortunately,
Dunkin caught my mistake before
it became serious.
Cessna avoiding any equivalentlevel-of-safety
games when certifying
its big single under FAR Part 23,
preferring to meet the 61-knot Vso
stall speed limitation with pure
aerodynamic wizardry, at least at
the standard airplane’s 8,500-pound
landing weight.
As with all Caravans, approach
and landing chores are simple; no
landing gear to extend, no switches
to throw, just slow to as little 80
knots and drive to the runway. We
indulged in a 90-knot “high-speed”
22 TWIN & TURBINE DECEMBER 2011

final for the benefit of following
traffic, followed by an easy
touchdown on the tall gear. A bit of
reverse brought us to a halt in short
order; as it turned out, the inbound
jet was bringing FAA Administrator
Randall Babbitt to the Summit. As
with all PT6A-powered airplanes,
particularly those with four-blade
props, one must be judicious with
the power reduction to idle during
landing, which produces a rapid
increase in drag and a sudden
touchdown.
After shutting down and lowering
the gangplank to debark, we felt
it was apparent that Blackhawk’s
XP42A modification takes the 208B
Caravan to a new level of capability.
To repeat CEO’s Jim Allmon’s
statement, “Cessna built a good
airplane, we just made it better”.
We have to agree.
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DECEMBER 2011 TWIN & TURBINE 23