Subject: Re: Torque settings
Date: Sun, 25 Jun 2000 14:38:32 GMT
In article <7Ba45.3$Df6.firstname.lastname@example.org>, "John Eacott" <email@example.com> wrote:
>It occurred to me that the cruise power settings that I use are mostly
>through habit, rather than any parameters laid down by the manufacturer.
>Most endorsements and FM's have emphasis on max and min Tq's, Nr, Nf etc,
>but nowhere do I (usually) see manufacturer's recommendations for cruise
>power on turbines.
>Out of habit, I was taught back when the air force was painted blue, not
>wearing it, to use 62% Tq for the Sea King/S61, and have applied that ever
>since to the 212 & BK117 for convenience. The A109 I use 90 - 95% (max
>continuous 121%), 206 about 75 - 80% (max continuous 85%), all with no
>Anyone know better? Nick, when are the manufacturer's going to put sensible
>figures, instead of such odd Temp limits, albeit that they were originally
>degrees F rounded to the nearest 100, then converted exactly to deg. C in
>some cases. I thought it neat when I got away from ft/lb of Tq to %, but
>there still appears room for improvement, IMHO.
This is a great observation, John. The problem is mostly due to the fact that
the FAA/CAA don't ask for recommended cruise power settings to be promulgated,
and actually stand in the way of creating another practical cruise power
rating. Since we publish Max Continuous power now, they balk at a lower
recommended cruise power. The S-76A was an exception, because Allison (Rolls
now) wanted to make a spiffy warranty that couldn't be promised if folks
blasted around at 100% torque "max continious" power. (I came up with the idea
of the white and green arc on the S-76A, as a way to sneak around this FAA
For all helos I fly, I like to find the two speeds that satisfy most cruise
situations, the high speed cruise and the best range cruise.
Usually they can be pulled from the marketing literature somewhere, or the
section II of the RFM, but you can always determine them yourself if
Some rules on HSC: The more the power, the more the wear on xmissions,
engines, rotors and such. Generally the loads build in proportion to torque,
of course, but rotors are chewed up by stall, which is speed and weight (load
factor). If you are maneuvering, knock off some speed (maybe .15 of Vne) to
keep the stall stresses down, or maneuver with lower power (collective) then
reset the power when the wings are level.
Most Sikorsky products don't mind about 80 to 85% power as good "get home"
HSC powers. Works for me with S-76 and H-60 models. We get about 145 to 155
knots true airspeed in most non-stratospheric conditions, at max weight. The
next 15% of torque to get to 100% max continuous power only buys a few
knots (maybe 5 to 7 or so).
Best range is not where range is optimal, but where it just falls off from
optimal (called .99 VBR by our folks). This is because if you fly right at
VBR, you may give up a productive 10 knots that could have been flown if you
gave back 1% fuel flow. This is because the best range place on the power
required chart is usually a pretty flat curve, so a few knots more or less has
little effect. If this is true of your machine, why not squeeze out the extra
What if you can't find this info in the literature? If you have fuel flow
gages, no sweat! Take your aircraft up to cruise altitude, at typical weight,
and run through speeds from Vy to Vmax at 10 knot intervals, and note the
engine parameters, especially torque and fuel flow, and the exact airspeed,
pressure altitude (29.92 inches) and OAT. Don't knock yourself out to get
exactly 100 knots, take instead a rock steady 101 of that falls out. relax at
each point, and be sure that you have NO climb or descent. Early morning is
best to be sure of no thermal climbs or descents to spoil your data. Do this
for each season, since OAT is a contributer.
This should take 10 minutes or so. Get home and plot the data on a set of
curves like this:
1) Power required, plot power on the vertical and True airspeed on the
2) At each speed point, divide true airspeed by fuel flow , which gives the
number of miles one pound of fuel will take you, called the specific range.
Make another plot of specific range vs true airspeed. The high point in this
curve is the place where 1 pound of fuel takes you farthest, your max range
3) Now plot the fuel flow vs true airspeed. The minimum in this curve is your
best endurance speed, where a pound of fuel keeps you up the longest amount of
time (for police guys, this is the speed at which you can blind the most
drivers per tank of gas).
As a note about famous pilots, Charles Lingburgh did this stuff with the
Spirit of St. Louis, and it took about 6 hours of flight test for him to then
launch the longest flight in the history of mankind. (Anyone who has not read
"the Spirit of St. Louis" by CL should go to the back of the class. A great
book!) When he went to the Pacific to help the Air Corps, he took similar
plots of P-38's and published his notes for the combat pilots. They gained
10% operational range based on his notes!
I still have my notes from 76006, which set a bunch of range records back in
the early 80's that still stand. I read the gas gages every 5 minutes,
exactly, to calibrate the fuel flow system. I brought a fuel hygrometer to
get the exact density of the gas I bought and tossed that data into the pile.
Chicago to New York at 200 MPH, with enough gas to go to New Haven, drop off
passengers, then land at the Stratford Ct plant with one fuel low light
blinking during the landing flare. Uh oh, I'm telling war stories now!
Subject: Re: Torque settings
Date: Sat, 01 Jul 2000 16:37:15 GMT
In article <jrQ55.9$Y8.firstname.lastname@example.org>, "John Eacott" <email@example.com> wrote:
>Thanks, very informative. IIRC, we had 76004 and 7, but 'twas a long time
>ago. What's the distance Chicago to NY, and on to the plant?
Its 610 Nm from Meigs field to Wall St, as measured on sectional charts strewn
all over the floor at Meigs (the Sikorsky President decided to have us fly the
record at the last minute). Thence about 45 nm to new Haven, then 8 nm back
to the plant. Lots of tail wind, so we used max power for the whole trip.
About 170 KTAS, and well over 200 knots ground speed. Flashed by Newark at
about 220knots ground speed in a shallow dive (no sense letting all that
energy go to waste!)