service ceiling of s92
 

Sikorsky s92 indicates a service ceiling of 15000 feet, however, the power graph for a CT7-8 turboshaft engine indicates only up to 14000 feet. How do I interpolate to get to 15000 feet?

I think you mean ‘extrapolate’ but what power graph are you referring to? The S92 RFM has all the graphs you need for the approved flight envelope.

The 15000. Ft limit ( I only have the original manual at hand ) isn’t a “ service ceiling “ but rather the enroute approved max altitude ( i.e., the max allude completely covered by flight load and handling qualities etc testing. Service ceiling in the defined sense is that altitude where the max rate of climb is 100 ft/min.

service ceiling
 

Hi guys thanks for the response. Agree it is 'extrapolate'. Alternatively anyone with graphical evidence that the helicopter has a service ceiling of 15000 feet or more. It is important please.

Altitude limits
 

The limits are shown on page 9 of the S92 type certificate data sheet.....

http://rgl.faa.gov/Regulatory_and_Gu...4BO_Rev_22.pdf
Files

Perhaps a communication directly to Sikorsky, citing the specifics of your need, would result in the detailed information you request.

You will have to fly around , not over the Himalayas.

VF might be able to "massage" it over the top...

Reminder that you can't extrapolate off a chart; only within it.

??? you interpolate within a chart. You extrapolate off the ends. Unless you are quoting a regulation somewhere.

OK, for the point-of-order police..

Reminder that you can't extrapolate off a chart; only interpolate within it.

Now I need another snort on the CO3 bottle.

For the original poster, I'm still not clear what graphs you are referring to? I now have access to my RFMs and the cruise torque and fuel flow graphs in the Part 2 Section 3 (supplemental performance) clearly go to 16,000 ft so I do know what graph you want for 15,000 ft? You can, indeed, interpolate the data from the 14,000 and 16,000 ft graphs if you really need 15,000 ft data from this section, but I get the impression you are talking about something else?

To find the service ceiling as a function of Weight, Altitude, and Temperature, go to Part 1, Section IV (Performance Information) of the Flight Manual and locate the chart entitled “Forward Climb Performance, Dual Engine, Max Continuous Power, Best Rate of Climb Speed”. Enter the chart at a rate of climb of 100 fpm (defined as the service ceiling), move up vertically to the desired gross weight, then left horizontally to the desired temperature, then down vertically to determine the associated pressure altitude. The 15,000 ft density altitude limit is shown on the chart. Depending on the weight, altitude, and temperature, the service ceiling may occur below, at, or above 15,000 ft density altitude, but the 15,000 ft density altitude limit must be respected.

Hi again, HeliTester could you please clear this doubt.

There is some doubt on use of power during validation of ceiling climb of a helicopter. Some information gathered from various manuals is given below, followed by the doubt

ETPS Flight Test Manual - Ceiling Climb Chapter, Para 4.2

Power: Tests are flown using the maximum power rating for a sustained climb;this is usually the "one hour power" or Maximum Continuous rating. It may be necessary to check the climb
performance at other specified power ratings, for example, single engine maximum and continuous ratings


Rather longish questin/doubt.
USNTPS Flight Test Manual Part 2 para 8.4.3

Another method of obtaining climb performance............The climb s flown until stop climb criteria is met.........These climbs can be flown in support of climb correction factor data requirements
or the parameter correction factor requirements(Kp or Kw). During Kw collection climbs, the power is maintained at MRP (Military Rated Power), throughout the climb. During Kp climbs the power
is maintained at the torque setting specified for the climb....

HELICOPTER DESIGN HANDBOOK Part 3 AD-785 000

Same as above in USNTPS Manual

HELICOPTER DESIGN HANDBOOOK PART 1 AD/A-002 007

Para 3.4.6.3. Service ceiling is defined as the maximum altitude at which the aircraft exhibits a 100 fpm rate of climb capability at a given temperature while combat ceiling requires a climb capability of 500 fpm. These ceilings normally defined are at best climb speed, using normal or intermediate engine power ratings

FAR 29

(a) The steady reate of climb must be determined --

(1) With maximum continuous power;
(2) With the landing gear retracted;and
(3) At Vy for standard sea level conditions and at speeds selected by the applicant for other condititions.


From the above definitions it is not very clear whether ceiling climb MUST BE done at maximum continuous power ONLY.

Now if a manufacturer makes a claim that service ceiling is y metres, however you need to use 30 minutes rating to climb from x metres to y meters (climb time from x metres to y metres is well below 30 mts), should one accept service ceiling as y metres .... or x metres?

It’s very clear - It’s a FAR Pt 29 certified Machine (Amdt 47 I recall) so use that definition. Vy at max AEO continuous power. But, also note John Dixson’s comments (he may know a thing or two about this programme!) that 15,000 isn’t a true service ceiling.

santynavayath......

Your original question deals with the S-92, and since the S-92 does not have a Dual Engine 30-Minute power rating (during forward flight), a service ceiling climb validation test must be done at Maximum Continuous Power.

I don’t understand your question. I recall that some military helicopters have both 30-Minute and Maximum Continuous Dual Engine power ratings, so they would have separate 30-Minute and Maximum Continuous service ceilings that would be different from each other. If you want to validate the service ceiling determined from the S-92 Flight Manual (see my previous post), I suggest you do a continuous climb using Maximum Continuous Power at the Best Rate of Climb speed, from the takeoff altitude to the Pressure Altitude at which the observed rate of climb decreases to exactly 100 feet per minute. Note the helicopter weight, Pressure Altitude, and Air Temperature at the 100 feet per minute ceiling for comparison with the ceiling determined from the Flight Manual Chart.

Purpose for Asking??
 

212, good point. The 15K altitude limit in the original manual is not a service ceiling, but is the enroute altitude limit which was certified. Thus, as I mentioned, SA performed all of the flight loads, handling qualities, power train etc testing prescribed in AC 29.2b ( I think rev c came afterward ). Just as aside, in preparation for a Portuguese Coast Guard program that never happened, we in fact did a flight loads survey at 31k+ lbs up to 9000ft.

Perhaps the poster of the original question could explain what he is looking for and why. There are no clues from what has been posted. The first post says that the 92 has a service ceiling of 15K, which is not what the flight manual says, and his subsequent posts include various sources defining service ceiling, so he apparently is familiar with the term.So, what is this about? Writing a spec for a new machine? Writing test requirements for a government entity? Trying to write a requirements document for a competitive source selection group so that it disqualifies one candidate in favor of another? Generating info for a school paper? Haven’t a clue.

I would suggest that someone with access to all those quoted documents could well be on a TP course and has been asked to evaluate S92 as part of their homework.