1、 AEROSPACE INFORMATION REPORT The Effect of Installation Power Losses on the Overall Performance of a Helicopter SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary
2、, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your writte
3、n comments and suggestions. Copyright 2005 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permissi
4、on of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: custsvcsae.org SAE WEB ADDRESS: http:/www.sae.org Issued 2005-06 AIR5642 INTRODUCTION The engine installation on most helicopters will inevitably result in some lo
5、ss of power when comparing the installed performance of the engine with the specification level for an engine run on a test bench. These losses are the result of a variety of mechanisms which are described in detail in ARP1702. In addition to these basic losses, there are additional sources of loss
6、associated with the installation of specific items of equipment, such as intake sand filters, additional electrical generators, hydraulic pumps and infra red suppressors. It is important to understand the impact of these losses on the overall performance of the helicopter so that basic aircraft miss
7、ion performance is not unnecessarily sacrificed and to ensure that the final combination of helicopter, engine and mission specific equipment will allow the mission performance objectives to be satisfied. 1. SCOPE: The purpose of this SAE Aerospace Information Report (AIR) is to illustrate the effec
8、t of installation power losses on the performance of a helicopter. Installation power losses result from a variety of sources, some associated directly with the basic engine installation, and some coming from the installation of specific items of aircraft mission specific equipment. Close attention
9、must be paid to the accurate measurement of these losses so that the correct aircraft performance is calculated. Installation power losses inevitably result in a reduction in the overall performance of the aircraft. In some cases, careful attention to detail will allow specific elements of the overa
10、ll loss to be reduced with immediate benefit for the mission performance of the aircraft. When considering items of equipment that affect the engine, it is important to understand the effect these will have on overall aircraft performance to ensure that mission capability is not unduly compromised.
11、Alternatively, a clear understanding of these effects at the aircraft design stage may have an influence on the initial choice of engine size to ensure that mission performance targets are subsequently met. This report aims to give a general understanding of the effect of installation power losses o
12、n helicopter performance by the use of a set of example calculations. SAE AIR5642 - 2 - 2. REFERENCES: 1. “Helicopter Performance, Stability and Control”, RA Prouty, PWS Engineering, 1986 2. “Aerodynamics of V/STOL flight”, BW McCormick, Academic Press, 1967 3. INSTALLATION POWER LOSS MECHANISMS AND
13、 THEIR EFFECT ON ENGINE PERFORMANCE: This section briefly reviews the loss mechanisms that can affect the installed performance of the engine and gives some typical relationships between the value of the loss and its consequent effect on engine power and specific fuel consumption (SFC). Clearly, the
14、 responses of individual engine types to specific loss mechanisms will differ and the actual losses will have to be obtained from the engine manufacturers performance specification or customer deck. The response of engines will also differ depending on the way in which they are rated. Most loss mech
15、anisms will reduce available power for temperature limited engines whereas some will yield no apparent loss for speed limited engines. The basic installation losses may be considered under the following headings: a. Inlet Total Pressure Loss: This has a powerful effect on engine performance with 1%
16、pressure loss being typically worth 2% power loss for a given engine gas temperature. For a given power the engine would have to run to a higher gas temperature and this tends to offset some of the effect on SFC. Typically 1% pressure loss will cause a 1% worsening of SFC at a given power. b. Inlet
17、Temperature Rise: This can result from exhaust gas ingestion, anti-icing air discharge and ingestion of hot zone air through leaks in the inlet ducting. This problem will tend to be worse for a front drive engine installation that places the engine behind the rotor gearbox and therefore makes it mor
18、e liable to ingest hot air from this source. A general rate of exchange is that 1 C temperature rise will cause between 1/2% and 1% loss of power at a given gas temperature. Again, the effect on SFC at a power is less marked and would only amount to between 1/4 to 1/2% SFC degradation for a 1 C temp
19、erature rise. c. Compressor Air Bleed: This is used for cabin heating, air conditioning, engine inlet anti-icing, etc. On most engines bleed air extraction is quite costly, but the precise relationship between bleed flow and power loss will be dependent on the location of the bleed ports on the engi
20、ne compressor. As an example 1% bleed flow taken from compressor delivery can cost 2 to 3% power for a given engine gas temperature. The effect on SFC is less marked because of the offsetting effect of the increased gas temperature at a given power. A 1% bleed flow taken from compressor delivery wil
21、l cost between 1 and 1.5% SFC for a given power. SAE AIR5642 - 3 - 3. (Continued): d. Exhaust System Pressure Loss: The aircraft tailpipe may impose a higher back pressure on the engine than the referee tailpipe. This may result from a less effective geometry giving reduced static pressure recovery
22、and from the need to provide energy to power an ejector to entrain additional air for bay cooling purposes. As a general rule a 1% pressure loss will cause a 1% loss of power and a 1% increase in SFC. e. Mechanical Power Offtake: Mechanical power may be extracted from either the gas generator rotor
23、or power turbine drive train in order to power a variety of accessories such as electrical generators, hydraulic pumps, cooling fans, etc. Power extraction from the gas generator shaft is generally more expensive than that taken from the power turbine. 4. POWER LOSSES ASSOCIATED WITH VARIOUS TYPES O
24、F EQUIPMENT: The losses discussed above can apply to any aircraft in its standard configuration. For many helicopters, both military and civil, it may be necessary to add items of mission specific equipment when carrying out certain missions. These additional items of equipment will often affect the
25、 power available to the helicopter and will therefore adversely affect aircraft performance. Some examples of equipment that can degrade the performance of the power plant on the helicopter are given below. a. Intake Sand Filter: This will usually impose additional intake losses on the engine and th
26、ese will have the same effect, only more severe, as the standard aircraft intake pressure losses discussed above. In addition it will usually be necessary to provide some means of scavenging the extracted sand and dust from the intake filter. This may take the form of a mechanically powered fan, com
27、pressor or turbine bleed air powered ejector or exhaust gas powered ejector. All of these scavenge mechanisms will further reduce the power available to the helicopter. b. Additional Power Offtakes: These may be required to power additional electrical generation or to provide the drive to hydraulic
28、pumps associated with heavy duty winches. The effect on engine performance will be as discussed above for mechanical power extraction. c. Infra Red Suppression: This will give rise to additional exhaust pressure losses resulting from the mixing of the engine exhaust with ambient air to reduce the pl
29、ume temperature. The effect on engine performance will be as discussed above for exhaust system pressure losses. The geometry of the exhaust pipe can account for some thrust benefit. If the exit area is changed, as part of the IR suppressor design, the thrust due to the engine could be changed. SAE
30、AIR5642 - 4 - 5. TYPICAL LEVELS OF INSTALLED POWER LOSS: The levels of installation loss suffered will vary greatly for different helicopter types. An aircraft with side mounted engines, forward facing intakes and straight exhaust tailpipes may well experience only a minimal loss of installed power
31、compared with the uninstalled engine. Installation losses as low as 1 to 2% are readily achievable for such an aircraft type. Alternatively, a helicopter with a “buried“ engine installation, radial engine air intakes and more convoluted exhaust tailpipes would be expected to suffer a significantly h
32、igher level of installation losses. It is not easy to give any general guidelines for the expected additional installed power losses associated with specific items of equipment. The performance objectives for this type of equipment can vary greatly. For example, the extent of the additional pressure
33、 loss associated with a sand filter may well depend on the level of separation efficiency that is required as well as the quality and quantity of space available for the installation. This type of equipment may be installed in different combinations when carrying out specific operations. To give an
34、indication of the possible additional effects of such equipment an aircraft with a standard loss of 4% might well suffer an increase to 15% when fitted with sand filter, bleed powered scavenge and infra red suppressor. Such an increase in installed power loss will clearly have a significant effect o
35、n the mission performance of the helicopter. 6. EFFECT OF INSTALLATION POWER LOSS ON HELICOPTER PERFORMANCE: The potential effect of installation power losses on the overall performance of the helicopter is best illustrated by considering an example. Accordingly, a simple performance model has been
36、devised for an example single rotor helicopter with a nominal gross weight of 10,000 lb. Case 1: The degradation in payload during hover when the example helicopter is fitted with a vortex tube inlet particle separator (IPS) and an infra red (IR) suppressor. Case 2: The degradation in range and payl
37、oad for the above example. Since this is intended to be a simple illustration, no attempt will be made to consider the possible breakdown of the individual loss mechanisms. Assumptions will be made to simplify the calculation procedure, for illustrative purposes. Tail rotor power, cooling power, acc
38、essory power and transmission losses are ignored. Certain variables are assumed constant. Power required is only considered at one weight. All of these simplifications could be expanded upon for increased accuracy. The first case will consider the effect of the increased power loss on the hover capa
39、bility of the helicopter. The various limits that a helicopter operates on will be discussed. Equations and a methodology will be presented that allow for the determination of the allowable gross weight during hover with various engine losses. SAE AIR5642 - 5 - 6. (Continued): For this second case,
40、it is also necessary to consider the direct effect on the performance of the helicopter due to the weight of the additional equipment and the increase in aircraft drag imposed by this equipment. These penalties will compound the effects on mission performance resulting from the engine performance pe
41、nalty. The other principal consideration when assessing the effect of installed power losses on helicopter performance is the impact on operating range or endurance. If we consider a helicopter limited to a given maximum gross weight we must consider the effect of reduced power available on the take
42、-off capability. If the helicopter is engine power limited then it follows that the reduced power available will require a corresponding reduction in the aircraft take-off weight. This in turn will mean either a reduced payload or a reduced fuel load. If payload must be maintained there will be a di
43、rect impact on range due to the reduced fuel available. Engine power limited cases will generally occur under hot and high conditions and so such a case has been considered for illustration. a. Hover Performance: For a given pressure altitude and ambient temperature use the ideal gas law to calculat
44、e the density. ()ambambRTP= (Eq. 1) Momentum theory allows calculation of the ideal rotor power: A2TP5.1idl= (Eq. 2) where: A = area swept out by the rotor T = thrust produced by the rotor In hover, the rotor thrust must be equal to the weight of the aircraft plus the download induced by the rotor w
45、ash. For the sake of simplicity, we shall just assume that the download is always a constant 4% of the gross weight of the helicopter. Thus, for our example, in hover: T = GW + download (Eq. 3) If one makes the simplifying assumption that for a given helicopter the download is merely a certain fract
46、ion of the gross weight, then the total thrust can be written as: T = GW (1 + %GW) (Eq. 4) SAE AIR5642 - 6 - 6. (Continued): The actual power in hover is equal to the ideal power divided by the figure of merit. The figure of merit accounts for the rotor profile power losses: A2FMTFMPP5.1idlact= (Eq.
47、 5) Using the above equations the power required to hover at a gross weight of 10,000 lb at an altitude of 1000 m is calculated for ideal conditions, as well as for conditions with a 4% download penalty and a figure of merit of 0.76. The transmission limit is sized for a gross weight of 10,000 lb on
48、 an ISA + 20 C day (on a standard day at 1000 m the ambient temperature is 8.5 C, thus at 1000 m an ISA = 20 C day ambient temperature is 28.5 C) with nominal installation losses at the IRP rating (see Figure 1). Power Required for Hover at 1000m, 10,000 lb GW Aircraft, Ideal Rotor and Rotor witha f
49、igure of merit of .76. With and Without 4% Download020040060080010001200-2 -100 1020304050Tamb (C)Power(HP)ideal rotor, no downloadideal rotor, download = 4% GWrotor FM = .76, no downloadrotor FM = .76, download = 4% GWxmsn limit set to ISA + 20 C 1000m for nominal installationISA + 20C 1000 mFIGURE 1 SAE AIR5642 - 7 - 6. (Continued): Assume that the helicopter is outfitted with a forward facing inlet and a low loss exhaust pipe in the nominal configuration. A customer wishes to add a vortex tube separator that raises the inlet loss to 4%, and requires 1.5% bleed flow to p
