Asymmetric performance for a/c less than 5700kgs
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Asymmetric performance for a/c less than 5700kgs
G'day all,
Some questions;
1.What is the critical engine on a light twin? (BE 76)
2.What effect will full flap have on VMCA?
3. How does single engine flight effect the range of the aeroplane?
cheers
downwind.
Some questions;
1.What is the critical engine on a light twin? (BE 76)
2.What effect will full flap have on VMCA?
3. How does single engine flight effect the range of the aeroplane?
cheers
downwind.
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Sorry can't answer question 1.
VMCA unpredictable with more than takeoff flap selected unless stated in the flight manual.
Range can be more or less. In some aircraft like the Cessna 402a cross feeding is only available from the main tanks and there are no tansfer pumps in the auxillary tanks. Calculate what range you would have on two engines at normal cruise speed and normal fuel consumption then calculate range on one engine speed and one engine fuel consumption and that will give you an approximate answer. There is a book published by John Chesterfield at Coolangatta QLD, try Skyshop at Coolangatta, great reading!
VMCA unpredictable with more than takeoff flap selected unless stated in the flight manual.
Range can be more or less. In some aircraft like the Cessna 402a cross feeding is only available from the main tanks and there are no tansfer pumps in the auxillary tanks. Calculate what range you would have on two engines at normal cruise speed and normal fuel consumption then calculate range on one engine speed and one engine fuel consumption and that will give you an approximate answer. There is a book published by John Chesterfield at Coolangatta QLD, try Skyshop at Coolangatta, great reading!
The BE76 is definitely counter-rotating.
Cheers,
TL
Cheers,
TL
Bugsmasherdriverandjediknite
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and just when you think you have it all nutted out..take the trusty ol 337 for a burn.
P.s if you read this towering cumes, I got the work and am now hovering around in Grasshopper, thanx mate.
P.s if you read this towering cumes, I got the work and am now hovering around in Grasshopper, thanx mate.
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Giday downwind, you are obviously doing an CASA Multi-Engine Endorsement Questionaire from the CAAPs. The first one I bet.
All the best with it.
The idea of the Quest. is to get you looking in the acft handbook and the twin theory books (some very good ones out there but I recomend "Understanding Light Twin Engine Aeroplanes" by Russ Evans), so giving you the answers is a bit like cheating. But I will offer you some pointers to help you find the way.
Q1. The deffinition of critical engine is important here " The engine if failed, which will create the most adverse effect on control and performance of the aircraft"
if you consider a contra rotating light twin then controll is effected equaly as well as performance.
Therfore the answer is both are equaly critical!!! But if the props go in the same direction, look it up and remember the definition.
Q2. Again find the definition of VMCA, there is a bit to it, but look closely at the amount of lift generated by flap and live engine power creating roll. More control required to overcome roll, therefore more airspeed for more control effect,
Full flap = (Higher AS or lower AS - VMCA)
Q3. Range is dependant on speed/time and specific fuel consumption. In most twins more power is required on the live engine so fuel flow goes up, and speed goes down (not forgeting as mentioned useable fuel may change ie 402). What you need to do is look at the performace section of the POH and determine if two engine cruise and fuel flow gives a better speed for time, than the single engine case. It does vary between acft types, and sometimes even fo diferent fuel tank configurations.
I have tried to give you good advice without giving you all the answers, in fact if I have given you anything, I hope it is the motivation to look it up and find the full answers yourself. You really will learn more that way.
Once again all the best, and remember there is a lot more to study when the twins get bigger.
All the best with it.
The idea of the Quest. is to get you looking in the acft handbook and the twin theory books (some very good ones out there but I recomend "Understanding Light Twin Engine Aeroplanes" by Russ Evans), so giving you the answers is a bit like cheating. But I will offer you some pointers to help you find the way.
Q1. The deffinition of critical engine is important here " The engine if failed, which will create the most adverse effect on control and performance of the aircraft"
if you consider a contra rotating light twin then controll is effected equaly as well as performance.
Therfore the answer is both are equaly critical!!! But if the props go in the same direction, look it up and remember the definition.
Q2. Again find the definition of VMCA, there is a bit to it, but look closely at the amount of lift generated by flap and live engine power creating roll. More control required to overcome roll, therefore more airspeed for more control effect,
Full flap = (Higher AS or lower AS - VMCA)
Q3. Range is dependant on speed/time and specific fuel consumption. In most twins more power is required on the live engine so fuel flow goes up, and speed goes down (not forgeting as mentioned useable fuel may change ie 402). What you need to do is look at the performace section of the POH and determine if two engine cruise and fuel flow gives a better speed for time, than the single engine case. It does vary between acft types, and sometimes even fo diferent fuel tank configurations.
I have tried to give you good advice without giving you all the answers, in fact if I have given you anything, I hope it is the motivation to look it up and find the full answers yourself. You really will learn more that way.
Once again all the best, and remember there is a lot more to study when the twins get bigger.
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BSB
If the singe engine figures are not avail. then simply halve the two engine MCP figures. This will give you the single engine figures. All the best. Do you fly a 55 or 58.??
There are also the considerations of level, leaning(not always available >75%), temp etc so some working in the graphs is normaly required. That is the reason for the question, so that you have an understanding of the basic figures and able to work the graph quickly and confidently if you ever need to in the air.
If the singe engine figures are not avail. then simply halve the two engine MCP figures. This will give you the single engine figures. All the best. Do you fly a 55 or 58.??
There are also the considerations of level, leaning(not always available >75%), temp etc so some working in the graphs is normaly required. That is the reason for the question, so that you have an understanding of the basic figures and able to work the graph quickly and confidently if you ever need to in the air.
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Gidday to all. (First Post.) Been watchin' for a while. B.S.B As a result of a recent Chief Pilot's interview with CASA, that very question came up. (From their side!)
Had to think about it but my answer went thus, Since these a/c are certified to provide a climb capability on one engine to 5000ft (!), I supposed that I could take that to mean at 5000 ft, r.o.c.would be 0. Therefore, I would be at m.c.p. on operating engine and at blue line. Blue line is a known speed, so I can calculate a tas from that.
Fuel flow is also given for m.c.p. Applying known or forecast winds I now have a g.s and fuel flow so everything else I can calculate. This would be a worst case scenario, (I hope), and as such should provide some buffer in real use. It worked for the interview, but it's really only a theory. As you have found, most light M.E mauals are less than helpful in this regard.
Had to think about it but my answer went thus, Since these a/c are certified to provide a climb capability on one engine to 5000ft (!), I supposed that I could take that to mean at 5000 ft, r.o.c.would be 0. Therefore, I would be at m.c.p. on operating engine and at blue line. Blue line is a known speed, so I can calculate a tas from that.
Fuel flow is also given for m.c.p. Applying known or forecast winds I now have a g.s and fuel flow so everything else I can calculate. This would be a worst case scenario, (I hope), and as such should provide some buffer in real use. It worked for the interview, but it's really only a theory. As you have found, most light M.E mauals are less than helpful in this regard.
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On having reread my post, I should point out (before somebody else does) that these a/c types do not necessarily have to provide climb performance per-se, however if they are to be used for I.F.R chtr or airwork, the 5000 ft thing must be demonstrated for certification in aust.
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29351 and all, check CAO 20.7.4 and learn it.
PVT OPS must have the ability to maintain 5000' ISA with the critical engine inop, dead engine prop stopped, IAS at not below 1.2Vs, gear and flap up, operating engine at MCP.
IFR Charter & AWK msut have the ability to climb with the Critical engine inop at a gradient of 1% to 5000' ISA under same conditions as above.
That means using the graphs and going at a weight to be able to do accomplish that.
From memory, in a be76, IT'S 1723KG.
PVT OPS must have the ability to maintain 5000' ISA with the critical engine inop, dead engine prop stopped, IAS at not below 1.2Vs, gear and flap up, operating engine at MCP.
IFR Charter & AWK msut have the ability to climb with the Critical engine inop at a gradient of 1% to 5000' ISA under same conditions as above.
That means using the graphs and going at a weight to be able to do accomplish that.
From memory, in a be76, IT'S 1723KG.
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AMRAAM,
I fly a C55
Now i'm really curious and I guess the only way to answer my own question is to go fly tomorrow and see what happens on one.
Somehow I think I will achieve much better than Blue Line @ 5000, probably TAS of about 140-150 I think, but will post results later.
I also believed that Blue Line was a variable figure based on weight and angle of attack, is it not?
BSB
I fly a C55
Now i'm really curious and I guess the only way to answer my own question is to go fly tomorrow and see what happens on one.
Somehow I think I will achieve much better than Blue Line @ 5000, probably TAS of about 140-150 I think, but will post results later.
I also believed that Blue Line was a variable figure based on weight and angle of attack, is it not?
BSB
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B.S.B and Achilles, yes you are both right, had my memory for 20.7 been a little better I would have been able to be a little more accurate. B.S.B you are correct, blue line does vary, speed/weight etc. but the context I gave the answer in is pre flight planning, (as the question was posed to my by CASA!) I have perused the PA-31 POH in my possession, and unfortunately, like yourself, I cannot find single engine cruise figures. My approximation would be most accurate for max weight circumstances, and given that condition, I think it is a fair approximation, erring to the conservative. Of course, at lighter weights better performance would be obtained.
Seasonally Adjusted
Wizard,
nice to hear the Grasshopper has a new driver. Might look old and tired but great fun to fly. Warn your rear r.h.s. pax not to lean on that unusual little cargo door, it popped open for me once at 9500 over the bight. No harm done but the trip to CDU was a touch chilly.
nice to hear the Grasshopper has a new driver. Might look old and tired but great fun to fly. Warn your rear r.h.s. pax not to lean on that unusual little cargo door, it popped open for me once at 9500 over the bight. No harm done but the trip to CDU was a touch chilly.
Moderator
A few points to keep in mind when talking Vmca
(a) the quoted figure is for specific conditions and will vary in the real world, particularly at altitude as the engine output decreases. Configuration certainly can affect the data and some aircraft specify a range of data for different configurations.
(b) unless the manufacturer's data states otherwise (and that would not be usual), presume that the quoted figure was determined with the usual 5 degrees limit bank into the live engine.... and please keep in mind that, if you must play in the region of Vmca, then the actual Vmca is quite bank angle sensitive. This can easily result in a Vmca departure if the pilot is ham fisted and lacking a reasonable level of OEI currency on the aircraft.
(c) the Vmca 5 degree limit is not related to the condition for best climb performance, in spite of what a great many people may think.
Russ Evans ... now he was a character in NSW Regulation ....
[ 08 September 2001: Message edited by: john_tullamarine ]
(a) the quoted figure is for specific conditions and will vary in the real world, particularly at altitude as the engine output decreases. Configuration certainly can affect the data and some aircraft specify a range of data for different configurations.
(b) unless the manufacturer's data states otherwise (and that would not be usual), presume that the quoted figure was determined with the usual 5 degrees limit bank into the live engine.... and please keep in mind that, if you must play in the region of Vmca, then the actual Vmca is quite bank angle sensitive. This can easily result in a Vmca departure if the pilot is ham fisted and lacking a reasonable level of OEI currency on the aircraft.
(c) the Vmca 5 degree limit is not related to the condition for best climb performance, in spite of what a great many people may think.
Russ Evans ... now he was a character in NSW Regulation ....
[ 08 September 2001: Message edited by: john_tullamarine ]
Regrding VMCa with full flap, it depends on the aircraft type and more importantly, the type of flap the aircraft has.
However, the critical thing to remember is that with full flap in an asymmetric condition, you may not have enough aileron to controll the aircraft in roll to to the asymmetric lift.
In some aircraft, the Baron 58, the flight manual specifically states that once full flap has been selected, a go around must not be attempted.
However, the critical thing to remember is that with full flap in an asymmetric condition, you may not have enough aileron to controll the aircraft in roll to to the asymmetric lift.
In some aircraft, the Baron 58, the flight manual specifically states that once full flap has been selected, a go around must not be attempted.
Moderator
To operate with full flap OEI is to invite serious problems unless the larger flap deflection be taken rather late final following a commitment to land. Even then, the performance degradation warrants consideration of using reduced flap for landing. I presume that you are talking light twins in which case, while there are requirements for AEO climb performance, there is precious little performance requirement OEI, and none at all OEI with full flap. In general, any light twin at a decent weight will have no climb capability OEI with full flap selected - quite the contrary, one would expect it to be all downhill.
If one is operating under conditions where the pilot is not able to control roll, then methinks that the piloting technique being employed is inappropriate. Alternatively we are looking at a Vmca departure due to incorrect bank angle control. Perhaps you might give some more specific commentary.
I suggest that any admonition not to attempt a missed approach OEI with full flap is very wise. In the event that a missed approach became necessary after selection of full flap,one would seek to reconfigure to the normal clean OEI configuration at a speed somewhere near the appropriate best climb speed - and start the whole exercise at a reasonable height.
If one is operating under conditions where the pilot is not able to control roll, then methinks that the piloting technique being employed is inappropriate. Alternatively we are looking at a Vmca departure due to incorrect bank angle control. Perhaps you might give some more specific commentary.
I suggest that any admonition not to attempt a missed approach OEI with full flap is very wise. In the event that a missed approach became necessary after selection of full flap,one would seek to reconfigure to the normal clean OEI configuration at a speed somewhere near the appropriate best climb speed - and start the whole exercise at a reasonable height.
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1.What is the critical engine on a light twin? (BE 76)
The critical engine is the engine which, when it fails, gives you the greatest yaw. Yaw depends, amongst other things, on the distance the Thrust is from the A/c centreline. In the B 76 both sides have the downgoing blades inboard. Therefore no critical engine. Allthough some might say "with only 180 HP per engine - both are critical" (I do own one)
2.What effect will full flap have on VMCA?
VMCA is calculated / tested with flaps up. I look upon flaps as a lift multiplier. In assymetric flight we have assymetric lift = assymetric drag. Flaps or anything else that increses drag give you a higher speed at which you will lose directional control. Note: VMCA is a fixed definition speed. Ie. with flaps in the take-off position. In the BE 76 that is flaps up.
3. How does single engine flight effect the range of the aeroplane?
If you're light you should be able to get close to 100 kts at 5000'. If you're heavy use 90 kts. As per POH, MCP uses around 43 LpH per engine at 5000'. Using 90 kts and 43 Lph, you can work out the ground nm per litre. From memory, it has a greater range on one engine, in headwids of less than 15 kts.
The critical engine is the engine which, when it fails, gives you the greatest yaw. Yaw depends, amongst other things, on the distance the Thrust is from the A/c centreline. In the B 76 both sides have the downgoing blades inboard. Therefore no critical engine. Allthough some might say "with only 180 HP per engine - both are critical" (I do own one)
2.What effect will full flap have on VMCA?
VMCA is calculated / tested with flaps up. I look upon flaps as a lift multiplier. In assymetric flight we have assymetric lift = assymetric drag. Flaps or anything else that increses drag give you a higher speed at which you will lose directional control. Note: VMCA is a fixed definition speed. Ie. with flaps in the take-off position. In the BE 76 that is flaps up.
3. How does single engine flight effect the range of the aeroplane?
If you're light you should be able to get close to 100 kts at 5000'. If you're heavy use 90 kts. As per POH, MCP uses around 43 LpH per engine at 5000'. Using 90 kts and 43 Lph, you can work out the ground nm per litre. From memory, it has a greater range on one engine, in headwids of less than 15 kts.
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Just to straighten things up....criteria for determining Vmca.
Aircraft certificated by the US FAA
1. Failure of the critical engine
2. Engine controls set for tko or max power
3. Rearmost allowable centre of gravity
4. Aircraft trimmed for takeoff
5. Sea level mtow
6. Flaps in tko position
7. Landing gear retracted
8. Cowl flaps in tko position
9. Prop of inoperative engine windmilling (fx if auto-feather fitted)
10. Airborne & out of ground effect
11. No more than 150lbs force required to maintain full rudder deflection
12. Maximum 5 degrees aob into dead engines
Aircraft certificated by the US FAA
1. Failure of the critical engine
2. Engine controls set for tko or max power
3. Rearmost allowable centre of gravity
4. Aircraft trimmed for takeoff
5. Sea level mtow
6. Flaps in tko position
7. Landing gear retracted
8. Cowl flaps in tko position
9. Prop of inoperative engine windmilling (fx if auto-feather fitted)
10. Airborne & out of ground effect
11. No more than 150lbs force required to maintain full rudder deflection
12. Maximum 5 degrees aob into dead engines