Single vs Twin
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Single vs Twin
I'm sure this may have been discussed before but....
I would be interested in hearing peoples views on the perceived benefits of twin engined operations over a high performance single, lets say a Baron 55 or 58 / Cessna T310R v's a Bonanza or Mooney 252.
Very little difference in initial purchase price between them all right now due to the dollars position, so what factors would make you choose one over the other?
GG
I would be interested in hearing peoples views on the perceived benefits of twin engined operations over a high performance single, lets say a Baron 55 or 58 / Cessna T310R v's a Bonanza or Mooney 252.
Very little difference in initial purchase price between them all right now due to the dollars position, so what factors would make you choose one over the other?
GG
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Well Flyboy, its a difficult one! it all depends on what budget you have really.
You also have the safety factor over water and in IMC.
When you look at performance there isnt much in it, my Bonanza will see off some twins in the cruise with far less fuel consumption and less maintenance so really it depends on ya wallet.
Best of luck with your decision
You also have the safety factor over water and in IMC.
When you look at performance there isnt much in it, my Bonanza will see off some twins in the cruise with far less fuel consumption and less maintenance so really it depends on ya wallet.
Best of luck with your decision
Why do it if it's not fun?
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Summary of what I've read on other threads:
- Single: Cheaper to run. Obvious safety issues over large bodies of water, in or above low-level cloud, and at night.
- Twin: Expensive to run, but none of the safety concerns of singles as long as the pilot is current. However, a pilot who is not current is arguably more dangerous than the dangers of the single.
FFF
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- Single: Cheaper to run. Obvious safety issues over large bodies of water, in or above low-level cloud, and at night.
- Twin: Expensive to run, but none of the safety concerns of singles as long as the pilot is current. However, a pilot who is not current is arguably more dangerous than the dangers of the single.
FFF
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337....no thanks, far too noisy.
To clarify the situation, I already have a Bonanza, but am trying to decide wheter or not to move up to a twin. Do the benefits outweigh the extra fuel costs and maintenance on the second engine? Is there a real speed benefit? Is there anything else I have overlooked?
GG
To clarify the situation, I already have a Bonanza, but am trying to decide wheter or not to move up to a twin. Do the benefits outweigh the extra fuel costs and maintenance on the second engine? Is there a real speed benefit? Is there anything else I have overlooked?
GG
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It comes down to one word, safety. If safety is not your number one priority you may not wish to incurr the extra cost. It does appear from what you say you can afford to make the transition, and as to the marginality of some twins, the answer is don't buy a marginal model.
With the requirement for annual verification of piloting skills the old arguements about EFOT dangers are old hat.
With the requirement for annual verification of piloting skills the old arguements about EFOT dangers are old hat.
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Why not a turboprop single? According to some NTSB data I read a while ago, one of these is five times less likely to come down than a piston single.
Here's a good one:
http://www.grob-aerospace.de/get.php4?pageid=133
Does cost a bit more than your average 30 year old twin though
Here's a good one:
http://www.grob-aerospace.de/get.php4?pageid=133
Does cost a bit more than your average 30 year old twin though
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Some problems with handling on approach with some turboprop singles, see recent threads
Some thirty year old twins are better than some later twins. It is important to research the performance of the various models before buying.
Some thirty year old twins are better than some later twins. It is important to research the performance of the various models before buying.
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bluskis
Only because some have lots of power relative to the aileron authority at low approach speeds. But... can you ever have too much power? I would rather have 400bhp and remember to use the rudder, than have 200bhp.
Some problems with handling on approach with some turboprop singles
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Okay, so how do we define a 'marginal' twin? Is it based on single engine ceiling or single engine rate of climb? How much is marginal, how much is acceptable?
GG
GG
I like FFF's summary. Only thing I would add is field length.
The place the twin bites harder than the single is from about 60 knots on the t/o roll to the point at which you're climbing comfortably away well above blue line speed. Between those two points, you have some tough choices to make if you suspect an engine problem (note not "have an engine failure") in a twin. A long runway makes it easy -- close the throttles and land straight ahead if you're airborne. On a short runway, doing so becomes a hull write off.
So even if the twin's performance is well within the field declared distances, you may prefer a single where the decision making is easier.
J Mac McClellan of Flying went through a Bonanza to Baron upgrade many years ago. Why not email him for advice?
The place the twin bites harder than the single is from about 60 knots on the t/o roll to the point at which you're climbing comfortably away well above blue line speed. Between those two points, you have some tough choices to make if you suspect an engine problem (note not "have an engine failure") in a twin. A long runway makes it easy -- close the throttles and land straight ahead if you're airborne. On a short runway, doing so becomes a hull write off.
So even if the twin's performance is well within the field declared distances, you may prefer a single where the decision making is easier.
J Mac McClellan of Flying went through a Bonanza to Baron upgrade many years ago. Why not email him for advice?
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Will the BRS make the twin redundant?
Having seen the latest ultralights and the Cirrus, I'm inclined to think that piston twins will become redundant soon.
Those new planes I mentioned are equiped with BRS, a balistic chute with a rocket, wich can be deployed quickly and bring you and the airplane safely to the earth.
Except for the takeoff and initial climb, the chute should work properly and make a second engine redundant.
Well, as in many twins, with a high useful load, the safest procedure with one engine out may be to abort and crash ahead anyway (a forced landing is better than a spin dive), the safety advantage of the twins over singles are MUCH smaller if the single has a BRS.
I think that the "danger window", in a single with a BRS, would be too close to the window of a light twin, so the extra costs would not be necessary.
Those new planes I mentioned are equiped with BRS, a balistic chute with a rocket, wich can be deployed quickly and bring you and the airplane safely to the earth.
Except for the takeoff and initial climb, the chute should work properly and make a second engine redundant.
Well, as in many twins, with a high useful load, the safest procedure with one engine out may be to abort and crash ahead anyway (a forced landing is better than a spin dive), the safety advantage of the twins over singles are MUCH smaller if the single has a BRS.
I think that the "danger window", in a single with a BRS, would be too close to the window of a light twin, so the extra costs would not be necessary.
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On the occasions when this question is asked (and it is asked often) I am often tempted to roll out again an article I wrote for the PPL/IR network as to why I took the decision. Apologies to those who have read it before.
Until about ten years ago I operated a Cessna 172 Skyhawk as my business aircraft. It was airways equipped, I was instrument rated (indeed had an ATPL/IR and had been employed as an executive jet captain in the recent past) and there should have been little except (relatively rare) 500m RVRs to prevent me from flying on business all over the country.
But I didn't. Almost every time a meeting or trip came up which obviously demanded aviation I found myself deciding that using the 172 was not appropriate. The reasons that the flight might not be possible multiplied in my mind...icing, low cloud, thunderstorms, long water crossings, night flights, electrical and avionics failures, strong headwinds en-route, strong crosswinds on arrival...the list seemed endless.
I was not cancelling flights on the day because of these reasons. Rather, I was making alternative plans because I feared that the trip would have to be cancelled at the last minute, thus jeopardising my business.
There were two seminal moments in my decision to dump the 172.
The first was when I was sitting on the threshold at Fairoaks and the thought occurred to me:
"Here I am with one engine, one alternator, one vacuum pump, one pitot/static source and one pilot. If I were in the jet and any one of these situations arose I would declare an emergency and land...yet here am I about to take-off."
The second was when I had to go to an important meeting with the Blackpool Pleasure Beach, which is in walking distance of Blackpool Airport, a highly equipped, multi-runway, IFR, GA friendly airfield. Yet I still decided to drive from home, past the hangar where the 172 sat and then a further four hours, "just in case" there was a problem.
As I drove up the motorway and thought of the 172 sitting in the hangar, costing me a fortune in insurance, hangarage and maintenance I took the decision...either I get an aeroplane that has a reasonable expectation of delivering me or I give up on business aviation.
So, why was the 172 not reliable enough to be trusted to deliver me? There were a number of reasons, some demonstrable, others based on preference and prejudice.
The demonstrable reasons were icing, crosswind capability and speed.
Icing
I have never been one to get over-concerned about icing, and have from time to time carried a fair amount of ice on a non de-iced aircraft. Indeed I might go flying on a day when light icing is present in a height band. But the problem is that if icing is going to be present from the MSA up to FL100 you really cannot even think of getting the SEP out of the hangar.
Crosswind
Fewer and fewer airfields are offering a cross runway. A crosswind capability of 15kts means that the number of days which are outside limits at one end of the flight or the other reach significant levels.
Speed
Although at first glance going fast seems to be a luxury rather than a necessity, it becomes very relevant indeed when faced with a strong headwind. 50kt winds are not unusual at airway levels. This is nearly half the TAS of the single, leaving me with 70kts made good, whereas in a twin the groundspeed would be 120kts or better...nearly double the speed.
The factors based on preference or prejudice were all to do with system failures.
Engine Failure
I have had nine engine failures in my flying career. I know that they happen. This is why I always want a plan B available to cover the eventuality. Plan B in a twin is to divert at leisure. Plan B in a single should be to make a forced landing in a field. But that's rather difficult in hill fog, or even a 200' cloudbase, or at night, or over water, or over mountains. So if you fly a single and want to ensure that there is a plan B you are limited to flying over farmland, during the day, when the weather is reasonably good. So why bother with an instrument qualification?
Electrical or other systems failure
Almost as serious as an engine failure is an alternator failure in or above IMC. With no way of navigating or communicating you are left with some pretty unpleasant choices...flying triangles in the hope that someone will notice, then unrehearsed formation flying in cloud, or maybe dead reckoning to where you hope the sea is and then hoping that your guess at QNH is reasonably accurate. Similarly, loss of your single vacuum pump can be pretty fatal, particularly if you identify the symptoms late.
I know that there are counter arguments to some of the above. There are singles with redundant ancillaries, particularly alternators and suction pumps, there are de-iced and fast singles, and all of these make them more suitable for business flying than their lesser cousins. Nonetheless, they remain dependent on one power unit, and therefore everything continuing according to Plan A. Also, these highly equipped singles are relatively rare and expensive.
There are also some arguments against twins on safety grounds. The commonest are:
Risks associated with single engine failures on a twin
Most GA twins are not certified to be able to continue flying in the event of an engine failure below 200'. Twin training concentrates on failures above 200', recovery from such a failure and continuation of the flight. Unfortunately not enough emphasis is placed on the fact that below 200' the most prudent action is normally to shut down both engines and make a forced landing. The argument continues that if either engine fails, the result is a forced landing, and therefore the risk is at least doubled (I say at least because engines are marginally more likely to fail on a twin because of greater vibration and longer control runs.)
This increased risk is real and must be taken into account by the twin owner, but, at least in my mind, is more than offset by having the second engine available in the cruise, especially when conditions dictate that a forced landing is unlikely to be successful (water, mountains, night, low cloud etc).
Furthermore the time for which the aircraft is exposed to risk is very small (less than 15 seconds per flight) compared to the time spent exposed to risk in a single.
Finally, the pilot can do a great deal to mitigate the risk (using the full runway, rotating at blue line, avoiding built up areas in the take-off path etc). I have written an article in Flyer magazine on the subject.
Less protection in a forced landing in a twin
People do argue that in the event of a forced landing, uninjured survival of the passengers is less likely because the aircraft is going faster and the momentum is greater, the occupants are not protected by the engine going ahead of them and that the gear may be up and therefore not in a position to absorb impact.
I do not know if this is true, but even if it is, I consider it mitigated by the fact that a forced landing is much less likely.
Greater risks taken by twin pilots
There is an argument, developed, I believe, by Prof.Adams of London University, that no matter how safe a piece of equipment or transport is made, overall safety is not affected because the user will take greater risks until the risk level reaches the same point as it had been on the less safe equipment. Prof. Adams believes that Volvos should be replaced with paper cars with spikes in the middle of their steering wheels.
Thus, a twin is not safer than a single, because the pilot will choose to fly over water, in icing, at night, to IFR minima, where the prudent single pilot would not.
My counter argument is simply "...sure, maybe I am taking the same risk as a single pilot, but I am able to operate in much more difficult environments at the same risk."
Which means I can get to my business meetings. QED
Until about ten years ago I operated a Cessna 172 Skyhawk as my business aircraft. It was airways equipped, I was instrument rated (indeed had an ATPL/IR and had been employed as an executive jet captain in the recent past) and there should have been little except (relatively rare) 500m RVRs to prevent me from flying on business all over the country.
But I didn't. Almost every time a meeting or trip came up which obviously demanded aviation I found myself deciding that using the 172 was not appropriate. The reasons that the flight might not be possible multiplied in my mind...icing, low cloud, thunderstorms, long water crossings, night flights, electrical and avionics failures, strong headwinds en-route, strong crosswinds on arrival...the list seemed endless.
I was not cancelling flights on the day because of these reasons. Rather, I was making alternative plans because I feared that the trip would have to be cancelled at the last minute, thus jeopardising my business.
There were two seminal moments in my decision to dump the 172.
The first was when I was sitting on the threshold at Fairoaks and the thought occurred to me:
"Here I am with one engine, one alternator, one vacuum pump, one pitot/static source and one pilot. If I were in the jet and any one of these situations arose I would declare an emergency and land...yet here am I about to take-off."
The second was when I had to go to an important meeting with the Blackpool Pleasure Beach, which is in walking distance of Blackpool Airport, a highly equipped, multi-runway, IFR, GA friendly airfield. Yet I still decided to drive from home, past the hangar where the 172 sat and then a further four hours, "just in case" there was a problem.
As I drove up the motorway and thought of the 172 sitting in the hangar, costing me a fortune in insurance, hangarage and maintenance I took the decision...either I get an aeroplane that has a reasonable expectation of delivering me or I give up on business aviation.
So, why was the 172 not reliable enough to be trusted to deliver me? There were a number of reasons, some demonstrable, others based on preference and prejudice.
The demonstrable reasons were icing, crosswind capability and speed.
Icing
I have never been one to get over-concerned about icing, and have from time to time carried a fair amount of ice on a non de-iced aircraft. Indeed I might go flying on a day when light icing is present in a height band. But the problem is that if icing is going to be present from the MSA up to FL100 you really cannot even think of getting the SEP out of the hangar.
Crosswind
Fewer and fewer airfields are offering a cross runway. A crosswind capability of 15kts means that the number of days which are outside limits at one end of the flight or the other reach significant levels.
Speed
Although at first glance going fast seems to be a luxury rather than a necessity, it becomes very relevant indeed when faced with a strong headwind. 50kt winds are not unusual at airway levels. This is nearly half the TAS of the single, leaving me with 70kts made good, whereas in a twin the groundspeed would be 120kts or better...nearly double the speed.
The factors based on preference or prejudice were all to do with system failures.
Engine Failure
I have had nine engine failures in my flying career. I know that they happen. This is why I always want a plan B available to cover the eventuality. Plan B in a twin is to divert at leisure. Plan B in a single should be to make a forced landing in a field. But that's rather difficult in hill fog, or even a 200' cloudbase, or at night, or over water, or over mountains. So if you fly a single and want to ensure that there is a plan B you are limited to flying over farmland, during the day, when the weather is reasonably good. So why bother with an instrument qualification?
Electrical or other systems failure
Almost as serious as an engine failure is an alternator failure in or above IMC. With no way of navigating or communicating you are left with some pretty unpleasant choices...flying triangles in the hope that someone will notice, then unrehearsed formation flying in cloud, or maybe dead reckoning to where you hope the sea is and then hoping that your guess at QNH is reasonably accurate. Similarly, loss of your single vacuum pump can be pretty fatal, particularly if you identify the symptoms late.
I know that there are counter arguments to some of the above. There are singles with redundant ancillaries, particularly alternators and suction pumps, there are de-iced and fast singles, and all of these make them more suitable for business flying than their lesser cousins. Nonetheless, they remain dependent on one power unit, and therefore everything continuing according to Plan A. Also, these highly equipped singles are relatively rare and expensive.
There are also some arguments against twins on safety grounds. The commonest are:
Risks associated with single engine failures on a twin
Most GA twins are not certified to be able to continue flying in the event of an engine failure below 200'. Twin training concentrates on failures above 200', recovery from such a failure and continuation of the flight. Unfortunately not enough emphasis is placed on the fact that below 200' the most prudent action is normally to shut down both engines and make a forced landing. The argument continues that if either engine fails, the result is a forced landing, and therefore the risk is at least doubled (I say at least because engines are marginally more likely to fail on a twin because of greater vibration and longer control runs.)
This increased risk is real and must be taken into account by the twin owner, but, at least in my mind, is more than offset by having the second engine available in the cruise, especially when conditions dictate that a forced landing is unlikely to be successful (water, mountains, night, low cloud etc).
Furthermore the time for which the aircraft is exposed to risk is very small (less than 15 seconds per flight) compared to the time spent exposed to risk in a single.
Finally, the pilot can do a great deal to mitigate the risk (using the full runway, rotating at blue line, avoiding built up areas in the take-off path etc). I have written an article in Flyer magazine on the subject.
Less protection in a forced landing in a twin
People do argue that in the event of a forced landing, uninjured survival of the passengers is less likely because the aircraft is going faster and the momentum is greater, the occupants are not protected by the engine going ahead of them and that the gear may be up and therefore not in a position to absorb impact.
I do not know if this is true, but even if it is, I consider it mitigated by the fact that a forced landing is much less likely.
Greater risks taken by twin pilots
There is an argument, developed, I believe, by Prof.Adams of London University, that no matter how safe a piece of equipment or transport is made, overall safety is not affected because the user will take greater risks until the risk level reaches the same point as it had been on the less safe equipment. Prof. Adams believes that Volvos should be replaced with paper cars with spikes in the middle of their steering wheels.
Thus, a twin is not safer than a single, because the pilot will choose to fly over water, in icing, at night, to IFR minima, where the prudent single pilot would not.
My counter argument is simply "...sure, maybe I am taking the same risk as a single pilot, but I am able to operate in much more difficult environments at the same risk."
Which means I can get to my business meetings. QED
Excellent arguments
Well worded answer Timothy....
Even a Cirrus may not be safer due to pilot behaviour.
I have a healthy respect for multi engine flying and unless you stay current it's more dangerous than any single.
So the question is :
Do you need one?
Can you afford one?
Will you fly it enough to stay proficient?
I've recently advised somebody who was thinking about buying a multi to fly it at least 50hrs/year with a dual flight every month.
Less dual if you fly more than the 50 hrs but at least 2-3 dual flights a year even if you fly a lot!
Even a Cirrus may not be safer due to pilot behaviour.
I have a healthy respect for multi engine flying and unless you stay current it's more dangerous than any single.
So the question is :
Do you need one?
Can you afford one?
Will you fly it enough to stay proficient?
I've recently advised somebody who was thinking about buying a multi to fly it at least 50hrs/year with a dual flight every month.
Less dual if you fly more than the 50 hrs but at least 2-3 dual flights a year even if you fly a lot!
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I would use single engine rate of climb following EFOTO to distinguish marginal from acceptable performance.
You can always make a command decision relative to the risks of single engine ceiling.
A twin that will reach single engine control speed before rotation on a reasonable length runway, say 2200/2400 ft would be one way of making the selection.
You can always make a command decision relative to the risks of single engine ceiling.
A twin that will reach single engine control speed before rotation on a reasonable length runway, say 2200/2400 ft would be one way of making the selection.
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I would go for a twin with a CE ceiling of >10,000', which means turbo charging.
If you're going to do a substantial amount of flying, possibly IFR and crossing water, then the advantages of a twin will outweigh the disadvantages, though the costs will of course be 75% more than a single (Landing, parking, fuel fees etc). This may or may not be an issue to you. In a twin its still possible to complete an instrument approach on a single engine, in a SE there is no chance. A SE failure in the middle of the channel means you're going for a swim, in a twin it means you either a)aren't or b) have more time to get nearer to land before you go for a swim, and the helicopter can be waiting for you
A SE EF over mountains, and its probably curtains for you, in a ME, you may have a second chance. A SE failure at night over desolate areas could prove very nasty, in a ME it may prove to be an inconvienience. In a twin, you're no worse off if you have an engine failure after take off than you are in a single if handled right, chances are you're going down, though maybe at a lesser rate than in a single (unless lightly loaded, flat terrain, aircraft type, you do everything right then you may climb).
I think I'll hold out for a DA42 though....
Cheers
EA
If you're going to do a substantial amount of flying, possibly IFR and crossing water, then the advantages of a twin will outweigh the disadvantages, though the costs will of course be 75% more than a single (Landing, parking, fuel fees etc). This may or may not be an issue to you. In a twin its still possible to complete an instrument approach on a single engine, in a SE there is no chance. A SE failure in the middle of the channel means you're going for a swim, in a twin it means you either a)aren't or b) have more time to get nearer to land before you go for a swim, and the helicopter can be waiting for you
A SE EF over mountains, and its probably curtains for you, in a ME, you may have a second chance. A SE failure at night over desolate areas could prove very nasty, in a ME it may prove to be an inconvienience. In a twin, you're no worse off if you have an engine failure after take off than you are in a single if handled right, chances are you're going down, though maybe at a lesser rate than in a single (unless lightly loaded, flat terrain, aircraft type, you do everything right then you may climb). I think I'll hold out for a DA42 though....
Cheers
EA
A twin that will reach single engine control speed before rotation on a reasonable length runway, say 2200/2400 ft would be one way of making the selection.
The issue is whether you can get to a speed at which you can safely fly away before you have to make the decision of whether to close the throttles or take the problem into the air. That requires consideration of the accelerate-stop distance at that critical speed.
Whether you make that decision on the ground or in the air doesn't makee much difference. Vmcg is often higher than Vmca.