"Light Twin" fatal at Hawarden
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
If you get hold of that swatton book I gives the certification standards for Vmca.
Now I hesitate to give this link because it refers to heavy tin and has some pretty heavy maths in it.
http://www.avioconsult.com/downloads...0on%20Vmca.pdf
What you need to do is scroll down to page 5 with the graphs.
Yes I know its a 747. But it doesn't make any difference we are still dealing with a force on a wing giving a moment being opposed by a force by the rudder.
So to make the 747 into a twin we just fail two engines on the same wing.
So if you look at the graph in the top right corner effect of bank angle and weight on Vmca With engines 1&2 gone. Your aircraft will have different speeds but the form of the graph will be the approximately the same. As you can see the graph only goes up to 15 degs bank angle and in that time the Vmca more than doubles.
Unfortunately I haven't managed to find a paper which deals with twin propeller aircraft. As I said that 747 won't be exactly the same and the rates and gradients and obviously the numbers won't be the same. But it does show that you can be safe at xxx speed at -5 degree bank but if you go to -10 you going to have issues as the Vmca has increased by a reasonable amount if its over xxx speed. But as there isn't a series of speeds given for different bank angles you can only stay inside the certification standard of up to 5 degs of bank.
Now I hesitate to give this link because it refers to heavy tin and has some pretty heavy maths in it.
http://www.avioconsult.com/downloads...0on%20Vmca.pdf
What you need to do is scroll down to page 5 with the graphs.
Yes I know its a 747. But it doesn't make any difference we are still dealing with a force on a wing giving a moment being opposed by a force by the rudder.
So to make the 747 into a twin we just fail two engines on the same wing.
So if you look at the graph in the top right corner effect of bank angle and weight on Vmca With engines 1&2 gone. Your aircraft will have different speeds but the form of the graph will be the approximately the same. As you can see the graph only goes up to 15 degs bank angle and in that time the Vmca more than doubles.
Unfortunately I haven't managed to find a paper which deals with twin propeller aircraft. As I said that 747 won't be exactly the same and the rates and gradients and obviously the numbers won't be the same. But it does show that you can be safe at xxx speed at -5 degree bank but if you go to -10 you going to have issues as the Vmca has increased by a reasonable amount if its over xxx speed. But as there isn't a series of speeds given for different bank angles you can only stay inside the certification standard of up to 5 degs of bank.
I thought the 5 degrees with reference to VMCA was to do with being able to contain heading within 5 degrees in event of engine failure etc?
There is also the issue of applying a small amount of bank towards the live (typically 5 degrees) for better performance.
The accident I recall was the B707 at PIK many years ago. Lots of factors but one thing which came out of the report was that the difference between VMCA wings level and 5 degrees of bank towards live was 40 kts! If they had cranked a bit more bank towards the live they would have regained directional control but as to how much it would have affected the outcome is debatable.
There is also the issue of applying a small amount of bank towards the live (typically 5 degrees) for better performance.
The accident I recall was the B707 at PIK many years ago. Lots of factors but one thing which came out of the report was that the difference between VMCA wings level and 5 degrees of bank towards live was 40 kts! If they had cranked a bit more bank towards the live they would have regained directional control but as to how much it would have affected the outcome is debatable.
Join Date: Aug 2002
Location: Surrey, UK.
Posts: 0
Likes: 0
Received 0 Likes
on
0 Posts
No, that is MEP test standard or IR test standard, can't remember which, however it is nothing to do with Vmca.
Last edited by rustle; 28th Nov 2013 at 09:59.
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
Flying High Performance Singles and Twins - John Eckalbar - Google Books
Now weird but this article claims the opposite infact it claims that the more you bank into the live engine the more VMCA goes away ???
just a discussion point for you more intelligent guys unlike wot i am
pace
Now weird but this article claims the opposite infact it claims that the more you bank into the live engine the more VMCA goes away ???
just a discussion point for you more intelligent guys unlike wot i am
pace
Join Date: Jul 2001
Location: Belgium
Posts: 486
Likes: 0
Received 0 Likes
on
0 Posts
John is a very experienced professor of mathematics and Bonanza/Baron instructor. I would very much consider what he is saying. I have this book and several others written by him.
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
It makes sense that the more you bank towards the live engine the more you will negate those forces requiring rudder but with limited engine power on one engine you would I presume have to trade potential energy in the airframe to do so i.e. trade altitude for energy in anything other than a small bank towards the live engine.
Pace
Pace
Join Date: Aug 2002
Location: Surrey, UK.
Posts: 0
Likes: 0
Received 0 Likes
on
0 Posts
My understanding of the "bank into live" theory is that it means less rudder required (due bank) so more rudder 'available' (ergo lower Vmca)
Also means the aircraft is not flying quite so "sideways" with a lot of airflow into deadside fuselage, and therefore has a performance benefit.
Vmca is predicated on banking maximum 5 degrees for this reason.
Also means the aircraft is not flying quite so "sideways" with a lot of airflow into deadside fuselage, and therefore has a performance benefit.
Vmca is predicated on banking maximum 5 degrees for this reason.
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
Naah
Theory is one thing anyway both articles yours and this one contradict each other so prefer to fly highly tuned to FEEL ; )
Theory is for nimbies and armchair pilots ; )
Theory is one thing anyway both articles yours and this one contradict each other so prefer to fly highly tuned to FEEL ; )
Theory is for nimbies and armchair pilots ; )
McGraw-Hill Dictionary of Aviation:
VMCA /Vmca
The minimum control speed in the air. The minimum flight speed at which the airplane is controllable with a maximum 5° bank when the critical engine suddenly becomes inoperative with the remaining engines at takeoff thrust. The conditions for calculations of VMCA are (i) critical engine at idle power setting, (ii) critical propeller windmilling, (iii) operating engine producing maximum thrust, (iv) landing gear and flaps up, (v) aircraft loaded at the most aft allowable center of gravity, (vi) aircraft loaded to the maximum gross weight, (vii) up to 5° of bank toward the operating engine, and (viii) atmospheric conditions normalized to standard day at sea-level pressure.
rustle, thanks for the correction with reference to 5 degrees of heading
VMCA /Vmca
The minimum control speed in the air. The minimum flight speed at which the airplane is controllable with a maximum 5° bank when the critical engine suddenly becomes inoperative with the remaining engines at takeoff thrust. The conditions for calculations of VMCA are (i) critical engine at idle power setting, (ii) critical propeller windmilling, (iii) operating engine producing maximum thrust, (iv) landing gear and flaps up, (v) aircraft loaded at the most aft allowable center of gravity, (vi) aircraft loaded to the maximum gross weight, (vii) up to 5° of bank toward the operating engine, and (viii) atmospheric conditions normalized to standard day at sea-level pressure.
rustle, thanks for the correction with reference to 5 degrees of heading
Join Date: May 2001
Location: UK
Posts: 4,631
Likes: 0
Received 0 Likes
on
0 Posts
Pace
Rolling back to an earlier comment you made I am far from convinced regarding the need for special training.
Any training on type should consider the specific limitations of the twin. Of course you can chose to ignore the training, or the training can be poor or inadequate in the first place. However the former is your own fault, and the later is the instructor's fault. Changing the training requirements will not alter those facts.
Far more relevant is the dexterity of handling on marginal twins which only comes from flying time. The DA42 will climb at MTOW but, at least in my experience, the performance is hardly sparkling, and, if ham fisted, that margin is quickly eroded. Fly the aircraft out of balance and the margin is gone.
On the other hand an Aztec performs relatively well with one out perhaps unless full to the gunwales, albeit unlikely it will be flown in that configuration all that often. However if you disregard a critical engine the outcome may not be as good, and it is all too easy to do when confronted with an engine failure and a circuit to land.
Aviation Safety Letter 4/2001 - Transport Canada
Rolling back to an earlier comment you made I am far from convinced regarding the need for special training.
Any training on type should consider the specific limitations of the twin. Of course you can chose to ignore the training, or the training can be poor or inadequate in the first place. However the former is your own fault, and the later is the instructor's fault. Changing the training requirements will not alter those facts.
Far more relevant is the dexterity of handling on marginal twins which only comes from flying time. The DA42 will climb at MTOW but, at least in my experience, the performance is hardly sparkling, and, if ham fisted, that margin is quickly eroded. Fly the aircraft out of balance and the margin is gone.
On the other hand an Aztec performs relatively well with one out perhaps unless full to the gunwales, albeit unlikely it will be flown in that configuration all that often. However if you disregard a critical engine the outcome may not be as good, and it is all too easy to do when confronted with an engine failure and a circuit to land.
Aviation Safety Letter 4/2001 - Transport Canada
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
I can see the Vmca decreasing with more angle of bank but that means you will have to circle which is a bit of an issue when you want to land. For the plane to go in a straight line you need to input more rudder with angle of back so the Vmca will go back up. There will be a sweet spot when you have minimum rudder input When Vmca is the lowest.
Also as well the more Angle of bank you have means the more lift you require to maintain Straight and level which means more drag which then takes you closer to the stall. So you have multiple variables that are in effect. Once you have dealt with one of the issue then others become denominate.
Also there is the fact the more you fly cross controls side slip the more drag you have and any excess energy will quite quickly be wasted by drag and you may very well have no Vmca problems but you will be heading towards the ground at a great rate of decent.
Also as well the more Angle of bank you have means the more lift you require to maintain Straight and level which means more drag which then takes you closer to the stall. So you have multiple variables that are in effect. Once you have dealt with one of the issue then others become denominate.
Also there is the fact the more you fly cross controls side slip the more drag you have and any excess energy will quite quickly be wasted by drag and you may very well have no Vmca problems but you will be heading towards the ground at a great rate of decent.
Last edited by mad_jock; 28th Nov 2013 at 15:04. Reason: Got things the wrong way round
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
Rolling back to an earlier comment you made I am far from convinced regarding the need for special training.
Pace
Good explanation here of forces during asymmetric flight and effects on Vmca etc:-
Asymmetric Flight
Asymmetric Flight
Join Date: Jan 2003
Location: The Heart
Posts: 811
Likes: 0
Received 0 Likes
on
0 Posts
MJ,
The 747 is not really relevant as such types are perf A and required to demonstrate positive climb performance in the failure situation.
Vmca vs bank angle is still relevant to them as SID's will be calculated with a maximum of 15 degrees of bank. beyond this there is a marked decrease in climb angle, sorry, can't remember the percentage.
So back to the MEP, Vmca is effectively only there so you don't lose control by using full throttle below this speed while you accelerate to Vxse or Vyse and that is all you should be doing at that time.
The 747 is not really relevant as such types are perf A and required to demonstrate positive climb performance in the failure situation.
Vmca vs bank angle is still relevant to them as SID's will be calculated with a maximum of 15 degrees of bank. beyond this there is a marked decrease in climb angle, sorry, can't remember the percentage.
So back to the MEP, Vmca is effectively only there so you don't lose control by using full throttle below this speed while you accelerate to Vxse or Vyse and that is all you should be doing at that time.
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
There is nothing magical about perf A. The world doesn't have Perf A aerodynamic laws and GA flight laws.
You will be just as dead in either type if Vmca bites your bum.
The point about if your climbing or descending when you get everything right is a pretty much mute point in this discussion.
You will be just as dead in either type if Vmca bites your bum.
The point about if your climbing or descending when you get everything right is a pretty much mute point in this discussion.
Guest
Posts: n/a
Sorry, I've come late to this thread but having flown in and out of Hawarden I wonder about the option of closing the throttles and accepting a bit of a rough landing.
If I read the initial reports correctly the crash occurred near the upwind threshold which is nearly 2 km from the threshold.
All the discussion about minimum control speed seems to indicate a shorter timescale than an a/c flying around 100 kts along the length of the runway.
Apologies if this has already been aired I haven't had time to digest every post.
SGC
If I read the initial reports correctly the crash occurred near the upwind threshold which is nearly 2 km from the threshold.
All the discussion about minimum control speed seems to indicate a shorter timescale than an a/c flying around 100 kts along the length of the runway.
Apologies if this has already been aired I haven't had time to digest every post.
SGC
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
Sir Georgie C
These threads tend to drift sometimes right off subject, come back then go again.
The discussions have circled around the subject of minimal performance light twins and from my perspective whether the training is too specific to wannabe airline pilots who train in them then never touch light twins again,
or whether they are unique and the training should consider other options rather than a climb at all costs at blue line which seems the flavour of the day and the big killer when blue line is dropped or no climb achieved.
Very bad accident and fatality statistics on loosing an engine.
Yes I go with your statement about closing both engines and a controlled crash rather than falling vertically nose first into the tarmac which this twin and its poor occupants appear to have done.
Pace
These threads tend to drift sometimes right off subject, come back then go again.
The discussions have circled around the subject of minimal performance light twins and from my perspective whether the training is too specific to wannabe airline pilots who train in them then never touch light twins again,
or whether they are unique and the training should consider other options rather than a climb at all costs at blue line which seems the flavour of the day and the big killer when blue line is dropped or no climb achieved.
Very bad accident and fatality statistics on loosing an engine.
Yes I go with your statement about closing both engines and a controlled crash rather than falling vertically nose first into the tarmac which this twin and its poor occupants appear to have done.
Pace