A Question For Both Pilots and Engineers.
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A Question For Both Pilots and Engineers.
Hello all,
I am a student in the UK studying for my A2's in the second half of my A levels with a view to go onto study "Aerospace Engineering with Pilot Studies" at university. As a bit of background I am already training for my NPPL.
One of my A level subjects is design and for my final project I am looking at designing a system that would allow a light to medium weight aircraft to safely descend to the ground in the event of a serious engine failure, airframe failure or other such occurrence.
I am aware of one such system that exists called "The Cirrus Airframe Parachute System" (CAPS) however this only works for a light 5 man aircraft.
I am looking at designing a system that would work for anything up to a 50 passenger capacity aircraft, e.g the Bombardier Dash 8.
I realise that using parachutes to gently "float" the aircraft down, similar to CAPS, for a larger aircraft is impractical if not impossible, so what I am suggesting is a number of components that would decelerate the aircraft to a degree that it is traveling at a slow enough velocity on impact for the crash to be survivable. It would not be gentle and people may come away with broken bones but they would be alive.
My main idea would be to have a drogue parachute to deploy out the tail section, to reduce horizontal velocity, and then have several small parachutes to deploy out the top of the fuselage to slow the aircraft's vertical velocity. Airbags mounted in sections in the bottom of the fuselage would then deploy to cushion the impact force upon landing.
Some more outlandish ideas involve using small solid fuel "retro rockets" mounted in the nose that would fire to oppose the direction of motion, there by reducing horizontal velocity.
These components could be used together, e.g rockets to slow horizontal velocity and the airbags to deploy to cushion the vertical impact.
These systems are designed to be used in conjunction with the aircraft's own deceleration devices: air brakes, thrust reversers etc.
The main operating environment for this system would be when the aircraft is at a low altitude, particularly on approach, just after take off and on go arounds.
I would appreciate any opinions and suggestions from people who have much more experience in flying and engineering than myself and ideas from people in general
Please ask if you would like me to clarify anything.
I am a student in the UK studying for my A2's in the second half of my A levels with a view to go onto study "Aerospace Engineering with Pilot Studies" at university. As a bit of background I am already training for my NPPL.
One of my A level subjects is design and for my final project I am looking at designing a system that would allow a light to medium weight aircraft to safely descend to the ground in the event of a serious engine failure, airframe failure or other such occurrence.
I am aware of one such system that exists called "The Cirrus Airframe Parachute System" (CAPS) however this only works for a light 5 man aircraft.
I am looking at designing a system that would work for anything up to a 50 passenger capacity aircraft, e.g the Bombardier Dash 8.
I realise that using parachutes to gently "float" the aircraft down, similar to CAPS, for a larger aircraft is impractical if not impossible, so what I am suggesting is a number of components that would decelerate the aircraft to a degree that it is traveling at a slow enough velocity on impact for the crash to be survivable. It would not be gentle and people may come away with broken bones but they would be alive.
My main idea would be to have a drogue parachute to deploy out the tail section, to reduce horizontal velocity, and then have several small parachutes to deploy out the top of the fuselage to slow the aircraft's vertical velocity. Airbags mounted in sections in the bottom of the fuselage would then deploy to cushion the impact force upon landing.
Some more outlandish ideas involve using small solid fuel "retro rockets" mounted in the nose that would fire to oppose the direction of motion, there by reducing horizontal velocity.
These components could be used together, e.g rockets to slow horizontal velocity and the airbags to deploy to cushion the vertical impact.
These systems are designed to be used in conjunction with the aircraft's own deceleration devices: air brakes, thrust reversers etc.
The main operating environment for this system would be when the aircraft is at a low altitude, particularly on approach, just after take off and on go arounds.
I would appreciate any opinions and suggestions from people who have much more experience in flying and engineering than myself and ideas from people in general
Please ask if you would like me to clarify anything.
First point - ANY parachute-type drag device is going to slow the aircraft in all directions. I don't think you need to consider two different systems for forward speed and descent speed. One will do both.
Take a look at this deployment of the Cirrus CAPS. On initial deployment, the roof-mounted parachute is pulled backwards by the airspeed, and slows the forward speed, acting as a drogue. As forward speed approaches zero, it continually realigns with the relative airflow until it is directly over the center of gravity, slowing descent speed.
I.E. one chute does both jobs (in fact, it can't do otherwise). It will always be pulling directly against the net "relative wind" vector, whether from the front, or from below, or both.
http://www.aero-news.net/images/cont...CAPS-0404a.jpg
Second - in the simple event of an engine failure, most airplanes are pretty good gliders. Since most medium-weight planes need and have two engines, it is rare for both to fail at the same time, and when they do, the airplane is STILL a pretty good glider. So engine failure as such is a low priority, compared to more drastic failures.
Here's a partial list of airliners that had to glide, and you'll note that while there have been some disastrous outcomes (usually involving terrain) - the vast majority involve no fatalities: List of airline flights that required gliding - Wikipedia, the free encyclopedia
One not on that list is the BA 777 accident at Heathrow - likely because the "glide" was so short. Only seconds between realization of a problem and ground contact.
Which is a third consideration - deployment time. At low altitudes (after takeoff and during approach), you really have very, very few seconds for the pilots to react to an event, decide to deploy your emergency system, and have the system deploy to full effectiveness.
Again note, in the Cirrus photo, that that system results in an initial RAPID and SEVERE loss of altitude (and nose-down attitude) until it gets vertical speed under control. You wouldn't want to use that system, or anything approximating it, within 1500 feet of the ground - it would likely just reduce survivability, not increase it. Which leads to...
Fourth - remember that, so long as the wings are attached, forward speed is what keeps the plane up and oriented correctly. Certainly in the event of a major airframe failure, anything is preferable to a nose-dive into the ground. But be very cautious about anything that slows the forward speed. It will likely increase the vertical speed fatally. Especially - consider the effects of accidental deployment or partial deployment.
External airbags or retro-rockets - will the aircraft be controllable/fliable with all that drag suddenly hanging out underneath, or retro thrust killing the flying speed?
Fifth - keep in mind attitude, or the orientation of the aircraft. Touching down nose-first, even with the best parachute braking, will be less survivable than a "flat" landing at a higher vertical speed (up to a point, anyway). That Cirrus system has the chute mounted more or less exactly over the center of gravity (CG) for just that reason.
Sixth - (but not finally, since I'm sure others will have comments) - weight. A Dash-8 that is "crash-proof" - but now has payload capacity for only 18-20 passengers due to the weight of the crash-proofing systems - won't be economically viable.
But don't let this dissuade you from going ahead - ripping an idea to shreds and then salvaging the pieces is part and parcel to good engineering.
Take a look at this deployment of the Cirrus CAPS. On initial deployment, the roof-mounted parachute is pulled backwards by the airspeed, and slows the forward speed, acting as a drogue. As forward speed approaches zero, it continually realigns with the relative airflow until it is directly over the center of gravity, slowing descent speed.
I.E. one chute does both jobs (in fact, it can't do otherwise). It will always be pulling directly against the net "relative wind" vector, whether from the front, or from below, or both.
http://www.aero-news.net/images/cont...CAPS-0404a.jpg
Second - in the simple event of an engine failure, most airplanes are pretty good gliders. Since most medium-weight planes need and have two engines, it is rare for both to fail at the same time, and when they do, the airplane is STILL a pretty good glider. So engine failure as such is a low priority, compared to more drastic failures.
Here's a partial list of airliners that had to glide, and you'll note that while there have been some disastrous outcomes (usually involving terrain) - the vast majority involve no fatalities: List of airline flights that required gliding - Wikipedia, the free encyclopedia
One not on that list is the BA 777 accident at Heathrow - likely because the "glide" was so short. Only seconds between realization of a problem and ground contact.
Which is a third consideration - deployment time. At low altitudes (after takeoff and during approach), you really have very, very few seconds for the pilots to react to an event, decide to deploy your emergency system, and have the system deploy to full effectiveness.
Again note, in the Cirrus photo, that that system results in an initial RAPID and SEVERE loss of altitude (and nose-down attitude) until it gets vertical speed under control. You wouldn't want to use that system, or anything approximating it, within 1500 feet of the ground - it would likely just reduce survivability, not increase it. Which leads to...
Fourth - remember that, so long as the wings are attached, forward speed is what keeps the plane up and oriented correctly. Certainly in the event of a major airframe failure, anything is preferable to a nose-dive into the ground. But be very cautious about anything that slows the forward speed. It will likely increase the vertical speed fatally. Especially - consider the effects of accidental deployment or partial deployment.
External airbags or retro-rockets - will the aircraft be controllable/fliable with all that drag suddenly hanging out underneath, or retro thrust killing the flying speed?
Fifth - keep in mind attitude, or the orientation of the aircraft. Touching down nose-first, even with the best parachute braking, will be less survivable than a "flat" landing at a higher vertical speed (up to a point, anyway). That Cirrus system has the chute mounted more or less exactly over the center of gravity (CG) for just that reason.
Sixth - (but not finally, since I'm sure others will have comments) - weight. A Dash-8 that is "crash-proof" - but now has payload capacity for only 18-20 passengers due to the weight of the crash-proofing systems - won't be economically viable.
But don't let this dissuade you from going ahead - ripping an idea to shreds and then salvaging the pieces is part and parcel to good engineering.
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I don't think you need to consider two different systems for forward speed and descent speed. One will do both.
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Thanks for the reply,
Right I see, I know that any parachute device would slow the aircraft down in both directions however my reasoning for having a drouge parachute to deploy out the tail first to slow the air speed is to reduce the opening shock of the main parachutes deploying. (A lower speed would mean less shock force) As this would cause a sudden force perpendicular to the direction of motion, which would torque around the centre of mass, which I feared would cause the aircraft to be pulled into a nose up attitude that would stall the wings.
Yeah of course gliding is preferable, so the use of this system in the event of engine failure would be low down the list of priority i guess, maybe it could be used as a last ditch attempt if the glide goes to pot?
Relating to deployment time and loss of altitude i think that airbags could be deployed in seconds as compressed gas expands very quickly. Loss of altitude is a large problem I hoped to counter to a degree with the use of parafoils instead of round parachutes as they would produce some degree of lift to hopefully make the loss of altitude somewhat less severe.
I had hoped that having parachutes mounted near the nose section as well as through the centre of mass would help to keep the aircraft in a relatively stable atitude?
I imagine the additional drag from deployed airbags would have a large effect on the aircrafts performance as such i think they would be best deployed in the few seconds before impact and of course have safeguards to prevent accidental deployment.
I have also realised that retro rockets may destabilise the aircraft further if they fire unequally so i think they might not be that great an idea.
Yeah commercially viability is a main issue, I want to make the system as simple and as light weight as possible.
Don't worry i shall not let it dissuade me, thank you, this is just the sort of critical analysis i was looking for
Right I see, I know that any parachute device would slow the aircraft down in both directions however my reasoning for having a drouge parachute to deploy out the tail first to slow the air speed is to reduce the opening shock of the main parachutes deploying. (A lower speed would mean less shock force) As this would cause a sudden force perpendicular to the direction of motion, which would torque around the centre of mass, which I feared would cause the aircraft to be pulled into a nose up attitude that would stall the wings.
Yeah of course gliding is preferable, so the use of this system in the event of engine failure would be low down the list of priority i guess, maybe it could be used as a last ditch attempt if the glide goes to pot?
Relating to deployment time and loss of altitude i think that airbags could be deployed in seconds as compressed gas expands very quickly. Loss of altitude is a large problem I hoped to counter to a degree with the use of parafoils instead of round parachutes as they would produce some degree of lift to hopefully make the loss of altitude somewhat less severe.
I had hoped that having parachutes mounted near the nose section as well as through the centre of mass would help to keep the aircraft in a relatively stable atitude?
I imagine the additional drag from deployed airbags would have a large effect on the aircrafts performance as such i think they would be best deployed in the few seconds before impact and of course have safeguards to prevent accidental deployment.
I have also realised that retro rockets may destabilise the aircraft further if they fire unequally so i think they might not be that great an idea.
Yeah commercially viability is a main issue, I want to make the system as simple and as light weight as possible.
Don't worry i shall not let it dissuade me, thank you, this is just the sort of critical analysis i was looking for
Another little point in addition to those already made: For all of the systems installed, there is a "get out of jail" procedure involved, should it quit or start to work without being called to duty.
What about Your idea in such a situation? What if the retro rockets fire on a performance-limited takeoff and eat up the required performance? What if they fire after an engine malfunction that is otherwise under control but does not leave the aircraft with much remaining performance? The DH8-300 on a single engine is not exactly a performance wonder without this already. What if the parachute opens without being commanded while the aircraft is over nasty terrain but with landable, flat fields within gliding range? What if the parachute or the rockets fire in an approach at 1.3Vs, even more so when single engine? Also, what happens if the braking rockets fire, but the parachute fails to open?
You see where I am getting at. The desirability of such a system quickly becomes a statistical exercise. How often will such a system be of benefit to the aircraft, and how often will it turn an otherwise controllable and often trained situation into a non-manageable mess ending up in a total loss? If benefit outweighs the risks, it is worth a try. But if it ends up increasing the risks to the aircraft, it is highly undesirable to have such a thing on board.
I did not do the maths behind this. But seeing that a single engine failure on a twin engined airliner is very much within its performance envelope, that there were very few accidents if any where such a system would have saved the day, and such a system weighs more than a few grams and requires massive structural adaptations, new cables, pyrotechnics, controls, a maintenance program and so on, I would not think this to be a worthy addition to an aircraft.
What about Your idea in such a situation? What if the retro rockets fire on a performance-limited takeoff and eat up the required performance? What if they fire after an engine malfunction that is otherwise under control but does not leave the aircraft with much remaining performance? The DH8-300 on a single engine is not exactly a performance wonder without this already. What if the parachute opens without being commanded while the aircraft is over nasty terrain but with landable, flat fields within gliding range? What if the parachute or the rockets fire in an approach at 1.3Vs, even more so when single engine? Also, what happens if the braking rockets fire, but the parachute fails to open?
You see where I am getting at. The desirability of such a system quickly becomes a statistical exercise. How often will such a system be of benefit to the aircraft, and how often will it turn an otherwise controllable and often trained situation into a non-manageable mess ending up in a total loss? If benefit outweighs the risks, it is worth a try. But if it ends up increasing the risks to the aircraft, it is highly undesirable to have such a thing on board.
I did not do the maths behind this. But seeing that a single engine failure on a twin engined airliner is very much within its performance envelope, that there were very few accidents if any where such a system would have saved the day, and such a system weighs more than a few grams and requires massive structural adaptations, new cables, pyrotechnics, controls, a maintenance program and so on, I would not think this to be a worthy addition to an aircraft.
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To follow the theme of TU.144's response:
Beware of the law of unintended consequences.
System failures may present more problems than are solved.
Weight & complexity.
Structural integrity for all the ejectable stowage bay covers for the stuff you want to install.
Never mind the commercial penalty for the additional weight and maintenance burden.
And statistically, I think you are trying to fix a problem that does not exist.
Unfortunately not aviation related, but if you want to save lives, how about an examination of ways to increase survivability of bus transport in SE Asia?
Sorry for the negative response.....
Beware of the law of unintended consequences.
System failures may present more problems than are solved.
Weight & complexity.
Structural integrity for all the ejectable stowage bay covers for the stuff you want to install.
Never mind the commercial penalty for the additional weight and maintenance burden.
And statistically, I think you are trying to fix a problem that does not exist.
Unfortunately not aviation related, but if you want to save lives, how about an examination of ways to increase survivability of bus transport in SE Asia?
Sorry for the negative response.....
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Thanks for the reply TomU and Tu.114 you have both raised very important issues. I shall be quoting bits from both of your posts as you have talked about similar issues.
No system can ever be a 100% fool proof but to reduce the risk of accidental deployment I would look at using mechanical fail safes similar to those that are used to prevent accidental deployment of air brakes, thrust reversers or even emergency doors.
I was wondering if the statistical issues of cost verses benefit of such a system may be over come by offering it to pilots and small airlines that operate in more remote areas of the world, as such a system would have increased value if the routes being flown were over less hospitable terrain?
I'm starting to think that this may be a system that is best aimed at a niche market of customers on a case by case basis as opposed to a roll out for all airlines that operate the aircraft that the system could work for.
Obviously more complexity would increase maintenance costs and also increase the chance that something would go wrong so I am trying to simplify the design to the least amount of critical components that can work in tandem with what ever systems the pilot of the aircraft has command of at the time.
I would debate that, for major airlines an aircraft coming down in a situation where a system like this would be needed is fairly rare. However in the business of small airlines and privately operated aircraft I think this is a more common occurrence that does indeed exist
My main research has been on the categories from 2010 to 2014: List of accidents and incidents involving commercial aircraft - Wikipedia, the free encyclopedia
As an aside a system similar to this was deployed just this Sunday: BBC News - Splashdown as plane runs out of fuel midair near Hawaii
A nice idea, however it's a bit late for me now as i am already committed.
Another little point in addition to those already made: For all of the systems installed, there is a "get out of jail" procedure involved, should it quit or start to work without being called to duty.
Beware of the law of unintended consequences.
System failures may present more problems than are solved.
System failures may present more problems than are solved.
The desirability of such a system quickly becomes a statistical exercise.
I'm starting to think that this may be a system that is best aimed at a niche market of customers on a case by case basis as opposed to a roll out for all airlines that operate the aircraft that the system could work for.
such a system weighs more than a few grams and requires massive structural adaptations, new cables, pyrotechnics, controls, a maintenance program and so on
And statistically, I think you are trying to fix a problem that does not exist.
My main research has been on the categories from 2010 to 2014: List of accidents and incidents involving commercial aircraft - Wikipedia, the free encyclopedia
As an aside a system similar to this was deployed just this Sunday: BBC News - Splashdown as plane runs out of fuel midair near Hawaii
Unfortunately not aviation related, but if you want to save lives, how about an examination of ways to increase survivability of bus transport in SE Asia?
For commercial multi-engine operation, I dare say such a system is not an option. But consider the PC-12 for example. A high performance aircraft that is certified for IFR operations but uses one single engine. In case of a failure of this engine in IMC, a system like Yours might well be worth a thought. Have the pilot reduce speed to a defined minimum to keep the strain on the hooks, chains and parachute as low as possible (allowing them to be built a bit smaller and lighter than if the system was allowed for deployment at Vne) before allowing him to fire it. A big red lever might be installed that will close the normally open connection between the aircraft and the parachute when pulled, and arm the pyrotechnic launching system; this will both add an operational safety layer and allow the parachute to just depart the aircraft in case of inadvertent activation (of course, install it in a position where it does not take out the empennage on its voyage) without too much harm done to the aircrafts flyability.
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I see, that goes along with my thinking, I will have to adjust the project towards single engine commercial/private aircraft I think.
Thank you all for your comments, the analysis and points raised have been very helpful indeed.
Thank you all for your comments, the analysis and points raised have been very helpful indeed.
