Would you be interested in some form of back-up propulsion for your piston single? If yes, how much would you be willing to pay for it?

How much would you pay to have a back-up?

  • This is a dumb idea, I'll never want any back-up. Engines are reliable enough.

    Votes: 23 74.2%

  • 10-20% of engine overhaul cost.

    Votes: 0 0.0%

  • 21-30% of engine overhaul cost.

    Votes: 2 6.5%

  • 31-40% of engine overhaul cost.

    Votes: 3 9.7%

  • 41-50% of engine overhaul cost.

    Votes: 2 6.5%

  • 51-75% of engine overhaul cost.

    Votes: 1 3.2%

  • 76-100% of engine overhaul cost.

    Votes: 0 0.0%

  • Even more than what it would take to overhaul the engine, I would really like the added safety.

    Votes: 0 0.0%
  • Total voters
    31
AV8R_87

AV8R_87

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I've been looking at some of the high-profile piston single mishaps caused by some form of powerplant failure not related to lack of fuel (or fuel mismanagement). While there aren't that many of them, the consequences are usually not pretty. This question keeps coming back in my head almost every time, so I wanted to have this conversation with the community and see what your thoughts are.

If there was a way to keep your plane in the air for at least 10 additional minutes, at a useful load penalty of 5-10%, how much (if anything) would you be willing to pay for it? I've decided to make amount a percentage relative to the cost of a factory overhaul for the engine, since that would allow costs to scale with the installed power.
 
AV8R_87 said:
If there was a way to keep your plane in the air for at least 10 additional minutes, at a useful load penalty of 5-10%, how much (if anything) would you be willing to pay for it?
Click to expand...
How do you propose to keep my 3600lb plane aloft for 10 minutes with a weight of 150 lbs? This doesn't exist because of physics, not cost. There's already an expensive backup propulsion system available....it's called a twin.

Now, if a BRS were available for my plane, I'd be very interested.
 
Not enough info. Many attempts to create redundancy result in higher likelihood of failure of the primary due to additional complexity. Increased difficulty of maintenance of critical systems seems likely - which increases likelihood of failure. Etc...

10 minutes of flight? Not going to pay a whole lot for that frankly.
 
Jim K said:
How do you propose to keep my 3600lb plane aloft for 10 minutes with a weight of 150 lbs?
Click to expand...

A concept, probably not practical, would be a much more powerful starter motor and a solenoid that disconnected it from the engine and let it drive the prop, along with a battery with 10 minutes of capacity. That would also buy you a little more time in event of fuel exhaustion. But I’m skeptical such an electric motor and gearing could be made small enough.
 
Jim K said:
How do you propose to keep my 3600lb plane aloft for 10 minutes with a weight of 150 lbs? This doesn't exist because of physics, not cost. There's already an expensive backup propulsion system available....it's called a twin.

Now, if a BRS were available for my plane, I'd be very interested.
Click to expand...
You got a big enough rear door, just get chutes for the whole family.
 
Half Fast said:
A concept, probably not practical, would be a much more powerful starter motor and a solenoid that disconnected it from the engine and let it drive the prop, along with a battery with 10 minutes of capacity. That would also buy you a little more time in event of fuel exhaustion. But I’m skeptical such an electric motor and gearing could be made small enough.
Click to expand...
Let's say you need 50% of the power to keep the plane aloft. A lance is what 300hp? So let's call it 150hp = 112kW. For 10 minutes that's 19kwH with 100% efficiency. Driving an engine and prop with a mechanical system is probably closer to 50% efficient (if that), so you're talking 40kwh battery with no safety factor. That's a BIG MFing battery to carry around with for for a 'just incase', to fly for 10 minutes. Maybe what 800-1000lbs of battery?

Like other said. Physics is the issue. Fly something that lands slow, buy a twin or get BRS. The solutions already exist.
 
Mtns2Skies said:
Let's say you need 50% of the power to keep the plane aloft. A lance is what 300hp? So let's call it 150hp = 112kW. For 10 minutes that's 19kwH with 100% efficiency. Driving an engine and prop with a mechanical system is probably closer to 50% efficient (if that), so you're talking 40kwh battery with no safety factor. That's a BIG MFing battery to carry around with for for a 'just incase', to fly for 10 minutes. Maybe what 800-1000lbs of battery?
Click to expand...

Understood. I felt it wasn't practical (and so stated), so I didn't bother to run any numbers.
 
Jim K said:
This doesn't exist because of physics, not cost.
Click to expand...

Mtns2Skies said:
Physics is the issue.
Click to expand...
www.pbsaerospace.com

PBS TJ100

is designed for experimental aircraft, powered gliders, and other manned and unmanned vehicles.
www.pbsaerospace.com www.pbsaerospace.com
This with its own fuel supply would weigh less than 150lbs and give you 10 mins or more. And plumbing it in the aircraft's fuel supply would give you more. Cost is where it's not going to work.

Salty said:
10 minutes of flight? Not going to pay a whole lot for that frankly.
Click to expand...
Put that in the poll, please. Valid for all other replies.
GeorgeC said:
Backup propulsion for a single is called a twin.
Click to expand...
We see twin pilots getting themselves killed when one engine goes on strike.
Mtns2Skies said:
Let's say you need 50% of the power to keep the plane aloft
Click to expand...
Since 65% power gets you a nice economy cruise in most of them, you'd need less than 50% to go at bucket speed. I'll have to do some research on that, my ballpark was in the 35% range.

Sometimes it takes a bit of out of the box thinking to figure out viable ideas. I'm happy to hear your opinions, but for the poll, assume that solution would exist. Tell me if you'd be interested in it and at what price point, please.
 
Jim K said:
For our next thought experiment...how many moths would it take to keep a 60lb child aloft for 10 minutes...and what would you pay for them? :biggrin:
Click to expand...
100's of helium balloons would be better. don't have to feed them and they pack tight until inflation.
 
AV8R_87 said:
www.pbsaerospace.com

PBS TJ100

is designed for experimental aircraft, powered gliders, and other manned and unmanned vehicles.
www.pbsaerospace.com www.pbsaerospace.com
This with its own fuel supply would weigh less than 150lbs and give you 10 mins or more. Cost is where it's not going to work.


Put that in the poll, please.

We see twin pilots getting themselves killed when one engine goes on strike.

Since 65% power gets you a nice economy cruise in most of them, you'd need less than 50% to go at bucket speed. I'll have to do some research on that, my ballpark was in the 35% range.
Click to expand...
Look at the thrust on that. Ain't gonna cut it for a 3000+lb airplane.

Go try to fly your plane at 35% power. Hint (Economy cruise is your most efficient, any deviations from that and you get less efficient)

And then immediately after that sign up for physics 101.
 
Assuming that the engineering could work: I think the main problem is that most scenarios I can think of where I would want a back-up option wouldn't be helped much by only ten minutes.

But the engineering is hard. I can't think of any way that you are going to be able to pack enough power into 10% of useful. I can't think of anyway to attach that power to the prop. I gotta think that most scenarios where one loses an engine is also going to result in losing the ability to spin the prop using some other power source. The one notable exception being fuel issues.

So, at the end of the day, I'm going to be spending my "half an overhaul" on a BRS. Then, regardless of the terrain I'm over, my odds of survival go up by crazy amounts.
 
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Mtns2Skies said:
Look at the thrust on that. Ain't gonna cut it for a 3000+lb airplane.

Go try to fly your plane at 35% power.

And then immediately after that sign up for physics 101.
Click to expand...

Well, you don't necessarily need to maintain altitude. I mean a second engine only gets you to the crash site quicker, anyway.
Also isn't flying a twin on one engine only using 35% power?
 
rwellner98 said:
Assuming that the engineering could work: I think the main problem is that most scenarios I can think of where I would want a back-up option wouldn't be helped much by only ten minutes.

But the engineering is hard. I gotta think that most scenarios where one loses an engine is also going to result in losing the ability to spin the prop using some other power source. The one notable exception being fuel issues.
Click to expand...
It'd be a whole lot easier to put a 10 gallon reserve tank in for that.
 
I thought that was the reason behind the Cessna 337?
 
Mtns2Skies said:
Let's say you need 50% of the power to keep the plane aloft. A lance is what 300hp? So let's call it 150hp = 112kW. For 10 minutes that's 19kwH with 100% efficiency. Driving an engine and prop with a mechanical system is probably closer to 50% efficient (if that), so you're talking 40kwh battery with no safety factor. That's a BIG MFing battery to carry around with for for a 'just incase', to fly for 10 minutes. Maybe what 800-1000lbs of battery?
Click to expand...
Closer to 400 lbs for current EV battery tech, but the point is valid that the weight probably isn't anywhere near justified by the benefit.

BTW, this is the reason that we don't see battery-powered aircraft being pursued in the same manner as EVs. The energy density of battery storage is still ~6-7x less than that of hydrocarbon fuels.
 
Are we talking a potential bomb, like a RATO unit? Scratching my head on this one.
 
Mtns2Skies said:
Look at the thrust on that. Ain't gonna cut it for a 3000+lb airplane.

Go try to fly your plane at 35% power. Hint (Economy cruise is your most efficient, any deviations from that and you get less efficient)

And then immediately after that sign up for physics 101.
Click to expand...
It will fly a 1000-lb plane at 210 kts, in this application it needs to keep you in the air at 80kts or so. That's a lot less drag to overcome.
I see about 9gph at 75% power, but I can keep it airborne at bucket speed for about half the fuel flow.
 
RyanShort1 said:
Are we talking a potential bomb, like a RATO unit?
Click to expand...
No. For a multitude of reasons, one of which, as correctly pointed out, is that you wouldn't get the required power for the required time for the kind of weight we're talking about.
 
So giant helium ballon?

Like caps but keeps you in the air till it all leaks out?
 
AV8R_87 said:
Sometimes it takes a bit of out of the box thinking to figure out viable ideas. I'm happy to hear your opinions, but for the poll, assume that solution would exist. Tell me if you'd be interested in it and at what price point, please.
Click to expand...
The "price point" is not the only critical metric, and may not even be the most important.

1) What is the payload penalty? How does that payload penalty compare to something like CAPS?
2) What is the size? Does the installation increase drag?
3) What does the weight of the system do to aircraft performance? Take-off roll? Climb rate? Ceiling? Fuel consumption? Cruise speed?
4) What is the maintenance interval and average annual cost?
5) What is the reliability of the backup system? What is the risk of a Fukushima-style event where the failure of the backup system results in an even worse final outcome?
6) Does the system require additional pre-flight inspection or prep (like fueling, charging, arming, testing, etc.?)
7) Can the system readily be retrofitted to existing aircraft, or is it a new-build-only option?
 
Salty said:
It'd be a whole lot easier to put a 10 gallon reserve tank in for that.
Click to expand...
His design criteria specifically excludes fuel issues. It's centered around the engine itself failing.
 
AV8R_87 said:
www.pbsaerospace.com

PBS TJ100

is designed for experimental aircraft, powered gliders, and other manned and unmanned vehicles.
www.pbsaerospace.com www.pbsaerospace.com
This with its own fuel supply would weigh less than 150lbs and give you 10 mins or more. And plumbing it in the aircraft's fuel supply would give you more. Cost is where it's not going to work.


Put that in the poll, please. Valid for all other replies.

We see twin pilots getting themselves killed when one engine goes on strike.

Since 65% power gets you a nice economy cruise in most of them, you'd need less than 50% to go at bucket speed. I'll have to do some research on that, my ballpark was in the 35% range.

Sometimes it takes a bit of out of the box thinking to figure out viable ideas. I'm happy to hear your opinions, but for the poll, assume that solution would exist. Tell me if you'd be interested in it and at what price point, please.
Click to expand...
It's hard to convert between thrust and HP, but the equation I found suggests you'd need 450lb to maintain level flight at best glide speed, so you'd need two of those engines. They don't appear to run on avgas, so they'd need their own fuel supply. Total package for 10min of flight time comes in around 160 lb by my math, so you're right there. Impressive little motors. Each motor runs around $70K, so we're probably looking at buying the airplane again to get it done. For that kind of money I could have a really nice twin and some money left over to feed it.

I go out of my way to avoid situations that i don't think I'll have any options to put it on the ground. I'd say I have about 30 min. of my 772 hours where I would've been completely screwed if the engine quit. I have 29 hours of night time, which I would give about 50/50 odds of surviving, which is why I avoid that too. Takeoffs are the tricky one, as the Richard McSpadden crash graphically illustrated. Even twins struggle there though. A twin jet is the only way to solve that problem (and those still crash too....).

The crash in Nashville is an example of one that probably would've been survivable if the pilot had lined up with the interstate....or not flown away from the airport. I think we'll probably find out that one was fuel mismanagement in the first place. True engine failures are pretty rare and very survivable if the pilot does their part....which is easier said than done of course.
 
May I be the first to suggest taking that extra money and putting it into additional training to either avoid or be better prepared to handle these situations? It might not prevent crashing 100% of the time, but I'd give it better than 50/50 odds it would increase the survival rate and reduce the accident rate.
 
StraightnLevel said:
The "price point" is not the only critical metric, and may not even be the most important.

1) What is the payload penalty? How does that payload penalty compare to something like CAPS?
2) What is the size? Does the installation increase drag?
3) What does the weight of the system do to aircraft performance? Take-off roll? Climb rate? Ceiling? Fuel consumption? Cruise speed?
4) What is the maintenance interval and average annual cost?
5) What is the reliability of the backup system? What is the risk of a Fukushima-style event where the failure of the backup system results in an even worse final outcome?
6) Does the system require additional pre-flight inspection or prep (like fueling, charging, arming, testing, etc.?)
7) Can the system readily be retrofitted to existing aircraft, or is it a new-build-only option?
Click to expand...
Valid questions. First one sort of answered in the opening post, "at a useful load penalty of 5-10%".
The other questions, there will be a drag penalty, with the aim of minimizing it, but there's no such thing as a free lunch. Of course there's additional maintenance. Key point will be minimizing additional impact, it's obvious that if it adds 100% to your maintenance cost interest would be significantly lower or non-existent.
Retrofittable to existing airframes.

rwellner98 said:
His design criteria specifically excludes fuel issues. It's centered around the engine itself failing.
Click to expand...
Yes, if you're out of fuel it's all your fault. There could be an option to use existing fuel, but that's more of a plan B to extend airborne time, that might introduce additional complications and cost. Hence the 10-minute limit for now.
Jim K said:
It's hard to convert between thrust and HP, but the equation I found suggests you'd need 450lb to maintain level flight at best glide speed
Click to expand...
Agreed, not a lot of information out there. My napkin numbers for a typical 172/PA-28 were about 250lbs at best glide. I'm really curious what the real-life numbers are. Hmm, is attaching strain gages to the engine mount a minor alteration? (save this for another thread)

Jim K said:
They don't appear to run on avgas, so they'd need their own fuel supply.
Click to expand...
Most turbine engines can usually handle avgas for emergency use. Lead deposits are the limiting factor. I'd think for emergency use they could probably use the aircraft's fuel supply, but that might introduce additional complications not worth the effort.
 
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Mtns2Skies said:
That's a BIG MFing battery to carry around with for for a 'just incase', to fly for 10 minutes. Maybe what 800-1000lbs of battery?
Click to expand...
Well, the technology WOULD save your family's lives in the event of an engine failure.

Because your family would have been left behind safely on the ground, so that you could use your available useful load to carry the batteries.
 
AV8R_87 said:
There could be an option to use existing fuel,
Click to expand...
Your engine doesn't run on 100LL. Which introduces another issue. The odds of misfueling go up pretty high if you carry multiple types of fuel.
 
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