Engine failure loss up to 80%

ZombieAutoPilot

New Member
Hello! Well, I am training for my commercial multi engine license! and my instructor asked me: "Why when we lose an engine we lose up to 80% of performance? Shouldn't it be 50% if both engines are the same?"

I know it is not 50-50 because the operative engine will be struggling to maintain the airplane flying.
The operative engine will have to deal with the aerodynamics of the plane, as soon as you correct with rudder to the good engine and bank to that same engine, the longitudinal axis is not parallel to the flightpath and there is a space where the air doesn't produce lift in that part of the wing. So there's one, struggling to produce lift.
When you correct with rudder and aileron, down aileron produces more drag than the up aileron and the rudder will eventually produce drag as well, even if the prop is feathered it still as well producing drag, so theres the second one, drag.
And last since we only have 1 engine thats the one thats the only engine giving us thrust therefore I believe the sum of all those add up to the up to 80% loss of power. What am I missing?

He said that was not good enough, just part of the answer. I tried googling it and couldn't find an answer but this forum (which I found brilliant) so here I am with this question wondering if someone could help me.
Thanks :)


Gone flying-----sky high
 

tgrayson

New Member
None of those drag sources have much to do with the idea of losing 80% of our performance. In actuality, it was the very first thing you mentioned:
I know it is not 50-50 because the operative engine will be struggling to maintain the airplane flying.
Exactly so. Let me repost what I said 5 or 6 threads ago:
If you lost half of your income, how much would your entertainment budget decline? By a lot more than half, I bet. That's because your *entire* entertainment budget depends on your having excess cash over your expenses.

Same thing in an airplane. Pretty much all of the power of one engine is used just to maintain level flight. The other engine contains all the extra power that can be used to climb the airplane. So, when you lose half your engines, you've lost 100% (almost) of your climb ability, which is what they mean when they say performance.
So that's the most important idea to walk away with on the subject. Any increase in drag is incidental. You can't include the sideslip drag, because if you did, you'd probably lose more than 100% of your performance!
 

ZombieAutoPilot

New Member
None of those drag sources have much to do with the idea of losing 80% of our performance. In actuality, it was the very first thing you mentioned:
I know it is not 50-50 because the operative engine will be struggling to maintain the airplane flying.
Exactly so. Let me repost what I said 5 or 6 threads ago:
If you lost half of your income, how much would your entertainment budget decline? By a lot more than half, I bet. That's because your *entire* entertainment budget depends on your having excess cash over your expenses.

Same thing in an airplane. Pretty much all of the power of one engine is used just to maintain level flight. The other engine contains all the extra power that can be used to climb the airplane. So, when you lose half your engines, you've lost 100% (almost) of your climb ability, which is what they mean when they say performance.
So that's the most important idea to walk away with on the subject. Any increase in drag is incidental. You can't include the sideslip drag, because if you did, you'd probably lose more than 100% of your performance!
So.... If I was only flying with 2 operative engines BUT both working at 50% of performance EACH, it means I could not climb? Just cruise? Then why with only 1 engine operative I still have a service ceiling of 7400 ft? (according to the poh) (As far as my understanding of service ceiling goes is when the aircraft can still climb 100ft/min (Ive read 50ft also)) Am I correct with my service ceiling?

Theres no extra income (no extra to climb) but enough money to "live" (enough to cruise)?
Am I getting it right?
:confused:
 

tgrayson

New Member
So.... If I was only flying with 2 operative engines BUT both working at 50% of performance EACH, it means I could not climb?
I was using that as an example, but it will obviously vary per airplane. A twin jet can still climb like a madman single engine. Many of the common light twins publish a climb rate at sea level of about 200 ft per minute. The Seneca's is 190 ft/minute, which, at a gross weight of 4,200 pounds, equates to excess power of about 24 horsepower. Since the BHP of that single engine is 200 hp, it follows that the airplane requires 176 horsepower to maintain level flight at Vyse. Note that this is almost a 90% loss of performance.

Then why with only 1 engine operative I still have a service ceiling of 7400 ft?
See above.


(As far as my understanding of service ceiling goes is when the aircraft can still climb 100ft/min (Ive read 50ft also)) Am I correct with my service ceiling?
Service ceiling SINGLE engine is 50 fpm.

Theres no extra income (no extra to climb) but enough money to "live" (enough to cruise)? Am I getting it right?
There's no guarantee. I'm not sure an Apache will have enough income to live at max gross. ;)
 

Snickersnwa

Well-Known Member
An airplane's climb performance comes from an excess of power.

Just an example here...

Say you have 10 units of power (5 per engine), and you need 4 to maintain your altitude.

With both engines running there's an excess of 6 units of power. If you lose an engine you go from an excess of 6 to an excess of 1 unit of power.

Now, obviously this is a little simplification of things, but it helped me understand by puting some numbers to it (although arbitrary)

Just another way of sayin basically the same thing :)
 

Orange Anchor

New Member
http://forums.jetcareers.com/members/zombieautopilot.html ZAB, The simple way to answer the question is to ask the instructor to cite HIS source and provide you with the information he has.

You will find as you train, some guys pull stuff out of a hat and cite it as gospel and have no source to back them up. For years everyone KNEW if you flew lean of peak it would destroy your engine. Now we find what we KNEW was not true.

Just ask him for his reference and that should open a good discussion.
 

ZombieAutoPilot

New Member
Thank you very much all for your replies, they were very useful and helped me to understand and know that airplanes climb due to excess of power. For cruise it only needs like 30%-40% and the rest 70-60 is for climb. Yet, if we lose an engine we would only have 20-10% of the good engine to climb.
 

mjg407

Well-Known Member
Thrust is lost, but drag is also increased significantly due to asymetric thrust produced by the one engine carrying the entire load.
 

ZombieAutoPilot

New Member
What are you flying?
An F18 with extra large nitrogen cooled afterburners, 22 inch gold enkei rims, low profile michelin tires, leather sit, gold harnesses, tinted electric windows, sony xplod radio 2 sub woofers, 10 speakrs with 4 tweeters, and a pioneer dvd in the backseat, im about to install some hydraulics and lower my plane, took off the misiles for weight reduction oh and a pair of pink velvet dice hanging of my compass, magnetic to keep it old skool.

haha, nah im just flying a cessna 310r 1975(i believe or somewhere around there), doing my commercial checkride in it next week. It has 285HP per engine 3 blade constant speed propeller full feathering.
 

Bashibazouk

New Member
You got some good replies, so mine may be moot, but I'll offer it anyway in case it helps...

One of the things that sucks is that the units used in aviation (knots, HP, ft/min) tends to obscure the underlying physics. If we spoke in self-consistent units, things would leap out at you.

A horsepower is 550 ft-lbs/sec. In other words, if you lift a 550 lb weight at 1 foot per second against gravity (Earth's at sea level :)), you're developing one horsepower worth of power.

Take a 4,400 lb light twin...if you can climb at 1200 ft/min with two engines (i.e. 20 ft/s), you have an excess power of 88,000 ft-lbs/sec. Divide that by 550, and you get the excess power in HP: 160 or roughly one engine's worth.

That's why light twins are such dogs with an engine out. The excess power is now either small or negative. If you fail to clean it up, fly it at Vyse, or reduce the drag due to rudder, sideslip, etc. you have nothing left.
 

tgrayson

New Member
Or he read this book ;)
Nah, just because something is in a book doesn't mean that the typical reader will understand or learn it. Particularly when it involves math.

I was skeptical that Remer's book even addressed aircraft performance, but he does have one problem worked out on page 42 dealing with climb rates and power. I don't think most readers would get it.
 

Bashibazouk

New Member
Pretty talk.:) You must be an engineer.
Yup, 25 years ago I couldn't even spell enganear...now I are one, and I can talk purdy!

I took my AMEL checkride a few months ago. At the end of the oral, the DPE asked "Can you fly as well as you can talk about this stuff?" I replied "You'll let me know in about two hours!"

Cheers,
Martin
 

Bashibazouk

New Member
haha, nah im just flying a cessna 310r 1975(i believe or somewhere around there), doing my commercial checkride in it next week. It has 285HP per engine 3 blade constant speed propeller full feathering.
A 310 has one of the better single-engine ROC for light piston twins. Particularly if you're light, like on a training mission. It only gets worse from there with light twins.
 

av8or91

Well-Known Member
Nah, just because something is in a book doesn't mean that the typical reader will understand or learn it. Particularly when it involves math.

I was skeptical that Remer's book even addressed aircraft performance, but he does have one problem worked out on page 42 dealing with climb rates and power. I don't think most readers would get it.
We were forced to understand it and also work out some problems in my aerodynamics class but yea, for the average person its difficult to understand.
 

tgrayson

New Member
We were forced to understand it and also work out some problems in my aerodynamics class but yea, for the average person its difficult to understand.
That really is critical to understanding, IMO. I made one student calculate the aircraft stall speed using the lift equation, and he whined and complained throughout the process, but once he saw his actual stall speed pop out of the equation, he was delighted. He showed everyone at work how it was done.
 

E_Dawg

Moderator
Well think about it... if you lost all engines you'd be in a glide right?

So losing half your engines means you've just lost half the difference between a max performance climb and an idle power descent.


ie if a full power climb is 1000fpm, idle power descent is 1000fpm... lose an engine and you'll be able to hold altitude... nothing more.
 
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