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Lear 45 APU


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I fly the Lear 45 in FSX. There is a very rudimentary APU. All it does is provide power, no bleed air or anything like that. I don't see anywhere on the back of the plane where the APU would be located at. I think perhpas it's aft and below in the belly of the aircraft. Is that correct in real life?

 

Also. I can't remember what the minimum safe altitude it was that you can engage the APU if you needed power. I thought it was anywhere from 15,000 to 10,000.

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IIRC the LJ45 APU is not approved for inflight use, ground only.

 

Also, the TFE731 engines have electrical starters, not air.

 

The APU, which is optional by the way, is a convenience item to make life easier for ops where a ground cart might not be available.

 

You can do a battery start though there are temp limits and, IIRC, you have to wait for the battery to recharge before starting the second engine. This would not be simulated in FSX.

 

The TFE731 engines can air start up to 35,000, I think, so if you had a flameout above that you would have to descend before attempting to restart.

 

peace,

the Bean

WWOD---What Would Opa Do? Farewell, my freind (sp)

 

Never argue with idiots.

They drag you down to their level and beat you with experience

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IIRC the LJ45 APU is not approved for inflight use, ground only.

 

Also, the TFE31 engines have electrical starters, not air.

 

The APU, which is optional by the way, is a convenience item to make life easier for ops where a ground cart might not be available.

 

You can do a battery start though there are temp limits and, IIRC, you have to wait for the battery to recharge before starting the second engine. This would not be simulated in FSX.

 

The TFE31 engines can air start up to 35,000, I think, so if you had a flameout above that you would have to descend before attempting to restart.

 

peace,

the Bean

 

Thanks for your answer.

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By the same token, some planes don't windmill fast enough for an airstart in level flight anyway. Some, you have to descend to get it spinning fast enough to start. Or, I guess, be going fast at a relatively low level to get the thicker air to spin the engine fast enough.

I'd wager the POH or whatever, will give the details.

About the only planes I fly are military, and they either have 2 engines, so crossbleed is a viable way to do a start, or, for single engine jobs, they often need to be in a dive, relatively shallow, but a dive none-the-less, to get enough airspeed to get it to start.

All this is presuming the engine WILL restart anyway. It stopped running for a reason, after all. Compressor stall, dust from a volcano, bird strike, whatever. Any reason the engine stops, unless you stop it by cutting off it's fuel, may be enough to keep it from restarting, after all. Might be a good idea to figure out what stopped it, before you try to start it again, unless you REALLY need it running. Like the other engine quits too, for whatever reason.

A lot, if not most, multi-engined aircraft will fly adequately with one engine out, even ones with only 2 engines. I am pretty sure that applies to prop jobs as well as jets. You may need to dump some fuel, cargo, or passengers, if you're a really not-nice person :D

 

Have fun, however many you're flying on!

Pat☺

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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  • 2 weeks later...
A lot, if not most, multi-engined aircraft will fly adequately with one engine out, even ones with only 2 engines. I am pretty sure that applies to prop jobs as well as jets.

Unfortunately, if "flying adequately" involves maintaining altitude, it doesn't apply to GA aircraft certification for which the criteria is maintaining directional control after loosing an engine.

For this reason, a lot of people believe that a twin-engine plane is safer. It is not: the second engine is for performance (range, speed, load...) but not for redundancy. It can go all the way down to the ground as long as it goes straight.

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It is not unusual for small core turbine engines to have electric start vice "air impingement" starters (a type of turbine in its own right, geared to the engine itself). It allows battery start in many cases, or only a generic start cart vice a more rare air cart. However, larger jet engines with high rotational inertia and start rotation speeds would need a very big, heavy electric starter. Everything is a tradeoff.
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Unfortunately, if "flying adequately" involves maintaining altitude, it doesn't apply to GA aircraft certification for which the criteria is maintaining directional control after loosing an engine.

For this reason, a lot of people believe that a twin-engine plane is safer. It is not: the second engine is for performance (range, speed, load...) but not for redundancy. It can go all the way down to the ground as long as it goes straight.

 

 

True, up to a point. On some twins, if they're lightly loaded and you're not too high, you might get better than 500 fpm climb at blue line with one dead. I once had a Grumman American Cougar (twin 160 hp engines) doing 300+ fpm at 11,000 feet with one caged, and we had two on board and a little over half fuel. I've had both a Baron and an Aztec do that at 7K, or so (during training, of course).

 

So there actually is such a thing as a single engine service ceiling, but it might be as low as 2,000 feet density altitude on some birds under some conditions.

 

Of course, as spock says, the light twins don't have the same kind of requirements as the jets, or even as commercial airliners of the piston variety, but they may well get you to the nearest airport, if the conditions (weight, density altitude, etc.) are right, AND if you're sharp enough to maintain control after the engine loss.

 

Larry N.

As Skylab would say:

Remember: Aviation is NOT an exact Science!

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I was always under the assumption that since a 747 can fly with one engine, then if I ever bought an aircraft I'd want a King Air due to the cruise height, turbo props and you have two engines, one to fall back on in case one goes out.

 

So now reading all this, my assumption on if I were in a King Air, say FL25 and one engine goes out I'm gliding that thing down? The other engine won't provide any thrust at all given the conditions?

 

I also know that you could fly a B-17 from LAX to PHNL and just use two engines. That was what a former firefighter A/C pilot did in the sim. So I assume the B-17 could cruise with just two engines rather than all four. Granted if all except one goes out perhaps that will be a different story.

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my assumption on if I were in a King Air, say FL25 and one engine goes out I'm gliding that thing down?

 

A King Air is not a light twin, nor does it have piston engines. While it may not have the oomph of a jet, it's still pretty good. Spock and I were talking about light twins, such as the Baron, Twin Comanche, Aztec, etc.

 

Larry N.

As Skylab would say:

Remember: Aviation is NOT an exact Science!

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I also know that you could fly a B-17 from LAX to PHNL and just use two engines. That was what a former firefighter A/C pilot did in the sim. So I assume the B-17 could cruise with just two engines rather than all four. Granted if all except one goes out perhaps that will be a different story.

I know that P-3's on long patrols will often feather one engine as a fuel saving measure. Nothing so useless as fuel in the tanker. Better to have a bit more fuel than you need in your tanks than not enough. Of course they do tend to fly pretty low on patrols, so 3 engines are usually plenty enough.

I'm pretty sure C-130's can get away with doing that as well. Depending on how much weight they're carrying, and how much fuel they need as opposed to how much they've got in their tanks, and so on. I think that was a popular method on AC-130's, asked to stay on station longer than expected due to enemy action.

It's well recorded that B-17's would bring their crews back on 2, or even 1 engine, presuming they lighted them up as much as possible. Got rid of the bombs, machine guns, oxygen tanks, etc etc. But they would make it. Sometimes. A lot depended on how much other damage the plane had taken, adding to it's drag. But some pretty shot up planes, and crews, made it back, if not to their home base, then at least to England someplace.

 

Have fun, however many engines you fly on :D

Pat☺

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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Wrong assumption. Why shouldn't the other engine provide full power?

BTW, FL25 is really low as it's only 2500ft ;)

 

I wouldn't disregard this assumption: flying full power might damage the turbine. In other words, you might not be able to fly with maximum power for a long time (we would need the King Air POH to confirm it).

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That's new to me. Furthermore more engines means more drag, so more engines are decreasing range.

Even very low performance twins like the PA44 can maintain 4000ft at MTOW at ISA conditions.

NO plane can maintain it's 2eng cruising altitude with OEI. Hence they all have a drift down procedures.

Even in the worst case you can cover a much higher distance with one engine than with no engine.

 

Edit based on reply from bbrz (#20): Please disregard the sections in blue:

[i am not sure to follow you on this. I think that the calculation is a bit more complex. I agree that more engine is more drag from a design point of view. Nonetheless, shutting down an engine doesn't make it disappear.

Moreover, back on a twin, when 1 engine is out, you have to rise the dead engine wing (5 degrees on a Beech Duchess for example) and fly the plane in a crab angle maintain direction. As a result, the drag increases.]

 

The flying principles of the single engine are explained page 23 of the attached document from the FAA:

https://www.faasafety.gov/files/gslac/courses/content/30/248/FAA-H-8083-3a%20Chapter%2012.pdf

 

[Additionally, by descending from your optimum flight level, you are significantly reducing your range: at 50 tons, in ISA conditions, you will get, for an Airbus A320:

- at FL390 with both engines: 238 NM/ 1000kg

- at FL200 with 1 engine inoperative: 181 NM/ 1000kg.

You may argue that, in the second case, 1 engine isn't consuming fuel. That's if there is no fuel leak (another assumption)...]

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