kaddyuk
Posts: 3697
Joined: Thu Nov 08, 2001 1:04 am

Tri Jets

Wed Apr 10, 2002 5:58 am

Does anyone know if it is possible for a Tri Jet (MD11, DC-10, L1011) to run on the engine in the tail, or will it plummet to the ground if it was tried?

Whoever said "laughter is the best medicine" never had Gonorrhea
 
ThirtyEcho
Posts: 1409
Joined: Tue Jan 01, 2002 1:21 am

RE: Tri Jets

Wed Apr 10, 2002 6:08 am

Yo, Kaddyuk, you've been watching too many 1930s-era airplane movies. No airplane plummets to the ground with the engines off unless Errol Flynn is flying it. How much thrust do you think the engines are putting out as an aiplane makes a normal descent?
 
kaddyuk
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Joined: Thu Nov 08, 2001 1:04 am

RE: Tri Jets

Wed Apr 10, 2002 6:38 am

I know it wont "plummet" straight away, but if you turn both engines off on a 777 it will crash eventually
Whoever said "laughter is the best medicine" never had Gonorrhea
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Tri Jets

Wed Apr 10, 2002 7:29 am

Sure it's possbile, but under what conditions? Defining them is crucial...

Let's see...the books says a 727-200Adv, jt8d-7, Std OAT, 1 pack, no anti ice, clean, max cont epr. I'll give 2 points of a straight line curve, max alt (y axis) vs gross weight (x axis):

12000 ft at 110000 lbs to 2000 ft at 145000lbs

for a -15 powered a/c, same parameters

16000 ft at 110000 lbs to 2000 ft at 162500

Interpolate to find intermediate values...
So, yes, it's possible to fly on 1 engine.

Cheers
 
AA737-823
Posts: 4905
Joined: Wed Mar 01, 2000 11:10 am

RE: Tri Jets

Wed Apr 10, 2002 12:39 pm

What the hell just happened here?

I saw it coming... I saw it here... I saw it fly by STRAIGHT OVER MY HEAD and though, "geez, what was that?"

Interpolate this.

 Smile
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Tri Jets

Wed Apr 10, 2002 1:13 pm

OK - I'm bored tonight.

It's a linear relationship...

1. draw the x axis going from 0 to 200000 lbs, marked every 5000 lbs
2. draw the y axis going from 0 to, say, 20000 ft in 1000 ft increments.
3. the result is a graph w/ 40 units in the x axis, and 20 units in the y axis.
4. plot (for the jt8d-7) the points (110000, 12000) and (145000, 2000).
5. we're talking about a linear relationship, so determine the slope (delta y/delta x, which = 10000/-35000)
6. so the slope = -.2857. (common sense check, negative slope means the alt capability decreases as the weight increases, so that's good)
7. use the point slope formula. (y-y1)=m (x-x1)
8. (y-12000) = -.2857(x-110000)
9. solve for y
10. y= -.2857x + 43427
11. plug in x=145000 to check the math, should be 2000.
12. 2000.5. close enough (rounding errors)
13. So for any weight b/t 110,000 lbs (about as light as a functional 727-200adv can be) and 200,000 lbs, plug it in for x, and the equation in item 10 above spits out the altitude a -7 powered a/c can maintain w/ the prescribed limitations.
14. remember algebra????????


cheers-
 
rizzes
Posts: 5
Joined: Thu Dec 07, 2000 2:12 pm

RE: Tri Jets

Wed Apr 10, 2002 1:26 pm

While not a tri jet, there was a A330 that landed in the Azores last year without any power. According to a "Dateline" report last week, all fuel had leaked out of the aircraft and flew without power for 20-25 minutes to land successfully with minor injuries.

A quiet ride from 35,000 feet to sea level without power.
 
chdmcmanus
Posts: 372
Joined: Wed Mar 21, 2001 12:53 am

RE: Tri Jets

Thu Apr 11, 2002 12:08 am

This is a post from about 2 weeks ago…

http://www.airliners.net/discussions/tech_ops/read.main/35763/

As for the -10, yes. You have to get your GW down to around 380 or below. Above that the acft will not level off. For Single engine ops you perform a driftdown and either land or set up a cruise-climb Spec Range profile to make the closest airplane patch and land. If the Acft is light on cargo/pax, its no problem, just dump gas to performance mins and go. If you have cargo/pax (high ZFW) it gets tricky (The pax seem to object to being jettisoned). The acft handles acceptably in a clean config, and can handle around 22/ext on the Flaps/Slats, but once you get the gear down you are committed to landing. The apu is available to assist with Pneu/AC and elec but depending on why the 2 engines failed the hydraulics may get a little sluggish.

Regards,
ChD
"Never trust a clean Crew Chief"
 
kaddyuk
Posts: 3697
Joined: Thu Nov 08, 2001 1:04 am

RE: Tri Jets

Thu Apr 11, 2002 12:21 am

I wasnt really talkin about a glide slope to stay in the air,
A B747 Can FLY (ie:Not a lifethreatening emergency) run with 2 engines. Can a Tri Jet SAFELY maintain altitude and continue to fly SAFELY?

Whoever said "laughter is the best medicine" never had Gonorrhea
 
EssentialPowr
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

RE: Tri Jets

Thu Apr 11, 2002 12:46 am

What do you mean by "Safely"? Getting to the first available airport and landing uneventfully?

A trijet was designed to fly on 3 engines. If 2 engines are taken out of the equation, the a/c has been hugely impacted from a performance standpoint, which cuts redundancy and impacts safety greatly, but the overall anwser is, a trijet can fly on 1 engine depending upon the specific details such as weight, density alt, etc.....Got it???
 
chdmcmanus
Posts: 372
Joined: Wed Mar 21, 2001 12:53 am

RE: Tri Jets

Thu Apr 11, 2002 12:46 am

What EssentialPowr and myself have been saying; it depends upon weight. If the GW is low enough, yes, the acft will naturally settle into its altitude based on thrust (aka "Driftdown"). If the weight is above the thrust capabilities, the acft will simply descend until alt is 0 (that's bad). Effectively, you only have one method of reducing weight in an emergency, dispensing fuel. If the route of flight is over land with plenty of options, you dump to your weight capabilities and land at the first available cement strip. If you are over water or an area with no available airfields, you compute the amount of fuel required to a destination, add that to the ZFW, and dump to this limit (aka performance limit). If this weight is still above the thrust/altitude capabilities, you will be forced to ditch or emergency land. In this case you dump to the thrust/alt limit and fly it as close to civilization as possible, then perform a planned ditch/emerg landing.

Regards,
ChD
"Never trust a clean Crew Chief"
 
kaddyuk
Posts: 3697
Joined: Thu Nov 08, 2001 1:04 am

RE: Tri Jets

Thu Apr 11, 2002 7:13 am

OK, Thanx
All comments have been most helpful
Whoever said "laughter is the best medicine" never had Gonorrhea
 
ben
Posts: 1369
Joined: Fri Aug 06, 1999 9:27 pm

RE: Tri Jets

Thu Apr 11, 2002 9:32 pm

Part of the design specifications for the Tupolev Tu-154 was the requirement to be able to take-off with only 2 engines operational, and be able to fly straight and level (indefinitely) with only 1 engine working.... but that is an aircraft with a high thrust to weight ratio anyway.

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