Misc. Qs about Airplanes

Airplanes are such a "waste of fuel"... I hope they design more efficient airplanes...

or at least get rid of the "dumping fuel" procedure...

So...I'm guess airplanes in the future will never get much faster than mach 2 since a little increase in speed will led to a drammatic increase in fuel burn?

...unless we find a way to fully take advantage of the Sun's energies...

but still, it's just not worth it...

Lucien,

The Dornier Do-X had 12 engines...!



However, that wasn't even close enough for the massive airplane-cum-liner... It could only skim over the waves, and that's with the added bonus of the 'Wing-in-Ground' effect... It was, in effect, a very early Ekranoplane...

The Caspian Sea Monster, also a Ekranoplane, had 10 jet engines, each developping about 26,000 pounds of thrust allowing this massive machine (quite longer than a Jumbo jet, with a hull of over 90 meters long, and a max weight of 544 tons -that's bigger than a Jumbo too at 393 tons! -) to glide at just a few feet over the surface of the water... Each of the four engines of a Jumbo (747-400) developps at least 57,000 of thrust.

I spent 4 years in college learning some of this stuff and who knows how many hours of my life learning on my own, so I hope I am right on most of my conclusions below...

QUOTE: Originally posted by hou_ge2000 If a commercial jetliner at cruising alt or speed suddenly run out of fuel or had all engines fail, does it automatically implies death to all passengers?

This has happened several times and most made succesful landings. One was a 777 over the mid Atlantic. Fortunately they were able to glide something like 100 miles to the USAF base in the Azores. Airliners are pretty good glider... it makes them very efficient which equals $$$.

QUOTE: Originally posted by djmodels1999 I thought most modern aircraft could not glide well at all: F-16, F-22, Rafale, Typhoon, Su-27,... They are designed as 'unstable' aircraft, no?

Yes, modern fighters are unstable, but that has nothing to do with how well they glide. However, fighters usually have very short stubby wings to give them high roll rates. Unfortunately, short wings are not very efficient and hence they do not glide well. I believe they have glide ratios of about 5-10:1(every foot you drop, you travel 5-10 feet horizontally). As mentioned before, airliners are in the 10-20:1 range. Still, it's better than the Space Shuttle which I have hear describes as having the aerodynamics of a dump truck! But there have been occasions where fighters have lost engine power and been able to glide back to base. I actually found a video somewhere on the net from just such a situation. An F-16 lost his engine and was able to glide to a perfect landing.

QUOTE: Originally posted by hou_ge2000 Airplanes are such a "waste of fuel"... I hope they design more efficient airplanes... or at least get rid of the "dumping fuel" procedure...

Aerospace is all about weight and most modern airplanes are designed with landing gear to handle an aircraft landing with most of its fuel already used up. If they designed them to handle the full takeoff weight, then they would have to weight a lot more. So the reason most aircraft have a fuel dump option is to reduce the weight of the aircraft in the event it must land before enough fuel has been expended. It also reduces the amount of fuel to catch fire in the event that an emergency landing turns into a crash landing. No, I think we still need that fuel dumping option. However, Boeing is working to make its next generation of airlines much more efficient and engine technology has made huge improvements in efficiency and cleanliness over the last few decades.

QUOTE: Originally posted by shrikes QUOTE: Originally posted by djmodels1999 I thought most modern aircraft could not glide well at all: F-16, F-22, Rafale, Typhoon, Su-27,... They are designed as 'unstable' aircraft, no? what i hear that is bad for most modern fighters is total power loss. there aren't many analog back-up instruments on most western fighters. (unlike the russians who looove them dials and needles).

It is true that a total power failure in a modern fighter is bad, but not because they don't have analog backups. Actually, the F-22 (almost exclusively computer controlled and operated) has 3 back-ups (not sure, but I think they are altimeter, airspeed and compass). The problem go back to the stability of modern fighters. They are designed to be unstable to make them maneuverable, but that means a human can not react fast enough to control, and hence they use computers. If your computer goes out, then you can't control the airplane and it starts to fly out of control....that is about when you pull that yellow and white handle and enjoy the ride. [:0] I actually recall that happening out here in Colorado several years ago. A Colorado ANG F-16 pilot bailed out without giving any radio warnings that he was in trouble. I guess he decided that his time was better spent getting out of an unstable airplane than trying to let controllers know that he lost power.

Hope that helps answer some questions!

Thanks, Caine.

To the last original question, I saw Fat Albert, the Blue Angles C-130, do a rocket assist takeoff and start a brush fire near the runway.

If you never pressurize the aircraft you can never loose it! Long live the T-37! I spent 5 years as a crewchief on FB-111's at Pease AFB, NH. I heard stories of an F-111F that hit 3.2. In the Vark speed was life, the "F's" had the big motors so it's not too far out on the fringe. My experience with the KC-135 was that it had a great glide ratio as well. the R model could fly on one engine (up to 200,000 lbs GW)

Jim

"In a jet without hardpoints, knowledge is our only weapon."

Caine, FYI that mid - atlantic glider was an Air Transat Airbus 330.
The incident was caused by a fuel leak and made worse by bad fuel management and
poor crew co-ordination.
Damage was caused to the airframe on landing by incorrect flap selection by the crew.
It will take more than a few hull losses to get flight engineers reinstated.
Computers still can't beat a pair of trained eyes and a brain.
Pilots can do the flying, but they do not have the experience of an engineer and they can have all the information in the world, dut if they do not have the experience to back it up, its all useless.
Airlines have been relatively lucky so far, but it cant last forever.

Fuel efficiency in modern airliners, especially the Airbus models, is mainly because of better wing and engine design.
The BAC111 of the 1960's burned 3 Tonnes of fuel per hour (104 seat) compared to the
1980's 737-300's 3.1 tonnes (145 seats), the 737 is considerably heavier than the 111(17 tonnes MTOW if I remember correctly) - figures subject to fuzzy memory !
The old airbus A340 was powered by practically the same engine core as the B737-300
but can transport 300+ people over greater distance with better fuel efficiency than any other airliner of its time (early 1990's), although its rate of climb sucks big time!
The new -600 airbus is currently the longest airliner in the world with more powerful engines and can cruise forever.

I have been told that the Airbus A330 and A340's do not have fuel dumping capabilities because they can land at MTOW ( emergency services dont have ladders that reach that high and time spent dumping fuel can give a small situation time to snowball.

Urban legend has it that a lightning (UK) hit M3, but I suspect that it would have run out of fuel not long after that.

Its amazing that the best aircraft to supercruise was an airliner (payload/speed/range).
unsing adapted bomber engines (RR Olympus that flew on the Vulcan)
The strange thing is that if Concorde had to fly it subsonic speed at 30000 ft it probably wouldnt make it across the pond, it had to fly high and fast to get the range.
Last year I was listening to a BA conc talking to BA Ops about an engine problem, she couldnt make speed/altitude.
First it could make London, then they recalculated ten minutes later the destination changed to Cardiff, and got progressively worse until it looked like a Shannon landing, a difference of about 360 miles.
In the end their luck held and the made it to Shannon, and only just - not much west of here for a few thousand miles.

For the record:
The SR-71 has been retired by both the USAF and NASA. BTW, it set another coast to coast record (the record it set when it first came operational) during it's latest retirement.
The F-22 is NOT mach 3 capable. It does however have excellent supercruise capability.
The MIG-25 is mach 3 capable but for short duarations and it is unstable.
And as a guy who flys various taildraggers up here in Alaska, the supercub (PA-18) Citabria, Champ, and others use brakes and prop blast across the rudder during ground taxi. Sometimes its like a dance using a blast from the prop, rudder and differential brake control to maneuver around some of the various bush strips up here. I love to take guys up with me who have a bazzilion hours from the lower 48. I fly them up to a ridgeline up above the treeline in the mountains and say "lets have lunch". When they say "where's the airstrip" I point to the ridge and they tighten up their harness.
Anyway, that's all I've got on the subject...
Salbando

I have to take exception to the statement that the glide ratio of most jet airliners is better
than most gliders. I am a glider pilot as well as being licenced for powered aircraft.
The gliders (sailplanes) that I fly have a lift to drag ratio of 55 to 1. That's 55 feet forward
for every foot down. No jet airliner comes anywhere near that L/D ratio. However, if it flies, it will glide. The question is "how well will it glide. A rule of thumb for powered aircraft is gliding distance is one half the distance from the engine failure point to the nearest runway.
Ray

As far as fighter aircraft not having backup systems, yes they do. They have emergency generators to provide electrical power if the primary goes off line. They also have emergency back up hydraulic pumps to provide hydraulic pressure to the primary flight controls in case of a hydraulic failure. The F-16 can still fly with the engine shut down, but not for long.

Some aircraft have an onboard JFS (jet fuel starter), APU, (auxillary power unit) or RAT (ram air turbine), that supply electrical or hydraulic power in a emergency. If they aren't too far from a landing site, they can make an emergency landing.

A complete squadron of F-4E' were deploying to Germany from the US, for an exercise. One aircraft had a single engine failure, loss of utility hydraulic pressure, one primary hydraulic system failure, and loss of electrical power. Operating on only one primary hydraulic pump and battery power he was towed by a KC-135 over four hundred miles to a safe landing in Iceland.

modern jet fighters are unstable by virtue of their role. thats why they have multiple Fly by wire systems, allowing multiple corrections per second something impossible from a manually operation. That is they cannot fly without their computers.
Agree on gliders, a jetliner can not go anywhere near them by a factor of 2 at least.
There are many examples of decompression accidents, but most of them is the result of terrorist action rather than bolt failure.

Well, I think all the original questions have been discussed enough. I have a few that I think would be interesting so see some answers for.

What if a multiengine prop lost an engine and feathering?

What is the point of prop sync?

Do you think it is possible to survive a trip through a jet turbine engine?

What is the survivablility rate of flying a single prop through a flock of seagulls?

See a lot of very good answers, makes me not have to write as much. LOL All of which i have to totally agree on.

Bee17,

When I first was hired by the airlines I flew the EMB-120 Brasilia (30 passenger turbo-prop). I can tell you from flying that aircraft that if you cannot feather a failed prop (on this aircraft) you will have your hands full. The diameter of the prop (close to 8 feet, not sure of the exact distance) unfeathered created a lot of drag. The worst time for this to happen would be after V1 on takeoff.

The worst thing that could happen to the propeller system on the EMB-120 was for it to overspeed, which basically meant that the prop would go into flat pitch, which is like putting a big piece of plywood out there (huge amounts of drag). When we used to practice this in the sim it was very difficult to recover from and for the most part depending on the severity you could not recover from it. I know that my airline had an accident in a EMB-120 in which one of the props went into and overspeed condition while the crew was turning base to final and from what I understand they did not have time to react. The aircraft went straight into the ground.

Again this is my experience on the EMB-120, I am not sure about how other turbo props would react in this condition. A piston twin on the other hand, as far as feathering goes, many factors go into what would happen. To keep a long story short, if you cannot get a prop into feather on a piston twin and it is hot and you are heavy you might, depending again on the type of piston twin that you are flying, want to start looking for a place to land and hope that you are not in mountainous terrain when it happens. A good example of this would be the Piper Apache.

I do miss flying piston aircraft for fun. I do not miss flying the EMB-120 though and when the opportunity came up for me to move up to jets I couldn't get out of that turbo prop fast enough.

Now being a captain on a jet is great. If we lose an engine, as long as it has not exploded or caught on fire it is not even considered an emergency. We fly the airplane and pull out the checklist.

Hope this helps.
Steve

I think jetav8r covered the loss of prop scenario well enough and I have not heard of "prop sync" before but as for travelling through a jet engine... I can't think of any possible way you could make it though in one peice. There have been instances where ground crew have been sucked into engines and I don't think any have made it out the other side. I can't say for certain but you would either be pinned to the compressor blades or , more likely, be sliced up by those blades moving at high speed. There just isn't enough room between the blades for anything bigger than a large insect to get through. Not to mention the combustor section and the turbine coming out the back. Even if you went through the fan section of a turbofan engine I still don't think you could fit between the fan blades. I think NOVA had a show on the 777 and showed test footage of chickens being shot at the engines... lets just say they turned into chicken nuggets pretty quick.

Unless you were as lucky as that one Navy guy who got caught on a probe just short of the compressor blades on an A-6, then I think you would not have a good day trying to make your way through a jet engine!

Well, I didn't think you could survive a trip through, but I saw a guy on tv (he was on because he went missing shortly after this incident) what was stationed as ground crew on a carrier, and while a plane was warming up he got pulled in. I don't know much more than that, other than that he did somehow survive. I think maybe since the aircraft was just warming up and the pilot saw the incident and had quick reaction time he hit the compressor blades and when the pilot cut throttle he probably stopped then and waited for someone to pull him out. He wasn't in good shape though, i can tell you that. :)

I haven't heard of prop sync on real aircraft either, but a couple of them on one of my simulators (Microsoft flight sim. 2003 pro edition) have it, its a little toggle and a small dial that resembles a spinning prop, but the hub moves around until you hit the toggle, then it "equalizes". I think it has something to do with equalizing the engine torgue to help keep the twin turbo props easier to control. ??????

If I remember correctly about prop sync, its purpose is to "slave" one prop RPM to the other. I believe that the Beech Baron has it and I the King Air has it as well. I am going way back here and trying to remember but another example of the EMB-120 was the right engine was "slaved" to the left so you could better match prop RPM's. I believe this was done through fuel governing and it sync's the props together so you don't have the warbling (is that a word?) sound from one prop turning faster than the other.

Steve

Prop sync, on multi engine prop aircraft is nothing more than prop RPM matched together. An un synced prop will cause vibration as well as noise on the airframe. It is like having your tires on your vehicle balanced. One out of balance tire or wheel will cause vibration and noise on the car body, not the tire or wheel itself.

A person going down an intake of an operating jet engine will cause a compressor stall. An engine requires a specific amount of air to run correctly. When this air is blocked, the engine will compressor stall or "back fire". I have seen the results of one person being sucked down an intake. He did not survive the trip, even though the pilot shut down the engine when he saw him being sucked down the intake. Both of his lungs collapsed due to the air being sucked out of them. It took over ten minutes to get him out of the intake.

I hit a sea gull once when flying a C-180. The prop just splattered it all over the aircraft. There was no damage at all to the prop blade. But, I was only doing around 120 KIAS at the time. An aircraft flying much faster would most likely suffer damage to the prop. A bird going down a jet engine in flight would cause severe damage, if it was a large bird. At Homestead AFB, Fl, in 1981, a turkey buzzard was sucked down an intake on a F-4D on take off. The damage was severe. The inside of the intake had dents, torn metal and the engine had the compressor section completely wiped out. The engine was actually shoved back on its mount several inches, resulting in broken engine mounts. It took over six months to repair the aircraft.