Is it time for Booster Engines?

[barit1]

You maybe right about the 747 but then again it might also be because it had to fly at a lower altitude than planned.

Exactly. That's the natural consequence of OEI cruise, but I'm sure that's no surprise to you.

[galaxy flyer]

Actually, the reason was NOT the fuel burn, it was the crew's lack of understanding the fuel feed and pump arrangement that lead to land short rather than continue to LHR. In fact, they would have made it, training has cleared up the issue.

GF

[barit1]

True - I had forgotten that detail. But the suboptimum cruise altitude didn't help any.

And I'm still surprised BA main base didn't advise them on the matter.

[barit1]

Does this apply?

[autoflight]

Advantage of 4 engines. Engine failure on take-off only requires consideration of loss of 25% power compared to 50% loss for 2 engine aircraft. The principle was that this allowed a higher take-off weight. I am sure there are many other issues, like 4 smaller underslung engines allowed shorter undercarriage, but offset by outboard engines further to rear on swept wing aircraft during take-off rotation and also max bank on touchdown.

JATO interesting except that transport, storage, handling, training and time expiry were added expense for limited advantage.

[lomapaseo]

[-quote] Advantage of 4 engines. Engine failure on take-off only requires consideration of loss of 25% power compared to 50% loss for 2 engine aircraft. The principle was that this allowed a higher take-off weight. [/quote]

Need numbers to support that argument. The take off weight is a determined at ceritification assuming a single engine failure be it one out of two or one out of 10. You get what you buy. If you want more weight buy a bigger certified two engine or 4 engine aircraft not more engines

[bearfoil]

Why carry BOOSTERS?

Bury them under the centerline, with 1km cables. The NAVY does it.

[keesje]

I put a small tail engine in a concept multirole MPA in the militairy forum. For take-off performance/ engine redundancy during heavy take-offs. More optimized main engines for long range/slower speeds.



I could be far more efficient and flexible then 4 engined aircraft like P3C & Nimrod and still be smaller & cheaper..
http://i191.photobucket.com/albums/z...g?t=1311463937

http://i191.photobucket.com/albums/z...g?t=1311464000

[barit1]

I don't get it. A turboprop will always be better at takeoff than a jet or fan, in terms of thrust SFC and thrust/weight. This is because it moves a LOT more air.

[aviatorhi]

@lomapaseo

When comparing a 2, 3 or 4 engine aircraft, in which the total thrust from all engines is the same (2x50,000 lbs, 3x33,333.3 lbs and 4x25,000 lbs) the 4 engine aircraft will have the best performance (and therefore attain a higher performance certification), followed by the 3 holer and the twin. It's part of why my 727 is not performance limited in places where the competitions 737s are (as such we routinely take excess baggage and freight for the competition).

@lomapaseo

I admit that is a sleek looking aircraft, but 2 problems; (1) might want to rethink placement of the cargo door, (2) how much lost payload/additional weight etc. does putting the jet into the fuselage "cost", and how much does running it on the jet only and carrying the dead weight of the turboprops "cost"?

@barit1

There's too many engines to make effective comparison, but let's think small, a JT8D-17R vs. a PT6-67D, which do you think is gonna make more thrust at ANY altitude?

[barit1]

Not an apple-apples comparison, aviatorhi.

Pick engines with similar static thrust. e.g. For 10K lb static, the turboprop (including gears and prop) will be lighter and burn a lot less fuel than a turbofan. It's only when you get to m0.6 or so that the turbofan surpasses the turboprop.

[twistedenginestarter]

If you have more engines you have more capital and maintenance cost and more compexity in coping with technical faults in service. However the world has changed with a dramatic increase in fuel price, so we should expect to see some significant change in engineering solutions, yet 2021's 737 looks almost identical to one from 30 years ago. That doesn't seem a proportionate response to me. Someone should be coming up with more radical ideas. I know the manufacturers have their Ceeses sketching interesting concepts but they don't seem to be moving towards realizing these ideas.

[Vertical Speed]

The Bae 146 answer

For some years I flew the Bae 146 (Jumbolino) A strange little beast- a single engine failure didn't even require a different checklist! AND the range suddenly increased significantly. A double engine failure was a more serious situation and did happen on a few occasions, although not to me fortunately. The biggest problem with the little ALF502 engines was that they failed rather more frequently than the industry norms of the time. (Give me a B737 NG any day even if it only has two engines- but then the CFM56 is about the most reliable engine ever built!)

[twistedenginestarter]

single engine failure ... range suddenly increased significantly.

Well that's interesting (don't you think Barit?)

My assumption is internal combustion engines are more efficient when they are worked hard (as their efficiency rises with higher pressures). I can only think the increased range came from improved efficiency from the three remaining motors.

[barit1]

Well, I must agree.

This says something about the ALF502 engine. Apparently the aeroplane is overpowered to the point that at normal cruise, the engines run at very low power (thus very inefficient). OEI, the three remaining donks get pushed up to a more efficient regime.

And apparently fuel efficiency was not a primary design objective for the Bae 146. "A strange little beast" indeed!