Its all in the wings
 

This is strictly a comment by someone else in an article that I recently read but I found it interesting from a historical aircraft design point of view....

"The B717-200 is actually a very good Aircraft, much better reliability than the MD80 and MD90's. It has a big disadvantage in its old wing design from the DC-9-33 made in Korea. Douglas stopped making competetive wings after the DC-8-62/-63, not having their own big wind tunnel like Boeing was a big part of it. A consulting von Karmann could only do so much vs. Boeings George Schairer working the Boeing wind tunnel. Airbus benefitted from the RAE and other European wind tunnels to design the Airbus wings. Hence without great wings an Aircraft design is crippled no matter how good the rest is."

I have all kinds of problems with the quoted paragraph:

"wing design from the DC-9-33 made in Korea." ???? Not sure whether this is supposed to mean: a wing designed in Korea, or a wing manufactured in Korea, or a DC-9-33 made in Korea, or all of the above, or none of the above - poorly structured sentence.

The B712 wing was the DC/MD design that served for 50 years - outsourced to a Korean factory (Halla) by Boeing for that particular version. Unless one has an outdated view of Korean manufacturing skills, it's no different than the previous made-in-USA wings. It was (always) a simpler wing, appropriate for a less-expensive shorter-route jet (simple two-position slats (or none in the DC-9-10) and simple drop-hinged flaps)

I don't see any evidence that the B717-200 is a "crippled" design. Delta laps them up and jest luvs 'em. Certainly not aerodynamically (it may have been crippled during production life due to market positioning and changes, post-9/11 aviation slump, more modern competitive airframes overall, etc. etc. - but not the wing)

Not sure how much advantage a "big" wind-tunnel offers over some other size (MD did have their own wind tunnels, and access to others (NASA/Ames among others).

https://rotorcraft.arc.nasa.gov/Publ...cklin_1994.pdf

As with any logical chain - first one has to prove the assumptions are true, accurate and applicable - only then we can discuss whether the conclusions are true.

In other words, the "history" given above seems questionable - but your title is often very true - many aircraft have most certainly depended on unique wing engineering for their existence.

Try read Abbott and Vandoenhoff "Theory of wing sections":\

Perhaps being a bit anal here, but Boeing had nothing to do with outsourcing the wing to Korea - that decision was made by MacDac years before the MD/Boeing merger.
Unfortunately it was that same outsourcing mentality that the former MacDac execs brought to Boeing after the merger that crippled the 787 development...

No, that is a fine addition - I always value your Boeing and industry insights.

What's wrong with a piece of railway line for your wings? Tough-as!! :)

717 has a "dial a flap" system for takeoff: infinite angles between 0° and 20°; I assume, to extract the best out of/compensate for the "slab" of metal... :ok:

Fokker 28/100
 

I have had the honor to listen to the ex Fokker people at Screiner now Cae about how excellent the wing design was and I suppose it was in its days.
They went on and on about restarting the production of a F100Neo. And they claim Airbus used some of it!

As a pax and occasional Jumpseater on the MDs I loved it.
( Minus the odd time I was sitting in aft A seat, my goodness what raket.)

The new 717 must have been excellent, but there is a point were You need a clean sheet new design. That point was economical and coincided with Boeing and 9/11 .
Speaking of wich I still think the 737-800 is to noisy for pax behind , say, row 12. The tail mounted engines still is better for Pax comfort and gives a cleaner wing design.
Just look at the Global, and tell me I am wrong.

The wingmounted engine airplanes are in my book the WW Beatle of the sky.
Simple and unsofisticated and cheap. The MoneyMens dream.

Lastely , I love my old 738 but some times when heavy and gusty we are are looking at bloody Spaceshuttle Flyspeeds on approach.

You're not wrong- The NG was IMHO, a compromised design. They really should have moved the ailerons outboard and filled the space with more flap area.

Still no sign of it in the MAX after 20 years of poor crosswind control and limited short field performance as a result.

The MD80 has the dial a flap system as well
but we almost always used fixed flap
gates


Exceptions were departing MEX for example
when higher performance was needed

The problem with tail mounted engines is you need to know - to a very high level of precision - the engine weights very early on, and that's seldom the case. If the engine weight changes you end up carrying large amounts of ballast to keep the CG proper. Former MacDac guys tell me that's what ruined the MD-90 - late regulatory changes regarding blade out increased the engine weight by nearly a ton - which then required almost two tons of nose ballast to compensate.
Wing mounted engines are near the nominal CG so you don't end up paying twice when the engine weight inevitably goes up.

And, that’s not the only tail-mounted design done badly by an overweight engine! D9nt ask how I know.

Blu-y, don't be so dismissive of wing mounted engines. They are a very good practical compromise for so many reasons. Look up and think about engine wing bending relief, ease of maintenance, fuel line protection, fire safety of pods, fuel feed by gravity, lack of fuel lines through the fuselage, various aerodynamic advantages, the list goes on. It is definitely not because it is a cheap solution, rather it is a very good design feature.

"Dial a Flap" was a MD thing, at least DC8 through MD90 all had it, might be on earlier, pre-dating me, stuff too.

No dial-a- flap on the DC8, DC10 has it.

We might see tail mounted engines come back soon on future airplane layouts with all the new unducted fan engines envisioned to power them and their "clean" wings getting really complicated with all the morphing stuff in them.

Ballast now there is something You want to avoid in a new aircraft!
They gave us iPads and tossed out the navbag of 8kg, that is how allergic to carrying any extra weight the MoneyMen are. Now we have no paper charts WHATSOEVER, smart.!

Anyway , TD didnt some MacDc staff go to Embraer and continue the tailmounted engine saga?

So as I understand it , a tailmounted engine a/c is potentially a more efficient a/c but more challenging design wise. Ie more expensive.
And we all have seen the effect off lack of deice and all sorts of stuff being flung into the engines.

As I have already stated: The 737 born the same year as me is the ultimate Beetle and with the new wing on the 700 and 800 ( I think that is when the present one came) and the new engines, the basic 737 is going to carry on from 1967 to 2067!
Did the DC9 ever have that sort of potential? Me thinks not!

I find it absolutely fascinating that Aviation have become the Sick Old Man of technological development.

When Hitler was so proud of the WW Beetle that Herr Porche presented in 1935 , he sure as dirt did not expect it to end its days ,slightly modified in the 1990s from a Mexican factory!!

Thinking of that, I would not mind having WW Beetle , ca 1969.
At least I can fix the engine if needed, and fantastic on snow.
Aero dynamic and tailmounted engine.
Anyway, got to pull the net!

"I find it absolutely fascinating that Aviation have become the Sick Old Man of technological development."

I can't see that happening. Just look at CFRP use, aerodynamics, systems architecture, cockpit design, FBW and manufacturing. Way ahead of the car guys that still build the "new beetle" and chip tune their emissions.

We don't need to know how you know but I would like to know which type.......Please.

Surprised the overweight engine problem could not be offset by a slight extension forward of the wing. Ballast seems like such a desperate last minute fix.

I have difficulty seeing how a ton on a very short tail moment would require two tons in one of the longest nose moment arms in aviation (relative to the tail moment arm)...

The key is it's last minute. Adding a fuselage plug forward of the wing is a not a trivial change - it's a major fuselage re-design. Sure, if you don't mind delaying the project a couple years and tens (or even hundreds) of millions in additional costs.
The location of the wing relative to the fuselage is one of the first things that have to be established when designing an aircraft, not something you can mess with less than a year prior to first flight when you find out the engine just got a lot heavier.
PDR, one ton per engine, there are two (at least). Also, there is already a lot of stuff at the pointy end that can't be readily moved - hence when you start talking thousands of pounds of ballast you can't put it in the most efficient location.

Ah. It seems the weight growth in the anecdote is accelerating faster than it did in the engines. So was the two ton ballast requirement per engine as well? 1 ton of weight growth sounds like rather a lot in a 2-1/2 ton engine...

Yes, those pesky baggage holds can be so difficult to put stuff in, can't they. The last aircraft I was involved with where this order of magnitude of CG error needed correcting the favoured proposal was ti increment the material thickness in the skins and stringers of the forward fuselage, which would have* solved the problem quite easily. It's not rocket surgery.

* I say "would have" because the project was cancelled for other reasons.

Blu-y,
Tail mounted engines can cost a lot in design. Start with the simple fact that, because there are no podded engines to hold down the wings, the wing structure must be heavier to resist the moments generated by lift. Just for starters that is costly. It goes on - do some homework and you'll get the idea. Yes, I know, rudder can be smaller due asymmetrics and that is a saving but there is the fuel system etc, etc.

I thought the clue was 'D9nt' but perhaps it was a typo - all too cunning for me ;)

Not only that, but wing-mounted engines are typically used as torsional dampers, also allowing a lighter wing structure. And of course tail-mounted engines are much higher up, requiring more expensive platforms & lifting gear for maintenance/replacement.

Basil, I'd put my money on one of the Bombadiers, likely one of the Global kind, I'd further bet the 7000 and 8000 with the GE Passport engines. As usual, I'd probably lose the bet if horses are any guide.

PDR, go ahead and be the skeptic, but consider these facts:
The MD-90 incorporated new, 1990's technology V2500 engines to replace the 1960s technology JT-8D engines on the MD-80. This should have provided a huge improvement in fuel burn - but it didn't. The MD-90 operating costs were barely better than the MD-80. As a result, nearly 1200 MD-80s were delivered over 17 years, compared to 116 MD-90's over 6 years before it was euthanized .
People that worked on the MD-90 told me the problem was the aircraft was so severely overweight, with most of that due to the heavy engines and the associated nose ballast.

A little research shows the V2500 is about 900 pounds more per engine than the -217, according to Wiki. Add in the pylon flaps, structure improvements and certainly over a ton-plus total at the wrong location.

High compression turbofans are heavy, an inescapable fact. Also, a reason reengining the CRJ series is a non-starter.

To further your point, they also add operational challenges with FOD induction and lateral stability issues due to rudder blanking as evidenced by the Delta mad dog runway excursion at LGA in 2015.

How can wingmounted engines allow for lighter wing structure.
Torsion damping can not possibly be that heavy on a modern wing.
Compared to all the crap that is associated with an engine on a lifting surface.
Heavy engine on wing = more wing and heavy wing.

I think you misunderstand. With no engines on the wing the structure must be torsionally stiff, and that takes material to do (the torsion loads are usually reacted by the skins which must be thicker to take them). But if you have nice lumps of metal on lever-arms you don't NEED to make the wing torsionally stiff - you just give it a high rotary inertia so that the time-constant on reacting to a torsion upset to likely to be so long that the upset will disappear before it moves significantly. Pylon-mounted engines do just that; they act as torsion-mass dampers, so the skins don't need to be as thick.

I'm sorry, but that's not true. I'm also sure it has been detailed here and elsewhere many times before - google something like wing bending moment relief. Essentially if you put all the weight in the fuselage and all the lift in the wings then all the weight is reacted at the wing root in bending. But if you spread weight across the wings the weight pushing down balances the lift pushing up and that part of the lift never has to appear in the bending moments (either summed at the root or reacted progressively across the span) so the required wing bending strength is much smaller. Therefore you can get away with a much lighter structure.

That's the argument for wing-mounted engines, undercarriages, wing fuel tanks, tip tanks, military stores mounted on wing pylons etc etc.

All of this has been known about since the 707.

Actually since the B-47. When Boeing proposed a swept wing for the B-47 they ran into nasty flutter issues until they figured out how to use the podded engines as mass dampers.

That's the one! (I'd forgotten about the application on the earlier bombers)

The early B747-200s had ballasted nose cowls for the outboard engines for flutter damping we were told.
Another fringe benefit of the engine struts on #1 and #4 was that the inboard edge of the strut was made vertical about 3 inches high and brought aft over the leading edge as a cheap fence, making a virtue out of necessity.