Help For College

[plan_D]

I thought I'd just make a thread because I'm going to be asking a lot of questions now.

The first;

On a commercial airliner; would you aim for the maximum camber being around 30 - 40% along the chord (from the leading edge) or nearer the front. Because as we all may or may not know; the maximum camber being closer to the 50% mark gives better stall characteristics but more drag; while closer to the front gives worse stall, less drag (basic here).

In my opinion you'd balance it a little more toward less drag in this eco-friendly world, and more drag uses more fuel which is more money. While an airliner very rarely gets to its stall angle.

 

[FLYBOYJ]

You're right on the less drag. The only time an airliner gets remotely close to it's stall speed (on purpose) is during landing or during a post maintenance FCF where the crew normally does a "stick shaker." Most landings on modern airliners are just about automatic and even when a pilot dives it by hand, they are still no where close to plunking her down in a full stall landing.

 

[plan_D]

So, they're going to have the maximum camber more toward the front of the aerofoil then?

 

[FLYBOYJ]

Yes - and I double confirmed this with my father in law. For example a 737 will be "planted" at about 140 kts - the stall speed is about 110. Again this varies with weight but for the most part an airliner will normally ever see it's full stall speed under normal operations...

The airlines want fuel efficiency...

 

[DerAdlerIstGelandet]

Dont most airliners have a supercritical airfoil and that would put the high cambered aft section.

A supercritical airfoil increases fuel efficiency, and aircraft with this kind of wing have a higher take off and landing performance.

I know the Airbus A300 and the C-17 have a supercritical airfoil.

 

[Matt308]

And thats why some commercial airliners use slats and fowler/triple slotted flaps. This too changes camber.

 

[DerAdlerIstGelandet]

Yeap

 

[plan_D]

Would that change the position of the maximum camber? I understand that airliners want fuel efficiency more than anything. I have to justify the selection of certain wing designs - I've done light aircraft (Cessna 150) with a better stall characteristics.

 

[mkloby]

I might be wrong about this one - but deploying flaps would change your wing's chordline - thereby also changing the camber??

 

[FLYBOYJ]

Trainers (C-150s) and GA aircraft would want to have better stall characteristics because they are used for training and need to be able to exhibit to the student stall characteristics while still attaining stable and safe flight. Airliners, because of their revenue mission as well as being stacked with all kinds of bells and whistles wouldn't need that forgiveness since the landings are basically "driven" to the ground.

I remember reading somewhere that the MD-11 had a tighter landing/ stall "window" than most commercial airliners. I'll see if I could find something on this.

 

[plan_D]

The camber is changed by deployment of flaps, and slats - you're right. But I'm after the aerofoil shape as if all moveable parts were not deployed. The NACA No. or RAF No. shape - the thickness:chord, position of maximum camber and things that effect the lift, drag, weight-carrying, strength and such like without the usage of deployable surfaces.

I do justify the usage of the deployable surfaces in this assignment but I'm not doing that yet.

That's exactly what I thought Joe, that's why I estimated the maximum camber on the C-150 to be around 40% chord to give it much better stall characteristics.

 

[mkloby]

Would that change the position of the maximum camber? I understand that airliners want fuel efficiency more than anything. I have to justify the selection of certain wing designs - I've done light aircraft (Cessna 150) with a better stall characteristics.

You need to justify selection of certain wing designs - so you've done light A/C. Is the only other type of A/C you are going to do a commercial airliner?

W/ the C-150, I hope you didn't forget the basics: rectangular wing (root stall first, very easy to recognize, manage, and recover from), high wing (increases lateral stability; keel effect), and slight dihedral, also increasing lateral stability.

 

[plan_D]

No I didn't forget that mkloby, but thanks.

And I'm doing fighters (supersonic, general), transports (heavy lift), commercial airliners (large), executive jets (small), light (C-150 type, and stunt aircraft), high altitude (U-2) and I'm also doing the X-15 because it is unique as it has single wedge aerofoils.

 

[plan_D]

Right, to justify the the wing selection of the Cessna C-150.

Basic trainer aircraft; good stall characteristics (forgiving - Maximum Camber = 40% along Chord), basic flight controls no erratic manuevres - simple flight, easily handled. Basic flap design for better landing characteristics.

Anything else?

 

[mkloby]

I think that pretty much sums it up - I'd just go into detail about the wing's positive contributors to lateral stability, which really contributes to ease of flight. The flap design really brings down the approach speed - I think it's something like 55 knots or something insanely slow like that. It's been a while since I've flown Cessnas, but I remember them having a pretty good aspect ratio, helping to increase cruise performance and make them more economical.

 

[FLYBOYJ]

Short field landings with a 150 are 50kts. I gone over the numbers as slow as 45 (42 is the lower end of the white arc) and landed within a few hundred feet. A 150 is very forgiving at slow speed but because the wing had no dihedral you have to be aware of one wing dropping in a stall.

 

[mkloby]

I've flown 172's and 152's - and I thought I remember them both having SLIGHT dihedrals. Never flown the 150, but I thought the design looked very similar in most respects.

 

[FLYBOYJ]

I've flown 172's and 152's - and I thought I remember them both having SLIGHT dihedrals. Never flown the 150, but I thought the design looked very similar in most respects.

172s have a slight dihedral, 150s and 152s don't (unless if you want to count the 1 degree that the factory says it has). The "break" during excessive pitch power-on stalls on a 150 or 152 are a lot more severe than in a 172.

Basically the 152 is a 150 with a more powerful engine (a whopping 10 horse more) the landing light in the nose and the cowling has dzus fasteners for easier maintenance.

 

[mkloby]

172s have a slight dihedral, 150s and 152s don't (unless if you want to count the 1 degree that the factory says it has). The "break" during excessive pitch power-on stalls on a 150 or 152 are a lot more severe than in a 172.

Basically the 152 is a 150 with a more powerful engine (a whopping 10 horse more) the landing light in the nose and the cowling has dzus fasteners for easier maintenance.

Hey 1* is technically a dihedral I spent like 23 hours on a 172M - the A/S was in MPH which was funny. I flew I think 1.5 hours or so in a 152, so I am not very familiar - but I knew that the 172 had a noticeable dihedral. What is the "break" you are referring to? To me that means an overhead break entry to a pattern...

 

[plan_D]

Well I've moved on from the Cessna - and I've done a Su-26M for stunt aircraft. Joe, if you want I'll send you any of my assignments (that have been passed or yet to be done), if you PM me your e-mail.

Matt, I've changed that one I sent you to mention lateral stability. I'm now doing the Raytheon Hawker 4000 for executive Jets...

First ideas - it needs to have a maximum chord somewhere near the front for economic reasons - and it shouldn't get to a speed or angle to stall. The wings will be thick for high lift: low speed. Swept back as it's reaching near transonic region - increased efficiency as well. Low dihedral for lateral stability.