Short Skyvan/SD330/SD360 Lift Distribution

[Mechta]

I'm currently doing a college project which requires us to make and test a 'lifting body' fuselage. The lecturers frequently mention the Short Skyvan as an example of an aircraft which derives a significant part of its lift from the fuselage.

Despite trawling the net, what I can't find is answers to these questions (my questions, not the lecturer's):



Is the Skyvan fuselage still generating significant lift in the cruise, or just enough to give an approximation of elliptical lift distribution?
Is the Skyvan fuselage shape intended to be a non-pitching aerofoil?

If anyone can give actual figures for the proportions of lift from the Skyvan wing and fuselage either at different parts of the flight or at different angles of attack that would be really useful.

If your figures are for the Short SD330 or SD360 they would also be useful.

Thanks

[Piltdown Man]

I'm afraid you have got the wrong idea about these aircraft. Basically, they were so damn ugly the Earth repelled them. ;)

PM

[Speedbird48]

Mechta,

I cannot give you figures, but many years ago I was an Instructor.Tech rep, etc for Shorts and I went to the design people with a similar question.

My question was relating to de-icing the fuselage as well as the wing, and the response was that the fuselage does not produce lift but it has little drag!!

That is the sort of reply to be expected from the Irish I guess but, from that I deduce that there is indeed lift that overcomes most of the drag.

Hope this helps?

Speedbird48

[Emoclew]

Mechta,
I flew and was involved in training on SD330/360 for many years, and the fuselage was never mentioned as contributing to lift, or affecting the stall in any way.
It did collect a lot of ice, and the drag (on SD330) was sufficient to have you lean forward in your shoulder straps when the power was pulled off!
The people in Shorts now Bombardier were very helpful, and maybe they might be able to answer the question. Good luck with the project.
Emoclew

[Bill Macgillivray]

I just have a thought (not much use to you, I am afraid!!) that you might not get a sensible answer to this question, even on such a knowledgeable site as this is! Would love to help but, after approx. 5,000 hours on the 'Van, all I can say is that, despite its rather ungainly appearance, it did exactly what it was meant to do - and very well! I doubt that the fuselage shape contributed to any great extent to the superb performance of the aircraft!!!! However, it was an excellent STOL machine with not unpleasant flying characteristics. I can find nothing in my (limited) notes/publications about fuselage generated lift - does not mean that it does not exist!! :):)

[Jenson Button]

Mechta,

The wing provided the vast majority of all lift on the 330/360 design. There was a small component of lift from the fuselage but it was negligible. In fact there was probably more lift from the spars which were of an aerofoil design. The wing was a super-critical aerofoil design. Wrt to de-icing, procedures were to deice the wing and fuselage.

Yes it was ugly, but it was a darn fun plane to fly.

Jenson

[Brian Abraham]

The Shorts 330/360 used the following airfoil, Root NACA 63A418, Tip NACA 63A414. Nothing super critical, but it is a laminar flow section.

With respect to fuselage lift, it was a common statement in the days of the Victa Airtourer that the canopy generated some 25% or so of the lift. Whether that actually was the case I know not.

[twochai]

There was a small component of lift from the fuselage but it was negligible. In fact there was probably more lift from the spars which were of an aerofoil design.

In fact, the wing struts and the very high aspect ratio wing configuration were part of a design licence purchased from Hurel-Dubois, IIRC.

[Saint Jack]

Theories such as the fuselage generating 'significant' lift in flight are not confined to the fixed-wing world. Many people swear that the sponsons of the Bell 222/230/430 family of helicopters did this also.

[Algy]

And here´s why Hurel Dubois were involved (http://www.flightglobal.com/pdfarchive/view/1954/1954%20-%201780.html) (assuming they were.) Although the ambitions to design a "Dakota replacement" appear to have been a tad optimistic in hindsight. (You may want to pour yourself a glass of something comforting and transfer to a laptop before settling down to read the link - Sante!)

[ubique]

Having jumped fom them many times, on one occaision the refuellers had left the cap off the body fuel tank and during the short flight the skyvan lost a very large proportion of its fuel through the low pressure above its lifting body fuselage.

[Brian Abraham]

Mechta, may be of help Flow over Bodies (http://www.desktop.aero/appliedaero/potential3d/bodies.html) Given the shape of the Shorts fuselage it would seem reasonable to assume that is does produce significant lift. Remembering that lift is created wherever there is a turning of the airflow.

[Capot]

The wing on the Skyvan, and its longer derivatives, sat/sits on top of the fuselage. The fuel was/is stored in that part of the wing.

As this section went across the top of the fuselage, its upper side retained the aerofoil shape of the rest of the wing.

So to an extent that would have generated some lift, I guess. Whether that section counts as wing or fuselage is a matter of semantics, in my unscientific view. But this feature is why people talk about a "lifting fuselage", I think.

Any benefit would have been outweighed (if you'll forgive the rather loose use of that term in this context) by the shape of the rest of the aircraft.

As previously remarked, the Skyvan flew due to being repelled by the Earth.
None the less, it had a better STOL take-off performance, with a higher payload, than a Twin Otter. Not a lot of people know that.

[Mechta]

Thank you to everyone who has replied so far.

Brian Abraham's link is very informative, although it is largely about bodies with a circular cross section. It would appear that all conventional fuselages will develop some degree of lift if given an angle of attack, the only question is, how much?

I guess that testing a Skyvan fuselage by itself at different angles of attack will give the results that I want. It is interesting that the elevator extends right across the back of the fuselage, thus giving some control over the fuselage pitching effect (could also be for simplicity of manufacture). This is the best shot I can find of the tail surfaces (look at the amount of down elevator and how little actual tailplane area there is): http://basedreams.com/images/newsletter/may_2006/ces%20exit%20ing%20the%20skyvan%20.jpg



I found also this, Longitudinal Static Stability (http://adg.stanford.edu/aa241/stability/staticstability.html) but have not yet crunched numbers with respect to the Short Skyvan family: It does not take account of the cross-sectional shape of the fuselage though, which seems odd, as one would expect a circular section to generate a lot less lift than a square one.

We have now most of the pieces required to predict the airplane stability. The last, and important, factor is the fuselage contribution. The fuselage produces a pitching moment about the c.g. which depends on the angle of attack. It is influenced by the fuselage shape and interference of the wing on the local flow. Additionally, the fuselage affects the flow over the wing. Thus, the destabilizing effect of the fuselage depends on: Lf, the fuselage length, wf, the fuselage width, the wing sweep, aspect ratio, and location on the fuselage.
Gilruth (NACA TR711) developed an empirically-based method for estimating the effect of the fuselage:
http://adg.stanford.edu/aa241/stability/images/imagea26.gif

where:
CLaw is the wing lift curve slope per radian
Lf is the fuselage length
wf is the maximum width of the fuselage
Kf is an empirical factor discussed in NACA TR711 and developed from an extensive test of wing-fuselage combinations in NACA TR540.

Kf is found to depend strongly on the position of the quarter chord of the wing root on the fuselage. In this form of the equation, the wing lift curve slope is expressed in rad-1 and Kf is given below. (Note that this is not the same as the method described in Perkins and Hage.) The data shown below were taken from TR540 and Aerodynamics of the Airplane by Schlichting and Truckenbrodt:
Position of 1/4 root chord
on body as fraction of body length (X)
X Kf
.1 .115
.2 .172
.3 .344
.4 .487
.5 .688
Any further comments or info much appreciated!

[chevvron]

My main memories of the Skyvan are the Loganair one (GAWCS?) departing Glasgow and by the time he turned downwind, he was passing about 5000ft . Oh and the Shorts company hack departing Farnborough and depositing a cabin window pane on the runway, discovered during runway inspection next day.
I once owned a Monnet Moni homebuilt which definitely had a lifting fuselage; it would do 90mph indicated on a 29 hp engine.

[Capot]

Whereas the Percival Prentice had a sinking body fuselage and flew at 90Kts on an engine that was supposed to deliver 251 hp (187 kW).

[Say again s l o w l y]

From a long ago type rating on the mighty shed I seem to remember being told that around 10% of the lift was produced by the body rather than the wings.

Now, as to the vearcity of that statement, I will not go any further as I simply have no idea really, but I loved flying the thing. It looked like a dog's dinner but it was fun to fly if cold, wet and VERY slow...