C-130j

[megan]

A recent AW&ST magazine noted there were design issues with the interaction of the wing and the six bladed prop, and vertical fin icing. Could anyone provide details of these issues (aerodynamics, engineering changes from previous models with regard to fin icing) and nature of fixes to overcome problems?
Thanks and Blue Skies,
Brian

[passpartout]

I think you'll find it's because it's not as good as the 'K':E

[truckiebloke]

Nice try Passparttit but this wont turn into a j v k issue!!!

[passpartout]

I bet you 50p it does.

No need to be rude, either!

[average pilot]

yeh, treckiebloke, leave pisspotin alone!
Anyway the K is bitter, it's stands to reason, it comes later in the alphabet.:ok:

[The Rocket]

Anyway the K is bitter, it's stands to reason, it comes later in the alphabet.

The K certainly does SEEM to be bitter;)

[Cougar]

There is now a vertical fin de-ice boot (black rubber looking object at the base of the vertical fin) which i believe was an FAA requirement prior to civil certification.

The prop issue you allude to i believe is the extra vibration for pax sitting in the prop arc - originally a problem but now considered not.

[Brian Abraham]

How do the props affect the stall qualities? Prop solidity of the six blades disrupting airflow over the wing?

[propulike]

'Prop solidity'?

I think you've just made that up!

The issue wouldn't be 'solid' props disrupting airflow! They don't go 'flat on' and work as airbrakes, they'd overspeed. The prop is either feathered with min drag and edge-on, or running at => zero thrust. If running the prop isn't disrupting airflow, it's creating blown lift. (One reason why turboprops have the horizontal tail low down is to take advantage of propwash to give the elevator extra authority at low speeds. Unless you're the A400M and are still trying to think about being a jet... but I digress.)

As far as I remember, and feel free to quote this rumour as far and wide as you wish as long as you don't come back when it's outed as bo!!ocks, the stall issue with the 'J' during flight trials was that when being stalled with power on, the breakaway at 70-odd knots and 20deg nose up was quite dramatic. As you'd expect.

[500days2do]

...maybe a negative talk(torque) issue...hey but i still think the K and the J are great...just not enough of both to go around.

5d2d

[BEagle]

Solidity: The ratio of the blade area of a propeller or rotor to the total disc area.

Sometimes I wonder whether the RAF still teaches anybody anything in groundschool.

The A400M will have 4 x 8-bladed propellers. To eliminate the otherwise adverse C130 asymmetric effect of propwash and slipstream interaction, they will not all rotate in the same direction. The tailplane will be mounted well above the propwash to eliminate the potential buffeting it would suffer otherwise. The aircraft will cruise at a much higher IMN than the old C130, so the last thing which would be wanted would be the tailplane approaching Mcrit due to the combined TAS and propwash effects.

[megan]

When I started solidity was something you learnt about for your private licence. Of course everyone flew props then, whereas today props are seen as an anachronism – especially among the military, unless it has an afterburner hanging off the back end its not really an aeroplane. Surprised just the same that a 130 driver would not understand the term. Then again, some one said facetiously that to be an aviator today you only need to be able to type at fifty words per minute.
Aaaaaaaaaaaaah, Sigh for a Merlin (and not that helicopter for you beginners)
Or a 1820, or a 1830, or a 2800, or a 3350, or a Gypsy, or a ………………

[propulike]

The actual expression is

(Number of Blades x Chord at Radius r) / Circumference at radius r.
r is normally taken as 0.7x tip radius.

However, I still can't see the reasoning that this has an effect on stall speed by acting as some sort of barrier to the airflow!

[ORAC]

IIRC, When they stall tested the C-130J, they found that it wouldn’t stall at the predicted stall speed, the new props cleaned the boundary layer of air off the wing root. They flew it slower and slower - until it finally snap rolled.

They tried vortex generators, rakes, fences, and leading edge stall strips, nothing worked, so they had to fit a stick shaker and stick pusher.

[P-T-Gamekeeper]

Which the old OC XXIV proved to work!!