Jump to content
Aero Precision provides OEM part support for military aircraft operators across more than 20 aircraft
Sign in to follow this  
cfisher

Rudder Fin Stall

Recommended Posts

Guest

I just uploaded four .jpegs of an article from the July, 1975, issue of "The MAC Flyer": "The C-130 Fin Stall Phenomenon". These are of an old photocopy of the article that I've kept over all these years. For some reason, they are not in order and there are two of each page - go figure. I haven't figured out how to delete the duplicates. The article is here:

http://herkybirds.com//gallery/showimage.php?i=6759&catid=member&imageuser=3916

I cannot access the above URL. Has anyone the "The C-130 Fin Stall Phenomenon" article?

Thanks in advance.

Share this post


Link to post
Share on other sites

Better late than never for those who are interested in the HTTB...

http://www.ntsb.gov/doclib/recletters/1994/a94_101.pdf

This is the NTSB safety recommendation that was published a year after the 2/3/93 accident. As expected, it's a bit more thorough and expands on the initial probable cause report. I remember the day as if it was yesterday and I lost a great friend and idol.

Share this post


Link to post
Share on other sites

Jim Raycraft was the IP's name for the LRF incident in '72. I believe it was a 62TAS formation departure and he was #3. I came over the hill from the housing area just after he went in. From what I can remember, the report said that he got caught in the wake turbulence and in trying to get out of it, the airplane yawed to a point that the fin stalled. I seem to remember something about bushings on the rudder being worn which contributed to the whole problem. Later, Lockheed/Air Force issued a TCTO to the -1 stating that you had to reduce power and lower the nose to recover. Kinda tough when you're at most 300' AGL.

Share this post


Link to post
Share on other sites

We never called it "Rudder" fin stall, just Fin stall. (15-20 degrees of yaw)

The Evansville crash was the result of fin stall from what I remember. Practice engine out ball out, AC said step on the ball and the wrong rudder input was made.

Loss of directional control, the wing is no longer in the relitive wind and stalls.

Asymmetrical thrust, usually 1 or 4 out, and low airspeed are the problems. Never but never get below 140kts with an engine out. I briefed 160kts. I've had two engines out on 1 side (1 and 2 both times) and below 160 it was a handful. The insidious problem was not the fin stall in itself but the accompanied rudder reversal. In a an engine out demo the way out is to immediately bring up the power on the retarded engine. We had one at Cherry point that was at low altitude(in the pattern) that was so violent it tore a refueling pod off the wing. What saved the AC was the immediate application of power on the retarded engine.

Share this post


Link to post
Share on other sites

Asymmetrical thrust, usually 1 or 4 out, and low airspeed are the problems. Never but never get below 140kts with an engine out. I briefed 160kts. I've had two engines out on 1 side (1 and 2 both times) and below 160 it was a handful. The insidious problem was not the fin stall in itself but the accompanied rudder reversal. In a an engine out demo the way out is to immediately bring up the power on the retarded engine. We had one at Cherry point that was at low altitude(in the pattern) that was so violent it tore a refueling pod off the wing. What saved the AC was the immediate application of power on the retarded engine.

Guess your 'never but never' admonition would preclude doing any 3-engine takeoffs. ;)

Never speak in absolutes. ;)

I find your numbers 'good practice', but nothing more. Vmca is adequate to maintain lateral control, and airspeed appropriate to weight is necessary to maintain altitude. Both of these come in well under 140Kts. All that said, I live by the mantra that 'speed is life' and 'altitude is only life insurance'.

AFSOC is the last bastion of engine out work in the plane. Not sure for how much longer as they're trying to push everything to the sim like everyone else. They still do 2-engine work in the plane, windmill taxi starts, and simulated 3-engine takeoffs in the plane. Copilots even do engine out go arounds in the plane - it's all part of the respective checkride. My point is we do all of this every day without incident, often below 140kts. Granted, we're at training weights (generally below 135K for everything except the 2-eng & 3-eng T/O and then we're 120K and below) and heavier airplanes need more speed (Vmca goes up as does stalling speed).

140 is a great number for many things, but if you can hear the plane talk to you, it's nothing but a reference.

EDITED TO ADD: I retired last year, so I shouldn't talk in the present tense anymore about what AFSOC does. I do miss it, but at least I'm still flying the Herk!

Share this post


Link to post
Share on other sites

Fin Stall

Can occur at all speeds between stall speed and approximately 170 KIAS in all flap configurations with power on. The susceptibility of encountering the fin stall condition is greatest at low speed with high power on. Rapid yawing can be produced with (1) relitively low abrupt rudder inputs or (2) abnormally high rudder deflections. As the airplane attude approaches the critical sideslip angle, heavy verticle fin buffet will develop. WARNING If the airplane is allowed to proceed into sideslip angles beyond the onset of buffet, a wing may stall resulting in loss of lateral and directional stability from which it may be extremely difficult to recover. This could lead to the possible loss of the airplane.

Evansville misshap, engine out practice shortly after after T.O. I believe the crew had #1 eng. retarded to simulate loss, received a radio call to RTB from OPS. The IP, left seat looked down to his left into his brief case for instructions, felt the acft. yaw and noticed the turn and slip ball way to the left all while the #1 eng. was still in F.I. The young CP was flying the acft. The I.P. said "step on the ball" a common command for a side slip. The acft. did almost a complete stop, stalled and rolled over to the left, that is why the acft. left a crater in a parking lot.

No one is talking about "rudder reversal" which accompanies fin stall. That's the insidious part of the accidents involving engine out/slow speed/go around with high rudder inputs.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...