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Rudder Fin Stall


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I arrived in Little Rock Air Force Base in 1972 from Clark. There was a C-130 crashed on the end of the runway. The accident investigation team determined it was called by a rudder fin stall. Does anybody remember that. I can't remember what a rudder fin stall was does anybody else.

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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.

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We were briefed the Evansville crash was caused by using full or almost full rudder deflection away from the simulated engine out while turning into the "dead engine" with the two engines on the outside of the turn pulling the plane around the turn and then the co-pilot centered the rudder. The aircraft turned violently around much like a top and went to a 90 degree bank angle if not greater and fell with almost no forward flight. We had it demonstrated in the simulator for a few years. The first time the plane went to about a 105 degree bank angle. It was a situational awareness failure and not flying at a safe airspeed above VMCA while turning into a simulated out engine.

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Fin Stall only occurs (er, well I guess never say only) on the herk and the DC-3/C-47 and its only because of the way the airflow comes off the props/wings and impacts the stabilizers.

If they put counter rotating props on the two wings (like a P-38) this would be a non issue.

I would never say that it was simply a "situational awareness" failure, that is waaaay too easy a label to throw out for something that can happen quicker than the speed of human thought. You could call it "it was just your time" and be about as close to the truth.

Student story here from the 550th SOS, one night we were flying spare tanker for a formation refueling, IP in the left seat and student in the right seat.

We were heading south on the AR track by the Rio Grande, at one point on this track you will pass a ridge line that ALWAYS is bumpy as hell because of the way it funnels the wind.

We had the hoses out, 70 percent flaps and somewhere around 110 KIAS; the IP is watching the primary and the helo's to critique the students flying position with the student at the controls. We just pass east of this mountain and I knew that we were going to bounce, as soon as we do the student automatically tries to stabilize his flying position.

Before you know it the heading started to swing, the wing starts to drop, we start to lose altitude and the most unusual buffet I ever felt (and pretty damn violent) sets in. The IP was all over it almost as quick as I could (and did) scream “stall†or we wouldn’t have made it home that evening.

This whole sequence of events from start to finish happened within seconds and very few seconds at that, this is the reason that I say you cant call it a situational awareness failure as it happens almost too fast to really be aware of it.

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I remember 3 crashes blamed on Fin Stall 69-6578 Nov 71 at Little Rock.

69-6581 Ramstein Jan 81(blamed on rudder boost pack) and 58-0732 Evansville IN Feb 92

Bob

I didn't think the Evansville crash was attributed to a Fin Stall. That was simply incorrect flight control input. Or course that might have put them in a Fin Stall condition but at their altitude they had no chance of recovery.

You might could indirectly say the Ft Hood crash was caused by Fin Stall however. The crew assumed(incorrectly) they were in a Fin Stall and rode that one in. At that time it seems Fin Stalls were being driven into our heads without regard to a normal stall.

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Were there any survivors on any of these crashes.

The Fort Hood crash had two survivors. One was the IP (Mike Rogers) who was standing and the other was the EF (Dave Grimm) who was standing or sitting near the galley area. Interesting fact both their wives had just given birth a week or two before the accident.

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  • 1 month later...

Fin stall is encountered at low-speed high AOA condition with a significant side slip (15-20 degrees) in which the rudder and ailerons are cross controlled with the nose of the airplane in level or positive pitch attitude and engines developing power above flight idle. The scenario begins with significant rudder buffet which permeates through the fuselage and, if allowed to continue, progresses to a rudder hard over (in the direction of deflection) and a rapid roll in the opposite direction. Unless there is immediate action to stop it, the side slip exagerates rapidly to approximately 46 degrees and stops. It will bruise your ribs if the arm rests are down. Roll accerlerates rapidly in the opposite direction. The recovery is analogous to a spin recovery; throttles to flight idle; neutralize the rudder which might take in excess of 100 lbs force; level the wings and if able, move the control column forward (not abruptly) to get the nose down to a negative pitch angle; apply power to regain energy.

The condition is encountered (as suggested in a previous thread) typically with inappropriate use of the rudder during asymetric engine power conditions, in wake turbulence encountered in a traffic pattern or during formation flight, or intentional slipping of the aircraft with a nose-high attitude and power above flight idle.

It's been more than a few years, and I'm sure someone else around here has a little experience with this as well but I hope that helps explain fin stalls.

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Yeah, the rudder is the thing that flaps back and forth, the fin is the thing that doesn't. Two different things.

I would have use the word "thingy" to make your point. Speaking of which I think that was my point.

As far as fin stall, the process to get into the condition is immaterial, the effect is the discussion. Wrong input or lack of input will result in the yaw required to negate the vertical stabilizers ability to provide directional control.

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I would have use the word "thingy" to make your point. Speaking of which I think that was my point.

As far as fin stall, the process to get into the condition is immaterial, the effect is the discussion. Wrong input or lack of input will result in the yaw required to negate the vertical stabilizers ability to provide directional control.

Yep, I was jut agreeing with your point.

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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.

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  • 3 months later...

There was one survivor in the Nov 12th 1971 crash. Ten of the 11 crew members were killed. I am the sister to David Bloomberg who did not survive the crash. Interesting enough I later on became a crew chief on KC 135's and on a fighter. While stationed at Nellis I worked with Doug Grimm who is Dave Grimm's brother. If I remember correctly Doug told me that Dave had actually survived two aircraft crashes.

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Well - I only know what was going on one particular flight - Sarajevo bound, purge in progress. I was in the left troop door (we'd an ISU 90 in pallet posit five) leaning back against the thing while the purge on the right side was being called by that loadmaster. Felt the pressure in the ears and found myself bumpin' off the ISU. Nav was standing at the base of the crew ladder, made the call "whats that banging noise". Recovered and pressed on. I was later told we were on the edge of a fin stall - didn't sound all to spiffy a condition to be in.

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  • 4 months later...

I did my time as a Flight Engineer on C-124 - C-130 - C-141 and C-5s before retiring from the Air Force with 26 years, I then went to work as a pilot for Flight International, Continental and UPS Airlines for another 26 years. My entire civilian career was spent as an IP on the B-727 and the B-747. I state this experiance because I know many would disagree with me when I say that the "Rudder Fin Stall" was a design deficiency in the C-130 that could not be corrected. Lockheed was still working on the problem when the Test Bird crashed in the Hospital Parking lot at Dobbins AFB around 1991 or 92. They were testing modifications to the rudder on that flight, that day. When I went through C-130 training at Little Rock in 1974 we were not supposed to do two engine out approaches, yet the IP on one local training flight did just that and we nearly lost that aircraft before recovering. Two engines out on the same side and the student pilot could not hold the rudder. The G force of the sudden turn pinned me to the FE seat. I never flew with that IP again and soon went back to C-141's. We were not supposed to do no-flap takeoffs at that time either, but the IP's did that also at the base I was stationed at the time. I came to the conclusion that the C-130 was a great plane, but the pilots I flew with on it were hot doggers and were frustrated fighter pilot wannabes

Edited by Slyoldawg
Correct a misspelled word
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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

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  • 3 weeks later...
  • 8 months later...

(the Little Rock Crash of '71) I put this on another thread. Hope it's ok to do again here. First, a quick rememberance of Dintlemam, a recently arrived Loadmaster from our 36th Aerospace Rescue and Recovery Squadron, in Japan. It shocked us all, and he was missed.

Second: I distinctly remember that (not sure to how many variants of the C-130) there was an Air Worthiness Directive (or stronger, as I remember there was an immediate grounding) to check some part of the rudder assemly. I always assumed that that was the cause of the crash. I remember how vulnurable I felt knowing that a reliable, long term active aircraft, could suddenly show a flaw after so long a time in service. Hopefully that saved lives down the road. Regards to All

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I state this experiance because I know many would disagree with me when I say that the "Rudder Fin Stall" was a design deficiency in the C-130 that could not be corrected. Lockheed was still working on the problem when the Test Bird crashed in the Hospital Parking lot at Dobbins AFB around 1991 or 92. They were testing modifications to the rudder on that flight, that day.

The HTTB crash was trying to determine Vmcg, not fin stall. If you were flying Herks in the late '80s - early '90s, you'll recall that there was a TO Safety Sup to the -1-1 that advised us to add 25kts to Vmcg because they didn't know what the number was, they just new it was higher. This was due to the change in the prop governor that made the blade go flat quicker in the event of certain types of failures. The HTTB was a highly modified aircraft used to test all sorts of things on the C-130. No doubt that fin stall area may have been one of those regimes, but it was not the purpose of that test and it most assuredly did not crash as a result of it. But it crashed trying to research Vmcg.

When I went through C-130 training at Little Rock in 1974 we were not supposed to do two engine out approaches, yet the IP on one local training flight did just that and we nearly lost that aircraft before recovering. Two engines out on the same side and the student pilot could not hold the rudder. The G force of the sudden turn pinned me to the FE seat. I never flew with that IP again and soon went back to C-141's. We were not supposed to do no-flap takeoffs at that time either, but the IP's did that also at the base I was stationed at the time. I came to the conclusion that the C-130 was a great plane, but the pilots I flew with on it were hot doggers and were frustrated fighter pilot wannabes

We continued to do 2-engine out approaches until the Evansville crash in '89 or so. After that, only ACs or higher did single engine out go-arounds. Elmendorf kept their CPs doing engine-out go-arounds for a short period, but eventually caved to pressure from AMC. So CPs no longer do engine out approaches and ACs no longer do 2-engine out approaches in AMC - except in the sim. Of course, now they do EVERYTHING in the sim...a bad idea, but not germane to this discussion.

AFSOC never stopped. We continue to do 2-engine approaches to this day (and our CP do engine-out approaches & go-arounds). There is very little risk if flown at the proper speed and certain allowances are made. To make may point more dramatically, the RAF not only do 2-engine approaches, they do 2-engine out GO AROUNDS. I did them while I was there and there are some assumptions made (you can get your gear up, so you haven't lost both on the left side - even if you simulate that side for turns) and some precautions taken (you raise your minimums), but it is not only do-able, but relatively safe. It requires relatively accurate flying, but it can be done easily with a modicum of practice.

I cannot speak to your "fighter pilot wannabe" pilots on the C-130 during that time period. I can tell you that most of our strat airlift guys have a difficult time adjusting to tac airlift...or at least, it takes them a little bit longer sometimes. Some of my most cautious crew members are former strat airlift guys and some of my best crew members are former strat airlift guys - and those two "labels" aren't necessarily mutually exclusive. But even AMC slick guys can take some time adjusting to AFSOC. I'm sure we're viewed as cowboys to many, but it was AFSOC who formalized ORM. We used to be very good in its application, but we're succumbing to big blue-itis.

For a risk to be taken, it must justify the benefit. If it does, then control measures need to be put in place to mitigate that risk. You cannot eliminate risk unless you avoid it completely. But if you eliminate the risk, you lose the benefit and then you may decrease capability. The worst way to discover that is when you need that capability. Once you're less capable, then you turn down missions. Once you begin turning down missions, you fail the user. When you fail the user, you fail - period.

Back to the original topic - fin stall. It is not unique to the C-130, but there are design features of the C-130 that make it more challenging to recover from. However, to get into the regime of a fin stall requires effort - bad effort. If you're doing these types of things - on purpose - you're probably doing something terribly wrong. It is not a design deficiency or flaw. It is a flight characteristic that exists in a regime we don't operate in...routinely.

Edited by US Herk
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Here is a little more info on the cause of the HTTB crash on Feb 3, 1993 at Dobbins. In addition to evaluating Vmcg they were also evualuating the new fly by wire rudder actuator they were developing for the upcoming J model. This was the last high speed ground run (out of 7) and the acft became airborne and the pilot decided to fly it instead of trying to put it back on the ground. The acft was at approx. 250 feet and spun into a left decending turn (heading north) and impacted the corner of the Navy clinic. All 7 aboard died including one of our reserve FE's. For the test, the acft had a small paint sprayer on the tail skid and as the acft gained speed the # 1&2 engines were pulled back to flt idle (to simulate engine failure on take off) and the fly by wire actuator was suppose to put in enough rudder to off set the torque from 3&4 engines without any pilot input. The paint sprayed on the runway gave the engineers info on how well the new actuator was holding the acft on centerline. The speed was increased at each run and the last run was so high the acft became airborne. We came back from the desert on 4 Feb and saw the wreckage from the air, still in a burned pile at the corner of the clinic. A sad day indeed. I still remember all the unreal flying the HTTB did prior to the crash. It was like an air show every time they rolled it out and flew it at the DARB. Bill :(

Edited by Spectre623
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2 engines out reminded me of an interesting landing. I was an Airborne Rescue Radio Operator and this happened about ’71. (I still have the radio log) We scrambled for one of our sister ships on a training mission. They had shut down number one engine. We made the intercept about 100 miles out from Yokota at which time we also shut down number 1 engine. We escorted our sister and on final they shut down number 3 engine and landed with no problem. Ours was a bit different. On very short final we shut down number 2 engine. There was not time to discuss the ramifications of this. As we touched down I hit the mike button to tell our Rescue Control Center that we were ok. However, just at that moment the AC said over the intercom, “What the hell is going on?” (not a good sign) I let go of the mike button immediately. (seems normal braking was out) The working engine props were thrown into reverse and of course we swerved violently to the right. Flight idle input swerved us then to the left, at which time the right wing lifted up. The co-pilot (Lt. Roy Petit) saved the plane with immediate right aileron input. We spent the next 12,500 feet of the 13,000 foot runway swerving right to left, left to right, with the appropriate wing lifting up, rocking the plane. After we finally stopped, instead of finishing my radio log, in the quietness, the navigator (Old Bud [Major Lux]) turned to me and said, “Ok hippy (my nickname) let’s get off this thing.” We jumped down to the cargo deck and I opened the crew entrance door. As we stepped out, Pedro (twin bladed helicopter) was hovering very close with the fire suppression kit dangling below, and a few guys in fire suites standing there. We looked to the back of the plane and there was every fire truck on base in a semi-circle behind our aircraft. In the wheel wells were two crews, each spraying into the wells, where we saw flames. Old Bud and I started running forward. The pilot saw us running and hit the evacuation bell. Later we were told two things. Emergency braking caused the fire in the wheel wells, and that the sever rocking of the plane activated the fuel dumps, or at least fuel was flowing out of them. The whole squadron was out at the flight line watching this thing, and it’s the one time my friends (maintenance and admin) were not jealous of my flight status. The Loadmaster at the left scanning window swore that number one prop only missed the runway by an inch. Anyway, interesting landing. (I just remembered this forum is about “fin-spin.” Sorry for the war story.

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