Oops, darn it...

[skywagon8a]

I had 2 PA30s and the last one scared me with tail flutters. I use to descend from higher altitudes to approach altitude by putting descent rate at 300fpm until it reached the yellow arc and then it would start to flutter. Did it twice and nothing nothing seemed to fix it. It is now living in Australia.

Jim

That speed was too low for flutter. Perhaps the elevator cables were too loose or something else needed attention? Each version had different flutter speeds. The B model with the back window was different than it's predecessor. Tip tanks, Oxygen systems, deicer boots any combination, all had different speeds where flutter was noticed. In the end Piper reduced the Vne on all of them to the same speed rather than to have a variety of Vnes. The one I was involved in had all the extras. Turbo, deicer boots, prop anti-ice, oxygen tank behind the baggage, Tip tanks, B model windows, in other words it was loaded. Great airplane!

[Skywalker]

Descending from high altitudes is a classic. What was your true airspeed?

[frequent_flyer]

Descending from high altitudes is a classic. What was your true airspeed?

I had exactly the same though. I checked the TCDS and didn't find any reduction in limit speeds for altitude (or any TAS correction). I'm used to seeing that in glider limits and I have also found that reduction in some airplane TCDS. What determines if TAS compensation is specified for any given aircraft?

[skywagon8a]

Descending from high altitudes is a classic. What was your true airspeed?

What do you consider high altitudes for a PA-30? Also the airplane limits are based upon IAS in this airplane. It does not fly in the altitudes where this would mater to any extent..

[frequent_flyer]

What do you consider high altitudes for a PA-30? Also the airplane limits are based upon IAS in this airplane. It does not fly in the altitudes where this would mater to any extent..

10,000 ft is the altitude above which I have seen reduction in published limiting speeds. E.g. for DHC-6 ref TCDS A9EA:

[skywagon8a]

10,000 ft is the altitude above which I have seen reduction in published limiting speeds. E.g. for DHC-6 ref TCDS A9EA:

Thank you, that's my point. Unless the PA-30 was equipped with the optional STCd Rajay turbo charge system, it was unlikely to be used at those altitudes.

[frequent_flyer]

Thank you, that's my point. Unless the PA-30 was equipped with the optional STCd Rajay turbo charge system, it was unlikely to be used at those altitudes.

Maybe so but I take my PA-28 and Carbon Cub well above 10,000 ft. Perhaps Tcraft would comment on the altitudes at which those events were experienced.

[Steve Pierce]

I use to maintain this Maule. I met the owners when I took off behind them in a Pacer. After take-off they asked where I was and I replied that I was 1k feet above them. It was 160 hp and weighed well over 1500 lbs. Too bad, it was a nice airplane. A member here came and picked up the airplane when it moved from Texas to New York.

[Utah-Jay]

Sad to see this Maule ruined, luckily there was only one minor injury. Juan nailed it, 70/50 rule would have saved the plane. Pretty heavy plane and loaded with 3 people for a 160hp plane with a low AOA setup

[akavidflyer]

Holding the up elevator and keeping that tail wheel planted in the sand is what got him. Its a MAJOR anchor. Little tires and poor technique. Way too many try to learn off airport flying from youtube and google these days.

[cubdriver2]

Sad to see this Maule ruined, luckily there was only one minor injury. Juan nailed it, 70/50 rule would have saved the plane. Pretty heavy plane and loaded with 3 people for a 160hp plane with a low AOA setup

Into the wind might have helped also

Glenn

[TcraftF21]

Sorry I mentioned a Twin Comanche on this sight. Anyway it was a B model, tip tanks, counter rotator. Descending over Rockford, IL from 10K to Cedar Rapids. Auto pilot with programmable descent rate set to 300fpm. Started to buss at the yellow line at about 4K. Pulled it up and it stopped. Checked the tail weight and the jack screw and made some adjustments but found nothing wrong. Next time descend over RSW at night going into Naples. Same section with the same result. Made the right move after that, sold it and got a Bonanza. Faster and more sturdy.

Jim

[skywagon8a]

I'm the one who mentioned Twin Comanche because the discussion was about flutter. And I participated in and witnessed a flutter test of a Twin Comanche. Thank you for sharing your experience. It is the sharing which creates awareness and hopefully prevents an accident. Without seeing your airplane, your description suggests perhaps some loose linkage to the servo tab. All airplanes can create flutter. It is clear that many Super Cubs on this thread have been modified in some manner. So far there has not been a flutter report.

[TcraftF21]

Everything was up to spec. Even changed the jackscrew and nut. I took it out and took it to red line in a dive and no flutter. Thought it was cured until it did it again. I had that plane for 10 years and a 64 for 6. Go figure. Flew them coast to and north to south. Now just flying my little put put.

Jim

[skywagon8a]

You have my curiosity. Do you recall if the tip tanks were full or empty when the flutter occurred? Or was there a particular loading condition which was different at the time?

[StalledOut]

When I was a kid, for about the time I was born to late HS my dad had a twin comanche with speed mods. As I was growing up he flew that all over the place, Anchorage to St Thomas and Nassau in the Bahamas. Tip tanks for long range. I know we'd do Anchorage to Edmonton in a single hop. He;s in his early 80's now but doesn't remember any flutter on any flights. the counter rotating 160's were cool. The only enforcement action ever taken was in that plane, something about rolling inverted over a runway outside of Vegas. Never got the full story. Anyway, as far as I knew it was rock solid. In fact between that and the turbo arrow those were the two planes I wish he still owned. The Aerostar 602P was hot but short lived. Both the comanche and arrow were picked up new from Piper. I found the invoice on the arrow, $17,500 and $3,500 for the iFR panel option.

[dgapilot]

Everything was up to spec. Even changed the jackscrew and nut. I took it out and took it to red line in a dive and no flutter. Thought it was cured until it did it again. I had that plane for 10 years and a 64 for 6. Go figure. Flew them coast to and north to south. Now just flying my little put put.

Jim

Just got a PA-30. Haven’t flown it yet, long involved annual. The single Comanche had some flutter issues and several SBs to try and correct it. Hadnt heard much about flutter on the twin comanche. Control surface balance is a critical issue when looking at flutter. Any chance that airplane had been painted and didn’t have the stabilator balanced?


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[skywagon8a]

Hadnt heard much about flutter on the twin comanche.

I know of several cases of the stabilizers being severely bent on Twin Comanches at about mid span due to flutter. All during flight testing for various modifications. Chances are good this did not become public knowledge. I also know one of Piper's senior experimental test pilots bent so many of them he could sense exactly when the flutter was about to start, thus being able to take it right up to the limit without doing any damage. I chased him with Piper's flight test Aztec during one of the dives. A Vd dive with both props feathered.

[TcraftF21]

Tips empty in both cases.

Jim

[wireweinie]

Just got a PA-30. Haven’t flown it yet, long involved annual. The single Comanche had some flutter issues and several SBs to try and correct it. Hadnt heard much about flutter on the twin comanche. Control surface balance is a critical issue when looking at flutter. Any chance that airplane had been painted and didn’t have the stabilator balanced?


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Yup. Ya made me look!

The maintenance manual for the -30 and -39 calls out several notices to check for correct assembly, correct 'free play' (none allowed), stripping old paint before making repairs, and balancing stabilator after all repairs or paint. Kinda see a pattern developing here, lol.

Web

[skywagon8a]

Tips empty in both cases.

Jim

Thanks, At this point in time this can only be a brain cell maneuver. In thinking of the one I watched, I believe the tanks were also empty as there was no reason to put gas in them since it wasn't the tanks being tested. They were looking at the wing and prop deicing systems compatibility with the rest of the differences from a stock airplane. Had they been full in your case, the mass of the fuel in the tips would have changed the natural flexibility of the plane. A large mass anywhere in the airplane does this. Your buzz could have been the empty tip tanks vibrating at your speed, sending the vibration through the wing, fuselage and out the tail. Had the tanks been full, the mass of the fuel would have dampened the destructive vibrations.

While I am not certain, I believe the tip tanks were an STC approved on the earlier PA-30s. Both yours and the one I was involved with were B models with the extra back window. The window cutout in the skin changed the stiffness of the fuselage which contributed to the lower flutter onset speeds. I have no knowledge of whether the tip tanks were also tested on the B model or whether is was just blindly accepted without additional testing?

So here are two possible causes, empty tip tanks and repaint without a rebalance. Who knows, perhaps it was the combination of the two?

[dgapilot]

The one I have is a B model but no tip tanks. I can see how the overall dynamics would change with the tip tanks. The tanks are an STC for all the PA-30, -39, and all the -24 series. Supposedly the tanks work better than most aftermarket tips and are good for an extra 2-3 mph. All the turbocharged twins have the tip tanks and a few normally aspirated ones do as well. GAMI owns the STC now and is working to put the kit back in production.

My airplane is pretty much bone stock, no speed mods, original tips and 2 piece windshield. Still has the Altimatic III autopilot but was upgraded to King Silver Crown (KX155s) some time back. It does have a VFR gps. I need to add ADSB as I’m just outside the DC SFRA. Objective is to get it flying again and see what’s left in the bank account before looking at any upgrades.


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[TcraftF21]

My last one, a B, had tips, gap seals, counter rotator, onepeice windshield, small nose wheel, etc. Was fast for a Twinco at 170kts at firewalled and 2500 rpm. First one not nearly as fast nor any others I had known of. I a lot of time on it for business and only two flutter experiences.

Jim

[TcraftF21]

My old one is still flying around Virginia I think. N2VQ.

Jim

[skywagon8a]

..... only two flutter experiences.

Jim

Only two flutter experiences? One is too many!


More brain cells activated. I did the high speed dives and spin testing for Lake when they certified the fuel in the floats tanks. Their pilot was afraid of spins. The STC requirement for high speed dive was only to Vne not Vd as the test which is required for a TC. The spins were done with one float tank full and the other empty. I suspect that is also what was done for the Comanche tip tank STC, just to Vne. The test I observed in the -30 was to Vd. Or at least an attempt to get to Vd.... with the engines stopped!

[dgapilot]

My old one is still flying around Virginia I think. N2VQ.

Jim

Mine is in VA until I finish the annual. N55RD


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[BC12D-4-85]

A local Fairbanks C-185 fatality was reported today: 05-OCT-22 23:53:00Z N217C FAIRBANKS ALASKA CESSNA/185 ACCIDENT DESTROYED 1 AIRCRAFT CRASHED UNDER UNKNOWN CIRCUMSTANCES, FAIRBANKS, ALASKA. If the owner of record was aboard I knew him well since the 1960's.

Gary

Edit: This from another pilot:

Yes, jerry stansel, he drowned in the airplane. He had aborted a take off
and was taxing in and one float dug in and he went over. Someone at chena
marina has video of it. Bummer, guess the load pinned him in.

Update...better preflight floats now or watch out for night crawlers>

[ak49flyer]

https://www.seattletimes.com/busines...ossible-cause/

So much for the YouTube dude’s trim tab theory.

Terrible deal for all involved...

[wireweinie]

That's a tough pic to look at, seeing the actuator top unscrewed from the body.

Web

[mvivion]

I can only imagine the horror that pilot must have experienced……wow!

MTV

[BC12D-4-85]

Here's a more detailed summary of the DHC-3 accident and stab trim jackscrew. Further down in the article is a copy of and a link to the NTSB's initial discovery.

https://sanjuanislander.com/news-art...at-plane-crash

Gary

[skywagon8a]

Yikes! Brings memories of Alaska Airlines' DC-9/MD-80 which stripped the threads of the stabilizer screw jack, doing a nosedive into the ocean off LAX.

[frequent_flyer]

Yikes! Brings memories of Alaska Airlines' DC-9/MD-80 which stripped the threads of the stabilizer screw jack, doing a nosedive into the ocean off LAX.

That accident and this one made me wonder if the elevator could have been used for pitch control. Elevators could perhaps operate as a stabilizer trim tab controlling pitch in reverse sense. I supppose it would depend on where the stab was hinged. So counter intuitive though that I doubt many pilots could push even if they knew the possibility of control reversal.

[BC12D-4-85]

Here's some further reading regarding the DHC-3's stab jackscrew and elevator trim mechanisms. There have been prior failures of the jackscrew above allegedly due to improper maintenance or component wear>

1989 inflight failure of trim jackscrew crew survived by>https://www.aerialvisuals.ca/Airfram...p?Serial=15562
2003 Actuator lube: https://tc.canada.ca/en/aviation/ref...fficulty-alert
A summary from 9/2022 of prior trim failure and others: https://www.aviationlawgroup.com/ott...tch-movements/

Gary

[mvivion]

That accident and this one made me wonder if the elevator could have been used for pitch control. Elevators could perhaps operate as a stabilizer trim tab controlling pitch in reverse sense. I supppose it would depend on where the stab was hinged. So counter intuitive though that I doubt many pilots could push even if they knew the possibility of control reversal.

I'd bet the pilot didn't even have time to understand what was going on.....gives me the shivers.

MTV

[BC12D-4-85]

I think if I were a DHC-3 pilot I'd inquire about this prior incident liked in #3154. The details Docket in the original not linked form says never released:

20 June 1989 N41755 DHC-3 turbine involved in an incident.
The incident occurred at the Palmer Airport (PAQ) Palmer, AK, United States while on approach. The airplane pitched abruptly nose down following an inflight failure of the horizontal stabilizers trim actuator jack screw. The crew was able to maintain control of the airplane and make a successful landing by exerting a large amount of back pressure on the control wheel and adding nearly full engine power.

Edit: I assume upon trim actuator failure the forward hinged stabilizer assembly went rear down commanding a nose down attitude. The crew (two to three arms?) pulled back on the yokes (dual?) effecting up elevator to offset the dive. That and power blowing more air over the up elevator saved the day. One pilot with one arm available (maybe two if off power control) may not have the strength to accomplish that.

Gary

[BC12D-4-85]

One final thought re the DHC-3...I certainly hope a full elevator hand beats a trim at limits any day

Gary

[h2oavi8r]

AOPA has a good description and photo of the Jack screw. There’s also a diagram of the recovered parts of the accident DHC-3.

https://www.aopa.org/news-and-media/...m_medium=email

[skywagon8a]

Heads Up Cessna flyers!

This accident report of a 185E on February 4,2021 in Chitina Alaska was brought to my attention by a friend.
http://www.kathrynsreport.com/2021/0...25z-fatal.html

It appears the right lower lift strut fitting separated from the wing strut, apparently caused by the shearing of the countersunk rivets. This airplane only had 6569 hours total time, which doesn't seem to be high time for a working Alaska airplane of that vintage. Clearly it was used on skis which are known to generate a lot of punishment at times. Notice the pictures of the left wing strut ends where the paint is broken away around each rivet. That is a clear indication of motion between the rivets and the strut. It's likely that motion was sufficient for the movement of the right strut to shear the rivets. It looks like the lower rivets sheared first which created an uneven bending/shearing of the top rivets. It is also likely that the lower rivets had been moving or had been sheared for a period of time. How often does one look at the bottom rivets of the lower lift strut? Likely not often. One thing to bear in mind when using countersunk rivets in a highly shear loaded area, the strut material was countersunk which leaves a knife edge against the rivet. Then when the rivet starts to move, it acts like a guillotine shearing the rivets. Once one rivet shears the others have to take up the load with as in this case disastrous results.

I have noticed one or two smoking rivets on Cessna struts. On low time/years since new airplanes. Also have noticed that the countersinking in the struts as performed by Cessna was not very accurate. As in gaps around the rivet heads. Perhaps the countersinking of this strut was poorly done when it was manufactured? I've not heard of other Cessna struts separating, perhaps this was a fluke? Whatever, this is a good heads up for a more in depth strut rivet inspection.

What is a fix if this situation is discovered? Perhaps replacing the rivets with countersunk steel structural screws? Of course this would require an FAA blessing.

[BC12D-4-85]

It may not be related but those struts are used when accessing the fuel tanks by placing a weighted foot on them for support. Not sure of the stress on the strut's components if any caused by that procedure. Been lots of C-185's w/o strut failure, so maybe it's potentially a rare issue. Also, tying the plane down during high winds might create stress depending on method of securing (?). Examining the riveted area for wear would be good practice. What would be the best way to examine the strut fittings and rivets?

Gary