frequent_flyer
Registered User
Arizona, USA
10,000 ft is the altitude above which I have seen reduction in published limiting speeds. E.g. for DHC-6 ref TCDS A9EA:
Oops, darn it...
- Thread starter Anne
- Start date
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
MEMBER
SE Mass MA6
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
Registered User
Arizona, USA
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.
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Steve Pierce
BENEFACTOR
Graham, TX
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.
akavidflyer
FRIEND
Soldotna AK
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
FRIEND
upstate NY
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
Jim
skywagon8a
MEMBER
SE Mass MA6
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.
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
Jim
skywagon8a
MEMBER
SE Mass MA6
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
MEMBER
Anchorage
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.
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
MEMBER
SE Mass MA6
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.
wireweinie
FOUNDER
Palmer, AK
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
MEMBER
SE Mass MA6
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?
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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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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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
Jim
skywagon8a
MEMBER
SE Mass MA6
Only two flutter experiences? One is too many! :evil:
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!
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BC12D-4-85
SPONSOR
Fairbanks, AK.
Update...better preflight floats now or watch out for night crawlers>
https://www.seattletimes.com/busine...-crash-investigators-identify-possible-cause/
So much for the YouTube dude’s trim tab theory.
Terrible deal for all involved...
So much for the YouTube dude’s trim tab theory.
Terrible deal for all involved...
wireweinie
FOUNDER
Palmer, AK
That's a tough pic to look at, seeing the actuator top unscrewed from the body.
Web
Web
BC12D-4-85
SPONSOR
Fairbanks, AK.
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-ar...y-have-been-cause-of-sept-4-float-plane-crash
Gary
https://sanjuanislander.com/news-ar...y-have-been-cause-of-sept-4-float-plane-crash
Gary
skywagon8a
MEMBER
SE Mass MA6
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
Registered User
Arizona, USA
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
SPONSOR
Fairbanks, AK.
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/AirframeDossier.php?Serial=15562
2003 Actuator lube: https://tc.canada.ca/en/aviation/re...lland-dhc-3-aircraft-service-difficulty-alert
A summary from 9/2022 of prior trim failure and others: https://www.aviationlawgroup.com/otters-history-of-sudden-uncontrolled-pitch-movements/
Gary
1989 inflight failure of trim jackscrew crew survived by>https://www.aerialvisuals.ca/AirframeDossier.php?Serial=15562
2003 Actuator lube: https://tc.canada.ca/en/aviation/re...lland-dhc-3-aircraft-service-difficulty-alert
A summary from 9/2022 of prior trim failure and others: https://www.aviationlawgroup.com/otters-history-of-sudden-uncontrolled-pitch-movements/
Gary
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