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CTSW Cruise Speed


Skunkworks85

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Jacques, that’s a pretty old document, and I think more is known now.  The flutter problems (including mine) seem to be a result of two factors:

1) a full span stabilator anti-servo (trim) tab

2) inadequate structural stiffening forward of the tab hinge line

I know of mine and one other CT that had the flutter issue.  I had extensive discussions with the other pilot, as well as Tom Peghiny at FD USA, and I have a good handle on this problem.

The other affected pilot told me he thinks the problem originates with the swirling slipstream fromthe prop around the airframe, which sets up an airflow that pushes down on one rear corner if the stab, and up on the other one.  Add to this the pulsing from the individual prop blades, and you have a high frequency pulsing moment in opposite,  complimentary forces on the stab.  I think this is a good theory.

Most CTSWs, especially later ones, have a bulkhead wall just ahead of the tab hinge line, that provides a large amount of stiffness.  Early airplanes, and a few later ones like mine, didn’t have this reinforcement.  That allowed the forces describes above to flex the stab at high speed in a fluttering manner.  I actually think the movement in my case was better describes as “pre-flutter vibration” that was not terribly violent, but definitely noticeable.  In my case this occurred just past 120kt indicated at 2000-3000ft.

The fix in both airplanes was to send the stab back to the factory and have the missing bulkhead added into the stab. Since then I have taken the airplane to 140kt+ indicated several times without issue.  But I am wary of pushing beyond Vne or even close to Vne for extended periods.  There is no need for it and I’d rather be kind to the airplane and make sure it’s kind to me in return.

BTW, I have no concerns or hesitation about the safety of the airplane, and would not hesitate to fly it aggressively throughout the published limits of the airframe (and have done so).

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Jacques,

Why was the video you posted labeled "Ruderflattern" (which translates to "Rudder flutter"). The damage to the horizonal suggests excitation by the elevator trim tab or through the stabilator pivot. It seems unlikely that rudder flutter would excite the horizontal to such a degree.

Mike Koerner

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On 3/22/2019 at 9:03 PM, FlyingMonkey said:

 

Most CTSWs, especially later ones, have a bulkhead wall just ahead of the tab hinge line, that provides a large amount of stiffness.  Early airplanes, and a few later ones like mine, didn’t have this reinforcement.  That allowed the forces describes above to flex the stab at high speed in a fluttering manner.  I actually think the movement in my case was better describes as “pre-flutter vibration” that was not terribly violent, but definitely noticeable

I've got a 2006 CTSW, would like to avoid stab flutter!

I'm what way was the vibration noticable? Through the stick, or entire airframe?

Can you see this extra bulkhead with the stab attached to the aircraft?

Thanks. 

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My 06 SW had the problem, It was very evident thru the stick and happened at 142-145kt. The vibration could be stopped by light aft stick pressure.

As has been mentioned, the full span tab is the warning sign. FD came out with a fix which used new "pockets" to be glassed in at each hinge point to stiffen the wall.

Have a look at your log book to find if this mod has been done, but you should be able to see if you look through the underside gap.

The shorter span tab elevators are not effected. If you change the whole elevator to the later type remember to re balance the assembly because the mass balance is different.

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  • 1 year later...

IMG_3551.thumb.jpg.198bd503341d7547c6dea3ad267bff1c.jpg

I had previously claimed to probably have the slowest CTSW out there -   but i change my claim.  I am the fastest !!   228 KTS   
The modifications i had to do-  UNBELIEVABLE !!    Dont believe ?  You are correct haha    This was a result of a clogged static port.   On takeoff i knew there was something not quite right as the airspeed seemed a bit lower than usual.   I was climbing at 60kts indicated but gps was showing 80kts.  (not much wind so this confirmed the actual airspeed was off)  Continued flight up to 7500ft.   And on the way down i got the 228kts reading.  Was fun for the moment thinking i could fly that fast. :)

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My 2007 CTSW is a speed freak, with the smaller gear and apparently just set up well from the factory (and a prop setting optimized by me).  I see 127kt TAS at 5500ft at 5400rpm.  My typical IAS speeds at 2000ft (normal cruise altitude) are:

5000rpm:  110kt

5200rpm:  115kt

5400rpm:  122kt

These numbers are verified with GPS and against other airplanes.  They are not CT typical numbers, from what I see from other airplanes.  When I first bought the airplane the prop was set terribly and my WOT speed was 108kt.  If your speed is not what you want, the first step is to verify and adjust prop settings as necessary.

 

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GPS is irrelevant in comparison testing due to too many variables as is flying side by side.  Most vfr aircraft , about 75% I find have static leaks. A high percentage of IFR  aircraft also leak. I have done hundreds of certifications.  The only way to check is with pitot/static test equipment to eliminate all variables. I find airspeed indicators significantly off on some aircraft also. My airspeed was only off -1 kt when I calibrated it. I have found that the ctsw has one of greatest airspeed errors in flight with a static leak. In my sw when I first bought it my airspeed was 10 kts higher than it was flying. And this was only a small leak in the airspeed indicator case.

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1 minute ago, Madhatter said:

GPS is irrelevant in comparison testing due to too many variables as is flying side by side.  Most vfr aircraft , about 75% I find have static leaks. A high percentage of IFR  aircraft also leak. I have done hundreds of certifications.  The only way to check is with pitot/static test equipment to eliminate all variables. I find airspeed indicators significantly off on some aircraft also. My airspeed was only off -1 kt when I calibrated it. I have found that the ctsw has one of greatest airspeed errors in flight with a static leak. In my sw when I first bought it my airspeed was 10 kts higher than it was flying. And this was only a small leak in the airspeed indicator case.

Well sure.  How many of us are going to set up fully calibrated test equipment and fly that way?  Do you?  In absence of those tools do you just throw up your hands and declare your aircraft performance "unmeasurable"?

Assuming you're not a propeller-head with thousands of dollars in test gear attached to your airplane, GPS ground speed in zero wind conditions at low altitude is useful in validating whether your IAS indication is "in the ballpark" of correct.  If my indicated airspeed is 110kt, and my GPS ground speed is 110kt in zero wind conditions, then I'm "close enough" to claim my airspeed indication is pretty good and I don't have a wild static error.

Likewise flying next to other airplanes and comparing speed in zero wind is useful, as a check against gross instrumentation error.  If my IAS shows 100kt and another CT shows 100kt and we are static relative to each other, once again it's likely my instruments are "good enough" for real world accuracy.  If one or the other airplane indications is off by more than a couple of knots, somebody's indication is faulty. 

I have flown my CTSW throughout the entire speed range for six years.  I'm confident I do not have a static leak.  I don't know about his current bird, but when CharlieTango was flying Woodstock he reported cruise numbers similar to mine, in fact the exact same TAS numbers at the same RPM.  I routinely do 30° flap landings at 48kt, and the airplane will really start to sink hard at 45kt.  That tells my my low speed range is pretty close to factory numbers, which show a stall in that config at 42kt. 

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23 minutes ago, AGLyme said:

That’s amazing performance.  Meaningful on a long trip.

CTs are great traveling airplanes.  I went from Pontiac, Illinois to Winder, Georgia (485nm) at gross weight in 4hrs. 20min.  That's an average over 112kt including climb out and slowing into the pattern on arrival.  I was at 5400-5500rpm the whole way and landed with about 7 gallons of fuel.  I have zero complaints about my CT's traveling speed. 

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3 hours ago, FlyingMonkey said:

That's an average over 112kt including climb out

That's strong.  I think I averaged about 100kts on my way back from Illinois, first leg was 6 hours.  Glad I re-pitched, the plane takes off with more power and def cruises about 4 knots per hour more... Flying on some grass this weekend again, will appreciate the extra power.

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4 hours ago, Madhatter said:

A lot of shops have my test equipment. Its real easy to check the static, about 10 min. If anyone is 10 kts over on approach that's huge. I am not advocating everyone do this, I'm just describing the process. Don't want offend anyone.

Oh, I wasn't offended, just chatting.  I have had a pitot/static test, but I thought you were more talking about things like airspeed calibration and verification testing, which can take much more sophisticated equipment.  For those of us who are just comparing performance, I think careful comparisons of IAS to GPS ground speed and with other aircraft under ideal conditions can be useful.  

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