CTLS aerodynamics

[Juliet Golf]

In Europe, the ELA category doesn't suffer any LSA 110 Kt limitation. Many 100hp LSA planes have a much faster cruise than the CT. I was thinking if it is possible to improve CTLS speed, even by a few knots :

- propeller? I've the Neuform. Seems DUC has some better props, but the type is not listed for the EASA variant.

- aerodynamics? I saw in Toulouse some small wheel fairings and pants for uncertified CTLS, at the french importer. I asked and the kind reply was "not official, so not for sale".

Anyhow, the CTLS is not a very clean plane; I was wondering if anyone did anything to improve its air drag? Is anyone aware of an alternate wheel fairings maker? some magic tape / cover to improve our plane aerodynamics?

 

[Ed Cesnalis]

JG,

 

How's your prop pitch?  5,500 RPM @ WOT @ 7,500' is your best speed.

 

What is your best speed right now?

 

Which 100hp LSA have much faster cruise? 

[Anticept]

JG:

 

First is the flaps. european CTs go to -12 flaps.

 

Second is the prop pitch. Being able to adjust it in flight means we could set it for most efficient cruise, but the 120kt limit and the requirement that the prop not be adjustable in flight is the problem there.

 

That's pretty much it.

[Juliet Golf]

at WOT i get about 5300 rpm and 120 Kt with flaps -12°

a variable pitch prop would help but add more weight, I'm unsure it's worth the money.

the Pipistrel Virus SW flies 140 Kt with quite the same configuration (600 Kg MTOW, high wing, 2 seater, 100 hp rotax). CTLS is much more comfortable, and I would never switch, I'm just saying that Pipistrel did a more clean plane, and gets over 20 Kt cruise speed.

[Anticept]

It will add a little bit of weight, but it should get you 130kts.

 

Also, 2 blade props are more efficient than 3 blades. 3 blades will get you more torque converted, but close to top speed, it's offset by the prop streams interfering with each other.

 

Finally, the Virus SW that they used is a taildragger. Nosegears hit performance HARD. So comparing the Virus SW TAILDRAGGER version to nosegear CTs is kind of like mixing classes of wrestlers.

 

They are still good planes though.

[Anticept]

We don't have -12 flaps in the USA as others have noted.  But your performance numbers seem low even for a CTLS.  I have a CLTSi with a 912iS and at 90% throttle at 5300 rpm, 1100lbs, -6 flaps at 8k feet DA I get 120-130 KTAS easily.    I still can get 5500 rpm from there and go a little faster - much like the Pipistrel numbers.

 

Both the Pipistrel and FD CT are all carbon fiber with fixed gear.  They both have the same drag profiles, the FD CT maybe a little less drag due to the negative flaps.  As Anticept noted, the prop pitch is the only real variable in regard to speed once at altitude and cruise.  But it should not be anything like a 20% problem.

 

Check my edit.

[Ed Cesnalis]

a variable pitch prop would help but add more weight, I'm unsure it's worth the money.

 

You do have a ground adjustable prop?  You will get more speed as well as better climb and better economy if your WOT RPM is 5,500 at cruise altitude.

[FlyingMonkey]

at WOT i get about 5300 rpm and 120 Kt with flaps -12°

 

 

Change your prop pitch.  My WOT is 5700rpm @ 2500ft (I'm a flatlander and want it slightly over-flat at low alt so it will be ~5500rpm at 7000-8000 as CT mentioned).

 

With my prop set like that and -6° flaps, I can see 130 knots true airspeed on a good day at 5500rpm.  When I first got the airplane the WOT was 5200rpm at the same altitude, and the airplane would not get beyond 115kt true.

[GravityKnight]

 

 

Anyhow, the CTLS is not a very clean plane

 

Compared to what? There are a lot of LSA's out there that fly slower than a CT

[FastEddieB]

Compared to what? There are a lot of LSA's out there that fly slower than a CT

I know.

 

I own one.

 

I'm thrilled to see triple digit airspeeds, which is pretty rare.

 

I'd say 120k or thereabouts on 100 hp and a fixed pitch prop is pretty darn "clean".

[Juliet Golf]

Thanks all for your inputs. Indeed, the fact I can't reach 5500 with WOT : maybe an overpiched prop; I'll unmount the cone and try to see if I can read the pitch markings. Anyone has some values for their Neuform blades?

 

About comparing planes, it's always difficult; yes the CT is clean compared to most LSA, I was just referrering faster planes likes MCR-01, VL3, WT9. There, you see double slotted flaps, aileron links covers, aileron rudder and flaps hinges covers. They're different planes, I was wondering if there are any speed-kit released or such, as these small wheel fairings and pants i've seen.

[Ed Cesnalis]

I have small wheel pants, they came from FD installed on the new plane.  I think my speed is the same with the pants on or off.  You could take yours off and see if you get an increase.  If you get an increase it might be worth it to use small pants but it sounds like you have a problem with approval more than finding a source.

 

You said 'even a few knots' so I brought up the prop pitch because that will give  you a few knots for sure.  Speed mods have never become popular here on the CTSW because we have always been flirting with the speed limitation as is.

[Runtoeat]

JG, definitely want to be at 5500 to 5650 rpm when at the normal cruise altitude for best speed/takeoff performance.  Best to use a digital tool to measure and readjust the propeller angles.  Do this while each blade is at horizontal to ground and make the measurement at the same spot on each blade (i.e., same distance out from the hub or in from blade tip).  There is much posted on this forum about pitching a prop.  Enter "pitch" and search.  Here's one example:

http://ctflier.com/index.php?/topic/1503-rotax-recommended-rpm/?hl=pitch#entry11499

[FlyingMonkey]

Thanks all for your inputs. Indeed, the fact I can't reach 5500 with WOT : maybe an overpiched prop; I'll unmount the cone and try to see if I can read the pitch markings. Anyone has some values for their Neuform blades?

 

 

 

Make sure you mark your spinner and put it back on in exactly the same orientation.  You can throw off the balance a little by putting things together differently, assuming your prop has a good balance to start with. 

[FlyingMonkey]

Flatten your prop pitch by  1.25 degrees and go fly. You'll be happily surprised.

 

The prop adjustment should only take 45 minutes.

 

That is an understatement.  I followed this same advice from Roger last year, my prop was even coarser than JG's at barely 5200rpm WOT.  My CTSW went from a relative "dog" with max speed in level flight of 108kt indicated, to a "hoss" getting 115kt at 5200rpm and 120kt at 5400-5500rpm.  Climb increased 200-300fpm also.

 

Any CT owner who has not done this is leaving significant performance on the table.

[Anticept]

Just another little tidbit of info:

 

Props don't generate a lot of forward force when they rely on impulse force, which is where air is throw backwards from bouncing off of the blade face (the side of the prop that the pilot sees on tractor configurations is the blade face). All that really does is cause a lot of drag, and imparts a spin on the airstream (slipstream). When props rely on the bernoulli principle (reaction lift force), which requires very specific pitching, they greatly excel at their function, because air pressure is much lower in front of the blades and the pressure behind them pushes them forwards. Truth of the matter is, they still use a little bit of the impulse forces, but a LOT of reaction lift.

[Juliet Golf]

thanks all for the tips, I'll ask my workshop to reduce my pitch and let you know the results...

[207WF]

Check that your aileron trailing edges line up with your flap trailing edges when flaps are at -6 (or -12).  Mine drooped a bit lower than the flaps, and lining them up bought me a couple of knots cruise.  WF

[dadoumping]

Hello from france,

 

135 kts at 5400 with an e-prop prop ( french carbon madré ) -12

[Ed Cesnalis]

Wow

 

What was altitude and thottle setting?

[Anticept]

France allows the variable pitch prop, which goes a long way.

[coppercity]

Imagine a constant speed attached to a Rotax 914 in our CT!  Awesome..

[Doug G.]

Isn't there a difference between an adjustable (in air) and a constant speed prop?

[FastEddieB]

Isn't there a difference between an adjustable (in air) and a constant speed prop?

 

Yes, though the terminology can be confusing.

 

In-flight adjustable would typically give you a control that directly changes the pitch angle of the prop.

 

Constant-speed props use a governor to maintain a given rpm (to the extent possible).

 

Think of the former as a manual transmission and the latter as an infinitely variable automatic.

 

BTW, either would be a blessing in our planes - I'd get one in a heartbeat for my Sky Arrow were it legal. Even Experimental, I must still not make mods taking the plane out of Light Sport limitations.

[Doug G.]

That's what I thought. CTLS only comes (non US) as an adjustable prop, right? Not constant speed?