Stick Pulse?

Talk about airplanes! At last count, there are 39 (and growing) FAA certificated S-LSA (special light sport aircraft). These are factory-built ready to fly airplanes. If you can't afford a factory-built LSA, consider buying an E-LSA kit (experimental LSA - up to 99% complete).

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Jim Hardin
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Stick Pulse?

Postby Jim Hardin » Sun Jul 09, 2017 7:19 am

I have flown 2 LSA's that had this oddity.

In cruise flight there is slight moving of the control stick fore and aft. No response from this movement by the aircraft, which remains stable.

Not large movements, maybe 1/4" to 3/8" total and they can be stopped by holding the stick a more firmly. I have only noticed it during cruise but during climb and descent I really haven't been looking for it.

The 2 aircraft are very different, a CTLS which has a stabilator and a Remos GX using a horizontal stabilizer and elevator.

I checked for slop in the controls as well as the trim system and nothing was found. In fact they are tighter that your average piper/cessna systems.

I have reported it but the mechanic is on vacation at the moment (plane isn't used too often)

Just curious if this is unique to these 2 or have others come across this?

3Dreaming
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Re: Stick Pulse?

Postby 3Dreaming » Sun Jul 09, 2017 8:50 am

I can't speak for the Remos, but it is normal on the CT. When Flight Design came out with the CTLS they started by doing full size wind tunnel testing. The problem with the stick bump was more noticeable in the CTSW. What they found in the wind tunnel is that the laminar flow of air on the stabilator is un attaching and re attaching causing the stick bump. They made some changes to improve the issue, but it is still there and noticeable in smooth air. The CTlS was an improvement over the CTSW in this regard.

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MrMorden
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Re: Stick Pulse?

Postby MrMorden » Sun Jul 09, 2017 4:34 pm

3Dreaming wrote:I can't speak for the Remos, but it is normal on the CT. When Flight Design came out with the CTLS they started by doing full size wind tunnel testing. The problem with the stick bump was more noticeable in the CTSW. What they found in the wind tunnel is that the laminar flow of air on the stabilator is un attaching and re attaching causing the stick bump. They made some changes to improve the issue, but it is still there and noticeable in smooth air. The CTlS was an improvement over the CTSW in this regard.


I have a CTSW and have noticed this maybe twice, and it's very faint, not even worth noting. Could even be caused by small gusts against the stab. Why would the flow detach from the stab in normal cruise? Couldn't that lead to a tail stall, which is a VERY serious condition?
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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Jim Hardin
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Re: Stick Pulse?

Postby Jim Hardin » Sun Jul 09, 2017 5:43 pm

Detached airflow is not always serious.

In other aircraft I have seen raindrops moving forward across the wing. Unless the tide was changing some odd airflow was pushing it.

Likewise the twin Comanche used to suffer an airflow issue that cause a partial tail stall which delivered you to the runway with an embarrassing thud. Had a 310 that did the same thing at forward CG. Otherwise, very docile as the CG moved back.

Still adjusting to the ASTM way of letting things go. :shock:

3Dreaming
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Re: Stick Pulse?

Postby 3Dreaming » Sun Jul 09, 2017 9:49 pm

MrMorden wrote:
3Dreaming wrote:I can't speak for the Remos, but it is normal on the CT. When Flight Design came out with the CTLS they started by doing full size wind tunnel testing. The problem with the stick bump was more noticeable in the CTSW. What they found in the wind tunnel is that the laminar flow of air on the stabilator is un attaching and re attaching causing the stick bump. They made some changes to improve the issue, but it is still there and noticeable in smooth air. The CTlS was an improvement over the CTSW in this regard.


I have a CTSW and have noticed this maybe twice, and it's very faint, not even worth noting. Could even be caused by small gusts against the stab. Why would the flow detach from the stab in normal cruise? Couldn't that lead to a tail stall, which is a VERY serious condition?


Andy, what I stated is what I was told by Flight Design engineers. I don't think it was anything serious, but an annoyance.

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MrMorden
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Re: Stick Pulse?

Postby MrMorden » Mon Jul 10, 2017 8:57 am

3Dreaming wrote:
Andy, what I stated is what I was told by Flight Design engineers. I don't think it was anything serious, but an annoyance.


Oh I believe it, I didn't mean to sound like I was questioning the information.

It just seems "weird" that flow would detach and re-attach in normal cruise flight. It seems it would stay attached, or not, but not fluctuate like that. Of course, I am a complete layman on aerodynamics, so... ;)
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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MrMorden
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Joined: Fri Aug 17, 2012 7:28 am
Location: Athens, GA

Re: Stick Pulse?

Postby MrMorden » Mon Jul 10, 2017 9:01 am

Jim Hardin wrote:Detached airflow is not always serious.

In other aircraft I have seen raindrops moving forward across the wing. Unless the tide was changing some odd airflow was pushing it.

Likewise the twin Comanche used to suffer an airflow issue that cause a partial tail stall which delivered you to the runway with an embarrassing thud. Had a 310 that did the same thing at forward CG. Otherwise, very docile as the CG moved back.

Still adjusting to the ASTM way of letting things go. :shock:


Clearly not an issue, it just seems "weird". I can confirm that the CTSW has no tail issues at high AoA, aggressive maneuvering, and fairly high g-loads. :twisted:
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA


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