# XFLR5 update

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#### Topaz

##### Super Moderator
Staff member
Log Member
You win the award for the greatest-magnitude Cm I've ever seen. This is not a good thing.

#### Speedboat100

##### Well-Known Member
You win the award for the greatest-magnitude Cm I've ever seen. This is not a good thing.

Yes...but it is a working electricity creating wing...not an aeroplane wing.

#### Aerowerx

##### Well-Known Member
IIRC the negative Cm means that it will pitch up into a stall. Which means a H-tail is needed to counteract the Cm of the wing.

You already have a very high AoA of 18 degrees. With out seeing the polar plots it is hard to say what it is doing.

#### ScaleBirdsPaul

##### Active Member
IIRC the negative Cm means that it will pitch up into a stall. Which means a H-tail is needed to counteract the Cm of the wing.

You already have a very high AoA of 18 degrees. With out seeing the polar plots it is hard to say what it is doing.
Normal convention is negative Cm is a nose down moment. At 18+ degrees AoA I’m guessing he’s well past the linear increase in Cl and XFLR is throwing out weird results.

#### Speedboat100

##### Well-Known Member
IIRC the negative Cm means that it will pitch up into a stall. Which means a H-tail is needed to counteract the Cm of the wing.

You already have a very high AoA of 18 degrees. With out seeing the polar plots it is hard to say what it is doing.

Yes here are 0-12 degs AOA polars.

#### Speedboat100

##### Well-Known Member
Here with an other inviscid setting.

#### Topaz

##### Super Moderator
Staff member
Log Member
Inviscid results aren't terribly accurate. Calculate a Reynolds number and Mach number and run a polar for those conditions.

#### Aerowerx

##### Well-Known Member
Your polars show the max CL of about 1.45 at AoA of 10 degrees. I wouldn't trust anything beyond that.

And as Topaz said, inviscid isn't that good.

Remember this is a mathematical simulation of reality. The results are only reasonable* within the linear, not turbulent regions.

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*insert your own definition of reasonable here.

#### Speedboat100

##### Well-Known Member
Inviscid results aren't terribly accurate. Calculate a Reynolds number and Mach number and run a polar for those conditions.
Yes latter is such.

Thanks guys !

#### ScaleBirdsPaul

##### Active Member
Looks like there’s an update on a new version of XFLR5 called flow5. Looks to be much more powerful but will be a paid software.

https://flow5.tech/

There’s a series of YouTube videos that I’m working through to see if it seems worth the price.

#### Aerowerx

##### Well-Known Member
Looks like there’s an update on a new version of XFLR5 called flow5. Looks to be much more powerful but will be a paid software.

https://flow5.tech/

There’s a series of YouTube videos that I’m working through to see if it seems worth the price.
Not really a version of XFLR5.

There are several related programs, all from the same developer. My conjecture is that they used the same basic algorithms to solve the fluid dynamics, but each is tailored for different purposes.