Small Flightmodel Inacuraccy?

[Test1234]

Hey there, i'm really loving the Flightmodel on the IXEG great job!  Just something i noticed though, Normally with the Flap Extension the Nose should drop and with Flap Retraction the nose should go up, however i noticed the IXEG has a diffrent Behavior. From Flaps 1-5-10-15 The Nose goes Up when extending the Flaps, and when going from Flaps 15-25-30-40 The nose Initally Drops then instantly goes Back up again.

Merry Christmas to everyone and sorry for the sketchy username.

[Morten]

Hi, Merry xmas and welcome to the forums

The flap pitching moments have been fine tuned to our 6000 hrs in type pilot (Jan) preferences for each flap setting.  Not sure what your background in the classic is, but judging by my notes on this, you two disagree on atleast parts of the behavior, also your observations are not consistent with what we have actually modeled, so please clarify your background and re-check your observations.

M

[Test1234]

38 minutes ago, Morten said:

Hi, Merry xmas and welcome to the forums

The flap pitching moments have been fine tuned to our 6000 hrs in type pilot (Jan) preferences for each flap setting.  Not sure what your background in the classic is, but judging by my notes on this, you two disagree on atleast parts of the behavior, also your observations are not consistent with what we have actually modeled, so please clarify your background and re-check your observations.

M

Not Rated on the 737CL, but to my Understanding, normally on a plane like a 737 aerodynamically When you extend the Flaps the Downwash will be increased and that will move the CP Aft causing the Nose to Pitch Down, or am i mistaken?

[Sopwith]

Interesting. But as your flaps go down lift increases which could pitch you up. I will go and load it up and have a play. 

[Test1234]

12 minutes ago, Sopwith said:

Interesting. But as your flaps go down lift increases which could pitch you up. I will go and load it up and have a play. 

And as the Lift Increases the Downwash will also Increase, Lift and Downwash are Proportional to eachother because Downwash is a product of Lift. and the aft movement of the CP should cause a Nose Drop AFAIK, you can see this effect really well on GA Planes, for example on the Piper Cherokee,Archer its Really Obvious.

[Sopwith]

GA and this jet are of course very different aircraft when it comes to flaps. When all of the flap is trailing edge the moments will inevitably be to the rear. Jets with leading edge devices produce a more balanced response. 

I just had a play. Using the auto pilot - weather all parameters to nil - fly 2000feet - set vertical speed to 0 heading to whatever - auto throttle to 210 kts. give it a minute to settle down - then A/p off A/t off - and flaps to 5, results in a slight pitch down (PD) followed by PU. repeat to stabilise everything then flaps 5 to10 results in a slight PU.  

Repeat at 170kts - zero to 5 resulted in a slight pitch down, 5 to 10 was nil and 10 to 15 a pitch up. a result which demonstrates the extra lift being produced at a fixed speed.And of course in real and simulated flight the speed is altering all of the time. 

I think it comes back to your comment about a GA aircraft influencing your expectation. I had here a BA F/O who had flown the 300 and I couldn't get him off the sim which he thought was brilliant. 

[Morten]

On 24.12.2016 at 0:32 AM, Test1234 said:

Not Rated on the 737CL, but to my Understanding, normally on a plane like a 737 aerodynamically When you extend the Flaps the Downwash will be increased and that will move the CP Aft causing the Nose to Pitch Down, or am i mistaken?

It's not that simple.

1. Slats, they tend to move the center of lift forward (chord extended forward)

2. Fowler flaps.  For the first 2-3 detents they extend backwards extending the chord aft moving center of lift aft.

Typically this results in a pitch down because the flaps extend more than the slat and Center of Lift moves backwards. so kind predictable stuff so far aerodynamically speaking. (but as discussed øwith a 707 pilot somewhere here slat and flap type also play a role and the 707 pitches up)

However, when extending further, F15+ things get more complicated

3. Huge lift increase 

4. Huge drag increase

5. Flap starts "curling forward" again, CoL forward

6. Center of gravity

7. Gear drag

Is the center of flap/gear drag above or below the aircraft vertical CoG? Below -> pitch down, above -> pitch up.  Soo.. when talking about flap pitching moments on aircraft, you cannot generalize.  It depends on unique factors for each aircraft.  Either you need to do some very hard engineering calculations with data you probably don't have, or listen to experienced in type pilots.

Also, when testing this in sim you need do some very precise flying by the book, also recommended done by real pilots.

M

 

 

Edited December 26, 2016 by Morten

[Test1234]

40 minutes ago, Morten said:

It's not that simple.

1. Slats, they tend to move the center of lift forward (chord extended forward)

2. Fowler flaps.  For the first 2-3 detents they extend backwards extending the chord aft moving center of lift aft.

Typically this results in a pitch down because the flaps extend more than the slat and CoG moves backwards. so kind predictable stuff so far aerodynamically speaking. (but as discussed with a 707 pilot somewhere here slat and flap type also play a role and the 707 pitches up)

However, when extending further, F15+ things get more complicated

3. Huge lift increase 

4. Huge drag increase

5. Flap starts "curling forward" again, CoL forward

6. Center of gravity

7. Gear drag

Is the center of flap/gear drag above or below the aircraft vertical CoG? Below -> pitch down, above -> pitch up.  Soo.. when talking about flap pitching moments on aircraft, you cannot generalize.  It depends on unique factors for each aircraft.  Either you need to do some very hard engineering calculations with data you probably don't have, or listen to experienced in type pilots.

Also, when testing this in sim you need do some very precise flying by the book, also recommended done by real pilots.

M

 

 

Gotcha, Thanks for the Reply and Clarification