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  1. R

    Lift theories

    Yes the flow is turning, but you will find, without adding circulation, the flow on top and bottom of the airfoil will ‘turn’ exactly the same amount and so there will be no net force. IOW, yes the velocity ( and hence pressure) is changing all along the chord , but the total change is the same...
  2. R

    Lift theories

    Bernoulli tells you given a velocity what the pressure (a scalar) is at any point in the flow field and vice versa. But how do you tell what the velocity at each point in the flow field is ? I guess you can get it from the pressure. But then how do you get the pressure ? It is a circular...
  3. R

    Homebuilt Production During 2023

    Ron, how long is the tail- number of airplanes that have 10 or fewer examples ? Maybe the total on top ( 1411) include all airplanes?
  4. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    I did find the reading confusing so I checked with Jim at ASC and he confirmed that the exemption does apply to fixed wings as well, as long as the other requirements of empty weight, speed, and fuel etc in 103 are met. I think this certainly is an avenue worth exploring and a positive...
  5. R

    Lift theories

    Yes it is very good. He does invoke viscosity though. At one place he says there are many solutions to the rear stagnation point in non viscous flow. This is the classic explanation. Though it turns out due to compressibility effects, as shown in the video link I posted in the first post, there...
  6. R

    Lift theories

    Yes, though strictly speaking they all require little hacks (Kutta condition) that implies viscosity at the start to create a starting vortex which in turn generates circulation and consequently lift. Without that you get no lift or drag in a pure non viscous irrational flow. Classically the...
  7. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    Yes I think they are all covered by the Exemption No. 9785G that aero connections got.
  8. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    The link I posted seems broadly to address all ultralight vehicles as long as they meet all the requirements. And the FAA give a good rational as well for it. Also it is from 2022. I guess the availblilty of suitable UL may have been the impediment. With
  9. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    I have...also saw Jim's recent editorial and that further seems to confirm this option .... it all seems to do with availability of suitable ultralights that meet the part 103 but can take an additional passenger. Hopefully he confirms....Time to dust out the Pteradactyles..... Excerpt from...
  10. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    Here is the exception: Link Question is if this is limited to trikes and PPG. The reading is confusing but I do not see anything explicitly saying no (apart from the preamble that says it is for unpowered but the conditions (see below) includes powered . Here is an excerpt: All flights...
  11. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    I know the tandem PPG have a broad exception but the flex wings, have they had this for long? Seems like an individual case by case with the flex wings. I don't think everybody would be doing it. It is very different to the old fat ultralights. No additional allowance for empty weight or stall.
  12. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    I expect you would still have to meet the stall speed requirement. You make the calculation just as you do for single seater compliance per 103 appendix, using 170lbs for pilot and 30 lbs for fuel. In the case of the two seater it would be 254+30+170+170 = 624. Using a high camber single...
  13. R

    Change.org: Urge the FAA to Address the Deficit of Ultralight Aircraft Instructors

    The recent (last week) EAA series on trikes towards the end mentioned that there is a 2 seater air creations flexwing trike that has a FAA exception for ultralight training. This is an ultralight and not N numbered experimental or LSA. The way they got it is by meeting all the part 103...
  14. R

    Lift theories

    Does lift need viscosity?Great webinar on lift in super fluids, IOW you don't need viscosity to generate lift. Also in the middle of the talk a great description/review/explanation of lift generation in normal conditions.
  15. R

    Calculating Wing pitching moment/torsion using Cm?

    What is the geometry of the wing. For a rectangular wing (of any AR) the aero center is exactly where the section airfoil aero center is and the pitching moment coefficient of the wing is exactly what it is for the section. For an arbitrary platform you have to break it up into strips and sum...
  16. R

    Calculating Wing pitching moment/torsion using Cm?

    That is why I said moment about the aero center (AC) , not c/4. Aero center is only exactly at c/4 for symmetrical airfoils. If you see TOWS it will give you curves of cm about both c/4 and AC. Of course the C/4 curve will not be flat if the aero center is not exactly at c/4 because lift adds a...
  17. R

    Calculating Wing pitching moment/torsion using Cm?

    Oriol, see above quote ...Billski said Roncz did not differentiate between Csubm and CsumM. As I said before the only reason the TOWS value is different is because how they compute mean chord and area in the rounded wing tips. You are making a simple relationship very complicated. As Cm about...
  18. R

    Tandemwings and CG range

    The CG range is the distance between the CG aft limit and CG fore limit The location of the CG aft limit is determined by the tail volume. All configurations will behave badly when the CG gets behind the aft limit, though some more so than others. This does not mean it has a low CG range. A...
  19. R

    Calculating Wing pitching moment/torsion using Cm?

    Oriol, for a finite wing the Cm is simply the sum (integrate) of section cm across the span. In other words, cm = Cm for wings with no sweep and tapper. It is that simple! I think you confused yourself by looking at TOWS and noticed that Cm was greater than cm in one of the graphs (figure 13) ...
  20. R

    Calculating Wing pitching moment/torsion using Cm?

    Yes, of course you are missing something. Sorry got to say this...not many folks out there who can confuse themselves as much as you can. 1. The section you quoted (chapter 2) from Hiscocks is for calculating the section properties. In other words 2D or in other words infinite span. So AR is...
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