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Thread: Vertigo componant of lift and droop tips, recovering this winter, keep tips or not

  1. #1

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    Default Vertigo componant of lift and droop tips, recovering this winter, keep tips or not

    Recover and give it new paint, have Fergusen Boosters, considering going back to stock tip, wondering just how much lift force is actually being gained from the droop tips over stock bow tip? The tips are supposed to tilt the lift force more upward and not have as much rearward lift force as the stock bow tips, but have not flown a bow tip to compare it to.
    Last edited by PA-16; 11-19-2020 at 08:55 AM.

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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    You have higher pressure air under the wing and lower pressure air above it. If the wing had infinite span tip shape would not matter. But since you don't you get some spanwise airflow near the wing tips as the air under the wing moves around to the low pressure side. That creates a wing tip vortice and the greater the pressure differential the greater the vortice, so you see more effect at low airspeeds and high angles of attack where the pressure gradient is increased.

    You'll see some variation in "droop tips" with tips like the Demers tip having a lot more droop, than tips like the Plane Booster droop tips, which are a little wider but drop less. However they all work about the same, taking that spanwise airflow and redirecting the vortice to gain additional lift. They also square off the wing tip and increase the effective wing area slightly.

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    dbudd's Avatar
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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    I have owned pacers and tripacers with stock wings and ones with tips and I wouldn’t have one now without the tips. I do prefer the Ferguson because they give you more wing area. I just wish you could run the ailerons out to the tip for more authority


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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    Droop or hoerner, all reduce induced drag. Therefore, they give the wing more lift. Yes, more lift outboard of the aileron reduces roll rate. But, our Short wing planes already generally have good roll rate. Keeping a stock Piper wing tip is mostly for ascetics. If I had a Vagabond or a Clipper, I would keep it stock.
    "You can only tie the record for flying low."

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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    Plus the work it takes to convert back is not simple or quick.

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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    Installing vortex generators on the wings is arguably your biggest bang for the buck, but they also improve aileron response, so they are a way to get back most or all of the roll response lost with longer wing tips.

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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    Was thinking back about what I read in the old AC6121 flight training handbook, that most lift is the result of the downwash from above the wing, and that the wingtip vortices zoom up around the tip and hammer downward on the downwasn that is lifting the plane at the wingtips and this tilts the lift vector even farther backwards pulling the plane backward instead of upward. Lift acts perpindicular to the average relative wind, it gets deep, but to keep it simple the droop wingtips are supposed to decrease the downwash that those vortices are hammering the required downwash to make lift, and this tilts the actual lift vector back to where it should be more upward instead of pulling the plane backward.

    Just wonder if it really that much difference, it makes sense tilting the total lift more upward than backward it should lift the plane off the ground at a slower speed.
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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    An aeronautical engineer I am not. But thinking this through in my feeble brain, wouldnt simply squaring off the wingtip and putting a fence on the end accomplish the same as a droop tip? The advantage would be wing area increase and it wouldnt look so dumb
    For my money, vortex generators is what Id do too.
    ​Jan
    1960 PA22-150 "Spud"

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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    Quote Originally Posted by PA-16 View Post
    Was thinking back about what I read in the old AC6121 flight training handbook, that most lift is the result of the downwash from above the wing, and that the wingtip vortices zoom up around the tip and hammer downward on the downwasn that is lifting the plane at the wingtips and this tilts the lift vector even farther backwards pulling the plane backward instead of upward. Lift acts perpindicular to the average relative wind, it gets deep, but to keep it simple the droop wingtips are supposed to decrease the downwash that those vortices are hammering the required downwash to make lift, and this tilts the actual lift vector back to where it should be more upward instead of pulling the plane backward.

    Just wonder if it really that much difference, it makes sense tilting the total lift more upward than backward it should lift the plane off the ground at a slower speed.
    Well...yes and no.

    Producing lift always produces drag and the drag created by the production of lift is by definition "induced drag".

    The downwash around the wing tips changes the local airflow and contributes to increased induced drag at the wing tip. However, the reduction in effective wing area caused by the rounded wing tips and their much less effective airfoil cross section greatly reduces the lift created by that section of the wing. That means the rest of the wing has to produce nearly all the lift to balance the weight/lift equation. At any given airspeed that means the wing has to operate at a higher angle of attack to create that lift, and airfoils create more induced drag at higher angles of attack (partly due to the same lift vector issues discussed in your diagram, but across the entire wing).

    The effect then of squaring off the wing tip, and in some cases adding some additional span, increases the effective wing area, and allows the wing as a whole to create the required amount of lift at a lower angle of attack at any given airspeed, reducing induced drag.

    For example, the Sullivan wing tip mod straightens out the spar caps and installs a shear web between them to extend the spar, then adds a rib and a tip rib to support a Hoerner wing tip. it only increases the wing span slightly over all but increases the effective wing area by about 17%. That increased area allows the wing to operate at a lower angle of attack where lift is produced more efficiently with less induced drag.

    The increased area has the greatest effect on reducing induced drag at higher angles of attack and lower airspeeds, but also shows some potential benefit on cruise for the wing area challenged short wing Pipers, especially those at the higher end of the empty and gross weight ranges.

    One reason you see 75% cruise speeds on the Tri Pacer rather than 555 and 65% cruise speeds in the manual is that those aircraft were heavy compared to the Vagabond and Clipper, all using the same basic wing. "Slow" cruise speeds in a Tri Pacer were just not as efficient as the wing had to operate at a higher AOA to support an aircraft that had an empty weight that was 300-400 pounds heavier, meaning the wing has to carry 300-400 more pounds, even when the fuel and pilot/passenger load is identical. Add in the weight of two more passengers in a Tri Pacer compared to a Vagabond and the increase in AoA and induced drag at lower cruise speeds was significant.

    In that regard, wing tip mods and extended wings make more sense for the later Pacers and the Tri Pacers than they do for a Vagabond, a Clipper, or even an early Pacer as their higher wing loading has a larger impact on induced drag production.

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    Default Re: Vertigo componant of lift and droop tips, recovering this winter, keep tips or no

    Quote Originally Posted by J Ryd View Post
    An aeronautical engineer I am not. But thinking this through in my feeble brain, wouldnt simply squaring off the wingtip and putting a fence on the end accomplish the same as a droop tip? The advantage would be wing area increase and it wouldnt look so dumb
    For my money, vortex generators is what Id do too.
    I only have two years of aeronautical engineering - like Howard Hughes, just enough to be dangerous.

    But I agree with you, squaring off the wing tip would give you a useful increase in effective wing area.

    Fences help stop spanwise airflow and stall progression, but they are usually somewhere mid span with one usually placed just inboard of the airlierons. Combined with a little washout in the wing (slightly lower AoA at the wing tips or a different airfoil section at the tips that stalls at a higher AoA) a stall fence there will help keep the airlierons in clean air and preserve their effectiveness.

    You can install a flat plate at the tip, but they don't look great in my opinion and they really don't do much. There main advantage is simplicity in "finishing" the wing tip. A Hoerner tip would be more effective, or one of the wider and shallower droop tips might be a nice compromise.

    I also agree with you on the VGs. They will by far give you the most bang for the buck and the MicroAerodynamics STC also has VGs on the under side of the horizontal stabilizers just in front of the elevators to help keep the flow attached at low speeds and high deflection angles. It pretty well cures the falling out of the sky carrier landing trait that Pacers and Tri Pacers have at low speeds.

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