Test Pilot time: Short field landings.

Discussion in 'Flight Following' started by flyingcheesehead, Jan 1, 2019.

  1. tspear

    tspear Pattern Altitude PoA Supporter

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    If you can brake with exactly 1G of deceleration force you may match the additional weight assuming the brakes can take the additional heat.

    However I have never managed to perfectly balance the additional force with additional brake pressure. Maybe you have more skill with this perfect balance.

    I know even with antilock brakes in my car, weight affects stopping distance.

    Tim

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  2. tawood

    tawood Pattern Altitude

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    But its wrong to assume HOW it will affect stopping distance...since a human factor is involved, a person could skid when light, and not when heavy, resulting in shorter distances when heavy.
     
  3. tspear

    tspear Pattern Altitude PoA Supporter

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    Correct, but my point is that weight is a factor also. Based on comments from the OP, where there likely is not much fuel burn (the primary change in weight), it likely is a negligible error.

    Tim
     
  4. Mooney Fan

    Mooney Fan Line Up and Wait

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    It was a poor attempt at sarcasm. At my last BFR the CFI commented if I was on a PSEL check ride I would bust since I start my decent and approach abeam the numbers with the base turn soon to follow. He called that 'diving' at the runway, I responded no, it's the way I learned to fly. When the RWY is available, take it. He went on to comment on how the FAA wants to see a longer more stabilized approach, thus my comment, 'drag it in' on a 3-mile final.
     
    Last edited: Jan 2, 2019
  5. Salty

    Salty En-Route PoA Supporter

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    I do stabilized “simulated engine out 180” landings all the time. Being stabilized is even more important for that type of landing.
     
  6. MauleSkinner

    MauleSkinner Final Approach

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    Ask him where it says so in the ACS.

     
  7. Mooney Fan

    Mooney Fan Line Up and Wait

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    I hear you. But I think the FAA would not agree based on their guidance. Assuming a 300'fpm decent rate with an approach speed of lets say 75mph, that puts us on a 1 1/4 mile final.


    Factors of a Stabilized Approach
     Maintain a specified descent rate.
     Maintain a specified airspeed.
     Complete all briefings and checklists.
     Configure aircraft for landing (gear, flaps, etc).
     Be stabilized by 1,000 feet for IMC operations; 500 feet for VMC approach.
     Ensure only small changes in heading/pitch are necessary to maintain the correct flight path.
     
  8. MauleSkinner

    MauleSkinner Final Approach

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    Why assume 300 fpm? (Minute or mile...either can be substantially more and still be stabilized).
     
  9. Clip4

    Clip4 En-Route

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    The whole thing sounds silly to me. 1st, there is no landing where I would turn off the engine. 2nd, if the plane is equipped with speed brakes the shortest landings will be achieved with the brakes activated, but you are going to have a high sink rate that you had better be on your game in the flair. 3rd, you don’t have much flap on a Mooney and flap retraction after landing will have minimal effect.
     
  10. benyflyguy

    benyflyguy Cleared for Takeoff

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    I didn’t see the “runway” until the end of the roll out. That was crazy!!!!
     
  11. Clip4

    Clip4 En-Route

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    Heck if going to take a runway when available just land mid field from the down wind.
     
  12. Silvaire

    Silvaire En-Route

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    Seems unnecessarily way over-thought, land at slowest speed practical and stomp on the brakes. I doubt flaps or speedbrakes or elevator are going to have much of any effect at that point, at least not enough to justify all the effort put into monkeying with them.
     
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  13. SoCal RV Flyer

    SoCal RV Flyer Pattern Altitude

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    Until you heat them so much that they start to fade, and/or cook the O-rings in the cylinder bore, resulting in nasty, smoking fluid loss. Then the distances get reeeaaaallly long!
     
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  14. Eric Stoltz

    Eric Stoltz Pre-takeoff checklist

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    I like this idea for a test. I know in my airplane, Beech Sierra, that the huge placard that says, "raise flaps to increase brake effectiveness" is a very worthy endeavor. I have seen the effect with my own two eyeballs. I even have video of the compression of the struts compressing at the same time of raising the flaps, increasing the weight on the wheels... And therefore increasing the effectiveness of the brakes. I'm curious to see if it works the same for the legendary Mooney.

    I look forward to the results.

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  15. dtuuri

    dtuuri En-Route

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    Absolutely! However, I did mention "brake energy" in an earlier post:
    I think this is worth repeating. 1G of deceleration is the most any airplane can muster, mathematically, before the tires skid. So, yes you are right, I was talking in theoretical terms. It is a principle worthy of some thought, though, imo.
     
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  16. tspear

    tspear Pattern Altitude PoA Supporter

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    In the Aerostar I had previously, speed brakes and flaps both made significant difference in landing roll out distance.
    In the Cirrus I fly now, removing flaps also makes a huge difference in landing distance.

    Here is another reason to do it. Crosswinds, when you land you lose the ability to slip or crab. Slip or crab are what create the horizontal component which prevents you from moving sideways. The longer you have minimal weight on wheels, the more likely a gust is able to push you off the runway. Dumping the flaps actually gives you significantly more directional control faster. Something very critical in gusty/crosswind conditions.

    Oh, and those who state this is bad form because you may raise the gear instead of the flaps? Only if you fly Beech. Beech seems to be the only model which has this issue, and a host of other ergonomic issues where pilots do dumb things.

    Tim
     
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  17. Salty

    Salty En-Route PoA Supporter

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    The mooney flaps aren’t very big or effective.
     
  18. Bill Watson

    Bill Watson Pattern Altitude

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    Not a Mooney expert by any means, but I recall the Mooney’s flaps being very effective in ground effect. I assumed it was related to how close the wing is to the ground.

    So I’m thinking the flaps effect on braking effectiveness could be significant. Data on that would be interesting.


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  19. Hank S

    Hank S En-Route

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    They're plenty long, about 2/3 of each wing. But compared to Cessna 40º flaps, not very effective. Similar to 30º Cessna flaps, I thought. But what do I know, I rarely use mine for takeoff [except when loaded heavy for travel], and rarely use more than Takeoff flaps [15º] to land, but I do tweak them a little if I'm high. Landing flaps [33º] are reserved for dead calm days, or when I've blown it badly and am high, but I usually recover and remove some flaps by short final.
     
  20. eman1200

    eman1200 Touchdown! Greaser! PoA Supporter

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    this is so true that most mooney drivers have the flaps removed.
     
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  21. Salty

    Salty En-Route PoA Supporter

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    And installed as extra equipment on a bonanza?
     
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  22. Hank S

    Hank S En-Route

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    Is that why they glide like rocks when you pull the power on final??? :p
     
  23. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Who said anything about turning off the engine?!?!?

    You're talking about decreasing distance over an obstacle, and you're right... But I haven't found an FAA-standard 50-foot obstacle anywhere around here and the techniques that were being discussed in the original thread on Facebook had nothing to do with obstacles, only ground roll. I don't think there's as much debate over how to get down after an obstacle. Speed brakes, flaps, slips all work fine.

    With the speed brakes, it's not just the sink rate that causes trouble, as that is still quite manageable. The real problem is that you're blanking out 10-20% of your wing's lift, and when you're slow and need increased AoA to arrest the descent, that lift is important to have. While it can be done, after significant experimentation, I do not use the speed brakes during the round-out. Even if I have them out for the entire approach, I'll pop them in and then pop them back out a few seconds later. What I'm talking about for this experiment is extending them at the end of the round-out to help get the wheels on the ground as quickly as possible.

    I use takeoff flaps on every takeoff and full flaps on every landing and they're quite effective. You're right that they aren't like 40º 182 flaps, but while they have a shorter chord, they have a much wider span than the 182 flaps. Dunno what @Clip4 and @Salty are talking about...
     
  24. Bill Watson

    Bill Watson Pattern Altitude

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    If it’s only about ground roll, then all issues concerning roundout and descent rate are moot since you are measuring things only after touchdown.

    So you touch down at absolutely the slowest speed possible, speed brakes fully deployed, followed by maximum braking. Seems like the only variables left for experimentation is the dumping of the flaps and elevator position. Should be very doable and will produce interesting data.

    Getting over an obstacle and stopped in minimum distance is the real world situation I’ve always found most interesting. It has a built in spot landing requirement and is where pilot skill at executing optimal techniques is required. Crepe paper strung between poles would be the way to do the obstacle.



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  25. Silvaire

    Silvaire En-Route

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    The instrument panel of the original Bonanza was absurdly symmetrical. Everything was controlled by fourteen identical piano key switches, seven of which were blanks, along the bottom of the panel.

    https://goo.gl/images/ogcESS
     
  26. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Well, I guess "ground roll" isn't the right thing to say then. "Runway used" maybe. There was discussion about whether the speed brakes would do any good, so that's still part of the test.
     
  27. Clip4

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    In a 252 I have used the speed brakes from the last 50 ft to end of ground roll, but you are going to use a lot of elevator.
     
  28. Eric Stoltz

    Eric Stoltz Pre-takeoff checklist

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    I don't have speed brakes on my Sierra, and never have flown a little plane with them. Why would you deploy them at 50'? Just curious, not trolling with bait.
     
  29. Clip4

    Clip4 En-Route

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    You are defeating ground effect.
     
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  30. idahoflier

    idahoflier Pre-takeoff checklist

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    I have zero Mooney experience, so take that into consideration, but that said, if the flaps are as effective as you say, I would think retracting flaps after touchdown would afford maximum braking and therefore the shortest landing distance. As someone else alluded to, I would be concerned about flat spotting one or both tires. Possibly postpone until Spring when grass is available? Last thought, I have a Stratus which logs my position and speed around 10 Hz I think (tracklog feature), perhaps you have a device with similar capability? If so it should be easy to "normalize" your results so you're comparing apples to apples... Have fun!
     
  31. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Oooh, that's a good idea. The Stratus logs at 10Hz??? I thought most of those things logged at 1Hz. Are you just getting the track log out of ForeFlight then, or doing something else? I do have a Stratus but I don't really use it any more since we got the GTX345.
     
  32. idahoflier

    idahoflier Pre-takeoff checklist

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    Yeah, looks like I was mistaken. If the data is uploaded from my iOS device it looks like it's 1 Hz, but if it's uploaded from my Stratus it's ~3 Hz. I am pulling the .csv out of Foreflight and then doing the epoch conversion on the timestamp. I have a Stratus ESGi so my position is from the ESG GPS receiver so that's probably why it updates faster. I haven't cared enough to figure out why sometimes the tracklog source says "Ipad" instead of "Stratus", just figured it was a bug in Foreflight or the Status firmware (or operator error)...
     
  33. Kenny Phillips

    Kenny Phillips Cleared for Takeoff

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    Something my CFI had me practice.
     
  34. Kenny Phillips

    Kenny Phillips Cleared for Takeoff

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    Really? Why are planes limited to 1G, but not automobiles?
     
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  35. Clip4

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    The larger tire of an automobile has more surface contact per tire, 2x as many tires are used for braking, and an automobile does not have its weight on the tires reduced by a small amount of lift being produced by the wing.
     
  36. Kenny Phillips

    Kenny Phillips Cleared for Takeoff

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    While that may make it more difficult to attain one G decel, it certainly doesn't limit it.
     
  37. dtuuri

    dtuuri En-Route

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    My guess would be the road surface friction (OK, so I Googled). Imagine (my words now) having sprockets instead of tires to land on and that you land on long straight bicycle chains fixed to the runway. As long as the sprocket teeth don't break you should be able to stop a whole lot shorter than on dry concrete with a tire.

    I'm not an engineer and my knowledge of this one-G maximum braking phenomenon came from an ex-National Guard pilot I used to fly with who was familiar with aircraft brake testing experiments done at Edwards AFB long ago. He said to imagine a pendulum of one "G". As you brake, it swings forward, but can't go higher than horizontal, at which point there would be no more "G" force on the runway. I accepted the principle, but always suspected the explanation. Maybe one of the resident engineers here can enlighten me/us?
     
  38. FastEddieB

    FastEddieB Final Approach

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    You read my mind.
     
  39. Kenny Phillips

    Kenny Phillips Cleared for Takeoff

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    Yeah, I know for a fact that using two rear wheels ONLY for braking can exceed one G on some vehicles. It's possible, but not likely, in an airplane. The 1G limit may be practical, but it's not the limit. Of course, nobody wants larger stickier [and shorter lasting] tires and big brakes, and the associated weight and air drag.
     
  40. Bill Watson

    Bill Watson Pattern Altitude

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    I wish I had spent more time and effort in physics and math classes. With that said, the braking force, which comes from frictional forces opposing forward motion, is a function of the force applied normal or perpendicular to the runway.

    In the case of an aircraft, that force maxes out at the weight of the aircraft which I’m thinking is equivalent to 1G.

    In the case of automobiles, particularly race cars, the force can be more than 1G. It can be the weight of the car plus aerodynamic down force.

    With aircraft, we struggle to get all the weight borne on the braking wheels; 2 point rollout, spoilers, retracted flaps, minimal angle of attack.

    With automobiles all the weight is already on all 4 braking wheels, there is no lifting force, and in the case of race cars, there can be significant downforce. Downforce increases friction between the tires and road surface which can be used to keep the car on the road and for increased braking force.

    Am I getting close to something?


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    Last edited: Jan 6, 2019
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