[NSRCA-discussion] YS Questions+more - Rolls

Sun Mar 9 06:43:36 AKDT 2008

Chris, the datum line you use on the fuse should be a line that when running parallel to the ground will have your plane look the way you want it to when you're flying straight and level. I know on Bryan's designs he tries to make the canopy seam define this line so that visualizing it is easier. That way when he sets up to measure, all he has to to is pull the canopy and lay a level on the fuse. That's one thing that always baffled me about people sharing setups (hmm, I fly .5 pos on the wing, and .25 pos on the stab, and .5 neg and right thrust). All that means nothing if you're not using the same reference point, plus you might want your aircraft to present differently in the air, so you're screwed there too. Good luck with the trimming, I know it can be a pain, but it's well worth the work once you have an airplane that you don't have to fight throughout the sequence.

Matt
  ----- Original Message ----- 
  From: krishlan fitzsimmons 
  To: NSRCA Mailing List 
  Sent: Sunday, March 09, 2008 1:56 AM
  Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls

  Thanks Mike.. 

  I appreciate your well thought out response. 
  I guess, when I say I like a more tail heavy plane, I say that without really knowing what others fly. I just know I see alot of nose's dipping when going to inverted. And I use just a touch of down.. Knife's require a fair amount of rudder.. So maybe I'm not really any more tailheavy than the next guy.. I've always been told I roll good. Plus, I'm running the recommended cg from Jerry Budd, who has 3 Abbra's.. And he says his is a little nose heavy at 5/8" in front of the wing tube on his first setup. I believe he is now at 1/4" in front of the tube. Which is about where I am. I've tried 5/8" and had to add a butt load of positive incidence to get the ele back to center.. Now though, Bryan has me thinking outside my box. In my new thinking, that if I do have a little more up thrust, I may be able to keep my wing incidence at .5 instead of the+1 that its been ending up to get rid of the ele trim. Which may in turn when I go inverted make me require a little more down ele.. If I'm thinking correctly.. 
  So let me ask this as Bryan kinda brought it up, if anyone cares to explain, what is the correct way to find the datum line on a fuse then? To determine how much thrust you actually have. On my Abbra, it seems that the stab is in line with the motor centerline. Shot with a laser the stab is perfectly straight with the motor centerline. The wing is lower. 

  BTW, I shimmed my motor up one washer.. Going to try the more up thrust as Bryan was right when he said some people try to compensate by adding more down thrust.. I did.. I had a washer removed from it.. Adding extra.. I will take my shims to the field and maybe go more.. I can't wait to go now.. But, it'll be mid week I'm guessing. Gotta work tomorrow through Tuesday.. Sometimes I like being a contractor.. lol.. 

  Thanks Mike, hope I can keep it for now and get it flying good.. Would love to make my first nats and meet you guys!

  Chris

  Mike Hester <kerlock at comcast.net> wrote:
    Hi Chris,

    Everything effects everything else. If there's a "secret", that's it.

    You're starting in the right place with ..5-0. But where you end up might not be in the same place.

    Now you just nailed it on one thing you said: tail heavy. Tail heavy pattern planes don't do all that well. oh you can get used to it, but you will end up with a lot of mixes and wierd throws.

    Keep in mind that this is "generally speaking", every plane is different.

    I usually start the Black Magics around ..25 and trim in flight. Guess where I usually end up? Just about .5 on the wing. 

    If you're having to dig a lot of down elevator passing through inverted it doesn't necessarily mean that the .5 incidence is the culprit. you should have to add some down inverted, the question is how much. You can play with throws and expos to make it not a big deal. if it's REALLY digging inverted, check closer because you're missing something. As in flat out diving, not dipping.

    But this is why I try not to get into heated aerodynamic debates online. Unless we're talking about the exact same airframe/engine/prop...heck even the landing gear, what works on one may not necessarily work for another. Take the set up for a Focus and directly apply it to an Itnegral, and let me know how it turns out =)

    Bryan's advice is usually dead on. And so is Matt's. But as you can see thier theory departs and when it does, it's pronounced. They both have well trimmed and great flying planes. I have tried the zero or minimal thrust thing on my plane and it just well, didn't work out for me. Down thrust, yeah about .5 down. But right thrust....I never figured that one out without a lot of creative mixing. 

    And then Bryan makes one heck of a good point....why do the 22" props not require 10 degrees of right thrust? Set up on the ones I build seem to be exactly the same as an 18" prop. 

    So let's get to the real answers....it's voodoo. Black magic. Witchcraft. Theory gets you in the ball park. Then you have to put it in the air. Don't be afraid to try something different. Get aggressive. if you want to learn, you have to ask questions and be willing to try anything. Don't judge it in one flight though, always give a new method or set up a little time. Because "correct" might feel very strange if you're not used to it. In the end what you're looking for is whatever makes Chris' Abbra draw consistently straight lines, axial rolls, clean snaps and true (or easily correctable) tracking in knife egde. The answer is out there. But the seacrh for it could be pretty exhaustive.

    I have one VF3 that doesn't behave like all of the rest, and I have no idea why. I know that something is eluding me. And I know if I am dilligent, I'll find it. Incidence? Balance? A twist in the tips? Blowback on the surfaces? I don't know, but you can bet I will find out. 

    Now with all of that said, I know that some designs are a lot better and more forgiving than others. The Abbra, I couldn't tell you. I have only run across 2 planes that I considered "untrimmable", and neither are current designs. Some planes it takes a lot more mix and some things you just have to live with. 

    Bryan and I have had one particular discussion lately and I have come around to his way of thinking. Most people simply run thier planes too tail heavy without enough positive incidence in the wing. just keep in mind that this is to achieve what we are looking for, and someone else can be totally different. But I warn you now, if you try and set up a VF3 or a Shinden like a Focus, get a collar ready for that dog. You won't like it. 

    An Abbra may just have a wicked pull to the canopy you can't get rid of in a down line....or, you have to drop the incidence and live with a lot of pitch mix? I'm guessing.

    I could type a book on this and still not say a lot =)

    -Mike

      ----- Original Message ----- 
      From: krishlan fitzsimmons 
      To: NSRCA Mailing List 
      Sent: Saturday, March 08, 2008 8:10 PM
      Subject: Re: [NSRCA-discussion] YS Questions+more - Rolls

      Thanks Lance.. 

      As I said, I have alot to learn.. I usually start with .5-0.. Then adjust the cg and wing.. But on my Abbra, it's really messing with my downlines, my knifes, and my rudder sensitivity. I'm going to start to make a list though each time I go flying to let me know what I like and don't like with my changes.. Probably doesn't help that I like to be a little more tailheavy.. Nearly hands off inverted.. 
      This conversation has made me think alot about what affects what in different aspects of flight. And also that what I thought, may not be so.. 

      Chris

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  Chris 

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