Kang,
Did you use Hunt's spreadsheet to compute SSM? I find that program a little irritating because it factors in wing/stab separation when computing SSM, which in experimental practice I have not found to be valid, at least on my own models.
-Joshua Finn
--- In Indoor_Construction_at_yahoogroups.com, "Yuan Kang Lee" <ykleetx@...> wrote:
>
> My F1D has SSM of 2.1%
>
> --- In Indoor_Construction_at_yahoogroups.com, "Yuan Kang Lee" <ykleetx@> wrote:
> >
> > boom length is (1).
> >
> > If you're analyzing a F1D, I think 4% will be fine.
> >
> > --- In Indoor_Construction_at_yahoogroups.com, "mkirda@" <mkirda@> wrote:
> > >
> > > Bringing this old topic back up as I've played a bit with the program. Assuming you want a positive static stability margin.
> > >
> > > Four separate iterations give me values of 4, 6, 14, and 15 (rounded).
> > >
> > > Which should I try actually building? Part of the problem with the spreadsheet is the lack of documentation, so I have no idea what the SSM value should be.
> > >
> > > Second question: Is 'boomlength' defined as distance from
> > > 1) End of motorstick to end of tailboom
> > > 2) TE of wing to LE of stab
> > > 3) something else?
> > >
> > > Regards.
> > > Mike Kirda
> > >
> > >
> > > --- In Indoor_Construction_at_yahoogroups.com, "Yuan Kang Lee" <ykleetx@> wrote:
> > > >
> > > > Gary,
> > > >
> > > > In your experiment, there are two things happening:
> > > >
> > > > 1. lengthening of the tail boom
> > > > 2. moving an object with weight (the stab) back
> > > >
> > > > These have counter acting affects, and the combined result depends on the weight of the stab. This is because the first changes the neutral point, and the second changes the CG.
> > > >
> > > > To simplify the scenario, consider the stab to be very light or have no weight. When you lengthen the tail boom, you will move the neutral point backwards. Moving the neutral point backwards without changing the CG gives you MORE static stability. Although not shown on the Hunt spreadsheet, a longer boom also gives better dynamic stability. (As John Barker described.)
> > > >
> > > > Now, realistically, the stab has weight, but it is generally very light, so the backward CG move is not as great as the backward movement of the neutral point. Hence, the combined effect of (1) and (2) is more static stability.
> > > >
> > > > On the subject of whether you get better duration with more or less static stability, there are many opinions. *Generally*, duration is better with a less stable (but still stable) model. But this would be a different discussion, and I don't think I have the answer.
> > > >
> > > > Hope this helps.
> > > >
> > > > --- In Indoor_Construction_at_yahoogroups.com, Warthodson@ wrote:
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > I have been using Bernie hunt's program to see what the affect of varying the boom length might be. The version of the program I have has Steve Brown's F1D entered into it.
> > > > > The only parameter I changed was boom length. For the purposes of this experiment I did not change the boom weight. The result was as follows:
> > > > > Shortening the boom 1" (from 19.5" to 18.5") increased the time & reduced the static stability margin.
> > > > > Lengthening the boom 1" (from 19.5" to 20.5") decreased the time & increased the static stability margin.
> > > > > I was expecting a longer boom to increase time because I thought that the decalage (angle of attach difference between wing & stab) would be less with the stab farther back. Also, with the weight of the stab farther back I thought the CG would be closer to the neutral point & the static stability margin would be less. I would like to hear your opinions on the affect of boom length. And, yes I know that a longer boom length might require a heaver boom, but not necessarily.
> > > > > Thanks,
> > > > > Gary Hodson
> > > > >
> > > >
> > >
> >
>
Received on Fri May 24 2013 - 08:13:18 CEST
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:47 CET