Tapio
If I need to adjust the CG on my F1Ds as dictated by what I've told you, I use clay or similar to get CG right, then measure the weight of the clay. I can then calculate how far the CG has moved and if the clay weighs more than eg 30mg, move the wing posts the same distance. Tedious and can be tricky but I think it's worth it.
As you bring the weight down, the pitch inertia will also come down and will improve thestability as a result. This means you may then be able to move the CG back a little. How much, I can't say.
Bob
----- Original Message -----
From: Tapio Linkosalo
To: Indoor_Construction_at_yahoogroups.com
Sent: Monday, December 17, 2007 7:46 AM
Subject: Re: [Indoor_Construction] Re: F1D CG poll
On Fri, 14 Dec 2007, Mark wrote:
> 5.
> Wariness of suggesting anything "advanced" to someone building F1ds
> to 1.75 g or some such unecessary weight, which suggests more
> important problems than CG, (perhaps which also affects "best" CG for
> your case.)
Tsk tsk. I might get insulted of that. Please remember that it was my
first F1D, with structures based on F1M. At first the model seemed flimsy,
but after some flying I have noticed how overly-rugged it is. So I
anticipate that my next one will be right on 1.2 grams. I just would not
want to spend months of struggling with findinf a proper CG location
_after_ I reach the magic goal of building to weight, but would rather get
to the goal of properly flying models sooner rather than later.
> But a poll is a poll, and fairly asked. I bump around from 85% to
> 90%, but don't measure it often. It's not easy to change CG on F1d
> unless you're underweight and can mess with CG using ballast,
> meaning, some of us merely build to a preferred nose-to-wingpost
> length to clear steering line by a certain amount, and that pretty
> much sets CG. If I don't like the apprearance of how in flies (sink,
> or instability) then I'll think about messing with wing position.
Precisely. That is why I'm asking already now, even that I have not been
able to build to weight. Would like to have my next model into 1.2 grams,
and NOT make it then overweight by having to move the with to and fro on
the motor tube...
> But usually "it is what it is." I may try a flight with ballast on
> tail post, then one with ballast on nose, but usually that experiment
> is inconclusive on any of my good models. With proper component
> weights, CG should come out pretty close to "good."
Well yeah, quite a big margin though as my first attempt flies at 100%,
and Hunt's model shows 75%. OK, I compromise, aiming at 80 to 85% on the
next one.
-Tapio-
[Non-text portions of this message have been removed]
Received on Mon Dec 17 2007 - 04:31:23 CET
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