>I flew my Arreaux yesterday on an E16-7. Great boost, no ejection. I
>held my breath and watched it fall horizontally from an estimated 850
>feet (probably less because of weather conditions, etc). It landed
>horizontally on the sand and loosened two fins. I've repaired it, but
>I'm still wondering why it didn't come in nose down? I guess the only
>way it would have stayed horizontal is if it was moving forward at a
>relatively high speed (IOW it was remaining stable as usual, but just
>sideways). But it didn't drift very far to be moving very fast, and
>why didn't it arch over at apogee? Can wind cause it?? TIA
This is exactly what the Bumbling Brothers' (my brother Bob's and my) NARAM R&D
report was about.
Our goal was to make this a deliberate recovery mode.
The secret is in the angle of attack.
I'll assume you know about Center of Pressure (CP) and Center of Gravity (CG).
CP is the "average" point that air pushes on the model. CG is the balance
point of the model, and the natural pivot point of the model in free flight.
If the CP of the model is behind the CG, the air pushes on the model (on
average) behind the pivot point. So if the model points away from straight
forward, the air pushing on the model tends to push the rear of the model back
behind the CG. The model is stable, and all is happy.
You can find the CG of a model by balancing it on one finger. The CP is
trickier. The ancient method was the cardboard cutout method. Essentially you
cut out a profile of the model from cardboard and balance the cardboard cutout
on a pencil. Technicaly the balance point is the "center of lateral area
(CLA)." But this method turns out to be accurate only for a model travelling
directly sideways--a 90-degree angle of attack. Forunately, a model that tests
stable this way, with the CLA ahead of the CG, is stable--the method is very
Then came the great and powerful Jim Barrowman, who showed us the way to
clculate the CP for models that were already moving the way they were
pointing--at low angles of attack. and lo, Barrowman showed that models that
looked unstable with the cardboard cutout method wer indeed stable. And fins
became smaller, and models flew straight, and it was good.
But some models that pass the Barrowman test--the CG is in front if the
Barrowman CP (BCP), fail the the cardboard cutout test--the CG is behind the
CLA. This can be bad if you launch from a short rod in high winds. An
otherwise stable model goes unstable, and all hell breaks loose.
But our R&D hypothesis is that this condition, a CG ahead of the Barrowman CP,
but behind the Center of Lateral Area, leads to a miracle. A model that is
stable is stable going forward as long as the angle of attack is low, but one
that can experience a high angle of attack if it is pointing straight up at
apogee. For then it experiences a high angle of attack for a moment, and loses
When the air hits the model sideways, the model wants to point so that its CG
is ahead of the CP. But now the CP is the Center of lateral area, which is
ahead of the CG. The model wants to point backwards. But if the model goes
straight backwards, the angle of attack goes low again, and now the CP is ahead
of the CG. Argh! the poor model wants to crash, but backwards or forwards?!?!
The poor confused thing compromises somewhere in the middle, typicaly in a
something of a backwards glide.
And so your Arreaux fell sideways, just as a swing-stability tested model
sometimes kind of just wanders in direction as you swing it around your head,
kind of wanting to go backwards, but not having the heart to, but will go
foreward with great certainty if you start it right.
The trick is to make this happen in flight deliberately. Bob and I use a
little hole punched at the front of the body, so the ejection gasses throw the
model into a tumble.
This got us 4th place in a single flight in D R/G at NARAM and 1st place in
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