View Full Version : Knife Edge; security of Ventral Fin?
paulo
15th Dec 2002, 21:12
I've been pondering for a quite awhile whether one can knife edge a Robin 2160... the main thing that has been on my mind has been the ventral fin. It's a rather flimsy affair (as I remember, a hollow composite skin, possibly riveted on, and has no internal rigidity).
Instinct says that it's going to get a pounding during a knife edge, but then again that's probably true during a slip or some of the basic figures like a snap roll.
There's a seperate question as to whether you can knife edge a basic aero machine like the R2160, but I'm more interested in the theory at the moment. The practical will have to be dual with someone who knows how to do it. ;)
18-Wheeler
16th Dec 2002, 00:22
Knife-edge?
The security guards will stop you before you try. :D
Empty Cruise
16th Dec 2002, 18:16
Methinks ventral fin will be under some static load, but only limited dynamic load during the manoeuvre. The snap roll will put the fin under greather dynamic load (which may be what is needed to ruin your entire day).
Have encountered aircraft that may fly knife but are problematic in snap rolls - or at least requires mods to both stabilizer and fin to be approved to do snaps.
One thing to worry about is oil supply, though. Unless you have an inverted oil system, limit knife flight time to.... not much ;).
Enjoy!
cwatters
16th Dec 2002, 18:26
> I've been pondering for a quite awhile whether one can knife
> edge a Robin 2160... the main thing that has been on my mind
> has been the ventral fin. It's a rather flimsy affair (as I
> remember, a hollow composite skin, possibly riveted on, and
> has no internal rigidity).
I thought these sort of things were added to prevent spin/aid spin recovery? Would they get a lot more loading in that situation than in knife edge?
Even if you DO have inverted oil supply most systems don't cope well with Knife edge (effectively sustained zero-g, as far as the oil supply is concerned) so keep the duration of knife-edge down.
paulo
16th Dec 2002, 22:25
cwatters - good point. I've read that the ventral fin was added to the 2160 to aid spin recovery (which it seems to do very well).
And as for fuel system, the injected version is good for 20s inverted, so I'd guess that would be the guide for the manoeuvre