midrian

I have recently finished my first composite Glider ( a 3meter glass/carbon/kevlar high performance 6 channel glider). On the first day of flying while flying relatively fast (not nearly as fast as i have seen similar planes handle) the elevator stabs broke off. The amazing thing was that the plane still flew without any stabs afterwards, with a slight down on standard flight, and pulling up slightly if i engaged crow. I managed to land the plane by using crow/not crow for up/down without any major harm.

Now the question.

What does it tell you about the plane if it is able to fly without stabs. Most ppl i spoke to was completely amazed that i landed it without stabs. Does anyone know of any other experiences like this?

Thanks

BMatthews

I'm not really that surprised. You obviously had it trimmed very near the neutral point for "stab'less" operation and the crow was just adding the reflex needed for proper handling.

I have an old sailplane analysis tool by David Fraser and one of the items that comes out in the full print is the stab lift coefficient. It's interesting to note that when properley trimmed the stab is right around the Cl=0 point with slow thermal flight generating very small +'ve values and higher speed flight generating very small -'ve values ( or it may have been the opposite). This was for the higher speed low camber foils used these days.

Nice save. Many of us would have probably paniced....

FLYBOY

My Feedback: (11)

I saw a guy pull the left wing off 1 inch from the fuse and land the plane. never quit flying it. You can save many things.

Gotta wonder why the stabs broke though. Must have been messed up. It is way more optimal to have them just trail and not producing lift. If they are producing lift either up or down, it is added drag.

Jack Hyde

My Feedback: (1)

Most sailplanes pitch up when flaps are applied. Also most sailpanes have the cg set such that there is a slight nose down moment offset by a slight down force on the horizontal stab. So it follows that if the stabs fall off the plane will nose down (tuck) and the nose down moment can be cancelled by the pitch up moment caused by just the right amount of flaps. It isn't clear that the plane could be controlled using flaps for pitch. You showed that it can be done.
I had one flying stab fall off in flight and the plane was controllable in pitch with the one side that was left on the plane.

steve-kerry

Most airfoils generate a nose-down pitching force. This is especially true of heavily cambered airfoils like the old E385 and E387. Plenty of lift, but a strong nose down force as a result. This was counteracted by setting up the stab to keep the tail down.

If your plane flew both with and without tail feathers, you obviously didn't have much pitch from the airfoil (or you had the flaps set just right to reduce it to virtually zero). Either way, flying like that suggests your CG is too far forward (flying wings have the CG at about 17% which is a lot further forward than a conventional setup).

My initial thought is that your CG was too far forward so your plane wanted to dive, and you had been compensating with up elevator. That will work and it's quite stable, but fairly draggy as well. It also puts a lot of DOWN force on your poor tail feathers, particularly when you are flying fast. Look closely - when the stab halves came off, did they break UP or DOWN?