Nose cone dilemma (and warning)

[stebbins]

On Monday, after the incident with the downed glider, I was flying over by the 1500. All of a sudden, my base-tube started pulling itself in with no input from me. And my sink rate increased significantly. I pushed the bar back out (not all the way) but it really didn't want to go. It felt like it would be very easy for it to go all the way back and "tuck". That may have been an illusion, but it sure felt like it.

I immediately had an idea what the problem was, as I'd had the issue years before on another glider. But the time before, the "problem" was significantly less pronounced. This was really scary. So, I started back towards the LZ. It looked like I might not make it, despite being reasonably high. Then, all of a sudden, the glider started flying normally again. This fit the description of what happened before. I got to locals, and thought I'd fly some more, since it was fine now. Then I decided that was stupid. Just then, it happened again. So I went out to land. The mysterious "auto-pull-in" happened at least twice more on the way to the LZ. I radioed the LZ that I was having glider problems and I might need help. No answer. So I just set up a long final and tried to deal with it. Good approach. Good flare. Nose will not rise, despite full push-up. Like someone put 20 pounds on the nose. So, I bellied in.

And, just as I did so, the offending evidence dropped down in front of me. My nose-cone was loose. Just as I had suspected. This can happen if you don't attach the nose cone properly. It can also happen if the velcro is getting old. If that velcro gets old, REPLACE IT. Trust me, you don't want to go through this. It is generally the fuzzy side of the velcro that is the issue, not the hook side. Unfortunately, on my glider, the fuzzy side is on the glider, not the nose-cone, so the fix will be more difficult.

In any case, please please, make sure your nose-cone is attached correctly, and that the velcro is not too old, especially on the top attachments.

(If anyone wants to know the reasons behind why a partially detatched nosecone can cause a significant pitch-down, let me know. If not, that's fine, the key think is to know that it does.)

[jimshaw]

George,

I seriously want to know. Thanks in advance.

This will also get you some more writing time on this blog since you like to be so prolific herein

[Steve90266]

Inquiring Newbies want to know! Was it partially detached, fully detached, flapping in the wind above the glider, playing poker, out shopping with the wife and kids, what?

My Falcon 3 has a nose cone as well, so any information you can share is relevant and appreciated.

Note to F3 owners; if you fail to detach the nose cone prior to releasing the hold back on break down, it places an extreme amount of stress on the velcro of the nose cone. In time this could lead to the probem Stebbins is describing.

Steve

[skygeek AKA Seabass]

I had this happen to me on my Atos, the bar would pull in "by itself" speed up then slow down to stall speed then it would do it all over again, while this is happening the tail is shaking violently, so much that I thought that was the problem & hoped it would brake off so I can fly again. Lukily I had altitude to figure out how to fly this unfamiliar flying wing, so I started playing with the flaps & found that the glider was controllable with full 45 degree flaps, so I did some high test approaches & saw that it was managable & I would not have to throw my chute. Came in had a nice landing. While I was landing someone did notice my nose cone was off on top & this was also from fuzzy velcro. Because the root is so short this makes it worse, when the glider would pick up speed the nose cone would lift higher disturbing the air over the top of the wing, changing the cord line. Putting on the flaps helped stabilize the pitch & lowered the stall speed.
Now that know you dont have to learn the hard way. If your velcro is weak carry a role of clear packing tape & secure your nose cone that is what I did until I got it fixed.

[jcflies]

hey steve,
it doesn't make much (dare i say it makes no?) difference on a F3. i forgot to attach mine once and after i got over the initial shock of the racket, it flew like it always did--just way noisier! i think it was just one of those little additions that makes an F3 cost $1000 more than an F2! it's only on higher performance gliders that it makes a difference!
have fun!
(i used to be a hang-glider pilot...)

[stebbins]

OK, here goes, then off to bed for me. I'm only up this late because my son is having nightmares every hour or so (a not uncommon thing between 1 and 3 years of age - the brain doesn't like all that new wiring, it gets confused.)

There is a crude line-drawing at: http://www.georgestebbins.com/public/GliderPlanform.tif

I will refer to it. (I can't post a picture here.)

My nose cone came off on the top, not the bottom. I suspect (but don't know for sure) that if it came off completely, that would be annoyingly noisy, but less of an issue otherwise.

What happens when the nose-cone comes loose this way? The airflow is disturbed behind the "flapping" nose cone. It stops being laminar and is very turbulent, sometimes in varying ways.

Look at the image.

o The area between the red lines is where the air is disturbed.
o The green line is the approximate center of lift (in the fore-aft direction)

Note that the area between the red lines is much farther forward of the green line than the rest of the wing. That means that when the disturbed area loses lift (as it inevitably does when the flow becomes turbulent) then the lift in FRONT of the center becomes less than it was before. The lift behind the center is not lessened as much. So, the lift in the back is now greater than the lift in front. So, the glider tries to pitch forward. You can think of it as someone pushing down on the nose, or pushing up on the trailing edge near the tips.

The amount of the pitch-over depends on the geometry and twist of the wing, among other things, as you can probably see from my simple diagram. Hence Janyce's comment about the F3 & Sebastian's about the ATOS.

How much trouble does it cause? I always thought it stabilized with only a small pitch-over, as it did in my RamAir. But after my flight last Monday, I'm not so sure. It really did feel like the glider wanted to keep nosing over. And I wasn't about to test it out. No way, no how. Not gonna do it. Wouldn't be prudent.

I hate to recommend tape, as Sebastian did, but if you find yourself in that situation, it is a choice between a risky flight, tape, or no flying.

I'll be repairing mine shortly.

[Steve90266]

Good stuff. The diagram says it all and it makes a lot of sense. Thanks for the input.

[JT]

Check this with Greblo:

He told me once that our cuved-tip, double surface gliders absolutely needed the nose cone on to keep from inflating the sail and incurring all the changes to flight characteristics that result; that would be why Janyce doesn't notice the $1000 difference in her F3, too. It is probably a combination of both the disturbed airflow over the wing and the airflow into the wing. Again, Joe seems to have a bit more information to share on this subject.