icing

This video was mentioned on backcountrypilot.org. I figured I understood
tailplane icing, etc. But watching the video was an eye-opener. This also
very much applies to pilots who don't plan on flying in icing conditions. A
failed gap seal on a glider comes to mind as well.

At first I was going to skip this video as it's 23 minutes long. Please
watch it, there's not a boring moment. bumper

http://video.google.com/videoplay?do...23060735779946

Friend from Canada sent it to me yesterday. Hope NASA will produce more films as this!!! Everyone can understand the difference between aerodynamic theory and practice...

Safe flying!

VHZ

PS.
Other links for longer version here
http://video.google.com/videoplay?do...31008391&hl=en

short version here
http://video.google.com/videoplay?do...07889007&hl=en

This video was EXTREMELY interesting! Thanks for pointing it out,
Bumper.

Off topic a bit, what is the model aircraft in the background with two
turboprops and two jet engines? It says NASA 600, but I couldn't find
any info using Google. Is it just a model, or is there a real one
flying around?

-John

bumper wrote:
This video was mentioned on backcountrypilot.org. I figured I understood
tailplane icing, etc. But watching the video was an eye-opener. This also
very much applies to pilots who don't plan on flying in icing conditions. A
failed gap seal on a glider comes to mind as well.

At first I was going to skip this video as it's 23 minutes long. Please
watch it, there's not a boring moment. bumper

http://video.google.com/videoplay?do...23060735779946

I haven't watched the Google Video, but if it's the NASA video on
Icing (with discussion of SLD - Supercooled Large Droplets), I bet
it's a DeHavelland Twin Otter that NASA Lewis/Glenn used for one of
their many Icing Campaigns. I'm grateful for the work (and risk)
those guys have taken on. Changing flaps may be the key to staying in
control...

I've been involved in a few Icing Conferences (for work) and studied
Roselawn. The tools to predict the effects of icing on airfoils (and
airplanes) are getting better. There is still much left to be
done...and actual flight testing in icing (research or certification
of new airplanes) is dicey business -- especially since they de-
commissioned the USAF ice tanker (a KC-135 that sprayed water instead
of fuel).

The turboprop airplanes and commuter jets tend to not have
hydraulically driven controls (vice the big jets) and use boots
instead of hot air -- manual or tab-driven controls and boots are less
capable against ice accumulation. Even on the big jets, the hot air
systems are considered "anti-ice" as opposed to "de-ice" equipment:
they help PREVENT ice buildup (when used properly, or in icing
conditions that don't exceed the system capability). To "de-ice" a
big ice buildup takes much more capable equipment, which translates
into weight, power, complexity and so forth. Bottom line: have a
very healthy respect for icing (and hope your airline pilot does).

Good observation of the similarity with gap seals. For big jets, we
sometimes test missing parts (MEL or CDL certification), such as seals
-- to verify the airplane still has satisfactory handling
characteristics with seals missing (e.g. on one side of wing or
tail). It might be wise to find out how well our gliders work with
one or more gap seals missing or venting. A diminished L/D is one
thing. Loss of control is cause for alarm. As usual, don't try this
at home...

-Pete
#309

On Feb 15, 6:53*am, bumper wrote:
Off topic a bit, what is the model aircraft in the background with two
turboprops and two jet engines? It says NASA 600, but I couldn't find
any info using Google. Is it just a model, or is there a real one
flying around?

-John

On Sun, 15 Feb 2009 05:23:22 +0000, bumper wrote:

This video was mentioned on backcountrypilot.org. I figured I understood
tailplane icing, etc. But watching the video was an eye-opener. This
also very much applies to pilots who don't plan on flying in icing
conditions. A failed gap seal on a glider comes to mind as well.

Thanks for posting that. A real eye-opener. I haven't previously seen
photos of in-flight ice buildup and so never realised that it grows
outward inside the LE suction spike. A very nasty sight.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

The model in the background looks like a Gulfstream. Probably a
Gulfstream II ? The horizontal elliptical windows sure look like the
Gulfstream trademark to me. I guess they installed the turboprop on
the jet powered aircraft to study effects of tailplane icing on a
turboprop aircraft, but with jet engines as extra safety items (?)
Maybe the jets would provide not only extra thrust but also some "de-
icing" power???

Ray Lovinggood
Carrboro, North Carolina, USA

On Feb 15, 12:50*pm, rlovinggood wrote:
The model in the background looks like a Gulfstream. *Probably a
Gulfstream II ? *The horizontal elliptical windows sure look like the
Gulfstream trademark to me. *I guess they installed the turboprop on
the jet powered aircraft to study effects of tailplane icing on a
turboprop aircraft, but with jet engines as extra safety items (?)
Maybe the jets would provide not only extra thrust but also some "de-
icing" power???

Ray Lovinggood
Carrboro, North Carolina, USA

After actually watching the entire, sobering, video, let me change my
answer: I still think the model is a Gulfstream II, but it had
NOTHING to do with the icing experiment. By the looks of the prop on
the turboprop engine, I say the model was a testbed for the propeller.

Ray

We had an incident in our club G-103 in which the forwqrd edge of the
elevator gap seal lifted on tow, rendering the elevator ineffective. The
glider pitched up under tow and full forward stick would not get the nose
down. The pilot released at about 50ft and was able to land straight ahead
using the trim tab. No damage, fortunately. We have added that to our
pre-flight checklist.


At 05:23 15 February 2009, bumper wrote:

This video was mentioned on backcountrypilot.org. I figured I understood

tailplane icing, etc. But watching the video was an eye-opener. This also

very much applies to pilots who don't plan on flying in icing
conditions.
A
failed gap seal on a glider comes to mind as well.

At first I was going to skip this video as it's 23 minutes long. Please

watch it, there's not a boring moment. bumper

http://video.google.com/videoplay?do...23060735779946

I must be missing something. The nose pitch down is due to a stall on
the horizontal stabilizer. The advice is to pull back on the stick
immediately. Because the horizontal stab is an upside down wing, this
would have the effect of increasing the angle of attack even higher
and aggravating the stall. Is it just a wind deflector at that point,
and not a flying surface at all that is helping?

Matt

On Mon, 16 Feb 2009 01:52:14 -0800, Matt Herron Jr. wrote:

I must be missing something. The nose pitch down is due to a stall on
the horizontal stabilizer. The advice is to pull back on the stick
immediately. Because the horizontal stab is an upside down wing, this
would have the effect of increasing the angle of attack even higher and
aggravating the stall. Is it just a wind deflector at that point, and
not a flying surface at all that is helping?

Yes, I think you are.

What the film showed was that the flow separation caused by the ice build-
up is a low pressure area. Once it grows big enough to extend back onto
part of the elevators, the low pressure in the separation bubble will
snatch the elevators down, driving the stick forward and causing an
immediate pitch-down. The pilot needs to pull hard to counter this and
stop the nose from dropping further. At least, that's how I understood
what the nice lady engineer was showing with her diagram and bit of
tailplane.

One of the flying sequences showed this too: the pilot reported 80 lbs
forward pressure on the stick as the nose dropped and recovered by
pulling the stick hard back.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |