Flying in IMC

[Steve Innova]

there's no way you can fit a bike inner tube to our wing and have anything remotely close to the near-laminar airfoil we have now.

I thought flow was either laminar or turbulent.

[argoldman]

I see another problem with minimal heating.

 

While the heat will possibly melt the ice at the leading edge, the rest of the wing will be quite cold, as will be the atmosphere and the rearward running now liquid will re solidify on the wing at a more rearward and potentially dangerous position.. You will need a lot more heat than you think.

 

De-ice boots are not merely a inner tube glued to the leading edges. Most are inflated sequentially, either from wing root to tip, visa versa, or inflated sequentially top to bottom or bottom to top.

 

Don't take from this conversation that you shouldn't fly IFR on purpose. Clouds do not contain ice unless the temperature is below freezing, and then most don't even under these conditions. There are many factors involved in the production of ice. One of the best sources of information is pireps. Make sure that the ones that you pay attention to are for aircraft of similar size to yours.

[Kent Ashton]

I thought flow was either laminar or turbulent.

I suppose that's true but from what I understand, a nicely-finished EZ wing may well have laminar flow on the leading edge which will transition to attached, turbulent flow around the 25% chord position or sooner if the finish is rough or buggy. In any wing the flow goes turbulent past about the 25% chord.

-Kent

[Marc Zeitlin]

I thought flow was either laminar or turbulent.

Well, sort of. There's a transition region in between where it goes from laminar to turbulent, and it's not zero length. But for the most part, yes, you consider it one or the other. On the other hand, there are a couple forms of turbulent flow - attached and not attached. Only attached flow does us any good.

 

I suppose that's true but from what I understand, a nicely-finished EZ wing may well have laminar flow on the leading edge which will transition to attached, turbulent flow around the 25% chord position or sooner if the finish is rough or buggy.

If the finish is rough or buggy (or wet), the transition could be even further forward than that. On the Eppler 1230 airfoil (main wing), the transition region when clean is somewhere around the 35% chord point. On the canard (Roncz or GU) the transition region when clean is somewhere near the 50% chord point, which is pretty good.

 

In any wing the flow goes turbulent past about the 25% chord.

Not really. There are laminar flow airfoil, supercritical airfoils that can maintain laminar flow back past 60% chord, at the expense of a larger negative moment coefficient.

 

When dirty, however, the transition point does move forward to the contamination point.

 

Trading the reduced profile drag against the increased trim drag is one of the factors leading to a decision whether to use such an airfoil or not.

 

Still don't know what "plate lift" is, though.

[WileEZ]

Okay I can discuss the details now. I discovered that my "idea" is already being used as a deicer on the MD80.

 

http://www.azom.com/details.asp?ArticleID=1624

 

In my case, this started when I bought a new electric blanket, and noticed how much faster it heated up than my old worn out electric blanket. On inspection, I noted that the new blanket used much lower voltage (24 volts) than my old blanket. A quick search reveled that the blanket used carbon fiber heating elements instead of the nickle chrome (I think) wires my old blanket used. I noticed that even when I'm sitting outside in my balcony in cold weather (upper 20 degrees f, ~-3 degrees c), the blanket apparently did not have any trouble keeping me warm. In fact, I had to keep turning down the control to keep from "cooking"!

 

According to Wikipedia (http://en.wikipedia.org/wiki/Electric_blanket) "Modern electric blankets have carbon fibre wires that are barely noticeable and produce heat on the far infra-red part of the spectrum, penetrating through other clothes and making a better use of every watt."

 

Implementation of this would be simply run thin carbon fiber strands or perhaps very light woven carbon fiber tapes, perhaps in "zones" in the flying surfaces, between the foam and the top fiberglass skins. along with cheap sensors to monitor the temperatures. A cheap microcontroller can be used to monitor and control the heating elements, using PWM to deliver the currents. Since running the carbon fibers strands is easy, one can also heat up winglets and other critical areas. The power can come from a dedicated, modified cheap alternator of sufficient rating, coupled to the engine via an electric clutch.

 

An advantage of carbon fiber tape (1" to 3" wide) over single roving is that a break in a single strand would not render the zone inoperative.

 

A positive aspect of this system is that it would not get hot enough to cause problems to the foam and fiberglass, yet deliver enough heat to maintain a desired minimum surface temperature when flying in minus 40 degree air. A way to insure this would be to limit the maximum current to the zone.

 

What need to be researched is optimum layout, minimum temperature needed to prevent ice formation, just how much current is needed to run this and if it's even practical to begin with.

 

Also need to determine if normal carbon fiber roving will do the job, or if a special formulated carbon fiber is needed.

 

An idea regarding propeller deicing. Instead of using a brush arrangement to deliver current to the propeller deicer, use a "motorcycle" type alternator, with the coils mounted in the hub and the magnets attached to the non-rotating part. There's some issues with this concept, I'll admit. The brush method would probably be better as there appears to be the same level of complicity involved.

 

Regarding ice flinging into the propeller, I think it may be best to prevent ice buildup past the "trace" stage than to try to get rid of the ice after it accumulate.

 

To address the concern of ice melt running aft and freezing again. Part of this can be addressed by heating the entire wing, but my reading seems to indicate that the ice melt would sublime into gas rather than remain in liquid form.

 

Most in-flight, non-liquid, deicing system seems to focus on the leading edges and the airfoil "hump" rather than on the entire wing as a whole. But I'm still reading and researching this.

 

It appears the main concern about ice build up is not just on the leading edges, but also on the area just behind the "hump" of the wing (maximum thickness) where ice build up destroy the airflow and reduce lift available.

 

I wonder if a reflective material can be placed under the heaters without causing delamination issues.

 

More research needed. Still need the ideal minimum temperature.

[WileEZ]

Fun to dream but let's be realistic. there's no way you can fit a bike inner tube to our wing and have anything remotely close to the near-laminar airfoil we have now. It calls for a custom molded boot and a sophisticated inflator system. It would demand an entirely new wing designed for the deice system: expensive, complex, heavy, draggy.

 

Don't waste your time. Build to plans and go flying. Light IMC is possible. When there is ice, stay home or buy an airline ticket.

-Kent

Is this the guy that's flying a Cozy and is in the process of building a Long-EZ? What did you do to that guy?

 

What if the Wright brothers were "realistic", or Burt was "realistic", or Nate was "realistic". What if they listened to the people that told them not to "waste their time"? Would we even be here? I know you dreamed, and you're building. You did something with your dreams!

 

I've seen the inflatable deicing boots close up, the only thing I could think of was, "it looks a lot like inner tubes stuck in place". "Sophisticated", oh please, a compressor is a compressor when all is said and done. Some air valves and a microcontroller along with a small tank is pretty much it. Sure some custom molding may be needed, but how hard is that? We all (most of us anyway) know how to build custom parts out of fiberglass and foam. No new wing design needed, just some careful thinking. But my interest is not in that direction. (At this point anyway.)

 

Beside, I said "probably"!

 

C'mon, you're better than that! Join the party!

[Kent Ashton]

Is this the guy that's flying a Cozy and is in the process of building a Long-EZ? What did you do to that guy?

What if the Wright brothers were "realistic"

Well, there's a fine line between discouraging someone and trying to show them the difficulties of their task. If you think it will work, have a shot.

-Kent

[Quietgentleman]

There is no magical temp needed for deicing. You can do it at 33 degrees if the ice build up is super slow. Its the formation of ice and how fast if forms that will determine how high a temp you will need to keep your wing ice free. As far as bleed air is concerned on the biz jets they are only heating a short area of leading edge which is usually directly in front of the engines. This is done cause the jet engine absolutely will not take ice being injested into the compressor section. They are running extremely high tempuratures and thats why the leading egde of the wing in that area and around the engine nacelles are stainless steel.

 

QGM