tuhlhorn
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DA 20 And Lightning Strike

Fri Aug 24, 2007 9:19 am

So, I am told the reason why the Diamond DA-20 is not IFR certified due to the fact that it has no metal mesh inside the frame and could not take a lightning strike. Is this correct? What would happen if it were struck by lightning? Thanks
 
KELPkid
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RE: DA 20 And Lightning Strike

Fri Aug 24, 2007 10:30 am

Quoting Tuhlhorn (Thread starter):
What would happen if it were struck by lightning?

Well, in a typical metal airplane, not much would happen, you are inside a Gaussian cage, and the aircraft itself would just act like part of the "circuit" of the lightning bolt. If parts were damaged, it would be the non-metal parts like wingtips, cowlings, spinners, etc  Smile

Now, in a composite aircraft, since the skin and other parts don't conduct electricity as well, it would act like a resistor, and get hot, stuff would burn, etc. etc. I doubt it would fall out of the sky, but it certainly wouldn't be pretty  flamed  I'd imagine the radios and avionics would become part of the conducting path for the lightning bolt, and that would probably be the FAA's main concern for IFR certification. They don't want your radios and navigation knocked out all in one stroke.

The metal mesh in most composite aircraft is there to make sure the electrical current would conduct itself safely around the aircraft structure, and not through it, and behave more like a metal plane.
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onetogo
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RE: DA 20 And Lightning Strike

Fri Aug 24, 2007 11:08 am

Quoting Tuhlhorn (Thread starter):
Is this correct?

Yes.
 
MrChips
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RE: DA 20 And Lightning Strike

Fri Aug 24, 2007 5:50 pm

Quoting Tuhlhorn (Thread starter):

Honestly, if you were in a situation where being struck by lightning was possible and you were flying in a Katana, being blasted by lightning would probably rank rather low on anyone's current list of concerns. Big grin
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tuhlhorn
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 2:23 am

Well, the school I am instructing in just got 2 of these DA-20s and were are located in south Texas. Anyone who knows about south Texas weather in august knows little thunderstorm cells pop up all the time. This is why I was asking. So I understand that since the DA 20s dont conduct electricity all of the radios, and electricals in the aircraft would fry. Not the occupants right lol? I dunno, I just dont like this aircraft too much.
 
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Jetlagged
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 3:34 am

Quoting KELPkid (Reply 1):
Well, in a typical metal airplane, not much would happen, you are inside a Gaussian cage

Correction: Faraday Cage.
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DeltaGuy
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 3:46 am

I've never flown the DA-20 but I know the DA-40 is IFR cert, as I've done it before. Then again they are two different aircraft. In Florida I wouldn't want to do an x/c unless I had a plane that was capable to go IFR if need be....damn thunderstorms!

DeltaGuy
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SlamClick
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 3:57 am

Quoting Tuhlhorn (Thread starter):
Diamond DA-20

DA-20?
Wasn't this airplane...

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Photo © George Canciani


...also designated a DA-20 here in the US when it first appeared. I could swear that was what it said on they type ratings guys got at FedEx.

Quoting Tuhlhorn (Thread starter):
it has no metal mesh inside the frame

This brings up a question. How is the electrical system grounded?
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KELPkid
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 4:25 am

Quoting SlamClick (Reply 7):
This brings up a question. How is the electrical system grounded?

I'm guessing similar to a boat, where you have a return wire going to the negative battery terminal...  Wink Of course, this doubles the weight of any wiring...
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Jetlagged
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 4:35 am

Quoting SlamClick (Reply 7):
This brings up a question. How is the electrical system grounded?

With grounding strips to return rather than simply screwing things to the structure presumably.

I don't think the metal structure is used for grounding in conventional aircraft either, at least not in aircraft with modern avionics. Too much risk of earth loops. A separate ground is usually provided for each supply type (DC, AC, digital signals, etc) to reduce noise problems.
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SlamClick
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 4:37 am

Quoting Jetlagged (Reply 9):
Too much risk of earth loops

The one example where I approve of the use of "earth" instead of "ground" for that side of the system.
Reason: "ground loops" has a very different meaning and one, not very attractive to us old taildragger pilots.
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tdscanuck
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RE: DA 20 And Lightning Strike

Sat Aug 25, 2007 11:09 pm

Quoting Jetlagged (Reply 9):
I don't think the metal structure is used for grounding in conventional aircraft either, at least not in aircraft with modern avionics. Too much risk of earth loops. A separate ground is usually provided for each supply type (DC, AC, digital signals, etc) to reduce noise problems.

I'm not sure about GA aircraft, but aluminum commercial airliners use the structure as the ground for almost everything (DC, AC, coax shields, etc.). There are ground studs all over the place an a 737...they're just bolts with good metal-to-metal contact with the structure.

I think they keep the ground studs separate though...i.e. you don't ground AC and DC to the same ground stud, even though you might have an AC and a DC stud on the same piece of structure.

Tom.
 
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tb727
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RE: DA 20 And Lightning Strike

Sun Aug 26, 2007 12:36 am

Quoting SlamClick (Reply 7):

DA-20?
Wasn't this airplane...

...also designated a DA-20 here in the US when it first appeared. I could swear that was what it said on they type ratings guys got at FedEx.

That's what my type rating says, DA-20. We get that sometimes from ATC, "I didn't know a Diamond 20 could do 420 knots and what are you doing in the flight levels?"

I know a Dassault DA-20 can take a lightning strike and still function just fine. I've taken at least 1 hit that I know of in one, ironically in an old Fed Ex bird going into MEM of all places on Christmas Eve a couple years back.
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Jetlagged
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RE: DA 20 And Lightning Strike

Sun Aug 26, 2007 2:34 am

Quoting Tdscanuck (Reply 11):
I think they keep the ground studs separate though...i.e. you don't ground AC and DC to the same ground stud, even though you might have an AC and a DC stud on the same piece of structure.

I'm not going to argue with you but I'm amazed as the potential for noise and interference must be very great. There's not a lot of point in keeping some ground studs for AC and some for DC if they are connected to the same piece of structure. What do they do for ARINC 429 data bus screens?
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tdscanuck
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RE: DA 20 And Lightning Strike

Mon Aug 27, 2007 12:14 am

Quoting Jetlagged (Reply 13):

I'm not going to argue with you but I'm amazed as the potential for noise and interference must be very great. There's not a lot of point in keeping some ground studs for AC and some for DC if they are connected to the same piece of structure. What do they do for ARINC 429 data bus screens?

The impedance of the structure is so low compared to everything else in the wiring system that I don't think there's much risk of interference. It certainly appears to work in service.

I think they keep the ground studs separate because you would have a noise/interference issue if, for example, an AC ground passed through a DC ground tab on its way down the stack on the ground stud. Once it's in the structure, the path to ground is so much more direct through the structure I doubt any of the other systems can see it.

Not sure about the ARINC 429 bus shield grounds, but the FQIS grounds go to structure and that's one of the most sensitive systems on the whole airplane.

Tom.

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