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16 Nov 2018, 05:44 [ UTC - 5; DST ]


Greenwich AeroGroup



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 Post subject: Re: You say you want an Evolution ...
PostPosted: 03 Oct 2018, 07:13 
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Location: Asheville, NC
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Username Protected wrote:
...every "improvement"/deviation from the plans adds time.
Boy, that's the truth. You try to project "If I do this, will I be screwing something up later on?" Usually you get it right, but sometimes a small change comes back to bite you. I'm still making changes and improvements after four years of flying. It looks like you're getting close.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 04 Oct 2018, 11:38 
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Company: Retired
Location: Seattle KPAE
Aircraft: TN36, building Evo
The other day at the shop I walked into a 5-cornered discussion with an owner who had fried the starter generator on a new PT6. That’s expensive, of course. He wanted to design some kind of intake scoop to blow cooling air on the starter-gen. It took over half an hour but condensed, it went something like this:
How did the starter-gen get overheated?
Too much current from the (prop and inlet) de-ice. [IIRC, it’s like 60 amps].
Hmmm. That shouldn’t be a problem, recharging the battery right after start I’ve seen 100 amps, especially with lithium batteries.
This was at the same time.
But battery charging is well down from that peak by the time it reaches the runway.
It was on the ground.
But the de-ice is locked out on the ground.
I bypassed the lock-out for testing. OK, never mind.

Come to find out, he’d bypassed the safeties and been testing the de-ice with the engine off, so running down the battery, then fired it up and immediately went to full de-ice while the starter-generator was at max heat from starting and max current recharging. Not even moving, so minimal airflow for a scoop anyway.

What struck me about it was what it revealed of the Experimental mindset. With a certified airplane, we'd have started with what he could do to avoid this happening in the future, it would have taken a long time to get to considering hardware changes. But in the Experimental world it was the other way around, we started with ‘fixing’ the design and only slowly worked our way to changing behavior.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 05 Oct 2018, 00:51 
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Aircraft: TN36, building Evo
Username Protected wrote:
Left wing root at leading edge doesn't seem to line up with fuselage fillet
Eagle-eye Michael spotted the reason we were doing bodywork so late in the game, one of the previously-secret mods we made:

We moved the wing. Changed the angle of incidence. Yee ha, we be REALLY Experimental now!
Here's a closeup:
Attachment:
IMG_1970.jpg
It's less than a degree, but still the filets all had to be redone.

Why, you ask? Well, it's a long story ...


Please login or Register for a free account via the link in the red bar above to download files.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 05 Oct 2018, 06:16 
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Username Protected wrote:
Why, you ask? Well, it's a long story ...
We've got time to listen!


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 05 Oct 2018, 08:43 
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Holy smokes. Thats quite a mod. Do tell.

_________________
Flying....yeah, I love it...


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 05 Oct 2018, 20:50 
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Company: Retired
Location: Seattle KPAE
Aircraft: TN36, building Evo
Earlier this year an Evolution in cruise experienced a sudden, 2+G pullup and vibration so bad the pilot thought he'd thrown a prop blade. He shut down the engine, which didn't fix the vibration and created a second problem, as the vibration was too bad to free up his hands for a restart. Fortunately the Evolution can glide a long way from 24,000 feet and he was able to dead-stick into an airport 20 miles away. On the ground, he determined that the trim tab actuator had broken, freeing the trim tab to flutter, creating the vibration through the elevator.

The obvious first step was sourcing a more robust actuator, but the incident highlighted an older issue, that the Evolution's trim tab is under stress too much of the time. The horizontal stabilizer's angle of incidence of -1 degree results in an excessive nose-up moment at normal cruise that has to be counteracted with lots of down-elevator and trim to hold it there. Besides the stress on the trim tab, there's considerable trim drag.

The obvious fix is to change the angle of incidence of the horizontal stab, and we actually had tried to do that during the initial build of my plane but the factory wouldn't let it out the door that way. Part of that "standardization vs. innovation" conflict I've mentioned before. Once the stab is bonded in, it's hard to change. But moving the wings would have the same effect, along with a slightly more nose-up fuselage, and they are much easier to move, since they are removable by design.

When we came up with this idea we had a recently completed plane in the shop. The owner agreed to let us try out our crazy idea on his brand-new airplane before he'd even flown it.

Before the mod, our test pilot did a GPS box pattern speed test at 17,500; he repeated it after the mod and it came out over 5 knots faster, and this was without changing the filets to align with the new wing angle. Video from a chase plane confirmed that the elevator was nearly inline with the stab.

Our biggest concern was that since reducing the negative AoA of the stab reduces the maximum nose-up authority there might not be enough for the worst case corner of the envelope: forward CG, full flaps, minimum speed. But the test pilot reported it was fine, no noticeable change, it flew the same.

Today, I think there are at least 3 planes flying with the mod, with at least 2 more to fly before I do. So I'm not THAT close to the bleeding edge.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 05 Oct 2018, 21:15 
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How do you stabilize 1 inch of micro? A layer or fiberglass over it ? The iv-p wing fuselage fillets show minor stress caused by pressurization after a few hundred cycles,


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 06 Oct 2018, 07:12 
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Username Protected wrote:
The horizontal stabilizer's angle of incidence of -1 degree results in an excessive nose-up moment at normal cruise...
That's interesting because the 2-place Lancairs like mine have the opposite situation. When we get going fast, the plane wants to fly nose down like a wheelbarrow. The pitching moment is a property of the NLF-0215F airfoil itself. We solve that problem by reflexing our flaps 7 degrees up, which raises the nose. Reflexing the flaps requires a lot of nose-down trim, though. One of these days I'm going to mount a video camera somewhere with a view of the elevator position in cruise. Not that I'm going to change anything, but I'd like to know.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 06 Oct 2018, 11:02 
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Username Protected wrote:
How do you stabilize 1 inch of micro?...The iv-p wing fuselage fillets show minor stress caused by pressurization after a few hundred cycles
We try to avoid micro that thick. The filets are carbon, outside the pressure vessel; we cut them off, moved them and rebonded them, then minimize micro on top of them. I guess we'll find out if it's thin enough to avoid cracks.

Minimizing pressurization stress cracking was one of my criteria for choosing the shop that I did. Some shops like to deliver a porcelain-smooth surface, which requires lots of filler and layers of paint, adding weight and ultimately stress cracking. I know one Evo that's been touched up for them at least twice in just a few years. We'll see what happens.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 14 Oct 2018, 02:30 
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Aircraft: TN36, building Evo
Anybody know of a reasonably priced RS-232 to ARINC 429 converter?

A downside of the G3X panel is that it can't handle pressurization, a problem Garmin promised to fix, then delayed, then reneged. To schedule the cabin descent rate, the pressurization controller needs the destination field elevation and ETA, which the G900X puts out in ARINC 429 and the G3X/GTN combination doesn't. I understand the data is available in RS-232 but the converters we've found are priced for the military market. Any pointers welcome.


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 Post subject: Re: You say you want an Evolution ...
PostPosted: 14 Oct 2018, 07:41 
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Company: Aviation Tools / Avionics One
Location: KSMQ New Jersey
Aircraft: Socata Trinidad TB20
Username Protected wrote:
Anybody know of a reasonably priced RS-232 to ARINC 429 converter?

A downside of the G3X panel is that it can't handle pressurization, a problem Garmin promised to fix, then delayed, then reneged. To schedule the cabin descent rate, the pressurization controller needs the destination field elevation and ETA, which the G900X puts out in ARINC 429 and the G3X/GTN combination doesn't. I understand the data is available in RS-232 but the converters we've found are priced for the military market. Any pointers welcome.


I could build you one. Do you know which labels the pressurization controller is looking for?


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