You're All Trash*, Part 234,567,988 - DarkAero

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wsimpso1

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Hmmm, so you think the wing construction could be even lighter than the BV246?
What I am saying is that I doubt the dense egg crate of honeycomb sandwich will be lighter for a COMPLETE horizontal stabilizer than a more conventional COMPLETE horizontal stabilizer of the same strength.

The issues are several:

  • The skin must to be built to some min skin sturdiness and thus thickness, which sets a min weight for that portion of the structure without regard for internals;
  • The aft most web of the stabilizer must be sturdy enough to pick up elevator loads and distribute them over the stabilizer, which sets min weight for that portion of the structure without regard for the rest of the internals. This comment applies regardless of whether the hinge is several fixed hinges attached to the spar or is lengths of piano hinge fixed to one skin;
  • The bonding of internals to the skin must be reliably achieved in production, which usually means a significant overfill of adhesive. In a conventional construction, this mass is moderate, but with a large faying area for the multitude of honeycomb panels, this weight could be substantial indeed;
  • The bond joints must be resistant to crack growth under repeated load cycles. Bonding the edges of graphite composite to other thin sheets of graphite composites may induce cracking in the adhesive unless the adhesive volume is substantial.

Once you have a min gage skin and a min drag spar, the internals being proposed by Darkaero become largely superfluous.

Now, I do not contend that for their demonstrator, it was not the lightest scheme - it may well have been lighter than any other scheme for supporting the well distributed one ton load. Let's remember that their demonstrator did not have to contend with point loads from a deflected elevator at its limit loads, nor did it have to carry a reliable-in-production amount of adhesive bonding that large number of honeycomb panels to the skins, nor did it have to be reliably resistant to fatigue.

Marketing...

Billski
 
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Victor Bravo

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Young people are always smarter than old people.
Oh absoluetly... when I was young I was so much smarter than this sorry bunch of trained engineers and experienced pilots on HBA.

I was even smarter than that fat old guy that lives in the bathroom mirror. I have no idea why he cries when he looks at me.
 

Sockmonkey

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I was even smarter than that fat old guy that lives in the bathroom mirror. I have no idea why he cries when he looks at me.
Same here. Just the short time I've been on this forum learning from you guys is enough to make me cringe at what I thought I knew when I showed up.

So, I think the reason new designs get so much flak is a combination of over-hype, inadequate filtering of the crap from the actual good stuff, and the way the net oversaturates us on everything.
 

wktaylor

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In the 1980s John Thorp revisited the T-18 design from many perspectives: 'as-is' aluminum/riveted structure; new/revised aluminum/riveted structure design; 'aluminum, adhesive-bonded, some fasteners' structure; aluminum-honeycomb structure; and all-composites structure. Granted, the use of computers for design/analysis was not yet common place... however the study was seriously executed with assistance of other designers with similar experience levels in these various technologies.

Not only was the existing design very weight efficient; it was also very affordable from a cost-to-build and maintain perspective. Further new materials and fab processes could have lightened the structure somewhat... but at significant costs.

The other versions [including a sheet-metal re-design] could shed a small amount of weight but fabrication costs skyrocketed; and maintenance/durability/repairability became issues.

Besides... the overall weight of the structure was a relatively small fraction of the gross weight [designed 1250#] which actually included, flight controls, 'old fashioned instruments/radios', battery/wiring/lights, interior/seats/restraints, crew/baggage, landing gear, fuel, engine etc added-up to about 75% of the #1250-GW. The hidden facet to the design equation is that lots of improvements/lightening in GA have been derived based on digital avionics/systems, batteries, engines [with substantially better fuel efficiencies], interior materials/seating... and subsequent ability of composites to 'sculpt the shape' for higher aerodynamic efficiency.

NOTE. When a structure becomes so sophisticated that it has to be built as noted... and [for homebuilts] the 51% rule still applies... how does a company control quality ... while meeting 51%target?

NOTE. There is usually a finite limit to structural lightness... the cirrus design is a classic example. it is fast efficient light... but barely structurally adequate... and it can be damaged by rough miss-handling... or by rough runways/taxiways.
 

BBerson

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I was told the FAA has evolved to accept that factory assisted build is the best quality. The 51% is carefully worked out somehow.
 

wktaylor

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A few quotes/wisdoms worth repeat at this point are...

Learn the rules like a pro, so you can break them like an artist." -- Pablo Picasso, Spanish artist

The difference between school and real-life is simple. In school You learn the lesson; then take the test. In real-life, You take the test then learn the lesson.” -- version of Vern Law’s quote

The young know the rules: the old know the exceptions." --Bumper snicker

At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.” – Igor Sikorsky

Play by the rules, but be ferocious." --Phil Knight, Nike founder

Following the rules will not get the job done. --Dilbert

Getting the job done is no excuse for not following the rules. --Dilbert

Rules are made by man. Laws are made by the universe [God].” -- Unknown

You are remembered for the rules you break." -- Douglas MacArthur, American military leader [good and bad outcomes]

If you obey all the rules, you miss all the fun.” --Audrey Hepburn, actress

Hell, there are no rules here - we're trying to accomplish something!" - Thomas A. Edison, inventor and businessman

If you try to apply the same rules to every person or circumstance ... creativity will wither and die.” --Nolan Bushnell, electrical engineer and entrepreneur

There are no rules of architecture for a castle in the clouds.” –Gilbert K Chesterton

Hire a teenager while they still know everything!” -- Unknown
 

BJC

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Maybe I'm being too cynical, but I'm sick of people claiming all the paradigms are just no good, and, By God, We Have Found THE Solution.
I talked to all three of them at Oshkosh, and found them to be enthusiastic, eager, dedicated and very naive, but never heard a hint of a “you are all trash” attitude.

While I believe neither their stated developmental timeline nor their forecasted performance will be achieved, I did find a few positives.

They are young people with a passion for sport aviation who have made significant personal commitments. (They have been working full time for a year and a half on the project.)

They are trying something different from the norm. Whether they will be successful or not remains to be seen, but I give them credit for trying to demonstrate a better way.

Even if their performance forecasts are not achieved, they may still have a viable product based on resonable performance, reasonable cost (which will be difficult) and really fast build time (and, possibly, a factory built Experimental under the rule changes that the FAA is talking about.)

Sport aviation needs more people like them.


BJC
 

Riggerrob

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Funny, factory airplanes have been using aluminum or Nomex honeycomb covered with aluminum or composite skins for the last 50 years. It is a light-weight, simple way to maintain exterior loft lines for less labour than purpose-built ribs. Balsa wood or foam blocks can achieve the same shape. Delaminations are rare in service.
I do not understand the negativity spewed by the OP.

Yes, junior engineers tend to underestimate strengths needed to resist hangar-rash ...... because end-users abuse airplanes in ways never imagined by designers .... in their worst drunken-nightmares!

As for Burt Rutan/Beechcraft’s Starship being unsuccessful ..... Since it was one of the first all-composite airframes certified by the FAA, the feds insisted on such large structural margins of error, that Starship eventually weighed as much as the King Air it was meant to replace. With no performance or economic advantage, Starships sold poorly.
As for dissing Rutan for his “failures” .... that is shallow and outside the realm of homebuiltairplanes” or “experimental aviation.” We only learn new things when we venture outside the conventional. The challenge is making small mistakes .... mistakes too small to kill test pilots .... then learn from those mistakes.
Young engineers rarely achieve perfection on their first try.
Consider that Burt Rutan built model airplanes, worked as a flight test engineer for the USAF, tested Jim Bede’s airplanes And designed three of his own homebuilts before he achieved success with the Long-adze: his third design.
After that, Burt continued making small mistakes - on sub-scale proof-of-concept airplanes - for major aerospace corporations.
 

Andy_RR

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How do they plan to make 275mph with only 200hp when it arrives at 3300rpm? That's not a good start for decent thrust efficiency.

It looks like a lot of good effort being applied to a very conventional and under-analyzed design, but that's just me looking from afar. What have I missed...?
 

DangerZone

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How do they plan to make 275mph with only 200hp when it arrives at 3300rpm? That's not a good start for decent thrust efficiency.

It looks like a lot of good effort being applied to a very conventional and under-analyzed design, but that's just me looking from afar. What have I missed...?
The homebuilt Osprey GP-4 cruises at around 215kts with a Lycoming 200HP engine, it's empty weight is around 580kg (1270lbs).

https://en.wikipedia.org/wiki/Osprey_Aircraft_GP-4

There is a guy who built the GP-4 lighter by using some wooden composites and woven fabrics. This allowed him to use a less powerful 160HP/130HP (peak/cruise) engine with similar performance. This aircraft is a great design, but it takes approximately around 4000 man hours to complete it.

Hence I bet the Darkaero team had the idea to make a two seat aircraft out of conposites as light as possible, and use a lighter engine than the Lycoming IO-360. The Darkaero aircraft is optimistically set at 340kg empty weight (750lbs) and declaring a 1500lbs (680kg) MTOW. This seems a bit stretched, but I've seen some homebuilt aircraft do that. There was an Asso X which weighs 340kg empty and cruises at 370km/h (200kts) with a 130HP Turbocharged Sauer engine on sale a couple years ago. Many did not believe this is achievable, but if you make an aircraft light enough and reduce the drag down to a minimum, a 200kts cruise speed is possible.

Now, here comes the ugly truth. Most such high performing homebuilt aircraft need a lot of man hours if you want to build them. If Dark Aero really plans to make such a light 200HP aircraft, only serial production in high volumes would allow the needed return. Hence this aircraft should be cheap enough to allow sales, and the man hours needed for production should be lower than 400 per aircraft. Even with a proven design and experienced people in production, this is very optimistic.

If we'd take a look at previous similar projects, there were usually two ways this could have gone south. One is that during the building of the prototype - the empty aircraft gains weight. Cruise speed goes down, stall speed goes up, costs go up, number of buyers goes down. This is the most common problem, and then investors have to throw more money in or ditch the idea. More money they throw in, the more expensive the aircraft. In the end, it results in a heavier than anticipated aircraft. Combine that with being more expensive and you'll see why the Pipistrel Pantera has orders up to year 2023 and all aircraft sold in advance. Panthera got 4 persons and carries more weight on 200HP with a decent 200kts cruise in ideal conditions.

https://en.wikipedia.org/wiki/Pipistrel_Panthera

I haven't seen much of this DarkAero aircraft, but hopefully they will succeed in making the empty weight 340kg. This seems highly optimistic for people without much experience in building aircraft, but it's their time and money. I just hope they did not really say other builders and aircraft are trash, because this would mean they are unrealistic about reality. It would certainly hurt them a lot if they'd fail epically by not realizing their aircraft is gonna have at least 10% to 20% more empty weight than planned.
 

Doggzilla

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Come on gentlemen.

There is literally an entire league of aircraft that break 250mph with O-200 engines.

Where is everyone getting the idea that this is not possible? It's been possibly for 20+ years.
 

BJC

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An entire league of racing aircraft that operates at almost identical specifications?
Over the past three years (I didn’t look further back) only two airplanes with four cylinder engines exceeded 275 MPH in the AirVenture Cup race, and they likely had a tailwind that year.

91 Glasair I TD N91LH Bruce Hammer 280.61 MPH
2 111 Long EZ N360KS Klaus Savier & Jenny Tackabury 275.72 MPH

Past results here: http://www.airventurecuprace.com/racers/race-results/


BJC
 

DangerZone

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Over the past three years (I didn’t look further back) only two airplanes with four cylinder engines exceeded 275 MPH in the AirVenture Cup race, and they likely had a tailwind that year.

91 Glasair I TD N91LH Bruce Hammer 280.61 MPH
2 111 Long EZ N360KS Klaus Savier & Jenny Tackabury 275.72 MPH

Past results here: http://www.airventurecuprace.com/racers/race-results/


BJC
The Polen Special comes to mind, too.

https://en.wikipedia.org/wiki/Polen_Special

Yet these guys want to make us believe they can make an aircraft more than a hundred
kilos lighter with more surface area and drag. Wouldn't that seem a bit... optimistic? :)
 

DangerZone

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Come on gentlemen.

There is literally an entire league of aircraft that break 250mph with O-200 engines.

Where is everyone getting the idea that this is not possible? It's been possibly for 20+ years.
It is possible, but has anyone managed to make it - profitable in a serial production? :)

How many of these aircraft are lighter than 340kg/750lbs?
 
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