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

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wsimpso1

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The assumption being made is that it's possible to push both pedals and have both rudders deploy, but they may have the pedals designed to prevent this. Symmetrical deployment, if needed, may be on a separate control.
Yes, that assumption is being made. According to plans, Long EZ and its derivative airplanes have rudders that deflect outward only, are spring loaded into trail, one cable is rigged from the pilot's left pedal to the left rudder, one cable from right pedal to the right rudder, and there is no interconnect. Pushing down on them simultaneously deflects them both outward.

I have looked at a lot of Ez's and their cousins, and have yet to notice one with rudders rigged to deflect inward. Now maybe there are some rebels out there who have rigged rudders to run both ways or who built in a rudder bar, but I have not noticed them. Let's call it unlikely.

Billski
 
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Marc Zeitlin

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... Long EZ and its derivative airplanes have a rudders that deflect outward only, are spring loaded into trail, one cable is rigged from the pilot's left pedal to the left rudder, one cable from right pedal to the right rudder, and there is no interconnect. Pushing down on them simultaneously deflects them both outward.
All correct.

I ... have yet to notice one with rudders rigged to deflect inward.
There are none, other than by mistake.

Now maybe there are some rebels out there who have rigged rudders to run both ways or who built in a rudder bar, but I have not noticed them. Let's call it unlikely.
No, it's not unlikely, it's specifically contraindicated, for flutter reasons. EZ rudders ONLY deflect outward - any negative loading creates a flutter susceptibility issue, which some folks (ahem) have had, and have had to remedy.

I find that deploying both rudders on my COZY MKIV gives me an extra 200 fpm of descent rate (over the 400 - 500 fpm that the landing brake gets me). But a slip will get me an extra 1000 - 1500 fpm, so there are three ways of adding drag, slowing down and increasing the glide slope angle.
 

12notes

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Yes, that assumption is being made. According to plans, Long EZ and its derivative airplanes have a rudders that deflect outward only, are spring loaded into trail, one cable is rigged from the pilot's left pedal to the left rudder, one cable from right pedal to the right rudder, and there is no interconnect. Pushing down on them simultaneously deflects them both outward.

I have looked at a lot of Ez's and their cousins, and have yet to notice one with rudders rigged to deflect inward. Now maybe there are some rebels out there who have rigged rudders to run both ways or who built in a rudder bar, but I have not noticed them. Let's call it unlikely.

Billski
I wasn't attempting to imply that they deflected inward, it's possible they have the pedals interconnected and the controls rigged so that each rudder only deploys past the middle point of the corresponding pedal, with symmetrical deployment for air braking done on a separate control using a mixer on the cables/rods.
 

davidb

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The assumption being made is that it's possible to push both pedals and have both rudders deploy, but they may have the pedals designed to prevent this. Symmetrical deployment, if needed, may be on a separate control.
In one of their videos they described it as left, right or both. Pushing both pedals simultaneously achieves the symmetrical split per their description.

IMO, it seems like an awkward way to achieve minimal speed brake effect. Is there some other advantage to a split rudder on a conventional airplane? Wouldn’t a conventional rudder be lighter?
 

BBerson

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Pushing both brake pedals (instead of rudder) could do it. My dive brake handle also activates the wheel brake at end of dive brake travel.
 

wsimpso1

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I wasn't attempting to imply that they deflected inward, it's possible they have the pedals interconnected and the controls rigged so that each rudder only deploys past the middle point of the corresponding pedal, with symmetrical deployment for air braking done on a separate control using a mixer on the cables/rods.
On a classic canard ship, that is a lot of work and weight to make something not work any better while eliminating a useful feature, but I suppose they could do that.

For the Dark Aero, not so sure it is worth the trip...
 

wsimpso1

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In one of their videos they described it as left, right or both. Pushing both pedals simultaneously achieves the symmetrical split per their description.

IMO, it seems like an awkward way to achieve minimal speed brake effect. Is there some other advantage to a split rudder on a conventional airplane? Wouldn’t a conventional rudder be lighter?
I think it almost has to be heavier if it is to achieve the same flutter margins. On the Dark Aero it seems a feature better left out.
 

Rik-

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Marketing.

edit: “Look at this advanced technology that everyone but us has overlooked.”


BJC
You forgot to mention that they are basically taking ideas from Rutan, ideas from X and Y due to the fact that they don't have any original ideas of their own.
 

BBerson

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The grid core is rather different than Rutan or anyone else, as far as I know. They probably didn't invent it, but they are building it.
 

BJC

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The rudder concept. It’s principle is from the LongEz. One of their interviews they stated this.
I don’t doubt that they said it, but, to me, that is not a good comparison.

From my perspective, the primary purpose of the outward-only deflecting rudders on winglets is to create drag well away from the C.G. to drive yaw. The purpose of a rudder located aft of the C.G.is to generate lift, with minimum drag, to drive yaw. Perhaps I’m splitting hairs there, but I don’t recall seeing split rudders on any Rutan designs with centerline rudders. HBAers, please educate me if I missed a Rutan centerline split rudder.

Assuming that they plan on a constant speed propeller (to have a reasonable percentage of rated HP available for takeoff and climb), they don’t need a drag brake to slow down, so creating drag to help avoid rapid cooling of the engine is the only potential benefit that I see. HBAers, please ID other potential benefits. To me, the added complexity is not worth it. Apparently, they see it differently. Time will tell. Note that VanGrunsven started with ailerons that drooped when flaps were deployed, to reduce landing speed, then later removed that feature.

The details of their yaw trim system will be interesting to see.

edit: I’m not saying that they have “done it wrong”. I am saying that my choice would be different.


BJC
 
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Rik-

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edit: I’m not saying that they have “done it wrong”. I am saying that my choice would be different.
Understood, but this is why I say they have kinda picked and chosen features from others rather than designed their own ingenious ideas.

My concern is that when you copy someone else, your copying their mistakes and throwing in a few of your own so the outcome can be drastically different. Hello Raptor scenario.
 

Vigilant1

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Understood, but this is why I say they have kinda picked and chosen features from others rather than designed their own ingenious ideas.

My concern is that when you copy someone else, your copying their mistakes and throwing in a few of your own so the outcome can be drastically different. Hello Raptor scenario.
I see things as being exactly the opposite. The Raptor didn't copy enough things, and didn't do it well enough.
Nearly everything about a modern airplane is the product of gradual development over many iterations. The best designs stand on the foundation of hundreds of failed, or at least less successful, earlier designs. A body of knowledge is developed. A designer who, out of ignorance or hubris, deliberately disregards all that hard-won knowledge and plans to do a lot of new things all at once (powerplant, structural design, aerodynamic design) without depending on, or even respecting, prior art is either a fool or, to be successful, must be a genius.
This isn't "modern art" where creators earn points for originality. This is cold, hard, engineering where the truth and "better" is revealed in a very harsh light.
Not enough has been "copied" in the case of the Raptor..
 
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Rik-

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I see things as being exactly the opposite. The Raptor didn't copy enough things, and didn't do it well enough.
Nearly everything about a modern airplane is the product of gradual development over many iterations. The best designs stand on the foundation of hundreds of failed, or at least less successful, earlier designs. A body of knowledge is developed. A designer who, out of ignorance or hubris, deliberately disregards all that hard-won knowledge and plans to do a lot of new things all at once (powerplant, structural design, aerodynamic design) without depending on, or even respecting, prior art is either a fool or, to be successful, must be a genius.
This isn't "modern art" where creators earn points for originality. This is cold, hard, engineering where the truth and "better" is revealed in a very harsh light.
Not enough has been "copied" in the case of the Raptor..
Sorry, it this thread isn’t about bashing Raptor.
 

Marc Zeitlin

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From my perspective, the primary purpose of the outward-only deflecting rudders on winglets is to create drag well away from the C.G. to drive yaw. The purpose of a rudder located aft of the C.G.is to generate lift, with minimum drag, to drive yaw.
Pretty sure we've had this discussion before, but this is the internet :). The outward only deflecting rudders on the EZ aircraft are not drag devices (although they DO create some drag which assists in yaw). They are lift devices, just like all rudders - they change the camber of the winglet. Since the winglet is well aft of the CG of the aircraft, the change in lift on the winglet creates a yawing moment. While they do also create drag in a favorable yaw direction, the drag is only about 10% of the total yawing force - 90% is lift. At least on an EZ, the excess drag helps with yaw - on a centerline rudder aircraft, the drag is just drag :).

The original Rhino rudder on the Defiant was centerline, forward of the CG under the rudder pedals. Worked fine, but destabilizing when both feet were on the pedals and it couldn't float. Most folks have switched to winglet rudders on Defiants.

... so creating drag to help avoid rapid cooling of the engine is the only potential benefit that I see.
Since "Shock Cooling" on normally aspirated engines is a long-debunked myth, doing anything to prevent it is a waste of time...
 

Rik-

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Since "Shock Cooling" on normally aspirated engines is a long-debunked myth, doing anything to prevent it is a waste of time

it’s amazing how many people preach the fear. Ironically even the Rotax guys fear it too.
 
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