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Kent Ashton

hangar electricity and other rants

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Some thoughts on that Commuter Craft Innovator that crashed:  I am getting way outside my knowledge base but here goes:

They had a prototype #1 that flew (pic below) however they apparently wanted more horsepower and stretched prototype #2  by three feet (pic above).  I imagine that was for weight and balance.  Then they widened the nose A LOT but it appears they made the front canards smaller.  They also moved the horizontal stabilizer out of the clean air above the aircraft and down behind the prop.

Now, I'm thinking that a wide nose at a positive AOA is a pretty good additional lifting surface and the horizontal stab (H.S.) in the prop blast is pretty effective at controlling pitch but what happens if you would get a little negative AOA on that nose?  Does it become a negative lifting surface?  As the AOA changes relative to the nose,  is the wide nose going to amplify the pitch change?  Are the canards powerful enough to counteract a negative pitching moment?  Also, If you had the controls positioned for a steady climb and pulled back the power, would the H.S. lose effectiveness and result in an out-of-trim pitch change?  The H.S. in P.#2 must have been highly affected by prop blast.

It is said, I think, that surface area ahead of the aircraft center of pressure is destabilzing.  They added a whole lot of that in the pitching axis while subtracting area from the front canards that would control pitch.

Then there is the Center of Gravity.  It has to be somewhere in front of the axles to make the aircraft sit firmly on three wheels.  I could not find any good side views of P.#2 that would let us judge the relationship of the CG, wing Center of Lift but the pic above seems to suggest the CG might be at about the fuselage station where the strake leading edge is.  Perhaps the aircraft depended on lift from the nose and an effective H.S. to maintain balance.  If either of those goes away, it might pitch over.  

They flew 1/3rd scale models of their first prototype.  I could find no reference to model-testing of the 2nd prototype.  Perhaps P.#1 flew well enough that they didn't see the need to model P.#2.    Interesting to think about, eh?

 

commuter-craft-innovator-alpha.jpg


-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Ouch, sad ending. Do we call this aircraft design a canard? Maybe I missed it, but is the elevator in front (canard) or at the tail?

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It appears to have had a full-function canard with elevators, and possibly also on the tail (or just trim tabs -- I cannot tell).  

 


Jon Matcho :busy:
Canard Zone Developer & Builder
Rebuilding Quickie Tri-Q200 N479E
Building Cozy Mark IV+ (widened rear)

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Thanks, that picture seems to clear it up. Clearly appears to be elevators on the canard. I don't claim any aeronautical engineering capability, but balancing the canard and tail through all attitudes seems daunting to me.

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One time a buddy and I were rafting down the Rio Grande near Del Rio and we came to a weir.  It looked fairly benign--just a foot or two of smooth water moving over a low dam.  We hauled out and debated whether we could raft across it.  Decided not to try it.  Best decision I (we) ever made.  🙂  In the past few days I've seen several videos of weirs or weir-like situations killing people, like the poor guy in this video.     In the other videos, moped-riders trying to cross a flooded road got swept in the rotor.

How do you learn this stuff?   Youtube, in spite of all the crap, has done us a great service by showing many ways to die.

https://www.liveleak.com/view?t=RyOK_1554971362


-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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Posted (edited)

Saw this accident writeup recently: 300 hour pilot, non-IFR, night IMC, wife + two kids.  http://www.kathrynsreport.com/2019/05/cirrus-sr22-owned-by-linds-plumbing-and.html   No need to say how dumb this was however, the question that interests me is whether the pilot was trying to fly through a gap in the weather he saw on Nexrad, but due to Nexrad broadcast delay--which can be 8-10 minutes, he ended up flying into the green blob that moved north into his flight path?  There is no way to know but that has caused crashes before.  In another crash recently, a chap flew into a line of thunderstorms moving in his direction that he thought he was avoiding on Nexrad.

It is often some small deficit of knowledge or the unwillingness to take decisive action that kills a pilot.   Maybe this pilot did not know about Nexrad delay.  Even so,  had this fellow acknowledged the danger of his situation, climbed straight ahead to a safe sector altitude and relied on the autopilot, his family would likely be alive today.  It should have been an easy decision, actually.   It's a big sky.  All he had to do was to not hit the ground.  He lacked a little voice to say, "This has gone far enough.  Admit you're screwed.  Climb.  Use your autopilot", yet he mucked around with it too long for what?  Pride?  Panic?  Fear of not staying VFR?  Information overload?   Or perhaps, with all the mucking about, he finally met the old killer, vertigo.

 It is hard to develop that judgement with only 150 hrs PIC.  No one goes out thinking "I'm going to be stupid today."  We fly ourselves into precarious situations step-by-step.  Often each step seems reasonable until collectively, they are not.

KathrynsReport.png

Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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That is a painful read. I was surprised, probably shouldn't have been, that someone with that little time and only recently licensed would put their selves in that position.

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Here are other examples grabbed from a FB page of what seems to be a destabilizing nose forward of the aerodynamic center.  One flying, one under construction.  One of the comments was

Quote

Have you talked to ___ about Purple? He admits its too long and hunts in cruise. He keeps the pods on because it helps it. He is going to try putting the lower winglets back on to help it. He will tell you its too long...

I would think a pointy nose is going to act somewhat like an airfoil with the trailing edge pointed forward.  Any yaw will tend to increase the yaw.  I bet you would see that if you made a simple cone shape and held it out the car window.   I suspect it will also decrease pitch stability for the same reason.  Also it's lot of extra glass in a shape that will be harder to utilize.  Sort of ugly, too, IMHO.

65111140_10217340206834968_1912480930396635136_n.jpg

64467166_10217339472896620_2657389505480228864_n.jpg

Edited by Kent Ashton

-Kent
Cozy IV N13AM-750 hrs, Long-EZ-85 hrs and sold

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4 hours ago, Kent Ashton said:

Here are other examples grabbed from a FB page of what seems to be a destabilizing nose forward of the aerodynamic center. ...

Interesting that you bring this up. I discussed this issue in some depth in my presentation on canard aerodynamics at the Columbia Fly-In a few weeks ago. You can see the presentation here:

http://cozybuilders.org/Oshkosh_Presentations/index.htm

under "Other Presentations", down near the bottom. I also discussed the issue on the COZY mailing list a while back in relation to a Long-EZ I've flown that has a very long and rounded (but not THAT long) nose as well as very small lower winglets, and it has substantially less directional stability at lower speeds, especially.

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Lower winglets should help. Making the pod pylons longer chord-wise probably would too, as it adds even more vertical area aft. It would be interesting to see if wing fences helped noticeably.
It all adds weight and wetted area though. Ultimately the best solution would be cut off the nose and re-do it. Plenty of nice examples out there with nicer than plans shapes without being needle-nosed like this.
Looks like a nice example besides, as far as one can tell from small photos anyway. Clearly a lot of thought has gone into it, even if I don't necessarily agree with all the conclusions arrived at. :)


Aerocanard (modified) SN:ACPB-0226 (Chapter 8)

Canardspeed.com (my build log and more; usually lags behind actual progress)
Flight simulator (X-plane) flight model master: X-Aerodynamics

(GMT+12)

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