REFLECTOR: elevator range - increased drag

Mon Mar 20 11:56:33 CST 2006

You'll need the recommended down travel.  Up is less important unless you 
are planning to fly upside down - not recommended.  Bottom line, make sure 
you have the down travel.

Ronnie

----- Original Message ----- 
From: "John Tvedte" <JohnT at comp-sol.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Monday, March 20, 2006 12:28 PM
Subject: RE: REFLECTOR: elevator range - increased drag

> Keith,
>
> Exactly -
>
> Here are some inconsistant #'s in the manuals (for XL).
>
> Chapter 3 - states 24-26 deg. up, and 28 deg. down. total - 52-54 deg.
> http://www.velocityaircraft.com/manuals/03_XLG.PDF 
> <http://www.velocityaircraft.com/manuals/03_XLG.PDF>
>
> Chapter 10 - states 23 deg. up and at least 26 deg. down - so total of at 
> least 49 deg.
> http://www.velocityaircraft.com/manuals/10_XLR.PDF 
> <http://www.velocityaircraft.com/manuals/10_XLR.PDF>
>
> John
>
> -----Original Message----- 
> From: reflector-bounces at tvbf.org on behalf of Keith Hallsten
> Sent: Thu 3/16/2006 11:51 AM
> To: 'Velocity Aircraft Owners and Builders list'
> Cc:
> Subject: RE: REFLECTOR: elevator range - increased drag
>
>
>
> John,
>
>
>
> Yes, this was jus discussed within the last few days on the Canard 
> Aviators list with respect to the Long-EZ.  Excess down elevator will act 
> as a spoiler.  The elevator should have a stop so that maximum down travel 
> gives the canard-elevator system the maximum lift coefficient. 
> Unfortunately, I don’t know exactly what elevator deflection gives CL max 
> with the Velocity canard airfoil.
>
>
>
> Here’s an except from the “Canard Pusher” newsletter for Rutan Aircraft 
> Factory planes:
>
>
>
> CAUTION  CP 48
> ELEVATOR CONTROL STOP POSITION.  This applies to VariEzes as well as
> Long-EZs using the original GU canard (Roncz 1145MS not affected).  The
> design philosophy of the EZ canard type airplane calls for the canard
> airfoil to develop maximum lift coefficient (CLmax) at full aft stick.
> Thus the elevator trailing edge down (nose up command) stop must be set
> correctly.  On an accurately built GU canard/elevator, this will
> usually be at approximately 22 degrees (trailing edge down).
>
> Recently, we have heard from a few builders, both VariEze and Long-EZ,
> who have noticed stall characteristics that were not "per the
> handbook".  In all cases, the cause was the elevator nose up stop set
> to allow too much elevator travel.  If you have noticed any of the
> following symptoms, check that you have no more than 22 degrees to 22-
> 1/2 degrees trailing edge down travel on your elevator.
>
> 1)  Perform a 1-'g', wings level, straight ahead stall with sufficient
> power to maintain level flight.  Slowly pull the control stick back to
> full aft stick.  This should result in a nose high attitude with a
> "pitch bucking" that can vary from hardly noticeable to quite vigorous,
> perhaps "one buck" per second, with a deck angle change of several
> degrees per "buck".  This is normal and will vary depending on the cg.
> If, however, you notice a strong stall break (canard stalls) and the
> nose comes down through the horizon until you are in a stable shallow
> dive, even though you are still holding full aft stick, the speed may
> build up to over 100 KIAS before the EZ begins to climb again.  This
> very long period pitch "bucking" can be as long as 30 seconds per cycle
> and is indicative of too much elevator trailing edge down travel.  You
> can verify this by releasing back pressure on the stick during the nose
> down phase of the cycle and gently raising the elevator trailing edge
> perhaps 1/8" at a time.
>
> This should allow the canard to develop more lift and pitch the nose
> up.  Try to determine by experimenting with elevator position, where
> CLmax is, then set your elevator stop at that position.
>
> 2)  Another classic symptom may be noticed during a take off.  At full
> aft stick, it may take a longer take-off roll to lift off that it does
> at, say, slightly forward with the stick.  If you have ever noticed
> this, it should be corrected.  Under certain circumstances, this could
> become a serious problem.  A Long-EZ builder/flyer in Alaska,
> attempting to take off on a rather short runway, discovered that he was
> rapidly approaching the end of the runway and, even though he was
> holding the stick all the way back, was not rotating.  Realizing he was
> not going to make it, he backed off from the full aft stick stop and,
> to his surprise, the airplane literally jumped into the air!  Again,
> his trailing edge down elevator stop was set for too much travel.  This
> same scenario has also been reported to us by a San Diego VariEze
> pilot.
>
> What causes this?  If the elevator stop is set so that at full aft
> stick your canard can develop its maximum possible lift, this will
> result in the lowest possible rotation speed for take-off and a good,
> clean canard stall (limiting the main wing angle of attack) or classic
> "per the book" stall at full aft stick in flight.  If, however, you
> have set your elevator stop for too much travel (perhaps you thought
> you could lower your rotation speed?!!) what happens is that you are
> now on the "back side" of the lift curve, lift is less than maximum,
> and the elevator is creating lots of drag.  The result may be running
> off the end of the runway.  Keep in mind that this condition could be
> aggravated even further if it were raining.
>
>
>
> Keith Hallsten
>
>
>
>
>
>
>  _____
>
>
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On 
> Behalf Of John Tvedte
> Sent: Thursday, March 16, 2006 8:37 AM
> To: Velocity Aircraft Owners and Builders list
> Subject: REFLECTOR: elevator range - increased drag
>
>
>
> All,
>
>
>
> Factory Spec (minimum) is for 26 degrees down and 23 degrees up or 49 
> degrees total.
>
>
>
> Our Elevator has 30 degrees down and 28 degrees up or 58 degrees total.
>
>
>
> I am wondering if anyone knows if having too much elevator range can 
> result in getting the canard in the "back side" of the lift curve, lift is 
> less than maximum and the elevator is creating lots of drag?
>
>
>
> Wondering if I can get a survey of what people are getting for their down 
> and up elevator travel - flying airplanes greatly appreciated?
>
>
>
> Thanks,
>
>
>
> John
>
>

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