On May 17, 2018, at 5:43 PM, 'Jay Scheevel SGT' jay@... [Q-LIST] <Q-LIST@...> wrote:

Hi Ladies and Gentlemen,

 

Today, my Q moved one step closer to being an airplane. It is now certified. Witness the DAR and a happy builder/owner at the conclusion of the inspection/paperwork:

 

Cheers,

Jay Scheevel, Tri-Q2, no longer building

 

Well folks, Asheville is throwing in the soggy towel.  Won’t be heading north this weekend.  The historical high for rainfall on this date was in 1913 when 0.69” of rain fell.  Today it was a new record at 2.89”.  Flooding everywhere.  The weather forecast is for moderate/heavy rains for the next 10 days.  I am growing gills.  May be testing the floating capabilities of the Q down the local French Broad River.  It runs by the airport.

 

Hope you have a super time.  I sure hate missing the Fling.  Fly safely.

Jerry

On May 14, 2018, at 11:03 AM, quickieaircraft@... [Q-LIST] <Q-LIST@...> wrote:

Hi Jay,

Just got back from chasing Bruce's RV around this weekend.

Short version: A lateral angle in your pivot axis will indeed cause an off center behavior.  I'm surprised it is too much to correct with brakes, which makes it sound more like a brake problem.  At your low taxi speeds, small changes in caster angle will change steering effort more than centering behavior and I would not expect your problem is due to caster angle.

Long version:

The high speed stability of a castering nosewheel is sensitive to "trail," or the (horizontal) distance the steering axis intersection is in front of the wheel's ground contact point.  Think of this as the tire patch "trailing" behind the pivot axis intersection.

For most applications, Q included, we want positive trail, tire contact point trailing the pivot axis intersection.  There are several geometric ways to add mechanical trail : the big ones are steering angle and offset.

Bicycles and motorcycles add trail by adding rake angle, or inclining the pivot axis.  Big wheels, slower speeds, and they run 2-3 inches of trail, but they also can apply more steering effort and want some self-steering for stable turns. 

Our fork already builds in some mechanical trail, about 7 inches if I recall.  Most Tri Q installations benefit from adding more.  The plans call for about 2 degrees. A degree or two more reduces shimmy tendency, a degree or 2 less increases shimmy tendency.  Steering efforts are inverse.  It looks to me like Scott Swing picked 2 degrees as an acceptable compromise between shimmy avoidance and steering effort. 

Without any other data points, I made an effort to be very close to plans specifications at just a hair under 2 degrees trail.  The plans specify about 6lbs breakout force (see http://www.quickheads.com/index.php?option=com_content&view=category&id=55)

However, I have not yet inspected an aircraft that is operating with that low a breakout force, which has, among other things, to do with the fact that most of our aircraft are not mythical 500lb factory demonstrators (more on weight effects in a minute). The Kantrowitz method applied to a more typical weight indicates a kinematic shimmy bound breakout force somewhat higher, at 16.4lbs (see https://quickheads.com/index.php?option=com_content&view=article&id=2387&catid=48&Itemid=144)

I run a little bit lower, probably around 10.5-11.This produced a setup that is well-behaved in most conditions.  

One thing that has not been quantified is the change in steering angle under load transfer.  Under heavy braking after the wing has quit lifting, load transfers to the nosegear, which changes the caster angle (more vertical-->reducing trail) and can cause shimmy (see Fig 6(b) in last link for an illustration of the bend).  If you are heavy, have a forward CG location, or set your damper to the 6lbs breakout, you might occasionally see mild shimmy when braking hard somewhere between 21-28mph.  For those reasons, if I were building today, I would investigate setting my caster angle to 2.5 degrees.  I'd expect that load transfer will make your lateral angle more problematic when you are heavy or under load...might be best to address your lean now.

Great to know that Kevin is able to run more friction.  Kevin, have you ever experimented with other breakout forces?

if

Hi Kevin,

 

Tried it both ways. I had it tightened to specs when I first tried taxiing and it drifted left and I could not correct. Loosened it up, same result. I am narrowing down the causes at this point.

 

Cheers,

Jay

 

From: Q-LIST@... <Q-LIST@...>
Sent: Sunday, May 13, 2018 6:38 AM
To: Q-LIST@...
Subject: Re: [Q-LIST] Happy Camper

 

 

Jays know others have asked, but I have not seen the answer.

How tight is the nut on the bottom of the nose gear?

The one that holds the fork in place. It should take 15# of pull to get the nose fork to break free and turn. I don't know your situation, but I can tell when the nut needs attention, as the slow taxi control is degraded.

As Dave Dugas said, "see something, say something.

Random thoughts.

 

Kevin B

On May 12, 2018, at 8:57 PM, 'Jay Scheevel SGT' jay@... [Q-LIST] <Q-LIST@...> wrote:

 

Thanks Charlie. I had seen this years ago and forgot about it. Hmm, I wonder how that happens (as I stroke my grey beard)?  I will shoot for 2 degrees positive castor. I have not gotten the plane going fast enough to benefit from the positive caster yet. I am fighting it at very low speeds which leave me unable to get it to return to neutral after it starts turning left. Will work on it some more over the next week.

 

Cheers,

Jay

 

From: Q-LIST@... <Q-LIST@...>
Sent: Saturday, May 12, 2018 5:26 AM
To: Q-LIST@...
Subject: Re: [Q-LIST] Happy Camper

 

 

Reference 

 

http://www.quickheads.com/index.php?option=com_content&view=article&Itemid=265&id=1052

My You Tube Channel " One Sky Dog " 

On May 11, 2018, at 8:20 PM, 'jcrain2@...' jcrain2@juno..com [Q-LIST] <Q-LIST@...> wrote:

When you push it backwards you go immediately from push to drag.  A tail wheel airplane has the pivot point angled forward at the top of the bolt.  It’s all for centering the tail wheel to keep it from falling to one side or the other.  The nose gear needs the angle forward toward the bottom to keep it from shimmying..  Are both of your brakes equal or is one soft when pressing the toe brakes?  If so you may need to re-bleed the brakes.  If you aligned and cambered the main wheels according to plans they should be fine...  
Bruce

Please note: message attached

From: "'Jay Scheevel SGT' jay@... [Q-LIST]" <Q-LIST@yahoogroups..com>
To: <Q-LIST@yahoogroups..com>
Subject: RE: [Q-LIST] Happy Camper
Date: Thu, 10 May 2018 16:52:37 -0600


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