REFLECTOR: Thrustline change

Mon Apr 1 05:48:11 CDT 2013

David

You will still need to pull back when rotating. I suspect that if it is popping off the runway your airspeed is approaching 90kts before you get the nose up. (What is your empty nose weight on the plane? And what is the canard stall speed?). Basically if you are too fast when rotating as soon as the nose comes up your wings and strikes grab air and away you go. Makes for more of an abrupt takeoff. Try leading in back pressure at 65. 

The stiffness of your trim spring can also play an effect. If it is weak the air load is pulling all of your trim out. Those of you that have come in for training might remember that 94VA will trim out below 80kts and in flight it only looks slightly trailing edge elector down; but after landing and slowing down the elevator looks almost fully deployed. 

Higher nose angle does help, just be careful as this makes your CG on the ground shift aft. Gets expensive if it goes to far. 

Fly safe,

John

On Mar 31, 2013, at 10:36 PM, "David Ullman" <ullman at robustdecisions.com> wrote:

> Thanks for all the feedback.  Based on it, I am going to make two changes:
> 1. change the thrust line.  I will start with about a 1/4 inch and see what
> I learn.  I will report back.
> 2. Raise the nose about an inch.  Right now when I takeoff with just me on
> board and about 1" of elevator down trim , I get to about70kts and still
> have to pull back, then pop off the runway.  The pop is dramatic enough that
> I warn passengers before the TO roll. I can change the setting on the nose
> wheel (Fixed gear) with a spacer behind the rubber block  (the new verison
> of rubber).  Not easy to get to, but changeable.  It will be interesting to
> see if this also affects shimmy.  I don't have much now, but this will
> change the castor angle.
> 
> I expect these two changes to shorten my take off roll.  Stay tuned.
> 
> ON another topic.  I wrote a few weeks ago that I was throwing a lot of oil
> out the breather.  I took the advice of some and ran the engine for a couple
> of hours wide open.  Believe it or not, it worked!!!  My prop and belly are
> no longer oil coated when I land.  There is a little, but an order less than
> there was.  I have had two flights now with minimal oil loss.  Amazing!!!
> 
> David Ullman
> N444DX
> President EAA 292
> 541-760-2338
> david at davidullman.com
> 
> 
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>   1. Re:  Thrustline change (dennis.doc)
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> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Sun, 31 Mar 2013 10:58:08 -0600
> From: "dennis.doc" <dennis.doc at gmail.com>
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Subject: Re: REFLECTOR: Thrustline change
> Message-ID:
>    <CAG8_WT8Mmfj2nwbn7HY35LRG7q7Kdatc1KjRwUq_uoX76VYezw at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> I added over one inch of shim to my engine mount. I called Scott Swing to
> make sure it would be OK. He told me "no problem." He and a local friend
> said there are advantages in take off and landing (more downward thrust)
> and that I could change it later if it  proved ineffective. I'm still
> flying off the 40 hours, but in the 10+ hours I've flown, no perceivable
> problems. I do notice that in cruise, while trimming the elevator 100% down
> - the trailing edge remains virtually neutral.
> 
> Dennis Martin
> 
> 
> On Fri, Mar 29, 2013 at 11:29 AM, David Ullman
> <ullman at robustdecisions.com>wrote:
> 
>> When I cruise with only me in the SEFG I have to put in 1/2 inch of down
>> trim (elevator up) or more.  This is clearly inefficient.  I already have
>> 18lb of lead in the nose and don't want to add more.  A friend suggested
>> shimming the top of the engine mount for a little downward pitch moment.
> I
>> sort of like the idea but am worried that it might increase my take off
>> distance as it will drive the canard downward a little.  He thinks it may
>> help as the engine thrust line is slight more upward.
>> 
>> Any thoughts or experiences?
>> 
>> 
>> David Ullman
>> N444DX
>> President EAA 292
>> 541-760-2338
>> david at davidullman.com
>> 
>> 
>> 
>> 
>> 
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