REFLECTOR: Vortilions and/or VG's?

[Jim Sower]

The reason I took them off the wing is to try and get a handle on what 
they cost me in cruise.  I feel I still need them on the canard for 
takeoff as I am nearly always very nose heavy (350# front seat) on 
takeoff and am NEVER anywhere near aft CG.  I agree that VGs might cause 
a problem if they were only on the canard at aft CG, but I'm never in 
that situation.  I think they are useful to prevent separation over the 
elevator at the high deflections I need for nose heavy takeoff.  
Elevator deflection increases the effective AoA of the canard as well as 
changing the airfoil so the canard stalls at a lower incidence than it 
would with no deflection.

I do appreciate your concern though ... Jim S.


Scott Derrick wrote:

> jim,
>
> I'm confused and a bit concerned about your statement  " I have since 
> taken them off the main wing (left them on the canard)".  The intent 
> and ABSOLUTE requirement for VG placement to reduce stall speed is to 
> reduce the stall speed the same amount on the canard and the main 
> wing, so you don't move the lift relationship between the main wing 
> and the canard  into a deep stall area.
>
> We always want the canard to stall first.    Always, its kind of a 
> prime rule in canard planes. What the difference is in speed I don't 
> know, but I would think its one of those, the more the merrier kind of 
> rules.
>
> By putting VG's on your canard you have lowered its stall speed. By 
> omiting VG's on your main wing, your main wing now has the original 
> stall speed to be a match with your un-VG'd canard.  But since you 
> have VG's on the canard, you have now reduced the stall speed 
> separation between the canard and the main wing.  Possibly in some 
> flight attitudes your main wing may stall first?
>
> I think this is a very dangerous thing to do.
>
> Scott
>
> Jim Sower wrote:
>
>> My 173 with vortilons and lower winglets wallows a lot below about 85 
>> kts.  I carried 80 kts on final until I installed VGs.  Went to 75 
>> kts final, 70 over the fence and 65 or less touchdown with what 
>> seemed like about the same roll authority.  I have since taken them 
>> off the main wing (left them on the canard) and one of these days 
>> will put them back on and do a more detailed before-after test.  I 
>> also sealed my aileron hinge gaps when I put on the VGs, and that has 
>> have a lot to do with the improved in low speed roll authority.
>> It'll take some time to get decent test data for VGs and gap seals 
>> ... Jim S.
>>
>>
>> Ron Brown wrote:
>>
>>> I do have the lower winglets.
>>>
>>> I have the same wings as Jack so I think I will try flying without 
>>> the VG's and Vortilions and see how it compares with VG's.  My 173 
>>> handled well with the VG's on short final.  I do lead with rudders 
>>> when it is gusty or turbulent around the trees near the runway.
>>>
>>> I'll let you know my opinion in a week or two.
>>>
>>> Ronnie
>>>
>>>
>>> ----- Original Message ----- From: "Jim Sower" 
>>> <canarder at frontiernet.net>
>>> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>>> Sent: Tuesday, July 19, 2005 5:28 PM
>>> Subject: Re: REFLECTOR: Vortilions and/or VG's?
>>>
>>>
>>>> Oooops - I misread your message as NOT having lower winglets.  Mea 
>>>> culpa
>>>>
>>>> Jack Sheehan wrote:
>>>>
>>>>> Maybe since I do have the lower winglets the vortilons would not 
>>>>> have effect. I really don't have much experience in other 
>>>>> Velocities but Scott Baker has flown mine and H e didn't think I 
>>>>> was missing much or if he did he never said anything. The airplane 
>>>>> takes a little rudder in the turns at about 90kts and lands fine 
>>>>> at 80kts.
>>>>
>>>>
>>>>
>>>>
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