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aerosiam
Joined: 26 May 2008
Posts: 59
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 Posted: Mon Jun 23, 2008 9:20 pm Post subject: Vortex generators update |
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To answer Hugh's question in his post titled 'Vortex Generators' Stolspeed say the VGs can be placed at 8-12% of the chord. I wanted to place them quite far forward (7%)for the following reasons
The Allegro has a fairly sharp leading egde
Air velocity is probably highest around 7% chord at the stall
The tapered sections are quite narrow (and the most vulnerable to a stall) and the vortices need time to propagate.
I discussed this with the VG designer and he agreed.
Fitting is simple and the Stolsped instructions are very good. The tapered section takes a little head-scratching but is actually easy.
You only need to mark 3 points on the wing.
On the constant chord section mark 2 points 2.14 inches back from the leading edge. The first point (A) is at the wing root, the second (B) exactly where the chord changes from constant to tapered. Ping a chalk line.
Place the front tips of the VGs touching the chalk line. This puts the tallest part of the 'fin' at 7%
Now measure the chord at the wingtip fairing join (ignore the fairing itself) and mark point C at 7% minus 0.8 in (the distance from the front tip to the fin of the VG.)
Ping a chalk line from point B to C (start of tapered section to the wingtip - ignoring the fiberglass fairing)
The back of the template must be 90 degrees to the airflow. Mark a series of lines parallel to the main spar. It's probably easier in removable felt pen rather than chalk to avoid the dust for adhesion. Use the lines as a reference for the back of the template.
A couple of notes...
Suggest you try only the tapered section first then full span if you want.
If you are going to do stall tests with and without VGs, are you current and familiar with stall recovery? I flew with a chief instructor which was a comfortable feeling! Did you get your stall warning working?
Talked to the Italian dealer who said the Allegro will recover from a spin normally and immediately with full opposite rudder. After 3 turns autorotation speed increases.
See http://www.mcp.com.au/allegro/flight-test/flight-test.html about sharp stall and wing drop power on
See http://www.aero-siam.com/page143.html for VG flight report and pictures of VGs
Suggest you fit the horiz stab VGs and test fly before fitting the wing VGs
Aircraft will take off sooner and land and float a little later. Touchdown 31 kts CAS in ground effect.
Easier to bump the tail (and take off too soon) because the nose angle is higher for a given stick input.
I have a dynon pitot set several degrees below incidence. The factory pitot does not seem to suffer position error.
I will check measurements when I am next at the field.
Regards
Paul
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Wed Jun 25, 2008 7:50 am Post subject: Vortex generators update |
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Paul:
I have tried to reach Stolspeed at their email address with a few questions.
I keep getting my message returned. Can you give me the proper email address
to use to reach them?
Also from your dissertation on the use of the Feathers VGs, am I correct
that with the VGs on the outboard of the wings only, the landing attitude of
the plane is steeper than without the VGs? The landing attitude of the plane
at touchdown under normal conditions is still fairly steep (in my opinion).
Your statement that with the VGs on the wings only, one could easily drag
the tail on takeoff or landing disturbs me. I certainly don't want to begin
to do this. Please explain this further to me. I am certainly not going to
put something on my plane that causes me to risk dragging the tail!
Hugh
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aerosiam
Joined: 26 May 2008
Posts: 59
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| Posted: Mon Jun 30, 2008 5:51 am Post subject: Re: Vortex generators update |
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Hugh
The VGs have 2 benefits. They reduce stall speed and improve control effectiveness as slow speed.
The stall speed is less because the VGs allow the wing to fly at a higher angle of attack than before - I would guess only 1 degree more at landing full flaps so the tail will be slightly nearer the ground on a full flare landing
The improved control means that whatever stick inputs you are used to for landing and taking off, you will need slightly less back pressure for the same effect - it is like having a slightly bigger horizontal tail surface
In practice, the effects are not significant and it only takes a few take offs and landing to get used to it.
The effect is more with full span VGs over half-span.
The downsides of the VGs are very minor compared to the improvement in safety and handling.
Regards
Paul
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sun Jul 13, 2008 2:47 pm Post subject: Re: Vortex generators update |
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Are you guys getting factory approval for the VG's?
The factory may be agreeable, but if not then as an SLSA you can't do it unless you want to be out of SLSA compliance. This would then tag your insurance. You would also need an appropriate rated individual to do the work. I'm not trying to discourage you, but trying to keep everyone in good graces in case something happens.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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aerosiam
Joined: 26 May 2008
Posts: 59
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| Posted: Sun Jul 13, 2008 11:17 pm Post subject: Re: Vortex generators update |
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The VGs were tested on an ultralight/experimental aircraft in Thailand which has considerable flexibility in its regulations.
When I visited fantasy air to buy my aircraft, I suggested I would do a VG test. Their view (and the designer) was that VGs would not make that much difference.
I emailed them the report (which I posted on this site) but they did not respond.
I have no idea what would be needed to getting the factory involved but having flown for several months now with the VGs, I am very happy to have them on the plane. The landing characteristics and general handling are nicer all round.
Paul
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Mon Jul 14, 2008 3:43 pm Post subject: Re: Vortex generators update |
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Hi Paul,
I have done a few mods to my Flight Design CT. I did get factory approval and it has to be in writing. If you do not have that then that puts you out of SLSA compliance and out of insurance. You can bet the insurance company will blame the VG's if you have a accident. I have a form letter that is good for any factory mod and it has to have certain wording for the FAA to be happy. It is short and sweet, but needs to be sent to the factory. You need to take 3 pictures of the mod and send it in with the letter. Most Mfg's already know of this letter of approval.
You need to dog the factory and get this approved for your own benefit. Remember an SLSA is no different than a GA aircraft when it comes to mods. The FAA says if something is in the manual it is a minor repair, if it is not in the manual then it is considered a major repair and needs the factory approval and a rated mechanic for the mod.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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aerosiam
Joined: 26 May 2008
Posts: 59
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| Posted: Mon Jul 14, 2008 4:51 pm Post subject: Re: Vortex generators update |
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Hi Roger
Interesting. I imagined getting a mod approved would be a difficult process.
In the case of the VGs, I would think Fantasy Air would want their test pilot to do test flights.
The factory does not have the best reputation for responding to customers and I doubt they would make the effort to test the VGs.
If Hugh or anyone else is seriously interested, maybe we could get the factory interested.
When I was in Czech in 2005, I offered to pick up the tab for fuel if they paid their test pilot for a series of test flights.
Regards
Paul
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Mon Jul 14, 2008 5:43 pm Post subject: Vortex generators update |
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Roger/Paul:
My Allegro 2000 is an E-LSA so I don't have your paperwork and approval
problem. However, based on how my Allegro is performing I have not yet
decided that I need the V
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Mon Jul 14, 2008 6:07 pm Post subject: Vortex generators update |
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