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Jorgen
Captain
Gender: Male
Location: Lund, Sweden
Registered: Apr 2007
Status: Offline
Posts: 836
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 Posted Wednesday, August 1, 2007 @ 03:37 AM
Hi everyone,
as disclosed elsewhere on this forum I fly RF 4 D SE-XST, former G-AVNX. It features (among lots of things) a trim tab on the starboard aileron to counter a strong tendency to roll to the right. Former UK owner James Hallam claims that Fourniers "..all have twisted wings", but that was before I paid, of course 
Close scrutiny of all pics of RF 4´s does not show any trim tabs, so I guess it´s not that common with this problem after all. Possible explanation on SE-XST is a crash some 20 years ago that necessitated a repair to the left leading edge D-tube done exquisitely by the previousprevious owner Mike Wollard. Maybe the angle of attack is slightly higher on the port wing after that, I haven´t measured it (yet...).
The decrease in cruise and re-glueing the trim tab every now and then isn´t much of a bother, but I´m curious if someone else have encountered this problem and maybe found another cure. Is it perchance possible to tune the wing without re-building it completely?
Just 4 fun/ Jörgen, SE-XST
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andy1
Sergeant First Class
Gender: Male
Location:
Registered: Aug 2008
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Posts: 82
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Posted Wednesday, August 1, 2007 @ 05:08 AM
I have never seen any aileron trim tabs on any RF4D. Instead I've flown pretty long times hands off without noticing any tendency to roll to any direction.
-A-
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***** Antti Laukkanen, Helsinki, Finland - RF4D OH-371 - RF4D OH-370 - RF5 OH-386 *****
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Donald
Command Sergeant Major
Gender: Male
Location: Scotland
Registered: Jan 2007
Status: Offline
Posts: 489
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Posted Wednesday, August 1, 2007 @ 07:26 AM
My RF3 has a fixed tab on the starboard aileron set to lift the port side but my port wing D box has been damaged and repaired in the past and I imagine that is the cause of the slight rolling tendency.
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Markku
Master Sergeant
Gender: Male
Location: Kouvola, Finland, EFWB
Registered: Oct 2006
Status: Offline
Posts: 167
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Posted Wednesday, August 1, 2007 @ 07:28 AM
Actually Andy, you have flown a RF-4 with fixed trim tab (OH-380), which was screwed afterwards on the trailing edge of aileron. An old plane made of wood isnt't often completelly symmetrical.
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andy1
Sergeant First Class
Gender: Male
Location:
Registered: Aug 2008
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Posts: 82
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Posted Thursday, August 2, 2007 @ 06:34 AM
OK, thanks for correction. That's my memory then. Well, it must've been well balanced, because it was the handsoff bird... Sorry!
-A-
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***** Antti Laukkanen, Helsinki, Finland - RF4D OH-371 - RF4D OH-370 - RF5 OH-386 *****
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sericson
Staff Sergeant
Gender: Male
Location: Lancaster, CA
Registered: Feb 2007
Status: Offline
Posts: 40
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Posted Friday, August 3, 2007 @ 01:30 PM
I have yet to fly my RF4-D former F-BLPI. It does have a small trim tab mounted to the underside of one aileron.
Steve Ericson N505SE
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Collin
General
Gender: Male
Location: McMinnville. Oregon
Registered: Oct 2006
Status: Offline
Posts: 711
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Posted Saturday, August 4, 2007 @ 09:22 AM
Hi,
Mine RF4 needs one it pulls to the right. I will install a tab soon.
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Collin Gyenes
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JamesB
First Sergeant
Gender: Male
Location: Near Seattle, WA; USA
Registered: Oct 2006
Status: Offline
Posts: 257
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Posted Saturday, August 4, 2007 @ 10:07 AM
How would you know when to add a trim tab or just slightly adjust the ailerons so an aircraft won't "drop a wing" to one side?
It seems that measurements can get you very close. However, the Cessna Pilots Assoc. stresses returning adjustments to factory recommendations, then do any final adjustments so the plane flies correctly. I don't think they add trim tabs--they just fine tune the airlerons.
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SteveBeaver
General
Gender: Male
Location: Columbus, Ohio - USA
Registered: Jan 2007
Status: Offline
Posts: 457
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Posted Saturday, August 4, 2007 @ 05:43 PM 
On many aircraft, particularly the high-wing strut-braced type and biplanes, it is possible to adjust the angle of incidence of the wings, or at least the wash-out, independently left to right. On this type of aircraft, you adjust the wings to get the aircraft to fly straight. Other models, such as the Van's RV series allow the flaps to be adjusted independently and this allows a measure of roll adjustment. On other aircraft, like the Fourniers, there is no provision to adjust the wings or the flaps so the only possible adjustment is adding a tab to the ailerons.
On a number of occasions, I have had the fun of watching people (in some cases very experiences professional pilots) adjust the aileron push-rods thinking that it will affect the roll trim of the aircraft. - Of course all it does is move the stick in the cockpit. The ailerons still fly in trail with the slip-steam and the plane still flies with a heavy wing. 
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Donald
Command Sergeant Major
Gender: Male
Location: Scotland
Registered: Jan 2007
Status: Offline
Posts: 489
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Posted Sunday, August 5, 2007 @ 02:54 AM
A little story about adjusting ailerons.
When I bought my RF3 11 years ago the ailerons were set so as to ride very slightly high, whether with the idea of reducing drag or just in error I cannot say. At my first CofA renewal with a new inspector who felt this was wrong they were reset to what he thought a proper 'in trail' alignment. When I came to do the associated flight test I discovered that the stall, which had previously bordered on the aerobatic, was transformed into a gentle mushing which could be ridden almost indefinitely with rudder inputs.
Hard to believe the difference but they have been left like that ever since.
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Bob Grimstead
Captain
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Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
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Posts: 2043
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Posted Sunday, August 5, 2007 @ 06:39 AM
Hi Guys,
Aileron tabs on RF4s are correct. Every one of them left the factory with a transparent plastic (Perspex? Plexiglas?) tab below the inboard end of the left aileron. You often cannot see them on photos because they were transparent!
Both Matthew Hill (who not only flew them with both Sportair, the Tiger Club and the Skyhawks, but worked on them as a licensed aircraft mainteneance engineer) and I were intrigued. At the Gap-Tallard get-together, Matthew took the chance of asking Rene Fournier (via interpretation by his son) why this was. Rene admitted that it turned out that the jigs were not quite true. It would have been expensive to change them, and would have interrrupted production, which in those heady days exceeded one beautiful hand-crafted airplane per week, so they just fitted that tab.
Subsequently many RF4s have had minor (or major) accident damage to one or other wing, and the opportunity was often taken to adjust things so the tab was no longer needed, but I assure you all that they all started out with one.
Yours, Bob
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Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2043
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Posted Sunday, August 5, 2007 @ 06:42 AM
Hi again folks.
Now I have another wing rigging question for you all.
If you measure from the trailing edge of one wing-tip at the aileron cut-out to the base of the fin (vertical stabilizer), and then repeat that measurement on the other side, what difference do you get?
Yours, Bob
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Jorgen
Captain
Gender: Male
Location: Lund, Sweden
Registered: Apr 2007
Status: Offline
Posts: 836
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Posted Tuesday, August 7, 2007 @ 09:41 AM
Wellwell,
The RF 4 D featured in Brians gallery "Sportair and the Fourniers" is G-AVNX, nowadays SE-XST. The article is from 1968 so it´s a freshly hatched one year chicken on the photos. Apart from the possible but invisible transparent (left sided?) tab there is no sign of todays rightsided, white painted tab that depresses the right aileron.
Correct me if I´m wrong, but an aileron trim tab is preferrably fitted with an upward deflection to depress an aileron since this causes less drag than a downpointed tab would. I am thus strengthened in my belief that the repair of the left wing of G-AVNX in the 80-ies changed the wingstructure somewhat, perhaps a correction of the "factory twist" as Bob suggested was tried and became an overcorrection?
I´ll get back when I have done some measurements.
Just 4 fun/ Jörgen, SE-XST
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SteveBeaver
General
Gender: Male
Location: Columbus, Ohio - USA
Registered: Jan 2007
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Posts: 457
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Posted Tuesday, August 7, 2007 @ 02:24 PM
Any aileron tab will move one aileron up, and the other down so that a rolling force is produced. The tab is usually fitted to the aileron you want to move up so that the drag of the tab causes a slight yaw in the same direction as the rol lyou are trying to achieve. In theory, this produces a coordinated (no adverse yaw) turn in the required direction.
Steve
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Sam M.
First Sergeant
Gender: Male
Location: Santa Paula, CA
Registered: Jul 2008
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Posts: 228
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Posted Friday, May 16, 2008 @ 03:55 PM
EDIT: Our Rf came with a tab, and it does have a right roll, im going to put it on soon.
[Edit by Sam M. on Saturday, February 21, 2009 @ 02:07 AM]
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Jorgen
Captain
Gender: Male
Location: Lund, Sweden
Registered: Apr 2007
Status: Offline
Posts: 836
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Posted Saturday, May 17, 2008 @ 03:10 PM
Hi Sam,
thanks for all your inputs, you´re doing a great job of rejuvenating the forum! I think the wing twist refered to in the manual is the so called "wash-out" which is incorporated in the design. Most aeroplanes, gliders and hanggliders have this higher angle of attack at the center of the wingspan and lower angle of attack at the wingtips. This gives better stall characteristics, since the aileron end of the wing will still fly when the center begins to stall. With swept wings (like for example a hangglider) the center of the wingspan is in front so when it begins to stall, the nose drops and this way you get pitch stable characteristics.
Steve, I´ve been thinking about your idea fitting a downpointing tab which makes sense. My trimtab is just glued on the aileron, so I´ll try moving it to the other side.
Take 5(b) just 4 fun/ Jörgen, SE-UDI, SE-XST
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Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2043
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Posted Saturday, May 24, 2008 @ 01:16 PM
Hi Guys,
The British Fournier Matthew and I just bought (G-AWGN, hereafter referred to as 'the Red One') also has an upwards bent tab on its right aileron, rather than the correct downwards bent tab on the left aileron. I guess we should change it. I'll let you know if we do.
Yours, Bob
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jb92563
Second Lieutenant
Gender: Male
Location: Lake Elsinore, CA, USA
Registered: Mar 2007
Status: Offline
Posts: 583
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Posted Friday, February 20, 2009 @ 10:32 PM
Just some thoughts about the upward bent tab.
My understanding is that an upward bent tab produces less drag and less adverse yaw, but probably needs to be a bit bigger than a downward bent tab.
Another reason for a tab being needed is that the spoiler on one wing may be leaking air (not sealed) or not perfectly flush.
Perhaps even sealing the ailerons is not equal on both sides.
Perhaps modifying the tips slightly would require the least change since they are way out and have lots of leverage, but must be done carefully to ensure the wings stall straight ahead as opposed to dropping one tip first.(Dangerous)
Just some thoughts to consider.
Ray
Disclaimer(I'm NOT an aeronautical engineer so....)
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Jorgen
Captain
Gender: Male
Location: Lund, Sweden
Registered: Apr 2007
Status: Offline
Posts: 836
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Posted Wednesday, June 23, 2010 @ 05:47 PM
Hi Guys,
bumping an old thread for sure, but since twisted wings IS a Fournier characteristic we all have to think about this. RF 4 "SE-XST" has a right roll like every 4 which was adjusted with an upward tab, glued and taped to the underside of the right ailerons trailing edge. This worked less and less well, maybe because the tape/glue didn´t hold so the tab was depressed without really moving the aileron. Inspired by the excellent video Sam posted a link to I (FINALLY!) moved the tab to the underside of the left aileron's trailing edge as Steve suggested, so it pushes up and at least theoretically cause some drag.
Test flight today revealed a very noticeable improvment- now it flies hands-off at low speed, but I might have to adjust the tab's size. Size do matter, in this case it's probably a matter of at which speed you want the tab to be most efficient. So next question (there always is one, isn't there) is how wide and how long is the optimal tab and what angle should it be bent? Remember, a tab can stall so if you bend it too much it will not work. Thanks Steve for suggesting the mod, which can be recommended.
To comment Ray's suggestion, XST has aileron gap seals, so that factor should be equal. Interesting thought about the airbreaks, but I haven't noticed any differencies there.
May the 4's be with you/ Jörgen
[Edit by Jorgen on Saturday, June 26, 2010 @ 11:56 AM]
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