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Sam M.
Unregistered
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 Posted Tuesday, October 7, 2008 @ 00:50 AM
I have noticed in a full rudder slip i get a shake in the stick, is this another fournier characteristic? or have we missed rigged somthing?
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Collin
Unregistered
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Posted Wednesday, October 8, 2008 @ 03:52 AM
Hello,
I flew my Rf4 after work today. With spoilers mine will shake in a full slip without spoilers it is smooth. I have only flown two RF4 and the other I have not slipped.
Collin
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Sam M.
Unregistered
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Posted Wednesday, October 8, 2008 @ 12:27 PM
Thanks collin, i have only slipped with spoilers, i will try without spoilers next time i go flying.
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Jorgen
Unregistered
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Posted Wednesday, October 8, 2008 @ 05:07 PM
Hi Guys,
4 commuted to work today but was having so much fun (see aerobatics-aileron rolls-thread) that I forgot to test the slip. Forecast calls for another 4 commute tomorrow, I´ll check then.
Take 5(b) just 4 fun/ Jörgen
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Jorgen
Unregistered
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Posted Monday, October 13, 2008 @ 03:34 PM
Hello,
I remembered to slip into the 4´ today...Same as Collins, slight shake with spoilers, smooth without. No difference gear up or down. The slip angle is not as great as, say in a Cub with it´s bigger rudder with substantial control throw, but of course you already know that, Sam. Maybe turbulence from the spoilers hits the elevator in a slip?
Funny things can happen when the elevator hits turbulence, I always glide the RF 4 with the prop horisontal to minimize drag and keep the engine warm a little longer. At close to stall and in rough thermals I sometimes get violent stick shakes which I think has to do with turbulence from the prop hitting the elevator in addition to the usual stall shakes.
Saab Safari´s (http://www.aviastar.org/air/sweden/saab_safari.php) built under license in Pakistan is said to have had problems with stall characteristics, it turned out the Pakistanis had omitted a small seal at the wing root which caused turbulence that disturbed the elevator at high angles of attack.
I didn´t get that much additional sink compared to spoilers alone when side slipping, so maybe it´s not a big deal anyway. Close to ground I would caution against side slips, but that´s of course obvious.
Take 5(b) just 4 fun/ Jörgen
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Bob Grimstead
Unregistered
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Posted Tuesday, October 14, 2008 @ 02:02 AM
Hi Guys,
Fascinating stuff.
Sorry I haven't replied earlier, but I've been in Britain, flying 35 hours in WGN. That makes a total of 76 Fournier hours in the past 12 months. Can anybody beat that?
I haven't noticed any buffet/shake/tramp in the ailerons or elevator during a slip. Is the shake fore-and-aft or lateral? (ie elevator or aileron?)
Now I'm back in Austrlia, I'll try a few tomorrow and see what I get. That gives me something to do other than just aerobatics, which is getting a bit 'samey'.
A word of warning. If you are on a normal approach and find you are getting unexpectedly high and need to slip off some height, STOP. Is your wheel down?
When I landed wheel-up, being a dolt, I merely slipped off the height and crashed on to the runway. A moment's thought would have made me realise the reason for getting high and needing to slip was the lack of drag from the wheel!
DOH!!
Happy Fournicating.
Yours, Bob
[size=small][Edit by Bob Grimstead on [TIME]1224210824[/TIME]][/size]
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Sam M.
Unregistered
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Posted Tuesday, October 14, 2008 @ 01:21 PM
Mine only shakes is full spoiler slip. i can do a full slip with a little spoiler and be ok. i think the shake is lateral in the stick. but it seems the whole airplane shudders a bit.
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Bob Grimstead
Unregistered
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Posted Thursday, October 16, 2008 @ 10:54 PM
Hi Sam, Guys,
Yesterday I flew HDO (Aussie Blue or the Blue Angel) for the first time in six months. Going up to 3,000 feet, I tried a few full-rudder slips: all with the throttle closed, to the left and right, spoilers in and fully out, wheel up and down, at speeds from 80 mph back to almost the stall.
Slipping clean or with the wheel down but with spoilers retracted, slipping in either direction, and at any speed within that band, I got no buffet/shake/aileron tramping. Indeed, I got no aileron tramping/aileron buffet in any configuration.
Slipping with the wheel either up or down, but with the spoilers out, at almost any slip angle, I got slight low-frequency elevator buffet. It apparently increased with increasing slip angle. The stick vibrates at around eight to twelve cycles per second, mostly fore-and-aft, and oscillates through perhaps a quarter to a half an inch at the most. This buffet is still present, but at much lower amplitude (ie, it's weaker & the stick moves less) with spoilers fully out but with no slip. As I reduced the spoiler extension, the buffet reduced until it was no longer present with about one-third spoiler extension.
Looking over my shoulder either way, I could see the horizontal stabilizer (tailplane) waggling up and down maybe as much as an inch at the tips with the maximum buffet.
This buffet does not appear to increase with reducing airspeed, so I don't think it is pre-stall buffet. I suspect it is merely turbulent air coming off the extended spoilers. Because they are a little outboard from the fuselage, their turbulent flow only impinges on the tips of horizontal stabilizer when you are in balanced flight, but the bigger the silp angle, the more turbulent spoiler air impinges on the stabilizer. That's my guess, and presumably it is a normal Fournier characteristic.
I would be interested to hear anybody else's comments, but I would say you do not have a rigging problem Sam, it's just normal.
You might be able to see this airflow disruption if you tape a dozen or so, equally-spaced, four-inch wool tufts each side along the leading edges of your stabilizers, perhaps three or four inches back from the leading edges. Put them on both the upper and lower surfaces (because of course it is the underside of the horizontal stabilizer that's doing the work, creating downwards 'lift'). Go high, pull the spoilers and see how many tufts stand up and wiggle, then go itno a slip and see how many more lift. That's a great way to see what's actually happening around your airframe.
Have fun Fournicating everybody.
Yours, Bob
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Jorgen
Unregistered
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Posted Sunday, July 4, 2010 @ 06:15 PM
Hi Guys,
bumping this thread since I got some new(?) insight in this as Bob says quite fascinating phenomenom. As you know I love to glide the 4, which happens more now that RF 5b SE-UDI is unserviceable and we're in thermal season here. As you all know there are as many thermalling techniques as there are pilots, mine is a lot of "eeking it up"- a bit like "micro speed to fly".
Thermals most often have "uneven lift" or "more than one core", I usually almost stall in the lift and let the speed build a bit between cores. That makes me fly quite a lot in a stalled or "semi-stalled" condition, both engine at idle and engine off with the prop horisontal. I wrote in a earlier post that I got some buffeting that I thought was related to the prop, that's not true because I get the exact same buffets with engine at idle.
Looking over my shoulder, I can see that the buffeting shakes coincides with waggling up and down of the outer part of the tailplane just as Bob described, I'd say with a lower frequency than what Bob had, maybe 6-8 cycles per second. This makes me think the Fournier characteristics regarding buffeting is really stall shakes that maybe is similar to and occur easier with spoilers extended. It might be a good idean to check the tailplane bolts now and then if you "shake yer booty", eerr, tailplane often.
Anyone else have a different experience/thoughts?
May the 4's be with you/ Jörgen
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Jorgen
Unregistered
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Posted Tuesday, September 7, 2010 @ 05:21 AM
Hi Fournieteers,
I had a very nice soaring trip with the 4 a couple of days ago. It´s a great feeling close to cloudbase in a thermal so strong it allows you to actually see the cloud coming closer, visualizing the fact that you´re not flying in a circle- it's a spiral! I almost had the impression my rate of climb equalled my airspeed....
Speaking of airspeed- which we discussed also in the "Aerobatics- engine off"- thread. In the manual for the 4 I saw they recommend curving lift at 56 mph for min sink. That´s good advice, but I find slightly lower (52-53 mph) works better for me. That allows me to avoid the stall shakes most of the time while still having some extra airspeed to play a little with, to slow down in stronger lift. Everyone has their own curving technique, but you can always TRY new stuff- and then go back to your old habits....
May the 4's be with you/ Jörgen
[Edit by Jorgen on Tuesday, September 7, 2010 @ 05:27 AM]
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