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  #31  
Old 12-19-2019, 09:14 AM
eisnerrv4 eisnerrv4 is offline
 
Join Date: Sep 2006
Location: Halifax, NS
Posts: 179
Thumbs up RV-4 Slips

Don't worry about slipping the RV-4 with flaps. I've done it with no problem, works great.
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  #32  
Old 12-19-2019, 10:06 AM
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gmcjetpilot gmcjetpilot is offline
 
Join Date: Jan 2005
Posts: 4,310
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Folks talking about a full forward slip and getting STALL BUFFET... scares me. You should not be near stall in a slip or feel stall buffet. The buffet you are likely feeling (if IAS approach speed, above stall) is turbulent airflow coming off the side of the fuselage, buffeting the whole airframe ...

Slipping does not increase stall speed. The aerodynamics of the wings do not change with a slip. IAS may have some error in a slip but it is NOT from the pitot tube but static port. If you have dual static ports the error should be small (subject to phase 1 flight test calibration).

Not sure what "aggressive" slip is. A forward slip is full rudder, aileron to track and pitch to maintain approach IAS. This is standard.... I guess not aggressive is less than full rudder. If you are timid about using full rudder than you will not have full effective use of this normal maneuver to lose altitude w/o gaining speed.

Bottom line stall IAS in slip is similar to iAS in coordinated flight except for small IAS error AND high wing with down aileron is at higher angle of attack, so it will stall first and plane will snap roll over in the direction of the high wing. That affects stall speed slightly. You should be no where near stall when you do fwd slip on approach to lose altitude without gaining air speed.

The YT videos on previous post are fun. However I wonder about altitude lost? It look like the recoveries were very quick with min altitude loss. Except CFI no pilot training requires spin training. It would be good to go practice full stalls is skids and slips. The RV-4 with a passenger can get some weird control reversals near aft CG. I would not do this with a messenger in a RV-4 or RV-8 without chutes.... However the videos show HOW NICE RV's are to fly and honest, letting you know they are about to stall and having such a benign docile characteristic when they do.
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Last edited by gmcjetpilot : 12-19-2019 at 11:05 AM.
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  #33  
Old 12-19-2019, 11:22 AM
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skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 947
Default Angle of Attack Vs. Bank and Yaw

Quote:
Originally Posted by Vac View Post
SLIP

Here's another example looking forward...in this case, I reduce alpha before a spin (snap roll) develops fully. In other words, you really have to work hard to depart the airplane in a slip:
In the first and second video, the snap roll/spin is the result of centering the ailerons and relaxing the bank while keeping rudder applied. You generally need yawing motion to induce a spin and by flattening the bank with rudder still applied you are no longer maintaining the slip and the nose begins to yaw right while the wings are still at critical angle of attack. Also, the drop the of the nose preceding the "snap" increases rudder effectiveness, further increasing right yaw...

Skylor

Last edited by skylor : 12-19-2019 at 11:27 AM.
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  #34  
Old 12-19-2019, 12:37 PM
luddite42 luddite42 is offline
 
Join Date: Mar 2010
Location: USA
Posts: 458
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Quote:
Originally Posted by gmcjetpilot View Post
Folks talking about a full forward slip and getting STALL BUFFET... scares me.
Why? They were doing this deliberately at altitude to observe the behavior of the slip as AOA is increased up to potentially full aft elevator. Most airplanes are quite stall/spin resistant in a full slip while slowly increasing elevator to full aft, but nothing wrong with learning how your particular airplane behaves. I know of a Pitts pilot who killed himself spinning in on approach from a slip. The only real way to do that is to neutralize the aileron before you've removed the rudder. Even the Pitts is very stall/spin resistant in a slip.
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  #35  
Old 12-19-2019, 07:30 PM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 447
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Hi Skylor,

I'm actually maintaining full inside aileron during the departure sequence (to extent that I can). I had some spare gas today, so I flew three intentional departures using the same handling technique as the old videos that you are referring to.

What I think is occurring is roll coupling at high alpha (think high AOA rudder roll in a jet). There is sufficient stability to momentarily reduce alpha during the sequence, even though the stick is maintained full aft (nose bobbing)--which accounts for the ratcheting motion prior to the spin actually developing. I left full left aileron and full right rudder through the incipient stage of the spin and allowed the spin to wind up a bit. I'm working hard to force the airplane to depart in the slip--it would be difficult to miss the extensive aerodynamic warning the airplane is providing. The airplane (RV-4) weighed 1375 lbs, with the CG at 70.65" aft of datum:

https://youtu.be/I6tBNnoaB6w

Aerodynamically, if there is something else going on here at this weight/CG condition, I'm definitely open for critique or discussion! I may also be missing any engine/propeller effect that may be at play. Also entirely possible I’m ham-fisting something...wouldn’t be the first time.

Cheers,

Vac
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Last edited by Vac : 12-19-2019 at 08:42 PM.
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  #36  
Old 12-20-2019, 10:12 PM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
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Skylor/Luddite:

I ran an additional test today as I was concerned my elevator input in yesterday's example may have been too rapid. Today's test conditions were similar to yesterday's and RV-4 gross weight was 1366 lbs, CG at 70.65." I pulled my left leg out of the foot well to be sure the stick reached the lateral limit, and then applied slow elevator input with stick against the lateral limit while maintaining full opposite rudder:

https://youtu.be/DExPobxNyIE

In other words, I'm able to induce a departure without neutralizing ailerons whilst maintaining rudder input (i.e., sufficient yaw for a spin to develop). Obviously aircraft specific performance, with extensive aerodynamic warning. Thoughts on this departure sequence? It appears to me that there is sufficient yaw as a result of rudder input at high alpha + adverse yaw to induce some roll coupling prior to departure. I appreciate the critique. I'm always trying to collaborate to improve or correct the discussion in the training manual.

v/r,

Vac

P.S. RV's slip just fine. Forgive the deep dive.
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Last edited by Vac : 12-20-2019 at 10:21 PM.
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  #37  
Old 12-21-2019, 04:28 AM
swjohnsey swjohnsey is offline
 
Join Date: Nov 2018
Location: Kingsville, TX
Posts: 237
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When I was talking slip I meant cross controlled, I never even considered a skid. Don't think I ever deliberately induced a skid. Is there ever any reason to?
I did some slipping in the RV-4, no problem, air speed indicator is accurate during slip. I'm going to try some landing using slip instead of flaps. With the C/S prop I have to set up something artificial to be too high.
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  #38  
Old 12-21-2019, 10:31 AM
larosta larosta is offline
 
Join Date: Dec 2010
Location: Redlands, CA
Posts: 179
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Interesting and informative.

- larosta
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  #39  
Old 12-22-2019, 07:14 AM
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uk_figs uk_figs is offline
 
Join Date: Jan 2005
Location: Tulsa, OK
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Quote:
Originally Posted by Vac View Post
Skylor/Luddite:

I ran an additional test today as I was concerned my elevator input in yesterday's example may have been too rapid. Today's test conditions were similar to yesterday's and RV-4 gross weight was 1366 lbs, CG at 70.65." I pulled my left leg out of the foot well to be sure the stick reached the lateral limit, and then applied slow elevator input with stick against the lateral limit while maintaining full opposite rudder:

https://youtu.be/DExPobxNyIE

In other words, I'm able to induce a departure without neutralizing ailerons whilst maintaining rudder input (i.e., sufficient yaw for a spin to develop). Obviously aircraft specific performance, with extensive aerodynamic warning. Thoughts on this departure sequence? It appears to me that there is sufficient yaw as a result of rudder input at high alpha + adverse yaw to induce some roll coupling prior to departure. I appreciate the critique. I'm always trying to collaborate to improve or correct the discussion in the training manual.

v/r,

Vac

P.S. RV's slip just fine. Forgive the deep dive.
Interesting thread, and watching the video I was interested in the AoA tone throughout the maneuver. I have the dynon AoA pitot on the left wing and the thread indicates that in the slip the high wing will reach critical AoA first which in my case would generally be the right wing. How would this impact the AoA tone I receive and in particular the stall onset point of the AoA system? As I am generally head/eyes out when slipping on final the AoA tone is one of my Wake-Up calls if I get too slow
Sorry if a dumb question.
Figs
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  #40  
Old 12-22-2019, 07:58 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
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Figs,

Great questions.

First, a good rule of thumb for the coefficient of pressure pitot/AOA probes is that they can handle up to about 6 degrees of sideslip. I find I run out of rudder (generally) before I run out of tone in the RV-4.

Second, there are two tones in the video; they are being generated by systems we built that generate performance AOA and energy cues in addition to progressive stall warning. All of our work is on our website at http://www.flyonspeed.org (non-profit, volunteer, open source group).

Specifically, yes, the high (right wing) is stalling first--hence the ratcheting behavior in the departure sequence. My Dynon probe is mounted in the RV-4 plan pitot location under the left wing and there is a second, Alpha Systems probe mounted on the left aileron inspection plate as well, so in both cases any stall warning provided by either probe may be "optimistic" in a left slip. We've got a calibrated test boom that we can mount on either wing tip; so getting some comparison spin data is on the list of things to do to test that thesis and quantify it.

Additionally, the quality of the AOA tone performance is going to be affected by sideslip angle. I can't specifically quantify how much, as we haven't completed that testing yet either--but the 6 degree rule of thumb comes from wind tunnel test and correlates with what we've observed so far in flight. So, you are spot on with your "not too slow" game plan

My 2 cents would be to adjust your system to provide 5-7 MPH/KTS of stall warning tone to build a margin and realize the margin is probably less in a left slip. You could test that by flying a cross-controlled stall as I am in the video and noting the difference in time between hearing stall warning and that first nose bob. If you do, keep in mind the rate of back stick application will affect that result. If you pull hard enough, fast enough, you'll "beat" your stall warning system and stall before you hear the warning tone.

FWIW, we learned testing our first generation AOA tone generator that Dynon AOA calibrations vary from airplane to airplane; so your's is unique and the only way to know for sure is to flight test. Also, if you ever re-calibrate, that will reset your baseline and you'll have to re-test. The first test I'd run is to determine the amount of stall warning you have with your tone selection in a normal, straight-ahead stall and go from there.

Also, in the last video you probably noted that the airplane effectively stalled 4 times before I was able to force it into a spin. In other words, in a slip (left turn, left aileron, right rudder) the airplane is highly spin resistant, so even if you ham-fist it into a stall in the base turn, it will give plenty of aerodynamic warning. I.e., RV's slip great.

In a skidding departure the airplane will immediately roll (spin) at the first stall; which is why this is the last thing you'll want to try in an overshooting final turn.

Cheers,

Vac
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Last edited by Vac : 12-22-2019 at 08:22 AM.
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