Hi Fred,

Sounds like you are at the same point in your head that I was....

...the way I understand it now is, it's not the travel of the controls, its the angle of slip that is not enough. At full control ROF produces (arbatrary made-up numbers) a 40 degree slip....when Eco' would expect a 60 or 80 degree off when slipping with full control inputs.

Do I have that correct Eco'?

AGAIN, just made up numbers for simplicity of discussion, I dont know what they actually are, or what a maximum slip angle would be in these...

Slips eh ..... can we just go through this again because I'm confused ....

Forward slip ... thought this was wing down with opposite rudder to keep fuselage aligned with approach.

Side slip ... thought this was wings level but crabbing sideways with rudder while maintaining level wings with ailerons. Fuselage is not aligned with approach.

..... or is it the other way around

Other way around...

[MF] Gunloon

Well, the short of it is:

Both are "wing down with opposite rudder", neither name suggests the slip has wings level (none do/should), and they are exactly the same maneuver but done for different reasons and with the pilot looking through a different area of the windscreen (forward vs through a side window).

Now for the longer version:

In the US it's commonly called a "Forward Slip" when you look out the side window, as the aircraft continues "forward" along a reference line and a "Side Slip" when you look forward but the aircraft drifts laterally. This type of naming seems particularly odd depending on how you word it though doesn't it!

Perhaps you can see the logic of the US naming as the side slip will cause the aircraft to drift to the side relative to the point that they are looking at and in a forward slip the airplane will yaw off the heading you were looking at, but continue to track that reference line on the ground.

However the European nomenclature makes an equal kind of sense if you re-phrase the statements to refer to the direction the pilot looks - forward in the case of the wing low crosswind landing, and sideways when the nose is offset when scrubbing altitude and airspeed on a long final approach. Both are equally correct. . .or incorrect!

In Australia. . .who knows! Ask IvanK what he calls it. Just call it a slip and you'll be correct no matter where you fly.




Starting at the ~ 6 minute mark you'll see what a US pilot would call a "Side-slip" from the cockpit and external views: http://www.youtube.com/watch?v=I96s0VLB_rU


Here's a few interpretations of what a US pilot would call a "Forward slip" where the nose is offset from the ground reference point:

http://www.youtube.com/watch?v=M2CBx7x5GCI

http://www.youtube.com/watch?v=wW8GRJI6Kz4

Really though - the dang things are the same if you don't look at the ground track relative to the direction the nose is pointing. The airflow is doing the same in each case, the bank angles, slip angles, and pilot inputs will be the same in a generic sense.

Forward slips is used to loose an altitude without increasing airspeed



Side slip is mostly use for a cross wind landing

Yep. . .that's my take on it.

While some are worse then others, this is a global FM thing. Stabilize on approach in a slip with the maximum control inputs you can while maintaining a non-turning slip. Note that in order to maintain a non-turning slip you will have minimal bank angle and minimal slip angle. The slip must be very shallow or the heading and ground track will change in the direction of the low wing, and this will force you to lessen the magnitude of the rudder applied to maintain a non-turning slip. When it's all said and done, that will be a very, very, shallow slip. . .it will not lead to the significant increase in descent rate that a real tailwheel aircraft should have on tap. . .ignoring modern aerobatic aircraft, usually the older the design the more yaw authority they have, and the more extreme the slip possible.

My boldface.



I see a contradiction here? Perhaps a slip somewhere?

If I understand your later comment correctly, your concern is with the amount of bank achievable in a slip without the heading changing?

Would this be in the D.VII, by any chance? I find this aircraft to be very directionally stable, compared to the other aircraft in the game. Considering the long, flat empennage and the significant side area this presents aft of the CG, I don't find this surprising.

I don't see any contradiction - perhaps a slip. Your earlier quote includes additional info that was related to the issue though not at the heart of it. This was my observation, particularly in the earlier versions of RoF which I had tested more extensively. If you never encountered transitions from slips to skids at moderately low AoA then you didn't - but that's what I found when testing. In any case, in the old FM or the newer one, the only way for me to maintain a steady state non-turning slip is to reduce the bank angle to only a few degrees away from wings level (despite the slip angle, this also suggests minimal keel effect).




As posted in the later, the former, and all in between: "My complaint about the slips [in] RoF are to do with the fact that they are much shallower slips with lower slip-angles (the yaw offset from the flight path) and much smaller possible bank angles than in the real world aircraft."



Not in particular. Some aircraft in RoF slip better than others but all of them will only maintain very shallow slips (low bank angle, low slip angle).

With respect to the DVII, don't forget that the fuselage side area should also contribute to the keel effect which will turn the airplane in the direction commanded by the rudder, this means a greater bank angle would be needed for a given slip angle to oppose the yaw generated by the rudder inputs. . .so the bank angle should be more obvious here than in something like the N.28. Also, directional stability does not necessarily imply minimal yaw authority in response to control inputs.

Thanks for the info Eco ! And sdflyer ! Great detailed information. I think you're right that the interpretation can be different depending on the country .... and I find I always have to think about it whenever this subject comes up. But I won't confuse crabbing with slipping any more

Aluminum/Aluminium
Lisa pronounced like "Liser"
Color/Colour
Theater/Theatre

It wouldn't be the first time someone was hell-bent on going against the grain!



Yep. . .just remember that crabbing is coordinated, not cross controlled, and the relative wind meets the nose of the airplane directly (more or less) while cross controlled there is a shift in the relative wind direction. Like the difference between the forward vs the side slip, crabbing is "different" from straight ahead flight only when compared with the ground - aerodynamically it's the same.

You can't get a very aggressive slip going. Like has been said the angle of bank is very shallow to maintain a straight flight path.

These shallow slips aren't very effective at losing speed and altitude like a full blown real slip.

I'm from right in the middle of the US and I have never heard a slip called anything other than a slip. Here's what I say, and have always heard. A slip is for losing speed/altitude or looking around the nose. For landing in a cross wind its just crosswind controls or crosswind configuration. Nothing gets confused that way either.

It's the beta angle that gives you deceleration/descent, through increased drag. Not the bank angle. The bank angle OTOH depends on the keel effect, gotta tilt that lift vector enough to counteract the lateral force generated by the beta angle, and the keel effect of course also depends on the beta angle... but see the next paragraph.

Regarding keel effect, the D.VII has all that empennage side area well aft of the CG. Thus it will contribute more to directional stability than keel effect, compared to if it was closer to the CG. Going to play around more with the other aircraft! All there is to do in the simulator right now, anyway.

Thanks for the clarification regarding the middle of the US terminology. The hunt for the culprit goes on! Should we blame the French, as usual?

I have a better idea: Blame Canada!

Yes, the bank angle doesn't increase the drag, but as I recall (I could be wrong as I havn't flown ROF in about two weeks) that yaw angle is not all that much because you can't get enough bank in to counter act it.

So if you have to use full left aileron and half right rudder to maintain a straight path, then you aren't getting the full effect of the slip.


How about we compromise and blame French Canada?

I need to correct myself. The position of the side area relative to the CoG is of course completely irrelevant. What matters is the position of the side area relative to the lateral center of pressure. Still, lots of side area at the aft end -> Stable.

Now, something is off in the above.

You have two lateral forces:

- A horizontal component of lift, generated through banking the aircraft and tilting the lift vector. This will try to accelerate (and, through directional stability, turn) the aircraft in the direction of the low wing.

- A horizontal force perpendicular to the direction of flight generated by the aerodynamic forces on the fuselage as the top rudder causes the aircraft to skid sideways through the air towards the low wing. This force will try to accelerate (and again, through directional stability, turn) the aircraft towards the high wing.

If you are turning towards the low wing, you need to reduce the bank angle and not the rudder deflection.

Confusion abounds in the thread, and I think we need to get this straightened out (pun unintentional) for the discussion to move on.


Now, let's talk physics!

Assuming non-accelerated level flight, the lift generated will (essentially, at the small bank angles involved) be equal to the weight of the aircraft. This means the bank angle and the bank angle alone dictates the magnitude of the horizontal component of lift (yes, with a slight simplification). At small bank angles, the relationship will be more or less linear.

The rudder will act as a beta angle selector. Full top rudder and that's a beta angle which won't vary all that much in a given speed range. The horizontal force from the fuselage will then be roughly proportional to the square of the airspeed.

As the condition of unchanging heading means these two forces must equal each other, we can deduce that the bank angle will be proportional to the square of the airspeed. At low speed, the bank angle will be small.

Now, where does this take us?

Keep in mind that these aircraft are, compared to pretty much anything flying today, very slow.


This will also mean that the drag generated by aerodynamic inefficiency, such as skidding sideways through the air, will be proportionally lower. The drag will not, percentually, increase by as much when slipping as it would for a faster, more aerodynamic design. After all, you have all those struts and wires out in the slipstream already. How much will a bit of uncoordinated flying really add, relatively speaking... ?

Less drag increase means a slip will be a less effective way of getting down fast.

Help me out here and try it out in the sim. I'm not having any difficulties using full rudder, as long as I don't let the speed decay too much.

On a side note, I'll post an interesting application of slips in a separate thread if I can only find out how to add images.

okay, I just tried it out for the first time since the patch.

I tried it in the N17, N28, DVII, and SE5 before I got frustrated with the overall experience.

The most irritating thing to me was the gun sights that were tacked on and look totally out of place.

It seemed to me that if you wanted to maintain control of it, you had to constantly adjust both the ailerons and rudder while in the slip. If I put full rudder in, I just kinda got a flat turn unless I already had it banked over quite a ways before adding the rudder.

Even if the slips aren't quite right they are still the best of any sim. I flew FSX earlier today and it just felt like crap to me.

The N17 seemed to get the most bank while slipping, however it was pretty tricky to get out of the slip without going all over the place.

I still say the N17 has a problem with it's rotation point. It rotates around a point well behind the pilot instead of around the CG. You don't really notice it from the cockpit, but from external views it's very noticeable.

I agree. I have no problem performing a forward slip with full rudder deflection myself, as I've mentioned before. Alerons adjust the plane's track, and pitch as needed to keep the airspeed up.

Sigh...I said I was gonna shut my mouth about this, but since the discussion continues, well...

A day or so ago, I decided to land at an aerodrome on a whim while flying the SE-5a, and had no problem shedding the near 1000 meters of altitude I began at down to pattern altitude in a forward slip. The plane was tracking straight, no turning...I think perhaps the reason some have trouble with this is the application of too much control input initially, usually aileron, before full rudder travel is reached. If you enter the forward slip incorrectly, the plane will indeed wallow around like a drunken pig.

This would be easier to demonstrate in real life, of course, with a 2 seater trainer setup...but for myself, I saw again that the machine felt exactly right, as it always has in real life, and I could slip down almost to ground level under full control, recover, flare and land. In the SE-5a's case I mentioned, I was feeling sporty and with plenty of runway remaining did a touch-and-go for fun

I'll stress again, throw away all the performance charts and engineering data and concentrate on FLYING THE AIRCRAFT...airmanship is at least equally if not more art than science, and this sim reflects that. If your flying is sloppy or your touch indecisive the FM will respond just as badly as a 3-D airplane would.

I suppose I'll have to learn FRAPS, but a video of techniques like this would be more informative and convincing than any screenshot...but I swear, these slips are very doable. Practice at a safe altitude till you're comfortable, but by all means, quit worrying about the numbers and practice! Trying to fly while all wound up and fretting over whether something can be done or not distracts you from just DOING it.

On screenshots: adding them would be easier if SimHQ had an 'attach file/image' option, but since it doesn't appear to, one needs to upload pics to a web storage space (I use my clan's web storage, but a free service like Photobucket will do fine), then use the button along the top row (4th in from the left, 'Enter an image') when posting to insert the pic's URL.

A bit cumbersome, but it works decently.

[MF] Gunloon

[/quote]

Now, let's talk physics!

Assuming non-accelerated level flight, the lift generated will (essentially, at the small bank angles involved) be equal to the weight of the aircraft. This means the bank angle and the bank angle alone dictates the magnitude of the horizontal component of lift (yes, with a slight simplification). At small bank angles, the relationship will be more or less linear.

The rudder will act as a beta angle selector. Full top rudder and that's a beta angle which won't vary all that much in a given speed range. The horizontal force from the fuselage will then be roughly proportional to the square of the airspeed.

As the condition of unchanging heading means these two forces must equal each other, we can deduce that the bank angle will be proportional to the square of the airspeed. At low speed, the bank angle will be small.

[/quote]



That's exactly what I thought!


I'm the guy in the engineering class who turned the pages in the course book whenever I saw the others turn their pages...so that no one would know how completely lost I was!


Good thing I stayed in communications engineering (now retired).