ground effect

[jasonX 24]

Hi guys

 

I am building an aircraft in planemaker/blender. Currently I have the flight model coming along nicely except for one particular area.

It's a tail dragger and when landing it seems to float forever and lose speed way too slowly. any ideas anyone (apart from killing the engine)

[jcomm 5,890]

Maybe adding some additional drag from the undercarriage mounts (?). Have you experimented with different airfoils too?

[jasonX 24]

I had thought of adding a little extra drag here and there (which is certainly the case with the real model - open cockpit etc;). The reason I haven't got into that yet is it is going to mess with more than just the landing phase but it seems I might have to do this eventually though. Anyways I'll keep searching and testing.

 

thanks

[Hueyman 5]

Hi Jason,

 

If your ACFT is one equipped with constant speed propeller, you can lower the minimum pitch value ( low pitch stops ) reached when the Prop Lever is full forward, Throttle full retarded and the slipstream isn't strong enough to continue windmilling the propeller ( low airspeed, like in final approach )

 

When that kind of prop is in low pitch angle region, it can create a serious ammount of drag ( example, some planes like the PC-6 can reach impressive dive rates by throwing the prop in the Bêta range, in other words, very low pitch setting, near of flat ( 0° ) pitch.

 

Try it with values like between +8° and +12° and adjust as necessary, I'm sure you'll reach what you want.

 

Of course, if this is a fixed pitch one, all I said is useless..

 

Good luck,

Valentin

[jasonX 24]

hi Valentin

 

thanks for that input , some useful info there. I can't put into practice tho as it is a fixed pitch.

 

jcomm was on it in the end. I was using my own airfoil so I switched to one of the standard off the shelf ones that looked something close. My stall speed dropped 5 knots which is big plus and also it made the landing phase much more manageable. It still has a tendency to float but it is not so bad now.

 

I think it might be a good idea to put playing with airfoils on the back burner for a while

 

Thanks

[Hueyman 5]

Mm ok nice if you finally managed this ;-) !

 

Just another thing to know : After flying X-Plane since early V8, I always noticed it has a tendency to be very " clean " and " gliding " in many aspects. for example, helicopters in autorotation have overall less descent rate and bigger RPM rise compared to the real thing, and a plane in X-Plane while in descent gain speed quicker than in real life ( I compare this with a C152 that I know for example ). Globally, I would add a bit more drag to virtually anything in X-Plane to be more consistant but.. that's the way it is !

 

Maybe all that is because the flight physics are really precise and constant calcul-based.. making a very " living " simulator.

 

Back at my MSFS days, I didn't noticed that the slightest of my input ( prop RPM, mixture, Manifold Pressure etc... ) change affected the sim much..

 

Anyway, tell us the final result !

Valentin

[LAdamson 240]

Mm ok nice if you finally managed this ;-) !

 

Just another thing to know : After flying X-Plane since early V8, I always noticed it has a tendency to be very " clean " and " gliding " in many aspects. for example, helicopters in autorotation have overall less descent rate and bigger RPM rise compared to the real thing, and a plane in X-Plane while in descent gain speed quicker than in real life ( I compare this with a C152 that I know for example ). Globally, I would add a bit more drag to virtually anything in X-Plane to be more consistant but.. that's the way it is !

 

Maybe all that is because the flight physics are really precise and constant calcul-based.. making a very " living " simulator.

 

Back at my MSFS days, I didn't noticed that the slightest of my input ( prop RPM, mixture, Manifold Pressure etc... ) change affected the sim much..

 

Anyway, tell us the final result !

 

Constant speed X-Planes don't slow down nearly as well as they do in real life. MSFS aircraft don't either. Therefor, the prop & drag characteristics are certainly not precise enough. As to MSFS, as well as X-Plane, prop RPM & mixture settings do work, although they vary from the real life airplanes. For example, pulling mixture halfway back on a throttle quadrant may kill the sim plane's engine, while it's the actual takeoff position for a high altitude airport.

 

Note: there are variations with the abilities of a C/S prop & drag for slowing down. In my own case, it was easy to go from 120 kias on down wind, to 80 turning final............and then down to 70 at a fairly steep descent rate. I don't push the prop knob full forward until on final. Since the blades are changing pitch, you still slow down, even at the cruise setting of 2350. To do so before, is like slamming an engine into low gear. Engine 180 HP Lycoming with Hartzell two-blade constant speed on a Van's RV6. For reference, I know of a small single seat RV3 in which the lightweight three blade composite constant speed doesn't have nearly as much braking effect.

 

L.Adamson

[Hueyman 5]

Yeah LAdamson, your comments about mixture etc on both sims are so true.. unfortunately.

 

The overall braking effect of a prop is the result of several factors, some are too maths for me but, for us pilot, the simple clue we have to remember is : the lower the low pitch stop is, the higher the brake effect...

 

On general aviation ACFT such SR22 and so , the low pitch stop ( mechanical ) should stand around +12° positive pitch.

 

While it may create some significant braking effect at cruise airspeed when you fully retard throttle, it's nothing compared to what more advanced turboprop can do ( once again, I take the PC-6, which I know very well, for example ).

 

So, the low pitch stops IN FLIGHT ( because if reverse is available, low pitch stops on ground are more likely to stand around -11° ... ) and the blade chord, as well as its airfoil of course and obviously, the relative wind passing through the prop ( so determining it's AoA ) are such factors that determine the braking effect.

 

Finally, to answer

Constant speed X-Planes don't slow down nearly as well as they do in real life

I can tell you that in X-Plane, you can slow down EVEN FASTER than what you described, it's just a matter of having good blade chords, min pitch ( low pitch stops ) as well as airfoil. All of this is easily customizable in Plane Maker.

 

 

The last factor, and by the way, the most problematic for my work on Plane Maker and the PC-6, is that low pitch stops request low airspeed ( so, not much windmilling effect ) to be reached, cause of ther ( overspeed ) governor action. You can't reach PLPS ( Primary Low Pitch Stops ) just by retarding throttle, or PCL while in high airspeed conditions ( cruise, descent... )

 

Hopefully, I will find the solution for my problem. Anyway, many interesting things to exchange here, I'm pleased to see there are knowledgeable people there, flying in X-Plane ;-)

 

Have a nice day dudes,

Valentin