Washout??

[JG3]

What is the recommended washout for a Drifter wing???

 

JG

 

 

[Nobody]

Soap and water?

 

Just joking but I am sure someone will be along with the right answer soon.

 

 

[diesel]

If you cannot find anything try 2 degrees. Droop the aileron the thickness of the trailing edge as well? Chas

 

 

[skyfox1]

Hi JG3 centre the stick put straight edge on the bottom of the wing along the rib and adjust each aileron so the trailing edge just touches the straight edge and that will be set fine.

 

cheers Geoff.

 

 

[JG3]

The reason I asked is that I've built an ultralight with Drifter skins on a strut wing, and trying to optimize it. I set 3 degrees wash out, but now feel that could be reduced and maybe improve performance. I measured an Austflight Drifter at our airfield and found one wing at 1.5 degrees and the other with no wash out at all..... It seems to fly well enough, so I could probably reduce the setting on mine.....

 

 

[diesel]

Only flight test will tell especially low speed turns. As I said before a little aileron droop can make a huge difference here. It also helps stop hinge ware. It wont slow you down as some will claim. But it could save your life. Chas

 

 

[JG3]

Only flight test will tell especially low speed turns. As I said before a little aileron droop can make a huge difference here. It also helps stop hinge ware. It wont slow you down as some will claim. But it could save your life. Chas

Yeh I guess just suck and see as usual. That hersey bar wing with low loading is already pretty stable, then I have VGs to help tame a sudden stall, so probably can have minimum washout. I also have a progressive flaperon adjustment so can easily try aileron droop. Thanks for the tip.

 

JG

 

 

[Head in the clouds]

The reason I asked is that I've built an ultralight with Drifter skins on a strut wing, and trying to optimize it. I set 3 degrees wash out, but now feel that could be reduced and maybe improve performance. I measured an Austflight Drifter at our airfield and found one wing at 1.5 degrees and the other with no wash out at all..... It seems to fly well enough, so I could probably reduce the setting on mine.....

The main reason for washout, whether geometric or by using different airfoil shapes/thicknesses at the root and tip is to ensure that the root of the wing stalls before the tip.

 

If the tips stall first, inevitably one tip will stall before the other resulting in a wing-drop and potential spin entry, so for safety we really need to have the tips still flying when the stall starts to propagate from the root.

 

In general however, geometric washout (rigging the angle of incidence lower at the tip than at the root) is only required for tapered wings where the airfoil shape (or thickness ratio) hasn't been designed to make the tips stall later than the root. In general the tips will stall first on a simple tapered wing with the same foil and thickness ratio because the shorter chord at the tip means it is operating at a lower Reynolds number than the root.

 

Again, in general parallel chord wings, like those on the Drifter, will stall progressively from the wing root toward the tip without any washout. This would appear to be a good reason to not use washout on a parallel chord wing when considering that wings with washout might be considered to be less efficient since the outer portion of the wing is not producing as much lift as the inboard section, meaning that the inboard section has to be flying at a higher angle of attack, and hence less efficiently than it would otherwise. However that's not the case, the most efficient wing will have a bell-shaped (or elliptical) lift distribution and providing the wing with any form of washout helps us toward achieving that. That higher efficiency is primarily because having the tip producing less lift results in a much reduced tip vortex, and consequently much less induced drag since the tip vortices are a significant proportion of the total drag.

 

In short, getting rid of washout on your parallel chord wing might not cause a major hazard in terms of wing-drop in the stall (although it could, you'd need to test it extensively to be sure) but it is likely to reduce the efficiency of the wing by increasing its total induced drag.

 

A lot depends on what you're trying to achieve. If you want a better cruise speed you could rig it with about 2-3 degrees of washout to achieve something like the elliptical lift distribution and reduce your tip vortices. Then you could also reflex the ailerons slightly (I'm assuming full-span ailerons like the Drifter). That would give you a very noticeable cruise speed increase at the same power setting. The cost would be a greatly increased take-off distance.

 

If you want a short take-off improvement you could do the opposite, get rid of the washout and rig the ailerons lower (drooped), but you'll lose cruise speed and risk a wing-drop while trying to land slowly and that could hurt ...

 

I see you've posted while I was writing this, and that you have flaperons, in which case you will find it hard to do much better than add a reflex position for the flaperon, and leave some washout in the wing for reduced drag and stability in the stall.

 

 

[JG3]

Thanks heaps for that info. I hadn't realized that the washout would reduce tip vortex drag. In that case I'll keep it at 3 degrees as is. Short enough take-off roll already, and absolutely stable mush instead of a stall. I can adjust the flaperons in flight, but haven't experimented with that yet. Sounds like it will work out really well, reflex for faster cruise speed and deploy for slower landing, just as planned. This is going to be a fun machine. I call it my 'High Clearance Trail Bike'.

 

 

JG

 

 

[Old Koreelah]

If you cannot find anything try 2 degrees. Droop the aileron the thickness of the trailing edge as well? Chas

Chas surely you mean set the aileron TE slightly above that of the wing?

 

 

[diesel]

Chas surely you mean set the aileron TE slightly above that of the wing?

No Lyle. Only those who cannot feel anything and dont slow down do this. Well tested and with aileron washout on various Jodels like yours. Much nicer roll contrl. Chas

 

 

[Old Koreelah]

Interesting Chas. Maybe mine's different, but I won't be lowering my ailerons until I've completed my full stall test regime and totally eliminated that pesky wing drop.

 

 

[diesel]

Interesting Chas. Maybe mine's different, but I won't be lowering my ailerons until I've completed my full stall test regime and totally eliminated that pesky wing drop.

Lyle read above again then drop them around the thickness of the trailing edge. Then go and do some stalling right up to full power in a max rate turn. Note that different propellers have an influence. Torque. Chas.

 

 

[Old Koreelah]

Lyle read above again then drop them around the thickness of the trailing edge. Then go and do some stalling right up to full power in a max rate turn. Note that different propellers have an influence. Torque. Chas.

As I mentioned Chas, I have had some nasty right wing drops at the stall (Jab-powered, prop turns opposite to VW). Not all Jodels are the same: mine has quite a few changes to the original and until I've sorted out the problem I certainly won't be reducing effective washout by lowering aileron set.