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The PegaStol Wing??


We keep seeing inquiries on the forums asking what the PegaStol wing was like.

I say ‘was’ because it’s no longer in production, and last I heard it’s not likely to be, at least for some time....

That’s really unfortunate, because it’s really good.


This 701 is the only one in Australia with the PegaStol wing.

I’ve flown it, and really like it.

With the slats retracted, it’s much faster and more fuel efficient than the regular wing, yet when they’re deployed it has STOL capability pretty much the same as the slatted 701.  It’s even faster and more efficient than the original wing without slats, which we know really well, and very much prefer to those draggy fixed slats which we’ve left behind long ago....


This aircraft cruises at 75kts (95mph) on 12 litres/hr (3.2 gal/hr), and that’s real genuine figures determined over 800 hrs flying time.  A 701 with the regular wing without slats burns about 14 l/hr (3.7 gal/hr) for that speed, and with fixed slats more like 17 l/hr (4.5 gal/hr).  That gives 150 nm (180 miles) more range with 80 litres of fuel with retractable rather than fixed slats!  It’ll fly easily at more than 80 kts (100 mph) even with the 80hp 912, but the rest of the draggy fuselage causes efficiency to go down at these speeds.  So the pilot prefers to cruise slower at best fuel efficiency for these long trips, and enjoy the scenery.  It’s travelled over much of Eastern Australia, from Tasmania to the Gulf of Carpentaria, and into lots of short and hairy strips round about.  It’s proven to be as STOL capable as anyone could need.


These photos will really how totally different this is from the regular 701 slats.  It’s not just retracting those regular slats at all.  When you get to know this retractable slat wing, you realize how draggy and inefficient those fixed slats really are!


The airfoil is much thinner than the regular 701, and the bottom is semi-symmetrical.  When the slats are retracted it’s very streamlined.


The slats deploy not only forward, but also downward, thus effectively increasing camber of the wing to somewhat the same as the thick, high-lift profile of the original wing, so it gives very much the same lift coefficient at slow speed.  All retractable slats in other aircraft, such as the Hellio Courier, deploy downward to increase the camber.  Fixed slats can’t give that advantage. 


The first 701 plans had the slats mounted so that the bottom lip was below the bottom of the wing, but that caused so much drag and disruption at cruise speed that they had to be raised permanently thus losing some lift at slow speed.  Fixed slats are a real compromise problem between slow speed lift, and cruise speed drag.  The retractable slats give the best at both ends of the flight envelope.


Notice that the exit slot is much larger than that of the fixed slats on the 701.  This allows much greater airflow through that slot with less drag.


This shows how open the slot is compared to the regular 701 fixed slats, and also how the wing leading edge is sharp, and the slot is much more streamlined, so much less drag when the slats are deployed.


The retractable slats are in two portions on each side.  Each portion deploys independently, driven by the air pressure of the speed through the air.  In slow turns the portions deploy and retract separately as they feel the need from the airflow.  Their action in or out causes no change in yaw, roll, or pitch.  Even if one side jams in or out, it doesn’t effect handling enough to be a problem.  Only at fast cruise do you feel a yaw from the drag of a slat stuck out, no real roll effect because the slats don’t actually generate lift at cruise angle of attack.  To land with one slat stuck in, just don’t do a full stall landing, keep a bit of extra speed.  But the owner has never ever experienced a slat sticking unintentionally, and never ever heard of it happening to a PegaStol wing anywhere, it doesn’t seem to be an issue. 


Another view of how ‘clean’ and open the slot is.  Much easier airflow through here than the original fixed slat.  The mechanism is very simple, rugged, and trouble-free.  This aircraft has mostly worked off dirt and grass strips, with no problems with the mechanism.


 With the slats retracted the wing is now pretty clean and streamlined.


The flaperons are a streamlined symmetrical airfoil, so less drag than the original 701 style.  They’re just as effective for roll control as the originals.


The PegaStol wing was good enough that Zenair accepted it as an alternative, and you could buy the 701 kit without the factory wings and fit PegaStol.   I think it’s too bad that Zenith didn’t buy the rights to the PegaStol wing when it was sold off.  They could have offered an alternative - original 701 fixed slats or PegaStol retractable.  The PegaStol would have been really popular I reckon, especially for those of us who use our aircraft for cross-country flight.....

The PegaStol wing is clad with .020 skin rather than the .016 on the 701, and many more ribs, so there's no 'oil canning' at all.  So the PegaStol wing is heavier than the standard wing.  But that certainly isn't a problem for this particular aircraft that performs well with just 80hp.


One caution of using the Pegastol wing - it's only big enough to fly at best efficiency if you keep the aircraft nearly as light as the early 701 models, and don't load it down with too much crap.......


Of course that caution applies to any wing on any aircraft.  There are way too many builders who figure that as long as the aircraft structure is strong enough take the load, then they can build and load it that heavy.  So there's a lot of over-weight aircraft 'waddling' around out there and disappointing the builders.... 

Every pound makes a difference, must be on a strict diet always....


A reader, John D, has just sent me this link

That's a very good STOL aircraft. 

I just phoned them to see if that wing would fit on a 701, but not possible because the distance between the spars is quite different........

It was also interesting to find out that this Pegasair retractable wing was displayed at Oshkosh before the PegaStol was developed, so another case of copying, or at least inspired by....... 

Anyhow, this looks like a very good option for anyone looking for a proven STOL aircraft.