Rans S7

Rans S7

The Rans S7 is well-proven with vortex generators.

I owned a Rans S7 for 100 hrs. When I bought it, it wasn't equipt with VGs, and I had to fly it home (15 hrs) without them. I was trained on tail-dragger aircraft, and the S7 is well-behaved, so it was familiar, but several of those landings on the way were 'abrupt'. I was wanting to do slow three-pointers, and found that if I was a bit high when the stall happened, it would test the durability of the landing gear, just as it will in any aircraft...... When we got home I didn't put VGs on straight away because I wanted to get more of a 'feel' for it first. Eventually I could sit it down OK, but it was a fine margin to get the speed and height just right.

After adding the VGs that margin improved considerably. Now the the stall became a progressively increasing 'mush' that would sit me down gently even if I didn't get it just right. It became very forgiving, and far more relaxing. Now it's easy to drag the tail wheel on first and sit the mains down gently - really slow, and good control. ASI showing less than 30 kts! It's really easy to see why so many S7 fliers have gone to VGs.

I also put VGs under the horizontal stabilizer to get firmer pitch control. The S7 had just enough authority in that regard, but the VGs now give it more margin for security. I also sealed the hinge-line gap with the household weather stripping that has a fabric pile like carpet. Removed the elevator enough to stick the self-adhesive weather stripping to the back of the horiz stab. I had done video tuft testing and noticed the tufts being sucked down through that gap - not a good sign for good airflow..... Very pleased with the results all round!

JohnG

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Found on the Yahoo Rans S7 forum:

I also recently installed the Stolspeed VGs. The stall, as near as I can figure it -- believe it or don't -- is at about 21 KIAS with either 3 or 4 notches of flaps. There is no break; there is no wing drop. You go into "falling leaf", and that's it.

Not that I've ever tried a landing at Vs x 1.3 = 27 KIAS -- but you've got lots of safety margin.

The manufacturer specifies 9cm spacing on the inner part of the wing, 6cm spacing towards the wingtips -- and 3 CM SPACING on the underside of the stab. I found that last bit surprising, but only until I flew the plane. Those ridiculously close VGs on the tail gave me tremendous, precise elevator authority that I never knew I was missing. Landings are a bunch easier.

Hope this helps.

Griff

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As discussed in our recent telephone conversation I installed the VGs on my Rans S7 and while I have not done a full test on the aircraft I have done enough to convince me that they have made quite a difference.

Pre VG's at an AUW of about 410 kg the clean stall speed (power off) was 38kt IAS with a clean break and usually a slight left wing drop. With 2 stages of flap this would reduce to about 35 kt IAS.

With the VG's installed, and at the same weight, the aircraft does not exhibit any definite break, but simply starts to descend at a very high nose attitude with wings level and the stick on the aft stop. IAS is so low as to be meaningless.

If the AUW is increased to about 480 kg there is a slight nose drop as the IAS drops below 25Kt.

The aircraft can be flown with full control at 35 Kt IAS and now seems to be more stable in turbulent conditions. It is also much more forgiving when doing 3-pointers as it does not have the sudden drop at the point of stall that it had before, especially when using flap.

Another interesting aspect is the behaviour of the airflow at the wingtips. I have always been interested in the patterns left by accumulated dust on the upper surface of the wing when the aircraft has been flown in drizzly or dewy conditions. The airflow lines are clearly visible as dirty streaks over the wing. At the wingtip however, there was an area outside of a line from the outboard end of the wing leading edge to the rear of the most outboard rib where there was no apparent air movement at all. The dust layer in this area was untouched. After fitting the VG's (which go right to the tip) the lines left by the moisture flowing over the dust now show that the airflow is most certainly attached right over the whole of the tip.

Anyway those are a few of my observations.

Thanks again for your help.

Dean, Australia

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sS7><Savannah

For a few months last year I owned both a Rans S7 and a Savannah. I flew the S7 for 100 hrs in 5 months, comparing the two and having to decide which to keep – not an easy decision.....

I have to admit that one of the main reasons I wanted an S7 was to carry a bicycle. Many years ago I read of Tom Simko’s travels with his folding mountain bike in his S7. I do a lot of that sort of travel, and with country airfields always a couple of miles out of town, it sounded ideal. The Savannah could only take a small folding bike, and even then it would take up a lot of space in the cabin. The S7 has that large, easily accessible space in the pax seat for such a bulky item. I also do a lot of off-field landings in rough places, and was looking forward to trying that tail-dragger gear.

I especially like the tandem seating in the S7. I like to be up front with visibility both sides, and the passenger out of the way where they belong. My pax also liked the tandem seating, with excellent visibility both sides for photography, especially with the sliding windows that I installed. And very quiet back there, didn’t even need a headset at slow cruise. Also great for big fellas, with the most elbow and leg room of any aircraft in this class. The tandem arrangement with pilot up front makes for some CofG considerations, but it does work OK. It lands even easier with a heavy pax behind. But if solo, better carry some weight in the rear baggage compartment or be very gentle on the brakes…. The tandem seating also makes the slim front profile of the S7 look really great!

The S7 is faster than the Savannah, but not as much as I had expected. Using the same Warp Drive prop on both aircraft, and 4-way GPS measurements in the same conditions, I got a consistent 4 kts difference – had to do it several times to be sure. What with the drag from nose gear, thicker wing, separate ailerons, and wider more angular fuselage on the Savannah, I had expected more difference than that..... From what you read, you’d expect just the nose gear to give at least that difference by itself.... But it just confirms, that at our cruise speeds, it doesn’t make such a big difference. None the less, the S7 is a real good long distance aircraft, and it was good to be able to go comfortably at 91kts (105mph) at 17 litres/hr (4.5 gph) for four hours when I needed to beat the light with no fuel between.

Contrary to much popular opinion, and my expectations, I really do prefer the nose-wheel gear on the Savannah to the tail-dragger on the S7, even for bush use. The S7 is a well-behaved tail-dragger aircraft, and I was originally trained on a tail-dragger so I was comfortable in it. There’s a certain charm in handling a tail-dragger, and I enjoy that experience. But for real life bush use I find the nose-wheel a real asset, and no real problem even on rough ground, if designed with minimal weight on that nose-wheel, as is the Savannah. And of course the nose wheel gear must be steerable, rugged, and a full-size wheel. When I land the Savannah slow, the nose-wheel is way high above the ground, and I can hold it off as long as I want. Then when I do put it down I can jump on the brakes real hard with no chance of nosing over. And I can see the ground right ahead and have positive steering to dodge around rocks and whatever. On my home strip, which we share with cattle, those obstacles are often soft and messy, but good practice for bush flying.... That positive steering is a real asset when it comes to manoeuvring around in the bush; I often want to taxi around obstacles and between trees to get to a chosen campsite. The nose-wheel steers like a go-cart, but the tail-dragger is forever bogging in soft ground and snagging on obstacles. And this was with an 8” pneumatic tail wheel. Sure you can lock a brake and forward stick and a blast of power to jump the tail around – that works for showing off, but I can’t depend on it for tight manoeuvring in remote places….. Also, when the aircraft is stopped, I can swing the Savannah around to any direction just by pulling down on the tail to lift the nosewheel and it then balances on the mains, and swing it around; I found the tail of the S7 quite heavy and awkward to lift around…. A clear example was that time I landed on a strip a mile from the truckstop and wanted to taxi in for fuel. There was a grader track, but the odd tree too close so I had to manoeuvre around them. The tailwheel kept ‘hanging up’ in the loose dirt and I had to get out and lift the tail over to the new direction, until I gave up….. (See ‘Coast to Coast by S7) With the nose-wheel Savannah I could have just taxied around those obstacles easily. So it was quite a surprise for me as well, to find that I much prefer the nose-wheel for general bush use, at least that’s my experience, and it is real life experience not just armchair, opinion…….

A much larger and wider tailwheel would solve those problems. I also own a my-design single seat ultralight with a 3.50x4 tailwheel (that’s 10” diameter and 3” wide)! That super tailwheel gives it the same manoeuvrability as a good nosewheel, and is smooth running even on harsh ground. If I had kept the S7, I certainly would have tried to adapt such a tailwheel, and 8.00x6 mains.

Of course the nose-wheel gear is also a real boon in cross-winds. Get that nose-wheel down so you have positive steering, and the wing is at a neutral angle of attack, and any cross-wind is no problem. The only fright I ever had in the S7 was a strong cross-wind that lifted a wing just after touchdown….. There’s no way I could have handled the S7 on the ground in that 30+ kt wind at Horn Is. (See Flying Backwards)

I always found the ailerons on the S7 to be quite adequate, but I really love the all-flying ailerons on the Savannah. They have so much dependable authority without much adverse yaw at all speeds, right down to less than 30 kts. That aileron authority gives great slips and immediate control in strong and irregular cross-winds. But they must give more drag than conventional ailerons.....

I really do prefer the all-metal construction of the Savannah. I know that the tube and fabric construction of the S7 is traditional and well-proven, but I much prefer working and living with sheet metal, especially for ‘bush bashing’. I would have thought that the tube and fabric would be lighter, but the Savannah is actually a few pounds lighter.

Now my dream for an ideal bush/cruising aircraft:

If Rans was to build an all-metal S7, with 8.00x6 mains standard, and a REAL tail wheel, I’d be really interested! An all-metal wing pretty much the same thickness as the S7, with conventional ailerons for minimum drag at cruise, and big slotted flaps for STOL, and of course VGs for a ‘tame’ stall. Also, opening windows, please.....

But now I’ve added a storage compartment on top of the Savannah that can carry my bicycle! It’s a Dahon ‘Groove’, which with suspension fore and aft and 20” ‘Big Apple’ tires is really good on and off road. I’ve made simple brackets that hold a 20 litre jerrycan comfortably on the x-bar, and it balances really well that way. The compartment is a turtle deck on top of that flat fuselage, and faired into the back of the wing. See XXXXX This gets the bike up out of the way, and actually improves the airflow a bit. It works so well that it eliminated my need for the S7 to carry a bike, so I sold the S7 and kept the Savannah......

I sure enjoyed the experience of flying the S7, and still have withdrawal pangs....

Such is life......

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Opening Windows on the S7

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