Cautions to Savannah flyers.....

[JG3]

I keep hearing gossip that Savannahs with slats removed are having greater risk at heavy loads. I've done expensive testing years ago on this subject, and investigated several incidents. The results of all that work can be studied at http://www.stolspeed.com/flight-testing-slats-vs-vgs

 

Later Savannah owners maybe haven't studied this data, but everyone should. Yes, there is a risk in STOL aircraft such as Savannah and Zenith 701, from flyers trying to drag them off the ground at unsafe slow speeds. This is particularly risky with full flaps, as is analysed in the above article. The slower the aircraft lifts off the more the risk, so the Original wing with VGs could be slightly more prone that the 'VG' wing because it can lift-off a couple of knots slower, and of course the model with slats is considerably more so. This not a fault of the configuration of the aircraft, but the technique involved. My Savannah flight manual states, "...For Short Take-Off - full flaps, brakes on, full throttle, stick all the way back...." With this technique the Savannah will immediately rotate and lift-off, with less air speed than is required for the control surfaces to have enough authority. The tremendous torque of that 100hp at full bore causes a torque roll to the left. The flaperons are already at 40 degrees and providing heaps of lift. If the pilot tries to counter that torque roll with stick to the right, then the left flaperon could stall and cause that wing to drop even more, then the instinct is more stick to the right and the wing drops even faster and the drag that side causes the aircraft to yaw to the left and that wing stalls completely and it's all over so close to the ground. I know this to have been the scenario several times..... Not the fault of the wing, but rather technique.

 

Savannah and 701 flyers, please read and study and heed the lessons from that detailed analysis.

 

JG

 

 

[facthunter]

With flaperons and that technique I'm not surprised that what you describe happens. You seem to have put a lot of work into this. What reserve of thrust over drag do you have and having off centre load (left seat only occupied ) would be a factor too. Nev

 

 

[eightyknots]

I keep hearing gossip that Savannahs with slats removed are having greater risk at heavy loads. I've done expensive testing years ago on this subject, and investigated several incidents. The results of all that work can be studied at http://www.stolspeed.com/flight-testing-slats-vs-vgsLater Savannah owners maybe haven't studied this data, but everyone should. Yes, there is a risk in STOL aircraft such as Savannah and Zenith 701, from flyers trying to drag them off the ground at unsafe slow speeds. This is particularly risky with full flaps, as is analysed in the above article. The slower the aircraft lifts off the more the risk, so the Original wing with VGs could be slightly more prone that the 'VG' wing because it can lift-off a couple of knots slower, and of course the model with slats is considerably more so. This not a fault of the configuration of the aircraft, but the technique involved. My Savannah flight manual states, "...For Short Take-Off - full flaps, brakes on, full throttle, stick all the way back...." With this technique the Savannah will immediately rotate and lift-off, with less air speed than is required for the control surfaces to have enough authority. The tremendous torque of that 100hp at full bore causes a torque roll to the left. The flaperons are already at 40 degrees and providing heaps of lift. If the pilot tries to counter that torque roll with stick to the right, then the left flaperon could stall and cause that wing to drop even more, then the instinct is more stick to the right and the wing drops even faster and the drag that side causes the aircraft to yaw to the left and that wing stalls completely and it's all over so close to the ground. I know this to have been the scenario several times..... Not the fault of the wing, but rather technique.

 

Savannah and 701 flyers, please read and study and heed the lessons from that detailed analysis.

 

JG

It is well worth reading JG3 and a good reminder! I think the manual should be adjusted to remove the full flaps reference.

 

 

[Kyle Communications]

Been talking with Danny Leach about this subject. I never use full flap at all on my Sav and neither does Danny. I am looking at making a new flap bracket with different position notches in it to put full flap in between where it is now and the first stage and then also make the first stage a bit less. This will allow for better use. Then if you need full flap it is really only a bit more than the original first stage of flap. My flap bracket is modified from standard in regard to its position but the flap angles are still the same as standard so I will keep my new flap lever positions but adjust the amount of throw it has.

 

Mark

 

 

[facthunter]

The last stages of flap extension may give more lift but always give more drag percentage wise. It's almost a don't do if you want to climb as well. There is a big down load on the horizontal stabiliser as well, that the lift available has to contend with. Nev

 

 

[fallowdeer]

Hi Mark

 

I find full flap useful for shorter strips. ( paddocks for example with 200 m between fences either end) especially as my figures show about a five knot difference between clean and full flap stall.

 

However even on these shorter strips half flap is more than enough to launch out. Pretty much if you can get in you can get out.

 

Peter

 

 

[Marty_d]

Pretty much if you can get in you can get out.Peter

You'd hope so, judging by your avatar you shouldn't even need 200m...

 

 

[fallowdeer]

You'd hope so, judging by your avatar you shouldn't even need 200m...

Hi Marty

Sorry to say I'm only an occasional pax for work in the MD500E.

 

I took that pic on a SAR Op recovering a deceased hunter from the bush using human sling method.

 

Peter

 

 

[Kyle Communications]

Hi Peter

 

I find full flap is pretty much never needed and never for takeoff. If I ever use it at all for takeoff its just to pump it from first stage to full stage just to leap off the ground then back to first stage for climb out.

 

I find the Sav wallows quite a bit on full flap on landing if there is any sort of wind so only use first stage and none if it is really windy

 

 

[fallowdeer]

Hi Mark

 

Yes, I've never used full flap for takeoff, see no need and don't intend to try. And yes, with full flap and slowed right up for the shortest strips it's all about rudder, getting into the shorter spots I find three or four knots off the target over the threshold can make a huge difference when you're looking at the fence or whatever at the other end.....

 

Peter

 

 

[rankamateur]

If I ever use it at all for takeoff its just to pump it from first stage to full stage just to leap off the ground then back to first stage for climb out.

I had a few moments early in my solo career when I dumped both stages of flap on climb out and immediately stopped climbing, fortunately had the sense to take one stage straight back and got climbing again. I would worry about pumping anything to get it to jump off the ground before you have enough speed, you probably don't have much rudder or elevator authority at that speed either . Watch out it doesn't bite you on the butt.

 

 

[Turtle]

Been talking with Danny Leach about this subject. I never use full flap at all on my Sav and neither does Danny. I am looking at making a new flap bracket with different position notches in it to put full flap in between where it is now and the first stage and then also make the first stage a bit less. This will allow for better use. Then if you need full flap it is really only a bit more than the original first stage of flap. My flap bracket is modified from standard in regard to its position but the flap angles are still the same as standard so I will keep my new flap lever positions but adjust the amount of throw it has.Mark

Put the new plates in and they are just great one notch back of full makes all the difference to controllability thanks Mark

 

 

[Turtle]

Thanks for acceptance to the group, not a lot of hours up yet in this ugly duck but the Sav is proving to be a great little A/C even if wheels are in the wrong place cheers to all.

 

 

[Kyle Communications]

Turtle?..I have sold so many sets of brackets...where are you based. Yes I like the new positions as well...much better

 

 

[Kyle Communications]

Is that you Tim?

 

 

[eightyknots]

JG3, you wrote in your comprehensive report:

 

So I extended the original pitot tube, with a 10º downward cant to better match the airflow at high angles of attack. With this canted pitot, the ASI readings matched the Hall gauge right down to 30 kts. This canted pitot is especially essential for correctly measuring stall speeds at the corresponding high angles of attack that this wing is capable of.

 

I was wondering if the angled-down pitot tube is accurate at higher (say cruise) speeds? If so, it may be worthwhile to keep it permanently angled down.

 

 

[facthunter]

The location of the static vents can cause error as well. Don't the flaps reduce the angle change? Nev

 

 

[bobcharl]

I never, ever use full flap for takeoff for the reasons that JG3 details above.

 

However, rightly or wrongly, I always use full flap for landing except in xwind conditions. I don't find any control difficulties and it seems that touchdown speed is a bit slower which is a plus on my could-be-smoother farm strip. Also seems to be easier to keep the nose wheel off at touchdown as compared to one stage of flap, and I think that is important with Savs (as well as lots of others).

 

Bob