Savannah XL and S (Antibalance) Trim Tab Adjustment

[IBob]

I've heard two accounts of Savannah flaps not fully engaging, have also seen an instance where the rubber outer handle was fouling the button/latch mechanism, potentially with the same result. So, two things:
The latch mechanism needs to be very free, almost loose in action (the latch, not the handle) so as to be free of any possible binding and:

On setting flaps, get into the habit of then wriggling the handle to ensure they are fully latched.

 

[eightyknots]

3 hours ago, IBob said:

Hi Mark, and thank you for your detailed input. This is all really good info.

Yes, my battery is in the forward position, as now detailed in the S build manual etc, and yes I have difficulty keeping the nose off on landing (and as mentioned above, the original test pilot commented on this). SVA will sit on her tail, just, but I have never been sure about that as a measure, since fuel moves to the back of the tanks when the tail is pushed down: can you recall what the fuel situation was when you did this?

 

At present I am considering two temporary options: extra weight to the rear of the (extended) baggage compartment, in the form of a flat sand bag. And/or a lead strip attached at the tail skid.

 

Hank, I have the conventional lead/acid battery: the Savannah has no shortage of lift and I have no reason to be further reducing weight.

 

Dan, I have the Condors all round and they are quite heavy, I also have the adjustable seats, so am not sitting hard back as in the original design. And so it all adds up, I think.
Also, I initially had trouble with the full flaps lever position, as you mention: the angle was all wrong, and setting and releasing it was clumsy and difficult. In the upshot, I designed an angled lever that works very well. It is simple, but needs to be fabricated quite precisely. I was fortunate to have a very capable fitter do the required cutting and welding of the outer tube.

That modified angled flap lever looks nicely made.

 

I was wondering, however, is the "resting position" too close to the floor?

[IBob]

9 minutes ago, eightyknots said:

That modified angled flap lever looks nicely made.

 

I was wondering, however, is the "resting position" too close to the floor?

Not at all, Hank.

[eightyknots]

1 hour ago, AndyDrain said:

...

I assume that you have seen this Savannah Accident. Flap lever to blame.... I have heard of other cases of the flap lever retracting on final.

 

Many in New Zealand have the extended rudder (from the tail wheel) fitted.

That is a really nasty accident based entirely, so it seems, on the aircraft's ergonomics! I am glad that the pilot was able to exit as a survivor.

 

I am building my Savannah with a tall rudder after weighing up what Steve, an Australian, (rankamateur on the forum) suggested. 

 

The extended rudder (along with long range tanks and vortex generators) were all developed in Australia and adopted by ICP, with the last-mentioned appearing on all of their aircraft.

[IBob]

How's progress with your build, Hank?

[eightyknots]

1 hour ago, IBob said:

How's progress with your build, Hank?

My progress can best be described as "slowly but surely".

[IBob]

Just now, eightyknots said:

My progress can best be described as "slowly but surely".

Let me know when you are up for a visit..)

[eightyknots]

28 minutes ago, IBob said:

Let me know when you are up for a visit..)

Sure thing❕

[IBob]

On 07/06/2022 at 10:42 AM, AndyDrain said:

I assume that you have seen this Savannah Accident. Flap lever to blame.... I have heard of other cases of the flap lever retracting on final.

 

 

That is a curious accident report, though probably due to inaccurate press work, or talking to the wrong person:

The Sav flaps are 15 and 30 degrees, not 20 and 40.

 

If the bump occurred 2/3 of the way down the strip it must have been a big one, as the flaperons would have had air and prop blast under them, and would tend to go to 0 degrees if not latched properly.

 

And if the left wing was stalling, the best response (aside from also getting the nose down, if possible) would be right rudder. Not left, as reported, which would only aggravate the left wing stall.

 

Maybe I'm being picky, but I think the last item needs correcting, if nothing else.

[AndyDrain]

Some POH for the VG refer to 20 and 40 degrees for flaps. This was  a VG.

 

The official UK AAIB report is unlikely to get this wrong. 🙂 

 

 

 

[IBob]

My mistake then, Andy....though I'm greatly surprised, and the more so as the Zenith 701 seems to have 15 and 30deg flaps.

[eightyknots]

1 hour ago, IBob said:

That is a curious accident report, though probably due to inaccurate press work, or talking to the wrong person:

The Sav flaps are 15 and 30 degrees, not 20 and 40.

 

If the bump occurred 2/3 of the way down the strip it must have been a big one, as the flaperons would have had air and prop blast under them, and would tend to go to 0 degrees if not latched properly.

 

And if the left wing was stalling, the best response (aside from also getting the nose down, if possible) would be right rudder. Not left, as reported, which would only aggravate the left wing stall.

 

Maybe I'm being picky, but I think the last item needs correcting, if nothing else.

Does your Savannah have 10°, 20° and 30° flaps?

[IBob]

Hank, the jig provided with the kit has 0deg and plus and minus 15deg: these are used for setting up and checking the deflection of the flaperons with no flap selected. It also has FF, and this is used to check/set up the Full Flap position.

My flaperon setup is exactly as per the jig.

I have not measured the actual FF angle, it looks to be slightly less then twice the 15% marking, but the flaperon pivot points are under the flaperons, so that may be deceptive.

 

I believe the standard flaps are usually quoted at 15deg and 30deg.

Since I have a 3 position setup, mine will be 10/20/30deg or thereabouts.

 

[Neil_S]

My 2015 Savannah S manual states flaps should be 0, 13.5+-2, 27+-2.

Having checked them many times during services mine are at these values.

[IBob]

Question, then, for the aviation engineering gurus:

 

The Savannah C of G limits are quoted as 25% and 38.5 of MAC.

This being a constant chord unswept wing equates to 25% to 38.5% of the wing chord.

 

How is this range originally established or worked out?

 

[Kyle Communications]

Beyond me..although in my RC modelling days when you balanced a model it was always somewhere around that when you lifted it up with your fingers. There would be some calc to do with centre of pressure and moment but I am sure you could find it on the net somewhere. I just go on the manufacturers chart and do the plots. Iprefer to balance a bit more to the tail as it just makes the aircraft fly better but of course you must be well aware of this when loading it up

 

[facthunter]

1/3rd MAC was the rough rule for models. I would say by calculation firstly then confirmed by trial and adjustment. Mass to the rear is the most risky as a tailplane stalled means loss of control. Where the tailfeathers sit in cruise should be noted. If they are in a position of providing a lot of upward lift I would be wary of adding more mass aft.  Nev

[IBob]

Thanks facthunter.

I'm a bit surprised, I thought the engineers here would be all over, the question, which was;

 

How is the C of G range of an aircraft originally established?

 

A short search did turn up this, which makes sense:

 

From faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/12_phak_ch10.pdf

 

The forward CG limit is often established at a location that

is determined by the landing characteristics of an aircraft.
During landing, one of the most critical phases of flight,
exceeding the forward CG limit may result in excessive loads
on the nosewheel, a tendency to nose over on tailwheel type
airplanes, decreased performance, higher stalling speeds, and
higher control forces.

 

Control

 

In extreme cases, a CG location that is beyond the forward
limit may result in nose heaviness, making it difficult or
impossible to flare for landing. Manufacturers purposely
place the forward CG limit as far rearward as possible to

aid pilots in avoiding damage when landing.

 

In addition to

decreased static and dynamic longitudinal stability, other
undesirable effects caused by a CG location aft of the
allowable range may include extreme control difficulty,
violent stall characteristics, and very light control forces

which make it easy to overstress an aircraft inadvertently.

 

 

A restricted forward CG limit is also specified to assure
that sufficient elevator/control deflection is available at
minimum airspeed. When structural limitations do not limit
the forward CG position, it is located at the position where
full-up elevator/control deflection is required to obtain a high

AOA for landing.

 

 

The aft CG limit is the most rearward position at which the
CG can be located for the most critical maneuver or operation.
As the CG moves aft, a less stable condition occurs, which
decreases the ability of the aircraft to right itself after

maneuvering or turbulence.

 

 

 

 

[facthunter]

You need to delve into the effect of the tailplane stalling to get the full picture. Nose heavy does increase stalling speed because the extra aerodynamic down force needed on the Tailfeathers has to be counteracted by increased lift from the Mainplanes.  Weight on the nosewheel depends on the position of the mainwhels relative to the actual CofG. unless you are poling forward with the stick on the ground  tricyle gear or applying brakes which transfers weight. Nev