Savannah XL and S (Antibalance) Trim Tab Adjustment

[IBob]

With the (antibalance) trim tab position adjusted as per the manual (top of Page11/12 of appendix Chapter 1, Rev00 12Jan 2010):

The aircraft at full flaps with the trim set full up (10/10 on the bargraph) flies approach with a pronounced nose down trim.

The aircraft trimmed at cruise has approx 3/10 on the bargraph.

 

I saw a reference somewhere about altering the tab adjustment to give greater nose up trim.

Two questions:
1. Are there any aviation or engineering reasons not to do this?

2. How do other XL or S owners have theirs set? (I've left the VG out at this point as it has a smaller (non-antibalance) trim tab setup).

 

Thanks.

[perrynz]

Gidday Bob. My trim is set up pretty similar to yours, although my cruise setting on the bar graph is closer to 2/10 when flying solo. I do find that when two up, my trim requires close to full nose down in cruise. My thoughts are that holding a little rear stick for landing (read that: for relatively short duration) is preferable to holding ANY trim in cruise. Haven’t seen you down in our strip for a while Bob. Cheers. Perry

[IBob]

Hi Perry,

I certainly take your point that we need to be able to neutral trim for cruise.
I'm a bit surprised that you are almost full down when 2 up, if that's the case then it sounds as though you are to the limit of practical adjustment. That would be at approx 5000RPM?

Maybe your seats are set further back than mine?

 

I haven't been out so much for the first half of the year, but hoping to get back into it: will sharpen myself up on a couple of easy strips, then drop on you before too long, I hope.

How is your strip in the rainy part of the year?

Bob

 

[perrynz]

Yes, I have the seats all the way back. That would likely be the difference. 

[AndyDrain]

 Cruise Bar 2

Full flap approach Top Bar, slight back pressure.

Adjustable seats not fitted.

[IBob]

Thanks Andy, all good input.

[dan tonner]

Hi Bob;

     You seem more concerned with the nose-down attitude at full flaps than with the extra force required to keep the nose where you are comfortable at full flaps. Is it possible that because you need to “pull” harder on the stick you end up thinking you are flying at a nose-down attitude?

     You mentioned that in cruise, your trim is at “3 bars”; but you didn’t say whether this was nose up or nose down.  Since the RayAllen electric trim works opposite to the Anti-balance mechanical trim, depending upon whether you have a nose-up or a nose-down “3 bars” trim at cruise,  this will affect control “feel” at full flaps – especially if you are three bars from full nose-down trim in cruise. The anti-balance function would have the trim tabs way up (trying to push the nose down) when you are using flaps and trying to hold the nose up with the stick.

     Rather than over thinking it (I probably already did); consider adjusting the trim so that the bar is centered when you are in cruise (with your “usual” weight-and-balance configuration).

This works for me, along with NEVER using full flaps – but that’s another story.

     As for the “factory” settings, something as simple as where you mount the battery (mine is in the tail) will determine the “right” trim settings for your particular build.

     All the best, vfly safely,

     Dan

[AndyDrain]

Hi Dan

 

Interested in your never using full flaps story.  I have electric flaps and only use the full setting for shortest strips.  Most of the time I use a setting just short of full.

 

 

[IBob]

Hi Dan, thanks for your input. To clarify:
First, I am not concerned about the approach attitude; what I am interested in is the amount of stick back pressure (for a full flaps approach at 40kts).

Second, and to clear up any confusion over the trim indication: the trim bargraph has 10 segments. With 0 segments showing, the trim is full nose down, with 10 segments showing the trim is full nose up. So when I am cruising with 3 segments showing, I am 3 segments off full nose down, and for a full flaps approach I have 10 segments showing, which is full nose up.

 

I am interested in the amount of (approach) stick pressure, to see if different owners report different degrees of this: I had thought most builds would be similar in this respect, but I am now getting the impression there is some real variation.
If you never use full flaps, the effect would be far less for you, and with the battery in the tail as you describe, I would guess that you can fly a 40kt approach with most if not all nose down tendency trimmed out.

 

I have learnt to fly approaches, mostly at full flaps with 40kt approaches as per the POH, but this requires more than a little rear stick, so the controls are relatively unbalanced. It seems to me that more balanced controls would allow for more 'feel', and am interested in the views and experience of others on this.

 

Andy, I have the Mark Kyle flap handle bracket, which gives me 3 flap settings instead of the standard 2 settings.

 

 

Edited June 5, 2022 by IBob

[AndyDrain]

Just tried a couple of full flap 40kt approaches to check - I only need slight back pressure, quite comfortable to fly.

 

I have, but have not fitted, a set of vanes to go on the elevator.  I wonder what effect these would have.

[IBob]

Thanks again, Andy.

It would help if this were not subjective.....but I'm not suggesting anyone goes out there with a spring balance at this stage!
FWIW I have the adjustable seats, am average size and fly with them on the 2nd notch back (full back is 4 notches).

My tyres are Condor 6 x 6 and the build is as per the manual, with the battery forward.

 

 

I fitted Stolspeed VGs to the underside of my elevator (so they emerge at start of elevator up, though JG now recommends fitting them on the TE of the stabiliser). I did this early in the piece as SVH noted his Sav VG was much easier to get onto the back wheels pre-takeoff.

However, it was too soon in my own flying to be able to reliably judge the effect.

 

My (hugely experienced) test pilot on completion of build ran SVA through a very comprehensive documented test program, with no changes required apart from a minor tweak to prop pitch. He did, however, note that the aircraft tends to drop promptly onto the front wheel on landing.
I have 200+hrs on her now, with a large number of circuits and full flap landings, so the aircraft certainly works as is.

However, I frequently fly alone, with no baggage and partially full inner tanks, and this puts the C of G well within limits, but somewhat forward.

I am considering both the trim, and shifting the C of G back some, to see how that affects the approach handling.

 

All thoughts and comments welcome.

Thanks.

[perrynz]

Try a 20kg sandbag in the boot. Should give you some indication.

[IBob]

Yep, I'm looking at something very much along those lines, Perry.

Have also tweaked my trim for a bit more nose up, but need to fly to check that first.

[Kyle Communications]

The position of the antibalance trim is of course a function of CG also any deviation between your wing incidence and tailplane incidence. When I first flew my XL the battery was in behind the pilot..thats where the manual said to put it. The plane was noseheavy ..it wasnt a joy to fly really ..I couldnt keep the nose up on landing. I saw though on the web guys had the battery in the tail section and also there were holes there as well so I shifted the battery back there. What a difference. The planeflew very differently and I changed away from the manual for the trim tab dimensions and set it to how I liked it. My display I setup so it was positioned vertically and I set it so that level flight was 2 LEDS off at the top and full trim was no LEDS at the bottom.. I then set the trim tab in small increments so it flew level in cruise with the 2 LEDS off at the top. No LEDS was landing with flaps and I just needed slight pressure on the stick with flaps.

 

My antibalance tab was a bit higher than the spec which meant my aircraft CG was a little to the rear. I found if you put the tail on the ground it would stay there and only take about 1 to 2 kg of weight to lift it so that it would then want to put the nose back down onto the ground. Most with Savs I have talked to the tail would not stay on the ground at all. I tried many different setups and this is the one I ended up with and it flew just great. It was a joy to fly...and land

 

Mark

 

[eightyknots]

8 hours ago, IBob said:

Thanks again, Andy.

It would help if this were not subjective.....but I'm not suggesting anyone goes out there with a spring balance at this stage!
FWIW I have the adjustable seats, am average size and fly with them on the 2nd notch back (full back is 4 notches).

My tyres are Condor 6 x 6 and the build is as per the manual, with the battery forward.

 

 

I fitted Stolspeed VGs to the underside of my elevator (so they emerge at start of elevator up, though JG now recommends fitting them on the TE of the stabiliser). I did this early in the piece as SVH noted his Sav VG was much easier to get onto the back wheels pre-takeoff.

However, it was too soon in my own flying to be able to reliably judge the effect.

 

My (hugely experienced) test pilot on completion of build ran SVA through a very comprehensive documented test program, with no changes required apart from a minor tweak to prop pitch. He did, however, note that the aircraft tends to drop promptly onto the front wheel on landing.
I have 200+hrs on her now, with a large number of circuits and full flap landings, so the aircraft certainly works as is.

However, I frequently fly alone, with no baggage and partially full inner tanks, and this puts the C of G well within limits, but somewhat forward.

I am considering both the trim, and shifting the C of G back some, to see how that affects the approach handling.

 

All thoughts and comments welcome.

Thanks.

Is your battery midships as per the kit or behind the battery door at the rear?

 

 

[eightyknots]

Furthermore, do you have a lighter, LiFePo4 (lithium) battery or the ICP supplied lead-acid battery?

[Kyle Communications]

With Mabel being a S model and the battery behind the pilot I wont know until I get it finished but I have put the battery frame in that position but I do no expect the battery to be there. I think mine will be in the front  near the firewall inside the cabin. The reason is Mabel has 20 thou side skins not 16 thou  so it will be heavier in the rear a little bit and its a long moment. I will set it up exactly the same. I will do the W&B and see where it comes to on the chart and most likely set it up to do the same tail on the ground test. I am pretty sure this is the W&B  that I did after I shifted the battery..its close to the tail heavy side

 

 

 

 

[Kyle Communications]

Bob. do the tail down test...it should just sit there..if you cant hold it there without hardly any pressure then you are too nose heavy...by the sound of the nosewheel dropping down that was just like mine...way too nose heavy

 

 

[dan tonner]

Bob: my trim indicator is a single lighted bar that moves up and down a 10-step “ladder”. I set it so that in cruise, the middle “rung” (sometimes both segments 4 and 5 ) are lit up. I had already changed the offset servo connections to “straight-on“ clevis connections to the push/pull trim control rods on both sides of the horizontal elevator. It required a small repositioning of the servo – see picture (full nose down position shown in attachment).

Keeping in mind the indicator displays the servo ram position and not the actual trim tab position, here’s how I set the indicator:

·       I adjusted for cruise trim in flight then landed without making any more trim changes;

·       I secured the stick in a centered position and measured the trim tab deflection;

·       I pressed the trim rocker switch to move the indicator to the center position, then adjusted the push/pull rod lengths on both sides to achieve the previously measured trim deflection.

 

Having shared all this, I believe this procedure would actually worsen your situation. Currently, in cruise configuration, you still have 7 “segments” of nose-up trim available. Were you to “center” the indicator to your cruise  configuration you would reduce the “available” nose up trim segments to 5 and consequently require even more backpressure with flaperons engaged.

I think Mark has it nailed; you may be a little nose heavy. When I press my tail down, I pass the “balance point” when the skid is about 6” above the level surface; when the skid is on  the ground, it carries only an ounce or two of weight.

I have the battery (and and about 25’ of gauge 4 wire leading to and from it) mounted in the tail;

My tires are still the stock Carlisle “yard machine” tires…do you have a Condor on the front as well as the mains?

I’ll be watching to see how you make out….

 

ANDY:

     Like Bob, I have Mark Kyle’s flap lever bracket installed. The original required the lever to be awkwardly pulled into the pilot’s crotch for full flaperons. During a test flight just after completion, my plane suffered a hard landing when the lever “released” during the landing flare (according to the pilot.) I suspect the awkwardness of the original lever contributed to a failure to fully lock in place.  Broke my heart and cost lots in terms of time and money for repairs.   I try not to look at those photos.

I found with full flaperons  (even with Mark’s 4-position bracket) I was uncomfortable with reduced rudder / elevator authority. Perhaps with experience and practice I will grow into that configuration, but for the time being, I’m happy with longer strips and 45 – 50 mph touchdowns.

All the best,

Fly safely.

CanadaDan   (Dan)

[IBob]

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.

[perrynz]

Have you checked that the full flaps position is within specs Bob? 

[IBob]

Good point, Perry!

Yep, the flaperon positions are all crack on, as per the jig provided with the kit.

[Kyle Communications]

Bob has my flap bracket which you can see in his last picture...the full flap position is exactly the same for flap angle as the original. The geometry I made it so that it has the same travel but its all at th different angle. Then of course I the extra position. The first stage of flap with my bracket is about 1/3 of the full range and the second stage is about 2/3 of the range.

 

I found I use the first position for pretty much everything. The second position was for when I wanted shorter landings and pretty much never used the original full flap position as it was too aggressive especially if it was a bit windy. At full flap when its windy the Sav tends to waffle quite a bit as Don says so the repositioning really makes a difference on landings

 

Mark

 

[AndyDrain]

Does waffle/wallow with full flap. I find I can be very precise, without too much effort, provided I don't use full flap. 

 

I have found the electric flaps great. Originally went for them to remove the bit between the legs.

 

Dan

 

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.

 

I have flown mine without and with but probably don't have enough skill to notice much difference. Although in crosswinds the weathercock tendency needs to be watched.

[Kyle Communications]

On my flap bracket I made the notches a little deeper so the lever doesnt jump out