# Minicab GY-20 - Elevator Deflection

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#### Flow

##### Well-Known Member
Hey folks, does anyone know the elevator deflections for these?
It is currently at -25 +20. They have a tail-to-elevator-chord ratio of ~0.5. Is this too much?

#### Mcmark

##### Well-Known Member
I don’t, but my Wittman W-8 is +30 -25. It wasn’t when I got it. Only +18.
He told me he couldn’t get it to slow down.
I’d rather have a bit much and not use it than not enough.

#### Flow

##### Well-Known Member
Cheers, we are not worried about tail stall (and resultant entry into inverted stall/spin) at -25 with a Ce/Ch of 0.5 and say forward CoG? Looks like the reduction in tail stall angle would be ~11 degree for these numbers so 3 degrees off a typical critical angle. Noted that a C-130 runs -40 but then only at 0.35 Ce/Ch and ~10.5 degrees reduction in tail stall angle at full up deflection. Wondering if -25 @ 0.5 is getting a bit close to the edge or not.

#### TFF

##### Well-Known Member
First off, you can only use that much negative deflection If you are an aerobatic airplane. Why is that much there is probably more practical in terms of building. It’s the dangle left over from a comfortable stick position and the positive deflection stops. I don’t think it was ever a care on that particular airplane, just leftover throw from rigging up elevator.

#### Flow

##### Well-Known Member
Negative deflection is nose up. From what I understand positive deflection is for tail dragers to meet the tail up at ~50% take off speed requirement.

Still keen to hear if anyone thinks 11 degrees off critical at max - (up) is a bit sketch or not.

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#### flitzerpilot

##### Well-Known Member
It's not scientific, but I based my elevator deflection on what is used on the Zin 526, ie. 30 degrees 'up' elevator ad 25 degrees 'down'. The works extremely well for small biplanes with relatively short tail arms and steep ground angles (large diameter prop clearance).

##### Well-Known Member
HBA Supporter
I have drawings for the Maranda Minihawk derivative, and it shows +/- 27.5 degrees, if that helps.

#### Flow

##### Well-Known Member
Ah great, does it also have a roughly 50% tail chord to elevator chord ratio as well?

##### Well-Known Member
HBA Supporter
Yes, the Minihawk's tail surfaces are still nearly identical to the GY20.

#### Flow

##### Well-Known Member
Found it for the GY-20! -+27.5 confirmed. Wow that really is up there for a 50% chord..

#### BJC

##### Well-Known Member
HBA Supporter
Probably more than needed. The S-1S (from memory) is +/- 25 degrees, with the average elevator < 50% of the average stabilizer.

BJC

#### Flow

##### Well-Known Member
Agreed, will start at -/+ 25 degrees and for fwd CoG / MAUW note tail lift on roll speeds, stick position at flaps full, power off stall or abort the flaps full stall and have a rethink if >75% aft. Wouldn't hurt to tuft and monitor the right tail as well I suppose.