Trimming a BB

[Bennie Vorster]

How do I fit a trim flap to my Bush baybie and have it been done before?

[The Agent]

Hi Bennie ek en Sakkie het een gemaak en op die Bantam gesit en ek kry nou 5 knope ekstra.hier is a paar foto's wat ek van die Bantam s'n geneem het.

[The Agent]

En nog twee.

Die ding of mooi contraption het ons met die kabel R1200.00 gekos.

[Morph]

Bennie, your flapperon is the trim. You move the lever up or down to change the trim settings and as a result cruising speed. Eventually the trim stops working and the flapperons then act as flaps.

[The Agent]

Howzit Morph yes I agree with you but does that create more drag and less speed. I have really found an extra 5 knots on the bantam and no shitty comments on that piont as the knots are scarse mate.

[Morph]

If te BB is set up properly the flaperons will be in a neutral state wrt the wings when the flaperon lever is parallel with the floor of the BB. You should be able to push the lever down a bit or pull it up quite a bit.

When you pull the lever up, the flaperons drop and you are increasing drag. If pushed down, the flaperons go into reflex, i.e. upwards and drag is reduced. This improves the cruising speed and is how you trim the plane out.

[KFA]

Morph, the problem is when you fly slow with the flapperons partially extented or even without, you constantly have to put backpressure on the stick to keep the nose up to fly staight and level. This put's a lot of strain on the controls which will lead to excessive wear. I know Peter Chapman from Frigate air in FANS makes the trim tab's for the Bantams, when I asked him a while ago he said that the same system will work on the BB. The BB deffinately needs a trimtab. Monty's told me today that the are going to incorporate a trim in the near future. I will start work on my own system over the weekend.

[Bennie Vorster]

The eries nose is a bit hevey with the VW motor build into it and you have to hang onto the stick all the time to fly straite and level. I just thought it might help to fit a nice one like Agent's.

[KFA]

Bennie maak seker of daar 'n klein alliminium plaaitjie op die elevator is. Jy hoef nie 'n verstelbare tab op te sit nie. Jy kan net 'n plaaitjie op rivet wat soos die rudder s'n lyk en hom dan net bietjie op 'n slag op die grond buig tot jy level vlieg.

[Morph]

If you are constantly having to hold back pressure, put the trim tab on the bottom of the elevator and bend it to face down. THis will force the elevator upwards in flight

[Mogas]

I would be interested to know if there is space in Bennie's installation to allow the VW engine to be moved back. Either that or relocate the front spar bolt holes to move the wingtips forward slightly. Things I have read here are not lekker, "weights in the tail, 58mph stall speed, heavy stick" and so on. Adding a variable trim tab in this instance appears to be a band-aid fix to a bigger problem. If the Cof G is close to the centre published range a BB does not require a lot of trim at all as most of the variable weight (Fuel and drivers) are very close to the Cof G.
Wat se jy Boet??

[priester]

Bennie

Ek stel voor jy weeg die Bushbaby en bepaal of die CG binne perke is. Met die Hitlerfiets voor in gaan die CG te ver voor wees. (ek praat van ondervinding) Indien die CG binne die voorgeskrewe perke is, ek praat onder korreksie, tussen 20 en 28% MAC, sal die klappe heeltemal voldoende wees om te trim. As jy eksta trim benodig is jy besig om met die leeu se bal te speel. PASOP!!

Laat weet indien jy inligting benodig.

[Morph]

I agree,

additionally this plane has an extended tail, which makes it non-standard. The builders must have been trying to compensate for this CG problem.

Funny though, I know of other BB's with VW motors that are standard builds and as far as I am aware don't have problems with trimming and CG.

When I did my flight test in CMY with it's 912S motor she was stalling 2-up at about 45mph. 58Mph is way too high

[Mogas]

I recall Monty telling me that the origional BB airframe was designed to take a VW motor. If one was fitting a light engine like a 582 it was standard practice to move the wingtips slightly back in order to move the centre of pressure back therby compensating for the light nose.
Perhaps Bennies airframe was fitted with a 582 before the VW and the wings rigged accordingly. Or maybe it has a homemade engine mount that has the motor too far forward.
I agree with Priester, check the Cof G. Published data is CG range 265-368mm aft of the datum(wing LE at mainwheel) or 20.5-28.5% MAC.
My 912 BB at 500kg gross weight stalls at 40mph clean and 29mph full flap.
I have a small fixed elevator trim tab and there is not much trim change at all at different weights. There is very slight stick forward pressure required at MAUW. If on a long trip and I feel like trimming I sometimes just crack the flap to make the stick neutral but this is not really nescessary.