Bantam ASI

[Dirk van Dort]

The Bantam ASI is notorius for undereading by about 10 knots, due I am told, to the distance from the pitot tube inlet to the instrument. I have just had to replace the ASI on my Bantam due to a malfunction of the instrument, and wish to change the routing of the tubing by mounting the pitot tube on the front of the pod. This will mean the tube will only be about half a metre long and be directly in front of the ASI, with the pitot protruding slightly ahead of the pod. I then want to reroute the static line to the side of the pod. Some time ago, a Bantam owner recommended this installtion. I remember he used a washer with a small hole drilled through which was fixed to the side of the pod.
My question is, how big must this hole in the static vent be, and how critical is it.
Any help will be appreciated. Thanks.
Regards,
Dirk
ZU-EZI

[Morph]

An open cockpit aircraft does not require a static input. Most of the installations I have seen has been to just leave the static port open on the back of the asi. All you have to route is the pitot tube. A simple 5mm plastic tube would be more than enough here. My Challenger was like this as is my Bush Baby

[Dirk van Dort]

Thanks ever so much Morph, you are such an asset to this forum. As I tell my fellow flyers, when Morph speaks...listen....!!
It should have been obvious to me, the ASI and Altimeter static vents are inter-connected by a tee peice, but the VSI is left open, no connection at all. Certainly makes the installation much easier.
Thanks once again,
Kind regards,
Dirk

[Dish]

Wow Dirk?? is that true.... Underreading By ten knots is quite a substantial amount.... ??? wonder if mines doing the same>??

[Morph]

Easy to determine,

You need a calm day, a gps and this speadsheet

take off and fly a triangular circuit, using the gps to record the flight or have a pax writing down the values(ground speed and track). For accuracy you need to measure the speed of the 3 legs at 3 or 4 different speeds, i.e. 50mph, 60mph, 70mph etc. Fly according to the ASI, then read the airspeed off the GPS. Try and keep completely level on the 3 legs.

Fill in the values and the spreadsheet will give you the error

[Dish]

thanks Morpheus - will give that a bash

[Dirk van Dort]

Hi Dish,
I cannot vouch for that statement, it was made to me by Andrew Pappas when i recently had to replace my ASI, however, i have noticed, on both my Bantams, that the air speed was always slower than the GPS reading, only approaching parity when flying into a strong headwind. Apparently this is caused by the distance of the pitot tube from the ASI, yet if that were true, it would affect all wing pounted pitot's..??
I am in the process of relocating my pitot to the front of the pod, and will post a pic and a report when that is complete.
Thanks Morph, for the spreadsheet and the advice, i will try that exercise, and it will be good to get Dish's report too.
Kind regards,
Dirk
ZU-EZI

[Low Level]

This is very interesting. Why would they choose to put the pitot on the wing. I see the Thunderbird's, and my gyro's are mounted on the nose. Such an easy installation, why choose the difficult route.

I'n very curious about the outcome.

[Dish]

its a bantam, something has to be difficult about it.... the rest is sooo easy

[Dirk van Dort]

The problem of putting it on the nose is that when doing your pre-flight and walking around the nose, your concentration is on the pre-flight and the pitot tube is regularly bumped wih the leg.
As a friend has just said to me, the bantam is so ugly that they put it on the wing to make it look like a real aeroplane...!! He is no longer my friend....The paramedics will be arriving soon to revive him....