Newt Fan

[rfdesigner]

I'm at the point where I need to add a fan to my newt.

I want to cap the base of the scope, so as to seal it, flock this base to eliminate stray light, have a fan force air through it, to maintain the optics (mirror and window) at atmospheric temperature, and add a filter behind the fan so the air pushed through the scope is filtered and therefor dust free.

The tube is nearly as old as me, (fullerscope OTA).. so predates the earliest thoughts of fans on mirrors. so no, there are no preexisting mounting points for a fan. The best solution is to connect the base to the fairly robust tube.

The problems I have now are:

A: what materials to use

B: how to secure it to the OTA to create a fairly reasonable seal.

The window at the top of the tube will be supported on three points with a 10mm gap round it's perimeter to allow air flow.

Any further thoughts or suggestions?

Derek

[laser_jock99]

I'm at the point where I need to add a fan to my newt.

I want to cap the base of the scope, so as to seal it, flock this base to eliminate stray light, have a fan force air through it, to maintain the optics (mirror and window) at atmospheric temperature, and add a filter behind the fan so the air pushed through the scope is filtered and therefor dust free.

The tube is nearly as old as me, (fullerscope OTA).. so predates the earliest thoughts of fans on mirrors. so no, there are no preexisting mounting points for a fan. The best solution is to connect the base to the fairly robust tube.

The problems I have now are:

A: what materials to use

B: how to secure it to the OTA to create a fairly reasonable seal.

The window at the top of the tube will be supported on three points with a 10mm gap round it's perimeter to allow air flow.

Any further thoughts or suggestions?

Derek

Any pictures of the current configuration?

[rfdesigner]

try these

as you will notice it's not exaclty new. I bought it from this guy with a white beard that kept wanting me to see his pictures of some boat he'd built.

Derek

[laser_jock99]

I reckon you could get 3x 120mm fans on there. A round board fan cut-outs + some snap on fan filter kits

http://uk.rs-online.com/web/p/fan-filters/7374099/

http://docs-europe.electrocomponents.com/webdocs/0fda/0900766b80fda791.pdf

[rfdesigner]

Thanks

it's not the fans I'm worried about.. that's easy, just buy Papst. (I'm an electronic R&D engineer.. I've designed and built kit with fans before)

no the problem for me is what board, and where from.. how to create a decent seal. I have a couple of ideas, but tried and tested will always be superior.

Derek

[rfdesigner]

Just got off the phone with 'the plastic people'.

They recommend polypropylene. apparently it's good to -40C. just about enough for a cold snap this winter.. anyone knowingly used it?

[Merlin]

Some consider a cross fan to be more effective: http://www.crossflowfansystem.com/docs/SkyArticle_01-2002.pdf .

[rfdesigner]

Thanks, yes a cross flow will work better, but I'm not going that route for a reason.

In my case I have three major problems.

1. A thermal bubble forms below my window, causing static field disturbance.

2. My optical window attracts dew and ice in the same way a schmidt cassegrain does.

3. My OTA is front heavy, adding a long dew shield makes the tube even more front heavy.. plus the window doesn't reach the outside of the OTA, there's a rubber strip between it and the OTA meaning a dew heater has a hard time.

My solution is to keep a veil of air passing over the mirror AND the window. This should keep the window from dewing as its temperature is then controlled. It adds weight to the bottom not the top of the OTA which is better for me, and with the filter in place keeps my optics clean and spider free (I'm planning on keeping this running 24/7.. so I'll need a top notch fan.. a Papst in fact) wanting to use a decent filter is pushing me towards a fan beneath the mirror

The idea came from:

http://www.dreamscop...inDAtube-02.htm

I am planning on adding a baffle so as to encourage a high pressure on one side of the mirror and a low pressure on the other side, thus encouraging a flow of air across it's front surface.

Derek