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Rotax 914 Intercooler

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frans(at)privatepilots.nl
Guest

Posted: Sun Jun 06, 2010 11:41 am Post subject: Rotax 914 Intercooler

Talking about cooling...



I have the intercooler for the Rotax 914, per factory setup.

My airbox temperature sensor shows no difference if I seal off the

intercooler!



While solving my cooling problems, I learned a few things:

1) Naca ducts provide no ram air, but merely "allow air to get in".

2) The cowling is somewhat "pressurised" by the openings in front.



How is the intercooler supposed to work, "connected" on the inlet to a

naca duct which provides no pressure, and the outlet venting into a high

pressure area?



I know quite some folks are flying around with an intercooler. Has

anyone indeed measured the drop in temperature? Has anyone ever found

bugs or other contaminations in the radiator? If so, were they on the

bottom or on the top of the radiator?



Frans

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kevann(at)gotsky.com
Guest

Posted: Sun Jun 06, 2010 1:47 pm Post subject: Rotax 914 Intercooler

Hi Franz,

Very interesting. Have you tried this sealing off the intercooler up at high 

altitude? I think the cooler should be doing more "work" the higher you are 

cruising?

I don't have an airbox temp sensor, but I wish I could repeat your test 

below. I too have the factory setup installed. You pose some interesting 

questions on the installation. I wonder if air is flowing though the cooler 

from the naca inlet as designed?



Kevin

..

 	  Quote: 	
		  

 I have the intercooler for the Rotax 914, per factory setup.

 My airbox temperature sensor shows no difference if I seal off the

 intercooler!

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rparigoris

Joined: 24 Nov 2009
Posts: 808

Posted: Sun Jun 06, 2010 2:12 pm Post subject: Re: Rotax 914 Intercooler

Hi Frans. 

I did speak to John Hurst and he said he measured airbox temp and especial at altitude it dropped with intercooler. He mentioned it dosen't work so well you really need to worry about carb ice, but would allow one to fly to 18K without intervention of TCU. I am only repeating what he said, I have yet to measure. For what it's worth, my 1983 Volvo GLT-50 (245) turbo station wagon, with 2.3 liter 4 cylinder, pretty much same as 914 Garette air cooled turbo as 914, and ~ 185hp said intercooler lowered air temperature going into manifold from 145F above ambient to only 45F above ambient. I think boosts were similar to 914?? Size of radiator was about size of coolant radiator.

Intercooler installed as per factory instructions from John do in fact lead to further constipation of cowl air compared to not having it installed. A mono with gear down and factory located stainless firewall has far worst exit air ability than a Tri with firewall moved way back. None the less still not stellar on the ground and in climb.



Ron Parigoris

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frans(at)privatepilots.nl
Guest

Posted: Mon Jun 07, 2010 1:13 am Post subject: Rotax 914 Intercooler

On 06/07/2010 12:12 AM, rparigoris wrote:



 	  Quote: 	
		   Hi Frans. I did speak to John Hurst and he said he measured airbox

 temp and especial at altitude it dropped with intercooler.


	


I don't know how hey measured it. It is hard to make a valid comparison,

unless you have fitted a valve and can close off the supply of cooling

air flowing through the rad.

After I couldn't measure any temperature difference, I fitted such a

valve... And found out that the intercooler has no measurable effect.

Tested with 115% power, and at 10.000 feet...



My findings are supported by the following theories:

1) Naca ducts are bad in providing ram air. They merely "allow air to

get in".

2) The intercooler is in a 90 degree angle towards the supposed stream

of air getting in via the naca duct. Now, turn your water radiator 90

degrees into the airstream. Let the air first slam the wall, and then

find its way upwards to the radiator. I guess you wouldn't be surprised

to find out that the cooling rad almost stops working.

3) Is the cowling a high or a low pressure area? Where does the

intercooler exit its air into?

4) Radiators that work correctly collect contamination (dust, bugs) over

a while. I can find plenty of these in my water radiator, but have found

none in the intercooler. Has anyone find such contaminations in his

intercooler? I asked before but so far everyone keeps silent about this

(which may be an indication that some people are just starting to

reluctantly wondering whether their setup is effective at all)...

5) Intercoolers don't need "just some air" to work properly, they need

loads of air, due to reason that they need to cool something with a very

small temperature difference.



Frans.

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