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matronics(at)rtist.nl
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 Posted: Mon Nov 28, 2011 9:20 am Post subject: CHT still high after cowling modification (test flight with |
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Jose,
Glad you decided to abandon that flight without cowl. But before you go
modify the cowl, please install the equipment to *measure* the pressure
difference. Then take a test flight. That will become your baseline. For
any change after that it will immediately be obvious if it is an
improvement or not.
Without establishing a baseline, you are working in the dark. All you
will know after a change is that it is 'different', not if it is better
or worse.
Rob
On 11/28/2011 5:53 PM, Jose M. Toro wrote:
| Quote: | Pete:
I decided Not to fly without cowling. However, for educational
purposes, why it works in the X-air? What is different in that
installation?
Have you seen the latest pictures I posted in the list? I arrived to
the conclusion that the top of the cowling entrances were aligned too
low in relation to the top of the cylinders. So, the next step of my
"project" is to raise the top of the entrances about an inch. It will
take minor modifications to the cooling baffles for coupling purposes.
Will also modify the bottom of the cowling to close the entrance. The
objective is to route the air flow to the upper half of the cylinders.
After modifying the carb needles, I started the engine briefly without
cowling. At idle, I observed the temperature in the front cylinder 30
deg higher than the rear one. Being the cowling out the equation, I
wonder if there is a problem with the position of the deflector inside
the cooling baffles. (I posted a picture of booth cooling baffles).
It points the air flow approximately to the middle of the rear
cylinder. Should I move this deflector forward?
Jose
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jose_m_toro(at)yahoo.com
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| Posted: Mon Nov 28, 2011 10:39 am Post subject: CHT still high after cowling modification (test flight with |
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Rob:
Too late, I already cutted the cowling. Picture is posted. To put it simple, the objective of the next modification is to replicate the entrances of your cowling. If this doesn't work, I will definitely try the pressure difference test.
Jose
Sent from my iPhone
On Nov 28, 2011, at 1:17 PM, Rob Turk <matronics(at)rtist.nl> wrote:
| Quote: |
Jose,
Glad you decided to abandon that flight without cowl. But before you go modify the cowl, please install the equipment to *measure* the pressure difference. Then take a test flight. That will become your baseline. For any change after that it will immediately be obvious if it is an improvement or not.
Without establishing a baseline, you are working in the dark. All you will know after a change is that it is 'different', not if it is better or worse.
Rob
On 11/28/2011 5:53 PM, Jose M. Toro wrote:
> Pete:
> I decided Not to fly without cowling. However, for educational purposes, why it works in the X-air? What is different in that installation?
>
> Have you seen the latest pictures I posted in the list? I arrived to the conclusion that the top of the cowling entrances were aligned too low in relation to the top of the cylinders. So, the next step of my "project" is to raise the top of the entrances about an inch. It will take minor modifications to the cooling baffles for coupling purposes. Will also modify the bottom of the cowling to close the entrance. The objective is to route the air flow to the upper half of the cylinders.
>
> After modifying the carb needles, I started the engine briefly without cowling. At idle, I observed the temperature in the front cylinder 30 deg higher than the rear one. Being the cowling out the equation, I wonder if there is a problem with the position of the deflector inside the cooling baffles. (I posted a picture of booth cooling baffles). It points the air flow approximately to the middle of the rear cylinder. Should I move this deflector forward?
>
> Jose
>
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dons701
Joined: 22 May 2009
Posts: 80
Location: Hershey, PA
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| Posted: Mon Nov 28, 2011 7:03 pm Post subject: Re: CHT still high after cowling modification (test flight |
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Jose, here is a link for the firewall forward installation of the type of plane I have. My 701 is slower than yours and requires the large openings at both entrance and exit to enjoy low and slow flying reliably. Notice the "mailbox" sized openings on the cooling ducts.
http://www.usjabiru.com/zenith-ch701.html
What kind of temps did you get flying, with the cowling on of course, as this is how you are going to use the plane!!
The baffle in the back roof of the cooling duct is meant to "dam" the air flow. The more you trim away, the more air flow the back cylinder receives, at the expense of flow to the front cylinder. Only very little is trimmed away to find the balance of temperature front to rear. Finnish your modifications and test, only change one thing at a time, test and verify...DonB
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_________________
Zenith 701 #76120
Jabiru 2200A #2456 95 hours
Sensenich Wood 64-PJ-36 Prop |
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