From: "Finn Lassen finn.lassen@verizon.net" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: N214FL RV-4 First Flight
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Date: Sun, 21 Feb 2021 12:25:58 -0500
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 From the Max6675 datasheet:
For a type-K thermocouple, the voltage changes by 41μV/°C, which 
approximates the thermocouple characteristic with the following linear 
equation: VOUT = (41μV / °C) ✕ (TR - TAMB)

MPX10:
0 to 10 kPa (0 to 1.45 psi) 35 mV Full Scale Span

So 1.45 psi might show 35 / 0. 041 : 854C (1536F) on a 0C ambient day. 
Not sure why that would max out your engine monitor.

However the MPX10 could have as high as 50mV/1.45psi with as much as 
50mV offset: 100/0.041: 2439 C at 1.45psi and 0 C ambient at extreme end 
of MPX10 specs.

Yes, I also find 1.45psi = 40.176 inches of H2O
With nominal MPX10 specs:
6" H2O would be (0.217psi * 35mV + 20mV)/0.0.41 showing 673C or 1243F.
With extreme specs:
6" H2O would be (0.217psi * 50mV + 50mV)/0.0.41 showing 1484C or 2702F.

What was your max engine monitor reading?

Finn

On 2/21/2021 2:49 AM, Stephen Izett stephen.izett@gmail.com wrote:
> Hi Finn
>
> I see that I was reading your water temps wrongly. You were a little warmer than I first thought.
>
> The pressure transducers I am using are MPX10’s. I’m using 5 that I purchased on eBay. They are probably not true Freescale units but Chinese ripoff’s I’m guessing.
>
> I started wiring them directly to the EGT inputs with the dynon providing the 5v supply.
>  From memory Ive now added 1K in each leg.
> I just used Cat 5 twisted pair cable so the signals are noisy but readable.
> Engine Monitor is in the cockpit while box of stacked transducers are under the cowl in the heat.
> I’m using them with the differential inputs across the face 4 inches in from each corner and one in the middle of the core.
> Wish I had a bunch more for higher resolution of the face, but this gives me some picture of the pressures.
>
> A couple of issues:
> 1. When I tried to calibrate them with a water manometer to read inches of water on the Dynon they max’d out at about 6 inches H2O. The data sheet says 1.45 psi which I thought was 40 inches of H2O.
> I’m just not sure what the EGT input circuitry thinks of the transducers output impedance etc. or the temp compensation.
> 2. Ive had issues with a couple of the transducers now in flight. As in the data going haywire. Sometimes providing constant data but then at other times all over the shop.
> I thought it was temp related, however I’m beginning to suspect that there is substantial turbulence inside my diffuser.
>
> Either way, they still have given me comparative data which has been very illuminating.
> On the last test after squeezing the wedge end really tight the upper back transducer reported very low pressure (As in, the diffuser wall is now against the radiator face and there is now basically zero flow to that 4 x 4” section - perhaps larger).
> Having changed the shape of the diffuser, the flow through the front of the Rad has improved enormously. The result better cooling than previous flight data ever with that back corner section not flowing any air!
> So I’m going to sand off some of the foam in the diffuser and open up the end of the wedge slightly, and hope to improve the cooling even further.
>
> Cheers
>
> Steve
>
>
>
>
>> On 21 Feb 2021, at 11:50 am, David Leonard wdleonard@gmail.com <flyrotary@lancaironline.net> wrote:
>>
>> Congratulations Finn!
>> You must be walking on clouds.
>>
>> I agree that more cooling will make flying more enjoyable for you.  Getting cooling capacity at exactly the optimal level is very tricky.  So I say error well on the side of excess cooling.  Makes life easier, makes flying more relaxing, and the loss in performance is practically trivial.
>>
>> Dave Leonard
>>
>> On Sat, Feb 20, 2021, 11:25 AM Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:
>> N214FL left the ground this morning for an 18 minute flight.
>>
>> Main concern was engine (water) cooling. As you know, cooling is a compromise between drag from unnecessary air through cowling and adequate cooling during normal flight conditions. Climbed to 1,500' before pulling back on throttle to see if coolant temp would stop rising. It did. Still, I think I erred in too small fluid inlet openings in the A/C evaporator cores I used for radiators. Some more work in that area is in my future before hot days arrive.
>>
>> Cut the flight short due to a bit of smoke (didn't smell anything) briefly observed low in the cockpit at full throttle later in the flight. To be investigated.
>>
>> Van's RV-4 with Mazda 13-B Renesis (RX-8) stock engine.
>> RWS 2.87:1 Propeller Speed Reduction Unit
>> RWS Engine Controller and Monitor (modified)
>> Performance Propeller 76x88
>> Empty Gross: Approx 926 lbs.
>>
>> Engine log attached. Unzip and open with Excel.
>>
>> WTALR: Water temp after left radiator
>> WTARR: Water temp after right radiator
>> Use EGT and CHT Ref to compare to OAT and adjust accordingly.
>>
>> Finn
>>
>>
>>
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