flyrotary@lancaironline.net Mailing List Archive

Hi Bill,

Not Tracy, but let me see if I understand your question and can give you a meaningful explanation. Must explain, I have no EM2 - but did spend the night at a Holiday Inn once.

First, the MCT bin values are NOT manifold pressure NOR RPM values.

There are 128 “bins” or address locations at which an MCT value will exist. In the early EC2s these bins divided a manifold pressure range from approx 0” Hg to 30” Hg. Which factor (rpm or manifold pressure) used to select the bin for its MCT value depends on where you are operating the engine – it could be solely rpm (lower range) or solely manifold pressure (upper range). However there is NO manifold pressure NOR RPM values stored in the MCT bins. However, those factors are used as “Pointers” to the appropriate bin address (0 – 128) in which the fuel related MCT value resides. The only way I am aware to determine which bin address (pointer value) corresponds to a MCT bin value is to tune to that bin location (bar column on your display) in the edit mode. Then the address value will be display as text along with other data of that bin such as the MCT value.

Here is what may be confusing. The EC uses a range of 0 - 255 to store an MCT value, with a value of 128 representing a nominal stoichiometric ratio 14.7:1. So the value of 128 is technically neither lean nor rich so in effect with a value of 128 the EC2 needs do nothing (Zero) with the MCT value. Perhaps for that reason Tracy chose to represent and textually display an MCT value of 128 as ZERO on the EM. Anything above that value will be displayed as a positive number and any MCT value below 128 is displayed as a negative number.

As Tracy stated:

The default values in the table are supposed to be all zeros. There is a conceptual misunderstanding about these values in your question. It is not the Data that corresponds to the manifold pressure, it is the address. The data is a correction value for the corresponding manifold pressure. The values can be from -127 to + 127 with negative values causing the mixture to be adjusted leaner and positive values richer.

So if you see Zero displayed for an textual MCT value on your EM, that does not mean there is no value in that MCT bin, it means the value is 128 and that (in effect) represents ZERO change (neither lean nor enrich). Now if the MCT value is above 128 you will see a positive number and if it’s below 128 you will see a negative number displayed.

Since Tracy generally programs the EC with a default MCT value of 128 – guess what you would see regarding the MCT value on the EM – that’s right - 128 is displayed as zero for many/most bin numbers until you start to adjust the MCT value above or below 128..

Now since the EM is using the manifold/rpm factor to point to an MCT bin – all that is needed for display is which bin address and its MCT value. So the MCT bin addresses range from 0 – 128 being divided into several ranges. Bin addresses 0 -31 use engine RPM to point to the correct MCT bin, 32-64 uses some combination of rpm and manifold pressure and bin addresses 64-128 use manifold pressure to point to the correct bin number.

This screen (out of EC manual) shows the EM with 10 of the 128 MCT bins showing and the bargraph represents the MCT value at each of the 10 bins shown in the window. The numeral 6 is the specfic bin that has been selected for display of detailed data – the -95 shows that this MCT containts a “leaning” value < 128. The 12.6 is the manfiold pressure that “corresponds” to bin number 6 – it is NOT necessarily (and almost certainly is NOT) your engine’s current manifold pressure. Apparently when you select bin address 6 to display the bar graph corresponding to it will start to blink (again I don’t have an EM).

Ok up to this point all data has been associated with bin address 6, but that is ony because address 6 was selected from the bar graph. The next line 109 + 32 actually shows where the engine is currently operating. The EC is using bin address 109 which has a value of + 32 (which means its 32 points more than the default (zero) value of 128 or the actual MCT value at bin 109 is 128 + 32 = 160. No where do you see any manfold pressure associate with any bin – EXCEPT the bin you have selected for editing OR the bin at which the EC is currently using (109) to operate the engine.

Below the current operating data line of bin address 109 with MCT value of + 32 is the current engine manifold pressure (30” HG) – not quite certain what the 3 represents except perhaps staging status.

So to address your statement “…address 0-63 should have two values associated with them..” is technically correct, but not what you will see on the EM. When you scroll to bin 20 for example – it will ONLY show you the MCT (fuel factor) value that is located at that bin # 20 address as part of the bar graph – now if you select a specific bin for editing (or observing its values) then its detailed data will be displayed on the right. So if one of the bars reach only to the horizontal cross bar on the column graph it would represent a value of 128 – however if you selected that bin for display the bin address would be displayed on the first line with a value of ZERO – corresponding to the (zero lean, zero rich) meaning of a value of 128.

So for each selected bin (can only select one bin at a time) you get the bin address (6), the MCT value for address 6 (-95) and the manifold pressure the EC uses to point to bin 6 (12.6”Hg).

Now while the MC data value displayed textually is – 95. I suspect that the horizontal bar you see across the columns in the display represents a MCT value of 128. So if the MCT value of the bar you selected (6 in this case) is displayed as -95 then the bar height displayed would be 128-95 = 33. I notice that the height of the bar appears to be in segments – there are (according to my eyeball) 8 segments between the bottom of the bar column and the horizontal bar. If that is correct then each segment would correspond to a value of 16. 16 * 8 = 128. Therefore the MCT value of -95 at bin address 6 (which would be pointed by an operating manifold pressure of 12.6) should be 2*16 = 32 + 1 = 33 or over two segments which are what is shown on the bar graph.

So If I failed to understand your question and have not address it then I apologize for this long winded dissertation...

Best Regards

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.rotaryaviation.com/Rotorhead%20Truth.htm

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry
Sent: Wednesday, October 28, 2009 11:40 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: MCT values in the 0-63 area of the EC-2

Tracy,

I think I didn’t explain what I am seeing properly.

The addresses 0-63 should have associated with them two items. (I think)

The manifold pressure that is associated with each address and the mixture correction that is associated with that address and manifold pressure.

My table for addresses 0-63 ALL have a manifold pressure of ZERO associated with them. The mixture correction for each address varies, mostly zero, but not all.

It is the manifold pressures that are all zero! Shouldn’t they have either manifold pressures or perhaps RPMs listed??

On the addresses 64-127, the manifold pressures start at 10.0 and increase by .5 with each additional address. Not so with the earlier addresses. I think this is not correct, but I don’t think there is any way that I can affect the manifold pressure indications.

Since the EC-2 can flip back and forth between the high and low addresses at the same manifold pressures but different rpms, several folks have reported having to ensure that the corrections were similar at the two locations. I intended to verify that they were similar, but since I don’t have the manifold pressures in the table at the low addresses, I don’t know how I would compare them. But more than that, I don’t understand how the EC-2 could know what manifold pressure the lower address corresponds to and therefore which correction it should apply.

Perhaps it only looks for +/- 13 inches to go to addresses above or below 31? But then, wouldn’t it need an RPM in each address to determine the correction???

Bill B

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy Crook
Sent: Wednesday, October 28, 2009 11:09 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: MCT values in the 0-63 area of the EC-2

On Wed, Oct 28, 2009 at 6:35 PM, Bill Bradburry <bbradburry@bellsouth.net> wrote:

Tracy is back! What about this question, Tracy?

The below from a previous email…

Now I have more questions. I went over and copied down the information in my MAP table today. I was surprised to learn that the manifold pressures for all addresses from 0 to 63 were set to Zero. I expected to find actual manifold pressures in there. Starting with addresses 64 through 127 the manifold pressures increase from 10.0 at address 64 in 0.5 inch increments all the way to 41.8 inches at address 127. My engine is naturally aspirated, so the manifold pressures above about 30 or 31 will never be used. I understand that the 0 to 31 addresses are used when the RPM is below 2500 and the manifold pressure is below 13 inches, and that the addresses from 32 to 63 are used when the RPM is between 2500 and 3800 and the manifold pressure is above 13 inches. But I still don’t understand how the controller would know which address to use with no manifold pressures entered in the table. Tracy is this is OK? Will these pressures be added when the engine is ran??

Bill B

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