I GUESS, Dave runs a regular manifold pressure gauge like in any regular
(speak certified) aircraft with piston engines.
IF that is so, you read absolut pressure at whatever place you have the
probe (not necessarily the actual pressure in the manifold...but somewhere
close).
If Dave observes 36" og Hg (Mercury) on the gauge, it means it is roughly 6"
of Pressure (Hg) above sealevel.
If he sees 26" at 10.000 feet that is exactly what it should be, IF he
didn't increase the charging rate. You loose about 1" Hg per 1000ft climb
(at least that's what I teach my flight students, correct me if I am
wrong!!!).

Ed I think you got on the wrong track somewhere...... at least with the
manifold pressures...:)

I think you mic up boost rate (how many times do you compress ambient
pressure) and absolute pressure (ambient pressure + "boosted" pressure)
somewhere. You can get to the same "boosted" pressure value at different
rates at different altitudes)
To mix it up some more we could start to talk about ambient to boosted ratio
:)), which changes constantly wit haltitude IF you keep the absolute
pressure constant - that's where you run out of Turbo rpm sometime if you
keep climbing and boosting!! :))

IF MSD is so great for spark, why is not everyone running it? (as Jim
suggested....)
Lynn, how are the MSD's doing with Radionoise? Do you use any radios in your
racing? Might there be a problem with Aviation Radios (Com and Nav)?

Thomas J.


----- Original Message ----- From: "Jim Sower" <canarder@frontiernet.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, September 05, 2005 2:32 PM
Subject: [FlyRotary] Re: Another great flying day = another day of
troubleshooting

In any event, I read it as 36" of something at SL and 26" at 10k'.
Don't know how to make more of anything at 10k out of that with the
exception of pressure ratio which doesn't mean much to us.
Jim S.

Ed Anderson wrote:

> Could be, but - I don't think so, Jim.
>
> Most of the time if you are talking "Hg boost you are talking absolute
> pressure.  If you are talking "psi" boost then you are generally
> talking differential pressure "gauge" pressure(absolute - ambient =
> gauge).  66" HG of manifold pressure at sea level = (66-30) = 36 "Hg
> boost = 36/2 = approx 13 psi boost - that's a lot of boost for our
> application! Dave would  be producing considerably more HP than an NA
> 13B.  Something on the order of more than 260 HP! Hot Dog!!
>
> On the other hand, if his pressure was absolute of 36" then 36-30 =
> 6"hg of boost or approx 3 psi or so.  This would give Dave approx
> 200HP instead of the 260HP or more that a 66" Hg figure would give.
>
> But, perhaps Dave is producing 260HP - however, that was not the
> impression I got.
>
> Ed A
>
>
>
>
>
>
>
>
>
> ----- Original Message ----- From: "Jim Sower"

<canarder@frontiernet.net>

> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Sent: Monday, September 05, 2005 1:51 PM
> Subject: [FlyRotary] Re: Another great flying day = another day of
> troubleshooting
>
>
>> If you're defining boost as over pressure, his SL pressure was 30"
>> ambient + 36" boost 0 66" MAP and at 10k' he's got 26" ambient + 26"
>> boost = 54" MAP
>> I think he's talking 36" MAP at SL and 26" MAP at 10k.
>> Either way, MAP at altitude is a LOT less ... Jim S.
>>
>>
>> Ed Anderson wrote:
>>
>>> Well, actually it is absolute pressure that the spark plug is
>>> reacting to.  In this example, the absolute pressure in the intake
>>> is 1.234" HG higher at 10,000 with your 26 " boost than at sea level
>>> with your 36" of boost..  This would contribute to an increased
>>> pressure in the combustion chamber when it is compressed over the
>>> sea level compression pressure. Therefore, the spark plug is facing
>>> a tougher task at 10,000 than at Sea level (in this example).
>>>  Ed
>>>
>>>     ----- Original Message -----
>>>     *From:* David Leonard <mailto:wdleonard@gmail.com>
>>>     *To:* Rotary motors in aircraft
>>> <mailto:flyrotary@lancaironline.net>
>>>     *Sent:* Monday, September 05, 2005 12:57 PM
>>>     *Subject:* [FlyRotary] Re: Another great flying day = another day
>>>     of troubleshooting
>>>
>>>              Actually, Dave you had a higher pressure ratio (manifold
>>>             to ambient) at 10,000 feet with 26" boost than at sea
>>>             level with 36".  At sea level the pressure ratio would be
>>>             36/29.92 = 1.20.  At 10,000 ft ambient pressure = 20.57 "
>>>             hg , so the pressure ratio would  be 26/20.57 = 1.26. >>> Not
>>>             much greater, but it was higher by approx.1.23" Hg. (1.20
>>>             -1.26 = .06 *20.57 = 1.234" Hg).
>>>
>>>             Ed A
>>>
>>>     Right.  But what does the plug know about the ambient pressure? >>> I
>>>     thought that it was just the absolute density of the charge that
>>>     was contributing to SAG.
>>>
>>>     --     Dave Leonard
>>>     Turbo Rotary RV-6 N4VY
>>>     http://members.aol.com/_ht_a/rotaryroster/index.html
>>>     http://members.aol.com/_ht_a/vp4skydoc/index.html
>>
>>
>> -- >> Homepage:  http://www.flyrotary.com/
>> Archive and UnSub:   http://mail.lancaironline.net/lists/flyrotary/
>>
>
>
>
> -- > Homepage:  http://www.flyrotary.com/
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>

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