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Date: Sun, 03 May 2009 16:12:40 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] prop?
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Bryan Winberry wrote:
>
> I’m a novice when it comes to props. So, could I get some advice about 
> the following prop that a guy has for sale.
>
> I have a Renesis with the RD-1C (RV 7). Plan on using the rotary cowl.
>
> The prop is question is a 3-blade MT. Model MTV 7-C-187-139. that’s 
> 73” diameter, electrically adjustable.
>
> Firstly, the bolts are 7/16 and the PSRU is 3/8^th . Would there be a 
> problem opening the holes?
>
> Secondly, the website (MT) indicates that 160 is max HP for the prop, 
> but it also says that 175 is max diameter. This one is 187cm (73”).
>
> I have sent an email to MT regarding this, but want to let it get 
> kicked around here on the forum.
>
> Lastly, in the construction manual, Van’s doesn’t recommend aerobatics 
> with an electrically adjustable prop.
>
> Thanks in advance for your replies.
>
> Bryan
>
Like someone else said, the max hp sounds wrong, especially if it also 
says a smaller max diameter. Looking at the model #, it seems likely 
that the '187' in the model number is actually the prop diameter. Also, 
a 73" diameter 3 blade prop limited to 160 hp would have blades as 
narrow as toothpicks. Is that the case? Must be specs for a different 
model prop.

Van probably says no acro with electrics because they have much slower 
response time than hydraulic props. Still not as bad as *no* response 
time from a fixed pitch, & they do acro all the time. :-) The issue is 
over-speed if they are in flat pitch going up & can't respond quickly 
enough to limit rpm going down. The throttle can solve this, just like 
it would with a fixed pitch prop; just extra work load for the pilot. A 
more significant question is whether MT approves it for acro.

Charlie