REFLECTOR: CATTO

Tue May 24 08:55:44 CDT 2005

Anecdotal comments indicate the MT may be slightly slower at altitude cruise than a properly selected FP prop.  Not a big difference but some.  The MT is heavier and must surely make some design compromises that would not be necessary in a FP prop, hence a slightly lower efficiency than an optimized FP prop.  

I'm guessing (key word), given the DH's proposed range of operating altitudes, that a CS become more important.  It's easy to select an optimized cruise prop for 5,000' or 15,000', but is very difficult to find a FP that will operate well at both.  As the air gets thinner, the FP has less bite and the engine speeds up.  With a climb prop or one selected for lower altitudes, you run out of RPMs before you run out of HP at higher altitudes.  Since the DH says they maintain HP to high altitudes, the CS prop seems a necessary accouterment to take advantage of that engine's ability.

"Facts may vary from my opinions"
Chuck

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Grigore Rosu
Sent: Tuesday, May 24, 2005 9:23 AM
To: Velocity Aircraft Owners and Builders list
Subject: RE: REFLECTOR: CATTO

But suppossing that one is interested in just one factor, namely maximal 
cruise speed, would there be any reason to choose a constant speed 
propeller over a fixed pitch one?  Or to be more concrete, assuming 
all the other factors equal (even though they are not), would an MT 
constant speed propeller on a Velocity SEFG give one a higher cruise
speed than a fixed pitch propeller on the same aircraft?  I guess a CS 
propeller would give one a maximum cruise speed at any altitude, while a 
FP one would give a maximum cruise speed at just one, conveniently chosen 
altitude?

As many of you may already know, Deltahawk and Velocity will be providing 
a DH engine kit in the near future, including an MT constant speed 
propeller.  Since one of the major advertised advantages of a DH engine 
over a Lycoming is the overall cost of operation, I guess they could have 
chosen a fixed pitch propeller as part of the engine kit instead of a CS 
one, if there were no significant differences between the two.  Could the 
type of engine favour a particular type (FP vs. CS) of propeller?

Grigore

On Tue, 24 May 2005, Chuck Jensen wrote:

> Good morning Greg (or in your case, evening),
>
> If you have a very short runway, you need to select a fine pitch prop which will allow the engine to develop full RPM for max HP output for takeoff.  But when you get to cruise, you want a coarse pitch prop so the engine doesn't overspeed.  A cruise prop may limit your engine RPM on takeoff to 2500 RPM, or so, so you aren't putting out full power, hence longer TO distances.  Throw together max gross weight, high altitudes, high temps and short runway and the curve of the PF (pucker factor) goes up sharply.  That's when you have an extra 10,000 reasons why a CS is a good idea.
>
> Chuck
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
> Behalf Of Greg Poole
> Sent: Tuesday, May 24, 2005 8:39 AM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: CATTO
>
>
> Hmnnn....thought we were talking cruise? ...so what does a real long runway
> have to do with not sacrificing the 40kts you indicate would be lost from
> cruise?
>
> Greg
> (not a critic but if you dare to publish - you must dare to be questioned!)
> ----- Original Message -----
> From: "Dan Fast" <onefastvelocity at yahoo.com>
> To: <Jim_Agnew_2 at yahoo.com>; "Velocity Aircraft Owners and Builders list"
> <reflector at tvbf.org>
> Sent: Tuesday, May 24, 2005 10:32 PM
> Subject: Re: REFLECTOR: CATTO
>
>
>> That might be a little over stated, but at his density
>> altitude with a 173, and the fact that he now cruises
>> at 195kt,I believe he would loose close to that much,
>> unless he had a real long runway to depart from.
>>
>>   Dan
>> --- Jim Agnew <jim_agnew_2 at yahoo.com> wrote:
>>> Dan,
>>>
>>> Do you really believe that you will lose "40" KTS!!
>>>
>>> Jim
>>> --- Dan Fast <onefastvelocity at yahoo.com> wrote:
>>>> Tom at your airport altitude and with your
>>> Airplane a
>>>> fixed pitch prop would cost you 40kts min at
>>> cruise.
>>>>   Dan
>>>> --- Tom Martino <tmartino at troubleshooter.com>
>>> wrote:
>>>>
>>>>> I seem to remember someone talking up the Catto
>>> prop
>>>>> for their Velocity.
>>>>> I'd like to hear a first hand experience ... how
>>> is
>>>>> it pitched and do
>>>>> you get adequate performance at cruise?
>>>>>
>>>>>
>>>>>
>>>>> I was told ... not matter how you look at it you
>>>>> sacrifice performance
>>>>> with a fixed pitch.  Your thoughts from first
>>> hand
>>>>> experience?
>>>>>
>>>>>>
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>>> Jim_Agnew_2 at Yahoo.Com
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>>> Velocity 173 Elite Aircraft Completed & Flying
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>
>
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