REFLECTOR: Engines and High DA

[Jim Sower]

<... the stalled portion of the produces mostly noise and little thrust ...>
Actually, there's a lot of thrust there. Certainly not optimal, but 
significant.

When an airfoil stalls, the lift drops off. It does NOT VANISH. All most 
of us have seen on lift charts is the break in the curve to where it 
droops off. Shortly after that (a little higher AoA), lift levels off a 
good bit and stays at a relatively stable but substantial CL. Drag goes 
up pretty fast at stall, but also stabilizes.

Makes a lot more than noise ... Jim S.

Al Gietzen wrote:

> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] 
> On Behalf Of Scott Derrick
> Sent: Saturday, February 05, 2005 7:05 PM
> To: Velocity Aircraft Owners and Builders list
> Subject: Re: REFLECTOR: Engines and High DA
>
>>I'd expect the most effective way to reduce takeoff roll would be 
> going to a
>
>>variable pitch prop, no?
>
>>
>
> Maybe, maybe not. There are wins and losers for an MT, the only prop
>
> with a history and its checkered. You do gain in a reduced take off
>
> roll. You lose in a 65-85 lb CG demon on the end of the engine. I've
>
> been told to expect at least a 100 lb loss in net weight once you add
>
> weight up front to get the cg in line. They break easily & often. They
>
> are horribly expensive to get fixed. They take forever to get fixed.
>
> Many on this list have more time on there spare fixed pitch then there
>
> MT. You also loose 5 to 10 knots on the top end, something I don't want
>
> to do. And of course there is the added complexity for flying and
>
> maintenance.
>
> Yeah; I was thinking purely from the standpoint of translating power 
> into thrust – not all those other things. I don’t want one of those on 
> my airplane either.
>
>> For a fixed pitch cruise prop a good portion of
>
>>the blade is in stall condition until the speed gets up, and adding more
>
>>power would mostly just make more noise. I'm just guessing here; have no
>
>>data.
>
>>
>
> The data I have gathered says your wrong. Its not just noise. Its
>
> called Horse Power. The density altitude alone here in Grants reduces
>
> my HP by 20 %. I've been taking to a fellow with an E-Racer with a
>
> TIO540, using a Catto Prop. He breaks ground in less than 1000 feet at
>
> gross weight. With his old IO360 it was 2500 ft. Sounds like a goodly
>
> portion of those 300+ HP are pushing it along down the runway.
>
> I just meant that the stalled portion of the produces mostly noise and 
> little thrust, so more power into the stalled portion makes more 
> noise. Clearly the unstalled portion, and the power converted as the 
> speed picks makes a big difference. That’s good to know.
>
> Craig has done a marvelous job with the prop design.
>
> Al
>
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