silly question on best glide speed?

I was just wondering if best glidespeed in say a cessna 152 will be fast
enough to
get the engine started if you encountered a battery failure or starter
failure.

shywon

[George Patterson]

wrote:

> I was just wondering if best glidespeed in say a cessna 152 will be fast
> enough to
> get the engine started if you encountered a battery failure or starter
> failure.

Stopping the prop from windmilling generally requires slowing to just above
stall speed. That's well below best glide speed. If the prop is still
windmilling, best glide will be fast enough to let you restart.

Once the prop stops, though, it takes a lot to get it going. If you slowed the
plane enough to stop the prop, you will have to accelerate to well above best
glide speed to get the prop turning again.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

[Bob Gardner]

As George says, you really have to work at it to make a prop stop. It will
windmill at glide speed, and the magnetos will spark their little hearts out
during every revolution until the fuel-air mixture returns to the cylinders.

If you do stop the prop...on purpose, by sticking the nose way up in the
air...you will have to dive to about 120 to get it rotating again.

Bob Gardner

> wrote in message
...
>I was just wondering if best glidespeed in say a cessna 152 will be fast
>enough to
> get the engine started if you encountered a battery failure or starter
> failure.
>
> shywon
>

[[email protected]]

Did the stopped-prop thing in a 150 many years ago. It would not
restart even while diving at Vne. Maybe a worn-out engine with little
compression left would start at 120.

Dan

[Seth Masia]

Another problem, especially with small engines, is that if you're ever going
to get carb ice, it's now, with the fire out and the engine turning. The
exhaust manifold cools really fast on a smaller engine; you're pulling air
and water through a cold carb throat, with insufficient latent heat to melt
the resulting ice; and you may not get a restart at all.

Seth

"Bob Gardner" > wrote in message
...
> As George says, you really have to work at it to make a prop stop. It will
> windmill at glide speed, and the magnetos will spark their little hearts
> out during every revolution until the fuel-air mixture returns to the
> cylinders.
>
> If you do stop the prop...on purpose, by sticking the nose way up in the
> air...you will have to dive to about 120 to get it rotating again.
>
> Bob Gardner
>
> > wrote in message
> ...
>>I was just wondering if best glidespeed in say a cessna 152 will be fast
>>enough to
>> get the engine started if you encountered a battery failure or starter
>> failure.
>>
>> shywon
>>
>
>

[John McDoe]

Great point. I had the engine in a 152 die on me several years ago.
There was no restarting it at all.

Emergency landing at John Wayne Airport (KSNA), and after landing on the
runway it started right up.

John.

Seth Masia wrote:

> Another problem, especially with small engines, is that if you're ever going
> to get carb ice, it's now, with the fire out and the engine turning. The
> exhaust manifold cools really fast on a smaller engine; you're pulling air
> and water through a cold carb throat, with insufficient latent heat to melt
> the resulting ice; and you may not get a restart at all.
>
> Seth
>
> "Bob Gardner" > wrote in message
> ...
>
>>As George says, you really have to work at it to make a prop stop. It will
>>windmill at glide speed, and the magnetos will spark their little hearts
>>out during every revolution until the fuel-air mixture returns to the
>>cylinders.
>>
>>If you do stop the prop...on purpose, by sticking the nose way up in the
>>air...you will have to dive to about 120 to get it rotating again.
>>
>>Bob Gardner
>>
> wrote in message
...
>>
>>>I was just wondering if best glidespeed in say a cessna 152 will be fast
>>>enough to
>>>get the engine started if you encountered a battery failure or starter
>>>failure.
>>>
>>>shywon
>>>
>>
>>
>
>

[.Blueskies.]

> wrote in message ...
>I was just wondering if best glidespeed in say a cessna 152 will be fast enough to
> get the engine started if you encountered a battery failure or starter failure.
>
> shywon
>

Why would the prop stop in the air with a battery or starter failure?

Thank you all for the great answers.
I didn't say the prop stopped because of battery failure or starter failure.
It could be from too rich mixture or switching to an empty fuel tank.
I know, if you do something and the engine quits, turn the switch back
immediately.
Thanks again folks

".Blueskies." > wrote in message
...
>
> > wrote in message
> ...
>>I was just wondering if best glidespeed in say a cessna 152 will be fast
>>enough to
>> get the engine started if you encountered a battery failure or starter
>> failure.
>>
>> shywon
>>
>
> Why would the prop stop in the air with a battery or starter failure?
>

[George Patterson]

Seth Masia wrote:

> Another problem, especially with small engines, is that if you're ever going
> to get carb ice, it's now, with the fire out and the engine turning. The
> exhaust manifold cools really fast on a smaller engine; you're pulling air
> and water through a cold carb throat, with insufficient latent heat to melt
> the resulting ice; and you may not get a restart at all.

Depends on the reason for engine stoppage. The vast majority of the temperature
drop within a carburettor is from the evaporation of fuel. If the engine stopped
because you just ran a tank dry, that source of "coolth" disappears and the carb
starts to warm up.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

[Tony]

There's the other point: isn't glide range extended in a 172 if the
prop isn't windmiling?

[Stefan]

Tony wrote:

> There's the other point: isn't glide range extended in a 172 if the
> prop isn't windmiling?

It is in any aircraft.

Stefan

[john smith]

> There's the other point: isn't glide range extended in a 172 if the
> prop isn't windmiling?

Remember that picture in the different aviation rags several years ago
of the Mooney with the feathered prop?
Anyone remember what the add was for?

[[email protected]]

Tony wrote:
>> There's the other point: isn't glide range extended in a 172 if the
>> prop isn't windmiling?


>It is in any aircraft.

>Stefan

You'll start another windmilling argument with that. There are
some serious divisions over whether to stop a prop or not to get more
range after an engine failure.
When we stopped the prop on the 150, the airplane's attitude was
more nose-down to maintain the same glide speed, and the rate of
descent was higher. The theory here is that the much higher angle of
attack on the prop blades when stopped causes more drag that if it's
windmilling.

Dan

[George Patterson]

Tony wrote:

> There's the other point: isn't glide range extended in a 172 if the
> prop isn't windmiling?

Yes, but you will lose a lot of altitude slowing down to get it stopped.
Empirical experiments show that, if you're lower than about 6,000' above your
target landing point, you're better off trimming for best glide and letting it
windmill.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.