Seneca II question
phil cohen
(PA 34-200T)
The POH does not give it. I suppose that's because they think that the
chance of having both engines fail is almost nil.
Would best glide be the same as Vyse?
I'm just curious because in the ASA oral exam guide prep, it's one of
the questions to expect, and like many of those questions, the answer is
nowhere to be found in the POH.
phil cohen
phi...@worldnet.att.net
LFransson
In article <36BB8B...@worldnet.att.net>, phil wrote:
>Does anyone know what the best glide airspeed would be for a Seneca II
>(PA 34-200T)
>
>The POH does not give it.
No, it sure doesn't. The only twin I've ever seen a best glide speed published
for is the Cessna 414 (the only twin Cessna I've ever flown, so I can't speak
to what might be published for other Cessna twins).
>Would best glide be the same as Vyse?
Maybe. Maybe not. That's where I would start. But if I rememer correctly,
the best glide speed for the 414 is something like 120 knots, which is
significantly greater than either Vy or Vyse, neither of which I can
specifically recall because I haven't used them since May, but I seem to
remember numbers like 96 for Vyse.
So, in my mind at least, a valid answer to the question would be, "I don't
know. As far as I can tell, it's not published anywhere." If you really want
to impress people, see if you can call engineering at Piper and ask if anyone
there knows.
In any case, I wouldn't really sweat it. The only time I've ever been asked
for the best glide speed in a twin was on one or both of my Part 135 checkrides
in the 414 - the only twin I've ever flown with a published best glide speed.
The question never came up on my multiengine checkride in a Duchess, or my MEI
checkride, ATP checkride, and several Part 135 checkrides in a Seneca II.
Larry L. Fransson - ATP (CE-500), CFMEII
Macon, Georgia
"Pilots are just plane people with a different air about them."
phil cohen
have no published Vbg (i.e. most pipers.)
Is there a formula for determining best glide airspeed as a relationship
to other known V speeds?
phil cohen
phi...@worldnet.att.net
Herbal
>Wondering about how to calculate the best glide airspeed in twins which
>have no published Vbg (i.e. most pipers.)
>
>Is there a formula for determining best glide airspeed as a relationship
>to other known V speeds?
The E-2C's NATOPS manual has a range of airspeed for Vbg, based on
gross weight. Basically, if you're 150KIAS, your'e close enough. Glide
distance is based on a clean aircraft with one engine feathered and the
other one windmilling (to provide hydraulic power). This airspeed
does not relate to other numbers such as max endurance or max range
for powered flight. It's well above power on or power off stall at zero
angle of bank, and it's a good 15 knots above best single engine climb
airspeed. The closest airspeed numbers are those used for PEL
approaches.
So, my guess is that Vbg is based on a certain angle of attack that will
provide the longest glide distance, and is soley based on gross weight
and airframe (wing) configuration (regardless of prop configuration).
FWIW
Herbal
John T. Lowry
There is a fixed relationship between speed for best glide Vbg and speed
for minimum descent rate Vmd -- Vbg = 1.3161*Vmd -- but (since you probably
don't have Vmd) that won't help you much.
Vbg depends on the drag characteristics of the airplane, depending on 1)
W/sigma (W gross weight), 2) reference wing area S, 3)wing aspect ratio A,
4)parasite drag coefficient CD0, and 5) airplane efficiency factor e,
according to
Vbg = sqrt(2*W/sigma*S)*(Pi*e*A*CD0)^-1/4
If you're willing to cut the engines and feather the props, to find Vbg
experimentally, here's a rough outline of the procedure. Go to some nice
high altitude and pick a vertical interval of pressure altitudes, say for
purposes of illustration from 14000 ft down to 13000 ft. Time repeated
glides down through that interval and record the product KCAS*delta_t, where
delta_t is the time needed for the glide. When you've found, by trial and
error, the speed V which maximizes that product, that speed is Vbg.
John
John T. Lowry, PhD
Flight Physics; Box 20919; Billings MT 59104
Voice: 406-248-2606
phil cohen wrote in message <36BD32...@worldnet.att.net>...
>Wondering about how to calculate the best glide airspeed in twins which
>have no published Vbg (i.e. most pipers.)
>
>Is there a formula for determining best glide airspeed as a relationship
>to other known V speeds?
>
>phil cohen
>phi...@worldnet.att.net
Herbal
>If you're willing to cut the engines and feather the props, to find Vbg
>experimentally, here's a rough outline of the procedure. Go to some nice
>high altitude and pick a vertical interval of pressure altitudes, say for
>purposes of illustration from 14000 ft down to 13000 ft. Time repeated
>glides down through that interval and record the product KCAS*delta_t,
where
>delta_t is the time needed for the glide. When you've found, by trial and
>error, the speed V which maximizes that product, that speed is Vbg.
I don't think you need to cut the engines to find the Vbg. If you
consistently use the same power setting and altitudes and just vary
airspeed, I think you can find the Vbg through trial and error. Timing the
descent through 1000 feet doesn't give a Vbg. It does give a max endurance
speed, though. Remember that we're using Vbg to get the airplane to glide
as far as possible, not to remain airborne as long as possible.
I think the key is to find the speed that gives the longest distance you can
glide, and that's why Vbg is important.
phil cohen
> So, my guess is that Vbg is based on a certain angle of attack that will
> provide the longest glide distance, and is soley based on gross weight
> and airframe (wing) configuration (regardless of prop configuration).
You are correct that Vbg is based on AOA, but this is not helpful in an
airplane that has no AOA indicator or any published l/d curves.
phil cohen
phi...@worlndet.att.net
phil cohen
> If you're willing to cut the engines and feather the props, to find Vbg
> experimentally, here's a rough outline of the procedure.
Nope, not willing to do that.
phil cohen
phi...@worldnet.att.net
HLAviation
>(PA 34-200T)
>
I haven been in a Seneca for a while and I might be wrong with this but isn't
it the same as L/D Max? If I recall correctly the POH has an L/D Max chart in
it.
highflyer
>
> Wondering about how to calculate the best glide airspeed in twins which
> have no published Vbg (i.e. most pipers.)
>
> Is there a formula for determining best glide airspeed as a relationship
> to other known V speeds?
>
> phil cohen
> phi...@worldnet.att.net
An excellent approximation that will never get you in trouble is
to merely use the "best single engine rate of climb" speed. It
should be nicely marked on the airspeed indicator as will! :-)
Remember that you should never go slower than that speed in a
Twin until you are starting to roundout for landing with the
threshold made.
HF