4-blade Pawnee Performance?

Can anyone out there with experience behind both 2-bladed and 4-bladed
Pawnees give me an idea of what the performance losses are?

My club has debated this off and on, but I was recently at a field
with a 4-bladed Pawnee and was much impressed with the lower noise.

Problem is, I've got club members claiming that it'll cost over $10k
to do the job, and we'd give up 25% to 30% in performance due to the
extra blades.

Can anyone corroborate those numbers?

Thanks, take care,

--Noel

On Nov 19, 3:59*pm, "noel.wade" wrote:
Can anyone out there with experience behind both 2-bladed and 4-bladed
There are several Pawnees with 4-blade props and a few with 2-blade
props in Colorado. Yes, it will cost you $10k and be somewhat quieter
overhead and much quieter on approach, taxi and takeoff. The main
effect seems to be 4-blade props shifts the prop noise to a higher
pitch which is somehow less annoying.

As for performance, I've towed behind most of them and I'd estimate
that there is a small gain in initial acceleration followed by a small
loss in rate of climb - somewhere around 5% each way.

Mile High Gliding, the dealer for the Hoffmann 4-blade, uses them on
their 230HP Pawnees to tow over gross 2-32's from a 2200' runway with
a density altitude sometimes over 10,000'. Many of these tows go to
10,500 for their "Mile High Glider Ride". There's no way this would
work if there were a 25% performance loss.

Pawnees give me an idea of what the performance losses are?

My club has debated this off and on, but I was recently at a field
with a 4-bladed Pawnee and was much impressed with the lower noise.

Problem is, I've got club members claiming that it'll cost over $10k
to do the job, and we'd give up 25% to 30% in performance due to the
extra blades.

Can anyone corroborate those numbers?

Thanks, take care,

--Noel

On Nov 19, 5:59*pm, "noel.wade" wrote:

Can anyone corroborate those numbers?

Numbers? No...

A four blade Pawnee going low overhead at full power is still very
loud. The prop does nothing for the engine noise and the Pawnee has
quite a lot of that. What it eliminates is the 'snarl' from high
speed prop tips that is most noticeable to an observer in the plane of
the prop. If 'snarl' is your problem, maybe this is your solution.

The performance loss is noticeable and annoying, but not a deal
breaker in itself.

Clubs I know who've bought them have not been real impressed. For the
price, I'd like to be impressed. Ymmv.

-T8

On Nov 20, 9:09*am, wrote:
On Nov 19, 5:59*pm, "noel.wade" wrote:

Can anyone corroborate those numbers?

Numbers? *No...

A four blade Pawnee going low overhead at full power is still very
loud. *The prop does nothing for the engine noise and the Pawnee has
quite a lot of that. *What it eliminates is the 'snarl' from high
speed prop tips that is most noticeable to an observer in the plane of
the prop. If 'snarl' is your problem, maybe this is your solution.

The performance loss is noticeable and annoying, but not a deal
breaker in itself.

Clubs I know who've bought them have not been real impressed. *For the
price, I'd like to be impressed. *Ymmv.

-T8

It's interesting to do some highly oversimplified "back of the
envelope" numbers on Pawnee tugs. (The following ignores some
important stuff.)

Assume a 40:1 glider weighing 1000 pounds being towed at its best L/D
airspeed of 60KTS and climbing at 500FPM. 1000/40 = 25 pounds of
aerodynamic drag. 60x25/325 = 4.6HP to overcome that drag.

Of course the tug is lifting the glider at 500FPM or 8.33 FPS so
8.33x1000/550 = 15.14HP to lift the weight of the glider.

15.14+4.6 = 19.74HP which is the rate at which work being done on the
glider by the Pawnee. In other words, only approximately 20HP is used
to tow the glider.

If the tug engine is actually producing 230HP (highly doubtful), 210HP
is being wasted somewhere - most of which is probably just the Pawnee
hauling itself through the air. That wasted energy is where most of
the noise is coming from.

The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.

The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.

A tug like this: http://www.sportaircraftworks.com/ot...dynamicnew.htm
According to John Roake, turnaround on a 600m launch with this plane
averaged 4-5 minutes (takeoff to landing) and it only took 100 Euros
worth of fuel for 8 of these planes to launch a field of 60 gliders
(no other stats provided unfortunately). With efficiency like that I
bet these planes don't make a lot of noise though...

-Paul

On Nov 20, 8:51*am, bildan wrote:
On Nov 20, 9:09*am, wrote:



On Nov 19, 5:59*pm, "noel.wade" wrote:

Can anyone corroborate those numbers?

Numbers? *No...

A four blade Pawnee going low overhead at full power is still very
loud. *The prop does nothing for the engine noise and the Pawnee has
quite a lot of that. *What it eliminates is the 'snarl' from high
speed prop tips that is most noticeable to an observer in the plane of
the prop. If 'snarl' is your problem, maybe this is your solution.

The performance loss is noticeable and annoying, but not a deal
breaker in itself.

Clubs I know who've bought them have not been real impressed. *For the
price, I'd like to be impressed. *Ymmv.

-T8

It's interesting to do some highly oversimplified "back of the
envelope" numbers on Pawnee tugs. *(The following ignores some
important stuff.)

Assume a 40:1 glider weighing 1000 pounds being towed at its best L/D
airspeed of 60KTS and climbing at 500FPM. *1000/40 = 25 pounds of
aerodynamic drag. *60x25/325 = 4.6HP to overcome that drag.

Of course the tug is lifting the glider at 500FPM or 8.33 FPS so
8.33x1000/550 = 15.14HP to lift the weight of the glider.

15.14+4.6 = 19.74HP which is the rate at which work being done on the
glider by the Pawnee. *In other words, only approximately 20HP is used
to tow the glider.

If the tug engine is actually producing 230HP (highly doubtful), 210HP
is being wasted somewhere - most of which is probably just the Pawnee
hauling itself through the air. *That wasted energy is where most of
the noise is coming from.

The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.

Or lets guess around 30 hp assuming prop (in)efficiency, ~80% best
case?, but who knows in practice. And the wasted energy is where *all*
the noise comes from :-) And as a data point, the ~50 shp engine in my
ASH-26E give up to 700 fpm climb... on a good day.

A more efficient tug could reduce the amount of prop thrust needed and
therefore noise that needs to be made in the first place. If prop
noise is a significant factor, which it seems to be, adding blades
definitely seems to help.

BTW I agree with your earlier post about the apparent differences in
towing behind a Pawnee with a Hoffman 4 bladed prop. Soar Truckee
switched to a four bladed prop and did some good community PR work
around reducing noise, including a positive article in the local
newspaper. See -

www.soartruckee.com/pdfs/Pickle_part_1_0612.pdf and
www.soartruckee.com/pdfs/Pickle_part_2_0612.pdf

The rate of climb with a heavy glider (e.g. DG-1000S with two
occupants) at ~7k'+ density altitude seemed a little lower than a two
bladed prop, but that's not a scientific comparison. Mile High may be
able to provide data on that as well. Hopefully a tow pilot with
experience with these will weigh in.

Darryl

sisu1a wrote:
The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.

A tug like this: http://www.sportaircraftworks.com/ot...dynamicnew.htm
According to John Roake, turnaround on a 600m launch with this plane
averaged 4-5 minutes (takeoff to landing) and it only took 100 Euros
worth of fuel for 8 of these planes to launch a field of 60 gliders
(no other stats provided unfortunately). With efficiency like that I
bet these planes don't make a lot of noise though...

-Paul

The European "ultralight" tugs do a fine job. The Dynamic is really
quiet, fast, economical and tows well. The difference in towing behind
something like a Dynamic or Samba versus one of the heavier aircraft is
substantial. With the modern ultralight being a much better match to the
glider.

On Nov 20, 12:12*pm, Bruce wrote:
sisu1a wrote:
The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.

A tug like this:http://www.sportaircraftworks.com/ot...dynamicnew.htm
According to John Roake, turnaround on a 600m launch with this plane
averaged 4-5 minutes (takeoff to landing) and it only took 100 Euros
worth of fuel for 8 of these planes to launch a field of 60 gliders
(no other stats provided unfortunately). With efficiency like that I
bet these planes don't make a lot of noise though...

-Paul

The European "ultralight" tugs do a fine job. The Dynamic is really
quiet, fast, economical and tows well. The difference in towing behind
something like a Dynamic or Samba versus one of the heavier aircraft is
substantial. With the modern ultralight being a much better match to the
glider.

Someone said that the typical airplane engine is an excellent
transducer that converts money into heat and noise with a small,
although useful, amount of thrust as a side effect.

bildan wrote:
On Nov 20, 12:12 pm, Bruce wrote:
sisu1a wrote:
The above suggests that a tug with a highly aerodynamic airframe could
use far less HP which is why 80HP motorglider tugs seem to work so
quietly.
A tug like this:http://www.sportaircraftworks.com/ot...dynamicnew.htm
According to John Roake, turnaround on a 600m launch with this plane
averaged 4-5 minutes (takeoff to landing) and it only took 100 Euros
worth of fuel for 8 of these planes to launch a field of 60 gliders
(no other stats provided unfortunately). With efficiency like that I
bet these planes don't make a lot of noise though...
-Paul
The European "ultralight" tugs do a fine job. The Dynamic is really
quiet, fast, economical and tows well. The difference in towing behind
something like a Dynamic or Samba versus one of the heavier aircraft is
substantial. With the modern ultralight being a much better match to the
glider.

Someone said that the typical airplane engine is an excellent
transducer that converts money into heat and noise with a small,
although useful, amount of thrust as a side effect.
Indeed, consider the Wilga...

Something like a Samba or Dynamic tows smooth and at half or less of the
cost of the fossil fuel converters I am a fan. Last contest I had a
quicker ride to release behind a Rotax914 equipped Samba XL than the
preceeding run behind a Cessna 182.

The Cessna tow cost twice as much though.

No answer on your questions . . . however, I do know there was at least one
incidence of the 4-blade prop making like a Frisbee. One minute it was
dragging the Pawnee through the air, the next it was on it's own and
accelerating away from the plane.

Guess it's important to re-torque the prop bolts?

bumper

"noel.wade" wrote in message
...
Can anyone out there with experience behind both 2-bladed and 4-bladed
Pawnees give me an idea of what the performance losses are?

My club has debated this off and on, but I was recently at a field
with a 4-bladed Pawnee and was much impressed with the lower noise.

Problem is, I've got club members claiming that it'll cost over $10k
to do the job, and we'd give up 25% to 30% in performance due to the
extra blades.

Can anyone corroborate those numbers?

Thanks, take care,

--Noel