Pawnee with Tost internal tow rope system

Our club (in the US) is looking at a Pawnee that has the Tost cable retractor winch system and we are curious about it's operation.

For example, it appears that the rope requires a Tost weak link assembly at the glider end, but none at the towplane end. How are US operators setting it up? Tost weak link for glass and a "straw" for Schweizers?

How is the rope deployed on the ground? Does the ground crew just grab the rope end at the tail of the towplane and let the towplane taxi away?

Anyway - any info on club operating procedures with this system would be appreciated.

Cheers,

Kirk
66

At 18:11 06 February 2015, kirk.stant wrote:
Our club (in the US) is looking at a Pawnee that has the Tost cable
retractor winch system and we are curious about it's operation.

For example, it appears that the rope requires a Tost weak link
assembly at
the glider end, but none at the towplane end. How are US
operators setting
it up? Tost weak link for glass and a "straw" for Schweizers?

How is the rope deployed on the ground? Does the ground crew
just grab the
rope end at the tail of the towplane and let the towplane taxi
away?

Anyway - any info on club operating procedures with this system
would be
appreciated.

Cheers,

Kirk
66

Kirk, I have done some towing with the Pawnee and the retractable
TOST set up. We did not use the TOST Weak Link set up on the
glider end, we used rope that met the strength requirement for
weak link. There was a Tost weak link on the Towplane side at the
spool.
2.Rope is coiled up on a spool between pilots feet. When on the
ground, ground crew pull the rope out. The spool free wheels.
Generally you taxi to get the rope out. Tow pilot sees when he is
close to the end of the rope limit by looking at the spool.
3. Air loading goes higher on the rope after tow release. An effort to
not overheat the tost motor during recoil is paramount. The rope
can be recoiled a lot easier when flap extension is made and a
slower decent is conducted. Motors are not cheap to replace. The
recoil switch is a momentary push button switch. Push it and it
drives the motor. Release it and the motor stops. Example. If you
were to retract the rope in the air the motor would reel the rope in.
As soon as you released the button the air loading on the rope
would pull the rope back out freely. Once the rope is fully retracted,
there is generally not enough rope exposed to cause the air to pull
the rope out again.
The TOST set up is really nice and I prefer it but it comes at a
higher cost of maintenance if not following strict SOP's. If you have
numerous different tow pilots the costs go way up. You do save on
rope wear though.

On Friday, February 6, 2015 at 1:12:01 PM UTC-5, kirk.stant wrote:
Our club (in the US) is looking at a Pawnee that has the Tost cable retractor winch system and we are curious about it's operation.

For example, it appears that the rope requires a Tost weak link assembly at the glider end, but none at the towplane end. How are US operators setting it up? Tost weak link for glass and a "straw" for Schweizers?

How is the rope deployed on the ground? Does the ground crew just grab the rope end at the tail of the towplane and let the towplane taxi away?

Anyway - any info on club operating procedures with this system would be appreciated.

Cheers,

Kirk
66

I want to say that Harris Hill uses retractable tow ropes (Cubs & Pawnees), maybe someone there can provide some more insight.

Jim Indrebo (Crazy Creek Soaring) and Rex Mayes (Williams Soaring) have both built tow reels for the Pawnee. I copied some features of their design, and added some features of my own in building three tow reels for SoaringNV.

My reel mounts to the Pawnee tubing just ahead of the pilot. The tow reel uses a #35 chain drive for low maintenance. There are 3 magnets embedded in the reel flange that trigger a hall sensor. This allows a single push of the retract button to retract the full length of rope (pilot does not have to hold button). When the rope fully retracts the reel slows and the hall sensor shuts down the motor (there's a anti-bounce feature that prevents cycling if a magnet should line back up with the sensor).

On reel payout, the line person manually pulls out the rope, connect to glider, and Pawnee taxis forward. The reel motor, is wired to through a resistor to provide a small amount of dynamic braking to the spool so that on taxi forward the reel does not have a tendency to "over spool" (IIRC, resistor is 2 to 4 ohms and is connected across motor leads only when motor is not powered.

Motor is 1/15 hp (from surplus source and designed for robotics I think, cost $20 each) and is sized to allow retraction at any speed up to Pawnee VNE, no need to slow down to retract rope, which on the ground retracts at a rate of about 10 feet per second.

Reel is built "modular" in that electronic box and motor unplugs from reel frame to facilitate swapping out parts.

Note, I have no interest in making more reels!

bumper

On Saturday, February 7, 2015 at 9:07:03 PM UTC+13, bumper wrote:
Jim Indrebo (Crazy Creek Soaring) and Rex Mayes (Williams Soaring) have both built tow reels for the Pawnee. I copied some features of their design, and added some features of my own in building three tow reels for SoaringNV.

My reel mounts to the Pawnee tubing just ahead of the pilot. The tow reel uses a #35 chain drive for low maintenance. There are 3 magnets embedded in the reel flange that trigger a hall sensor. This allows a single push of the retract button to retract the full length of rope (pilot does not have to hold button). When the rope fully retracts the reel slows and the hall sensor shuts down the motor (there's a anti-bounce feature that prevents cycling if a magnet should line back up with the sensor).

On reel payout, the line person manually pulls out the rope, connect to glider, and Pawnee taxis forward. The reel motor, is wired to through a resistor to provide a small amount of dynamic braking to the spool so that on taxi forward the reel does not have a tendency to "over spool" (IIRC, resistor is 2 to 4 ohms and is connected across motor leads only when motor is not powered.

Motor is 1/15 hp (from surplus source and designed for robotics I think, cost $20 each) and is sized to allow retraction at any speed up to Pawnee VNE, no need to slow down to retract rope, which on the ground retracts at a rate of about 10 feet per second.

Reel is built "modular" in that electronic box and motor unplugs from reel frame to facilitate swapping out parts.

Note, I have no interest in making more reels!

bumper

So is there no facility to release the rope at the tow plane end?

On Friday, February 6, 2015 at 1:12:01 PM UTC-5, kirk.stant wrote:
Our club (in the US) is looking at a Pawnee that has the Tost cable retractor winch system and we are curious about it's operation.


Skyline Soaring has been using an internal Tost reel in its Pawnee for years. (Full disclosu I am NOT a towpilot, but a CFI(G)) It is fitted BEHIND the pilot. We DO use the factory supplied weak link/slug at the glider end, and depend on the guillotine on the towplane in lieu of a weak link there. The weak link is selected to serve all our Tost-equipped gliders, for the Schweizers we use a poly add-on (about 3' long).

There are many appropriate procedures, but we chose to pull out about 30' of cable and hook up the glider and then with the glider wheelbrake set unreel the cable by the towplane taxiing out. (The towpilot not only watches the wingrunner for signals, but can actually hear/feel when the retainer ball on the cable inside the fuselage rattles down the tubing and lodges in the receiver.)

Retracting is done on descent, which should not be too fast or the wind drag will trigger the tension-based cutoff switch on the reel (when it's fully retracted, that tension switch cuts off the motor.

The cables should be replaced after 1,000 launches; we run through about that many every year. It's not cheap, so we buy it in 300 meter rolls and cut it up ourselves.

The Tost cable is not spliceable, like poly, but we've not had problems with breaks. We DO get occasional breaks right at the glider end (curiously we've NEVER popped the weak link!), but just cut off the frayed end and re-attach the slug, shortening the cable by 5' each time.

Also, OUR club members didn't like the short cable length that comes standard with the reel, so we opted for an oversize reel so we could use ca. 200' of cable.

We find that it REALLY speeds up launch operations and eliminates the challenge of making high approaches (so as to not snag a powerline just off the threshold) and then finding the dropped cable in the grass.

Now . .. if we could just get the same system installed in our Husky . . .

So is there no facility to release the rope at the tow plane end?

Bruce - as far as I can remember, the original Tost set-up had a guillotine built in, which allowed the tow pilot to 'release' the line from his end, if needed.

Uli

On Saturday, February 7, 2015 at 4:02:36 AM UTC-8, Bruce Hoult wrote:
So is there no facility to release the rope at the tow plane end?

The Crazy Creek and Williams Soaring setups have guillotines aft of the drums.

At 16:49 07 February 2015, GM wrote:
So is there no facility to release the rope at the tow plane end?

Bruce - as far as I can remember, the original Tost set-up had a
guillotine
built in, which allowed the tow pilot to 'release' the line from his end,
if needed.

Uli

Uli is correct. there is a guillotine at the end of the towplane. Doug

I've towed with the TOST reel on the Skyline Soaring Club's Pawnee, the Rex Mayes reel on a tow plane I bought when SoaringNV opened, and Bumper's proprietary reel on another SoaringNV tow plane. All had guillotines: I never used that feature. I liked having the spool between my feet so I could see it spooling out and would be reminded to reel it in after glider release.

The best reel was Bumper's, but as he says, he has zero interest in building more. I don't blame him: he spent a whole lot of time on the installations he made for SoaringNV as he trouble-shooted (?) little features of the design.

One thing to remember about reel systems with guillotines is that if you use the guillotine you lose the rope and the weak link. At least with a hook on the tow plane tail you can drop the line and hope the glider pilot is sharp enough to remember to bring it back to the field so you can re-use it.

I liked using a reel mainly so I didn't have to approach high over fences, power lines, trees, etc. This is particularly important if you have a short towplane runway.

One thing to keep in mind with a reel is that if you break a rope, have it jump off the reel as it is reeling in, or have to guillotine it, you are probably out of service for about 30 minutes, maybe more. With a tail hook you just clip another rope on and start up again.