Tost reel system

Due to the type of towing we do. My club (Evergreen Soaring) is considering putting the Tost reel system in one of our Pawnee's.

I would like to hear everyone's experience on them pro or con. Not really looking for opinion from someone who hasn't operated with one.

Thanks
Charlie

Charlie:
We used the system for several years on our 2 Pawnees and finally got away from it. I found that it was a useful system for situations of limited operations - particularly where the pilot wants to do a tow and then carry on to a new destination ( like a cross country retrieve) without landing to drop the rope. It also had all of the expected advantages of not landing with a rope hanging behind you. But - we also found a few very significant disadvantages:

1) The system uses an electric motor that is operated by a manual switch. The tow pilot has a mirror that is focused on the tail cone so she or he can shut off the switch when the rope is fully retracted. The system depends on the tow pilot looking in the mirror at exactly the time & place where they need to be looking for traffic, checking cool down, etc. As a tow pilot I did not like that.

2) The system is non compliant with FAR 91.309(a) since it uses only one weak link (the FAR requires 2: one at each end) and there is no way to use a weak link at the towplane end. In a towing accident that could be an issue.

3) The system can't be used in cold weather. If the rope gets wet it freezes on the reel. If you switch over to use the manual Tost release you have to disconnect the guillotine cable and connect it to the Tost release. This is dangerous because if the reel is now used - the guillotine is disconnected. That happened to us twice and we had to tape over the housing to prevent a reoccurrence.

4) It is possible for the reel to get tangled so that the rope stops close to the end - but the glider load is on the reel (and not on the airplane airframe). The reel is not designed to take that load.

5) Tangles are frequent - and a PITA. Checking the portion of the rope that is hidden behind the guillotine is also a PITA. Changing the rope is a PITA.

6) The system is expensive and parts are expensive. We had lots of rope breaks (almost never at the Tost weak link) and that weak link unit is expensive, we lost several tail cones (also expensive) and had a motor burn out (really expensive and a long wait).

7) We had incidents were the tow plane "slack out" process was interrupted and the tow pilot didn't realize that reel was not fully played out. Then when the tow started it whiplashed the glider.

8) A&Ps are not familiar with the system and some were reluctant to work on it.

Bottom line - it's a complex system that makes sense in an operation where cost is not important, the same people are using it, and obstacle clearance is important. But in a busy club or commercial environment a simple rope/release system works better - I was happy to see it go.

Roy B.(GBSC Chief Pilot)

how many of the Tost problems were related to using nonstandard rope?

On Wednesday, April 26, 2017 at 7:57:36 AM UTC-4, wrote:
how many of the Tost problems were related to using nonstandard rope?

Gregg:
None that I am aware of. We used the manufacturer's recommended (and supplied) rope. Doing otherwise voids the warranty.
ROY

On Tuesday, April 25, 2017 at 2:57:59 PM UTC-4, Charles Longley wrote:
Due to the type of towing we do. My club (Evergreen Soaring) is considering putting the Tost reel system in one of our Pawnee's.

I would like to hear everyone's experience on them pro or con. Not really looking for opinion from someone who hasn't operated with one.

Skyline Soaring has used one in its Pawnee for years, and is quite satisfied with it. We operate off a public mixed-use airport with a paved runway, to for us not having to drop/re-attach a poly rope is a bid advantage, as is the efficiency of the hookup and launch.

One other responded mentioned having to watch the cable come in so as to cut off the reel - ours has an automatic shutoff which is triggered by the excess tension on the cable when the glider-end slug hits the receiver. (The only problem we've had there is if the towpilot tries to retract the cable at high speed, where drag on the cable can trigger stopping the reel.)

Cable wear and tear is, of course, dramatically reduced by not dragging it around.

True, sometimes the reel jams, but it's a simple fix. It's also possible to tie a knot in the cable, near the glider end, if the release is made under too much tension, but that's hardly unique to the Tost system.

The standard reel comes with a 50 meter capacity, which I think is pretty common in Europe, but OUR pilots didn't like the "short" cable. So, we opted to purchase a larger capacity reel that can hold ca. 200' of cable. We also purchase the cable in bulk (cheaper) so we can cut it down into pieces. We religiously replace the cable at the Tost-recommended launch limit.

We've also been curious as to why we NEVER break one of the built-in weak links, carefully chosen to be the appropriate ones for the weights of the gliders we tow, while on several occasions we've broken the cable just as it enters the glider-end slug. (I think the cable flexes more at that point, possibly weakening it over time.)

More questions? Ask at jim at kellett dot com and I'll point you to the Club's chief CFI and chief Towpilot and Pawnee maintenance meister for more details . .

We've also been curious as to why we NEVER break one of the built-in weak links, carefully chosen to be the appropriate ones for the weights of the gliders we tow, while on several occasions we've broken the cable just as it enters the glider-end slug. (I think the cable flexes more at that point, possibly weakening it over time.)

Yup - we had exactly the same experience - the rope would break in front of the Tost weak link unit or someplace else (resulting in loss of the weak link). Honestly, I can't remember ever seeing a Tost weak link break as it is supposed to.
ROY

There is another option. A tow reel that addresses the shortcomings of the Tost system while building on its advantages. The Tost system mounts in the fuselage behind the pilot, a slug on the tow line, near the tow plane end, transfers tow line load to the tug's tail fitting. But as mentioned, if there are tangles, it's possible to have the reel mount tear loose and head down the fuselage towards the tail (or so I've heard).

I believe Jim Indrebo (last of Crazy Creek Soaring - now closed and Jim retired) first came up with a tow reel that mounts ahead of the pilot to the tubing supporting the gear cluster and more that capable of handling all towing loads.

Rex Mays, (Williams Soaring Center) improved upon the design as well, but his used a 1/4" polyurethane tubing "belt" to connect motor pulley to spool pulley. The belt tended to slip and belt maintenance was a bit of a pain. This system used a sensor to monitor spool speed to shut down the motor upon retraction when the spool slowed. The rope passed through a guillotine mounted to the floor in front of seat, the handle at the left side of instrument panel. The rope then goes through a conduit to the tail fitting that's mounted to the tail wheel spring forward attach with a pivoting/sliding mount on the spring body further back. Jim/Rex used black plastic (Delrin?) for the tail fitting - this was a wear item due to rope friction. Mine used anodized aluminum for this fitting and was mounted to the tail "stinger" so it could freely rotate to equalize wear.

I made several other "improvements" on the Bumper version, chain drive, much stronger motor (adapted from a surplus robotics motor, this allowed retraction at any tug speed as with the belt drive one had to sometimes slow to pattern speed). In ground testing, the initial reel in was measured at approaching 200 lbs - it would rapidly pull my golf cart (the load), towards the back end of the Pawnee!

Electronics were housed in a modular/swappable plug in box for easy troubleshooting and to allow in-field replacement, hall effect sensor is used to shut off motor at full retraction. A momentary push button retract switch starts the automated retract and if held in, overrides the auto function to serve as an emergency rewind if the push and forget function failed - it didn't.

Pay-out rope "breaking" to prevent overspool tangles, is provides by motor control relay shorting out motor with a 2 ohm power resistor in series - resistor size can be changed to vary pay-out tension.

I built 3 of these the reels for SoaringNV, took at 80 hours each! And as with Rex Mayes, before me, I made a promise to myself that I would not be making any more. We got field approvals for the reels, there is not STC. I believe Soaring NV has the documentation.

The first two I made worked nicely. I goofed on the third, making the spool two inches too wide. Not realizing the impact that a wider spool would have, I proceeded to build it that way when I could have easily corrected the error while still under construction. We found with a wider spool, rope builds up in the center and when this build up collapses off to either side, it introduces slack areas in the rope that can overlap and potentially cause tangles. A narrower spool offers side support to the rope and prevents this.

bumper

On Wednesday, April 26, 2017 at 7:54:44 PM UTC+3, bumper wrote:
There is another option. A tow reel that addresses the shortcomings of the Tost system while building on its advantages. The Tost system mounts in the fuselage behind the pilot, a slug on the tow line, near the tow plane end, transfers tow line load to the tug's tail fitting. But as mentioned, if there are tangles, it's possible to have the reel mount tear loose and head down the fuselage towards the tail (or so I've heard).

I believe Jim Indrebo (last of Crazy Creek Soaring - now closed and Jim retired) first came up with a tow reel that mounts ahead of the pilot to the tubing supporting the gear cluster and more that capable of handling all towing loads.

Rex Mays, (Williams Soaring Center) improved upon the design as well, but his used a 1/4" polyurethane tubing "belt" to connect motor pulley to spool pulley. The belt tended to slip and belt maintenance was a bit of a pain. This system used a sensor to monitor spool speed to shut down the motor upon retraction when the spool slowed. The rope passed through a guillotine mounted to the floor in front of seat, the handle at the left side of instrument panel. The rope then goes through a conduit to the tail fitting that's mounted to the tail wheel spring forward attach with a pivoting/sliding mount on the spring body further back. Jim/Rex used black plastic (Delrin?) for the tail fitting - this was a wear item due to rope friction. Mine used anodized aluminum for this fitting and was mounted to the tail "stinger" so it could freely rotate to equalize wear.

I made several other "improvements" on the Bumper version, chain drive, much stronger motor (adapted from a surplus robotics motor, this allowed retraction at any tug speed as with the belt drive one had to sometimes slow to pattern speed). In ground testing, the initial reel in was measured at approaching 200 lbs - it would rapidly pull my golf cart (the load), towards the back end of the Pawnee!

Electronics were housed in a modular/swappable plug in box for easy troubleshooting and to allow in-field replacement, hall effect sensor is used to shut off motor at full retraction. A momentary push button retract switch starts the automated retract and if held in, overrides the auto function to serve as an emergency rewind if the push and forget function failed - it didn't.

Pay-out rope "breaking" to prevent overspool tangles, is provides by motor control relay shorting out motor with a 2 ohm power resistor in series - resistor size can be changed to vary pay-out tension.

I built 3 of these the reels for SoaringNV, took at 80 hours each! And as with Rex Mayes, before me, I made a promise to myself that I would not be making any more. We got field approvals for the reels, there is not STC. I believe Soaring NV has the documentation.

The first two I made worked nicely. I goofed on the third, making the spool two inches too wide. Not realizing the impact that a wider spool would have, I proceeded to build it that way when I could have easily corrected the error while still under construction. We found with a wider spool, rope builds up in the center and when this build up collapses off to either side, it introduces slack areas in the rope that can overlap and potentially cause tangles. A narrower spool offers side support to the rope and prevents this.

bumper

When was this, and what kind of electronics were used?

When was this, and what kind of electronics were used?

I built the tow reels guessing 5 years ago. I designed the electronics, a very simple circuit.

A single pole double throw power relay to drive the motor when energized, the NC (de-energised) contact put the motor braking resistor across the motor. The power relay was driven by an ELK924 sensitive relay. The input current required for the relay is low enough so that a simple RC time constant circuit, triggered and kept charged by a Hall effect sensor with 4 magnets embedded in the aluminum side of the drum, would keep things energised until rope reeled in. Push button to start, hall effect takes over until end of rope, RC circuit drops out and motor stops.

The sensitive relay was wired using both sides of the relay, one to drive the power relay, and the other to act as a anti-bounce back circuit. The reel slowing would drop the sensitive relay, but if the reel bounced back to align a magnet with the hall effect sensor, motor prevented from being energised again until the retract button again pushed.

All the documentation went to SoaringNV. I may have a schematic with the circuitry somewhere, though not on this computer, sorry.

bumper

El martes, 25 de abril de 2017, 15:57:59 (UTC-3), Charles Longley escribió:
Due to the type of towing we do. My club (Evergreen Soaring) is considering putting the Tost reel system in one of our Pawnee's.

I would like to hear everyone's experience on them pro or con. Not really looking for opinion from someone who hasn't operated with one.

Thanks
Charlie

What does TOST mean?