Boxing the wake cracks Pawnee tail tubings or long term fatigue?

[mt]

Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.

As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues.. FYI, our Pawnee has been hangared at least in the past 20 years!

What are your experiences:
1- with Pawnee tail fatigues
2- cause of repeated cracks, method of usage
3- methods of fixing them better next time
4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
Many Thanks,
C1

[[email protected]]

On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>
> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>
> What are your experiences:
> 1- with Pawnee tail fatigues
> 2- cause of repeated cracks, method of usage
> 3- methods of fixing them better next time
> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> Many Thanks,
> C1

Boxing the wake is essential to learning how properly control a glider on tow. I box the wake on virtually every tow, just to keep my skills sharp. If your tow plane can't handle this stress, it needs some structural reinforcement.

[[email protected]]

> Boxing the wake is essential to learning how properly control a glider on tow. I box the wake on virtually every tow, just to keep my skills sharp. If your tow plane can't handle this stress, it needs some structural reinforcement.

Boxing the wake might teach essential skills but if it's doing damage to a tow plane, why on earth should we continue the practice. Develop other training methods to teach that skill set. It's similar to the requirement in the Powered Aircraft training which requires a commercial pilot applicant to perform a "Lazy Eight". I'm a CFI and I can tell you that a lot of money is wasted teaching that maneuver for the commercial check ride. I'd bet that darn few of those commercial students can perform that maneuver 6 months after the check-ride. It's nothing more than a CFI meal ticket.

[[email protected]]

Do you know the history of your Pawnee? Was it ever used for aerial application of agricultural chemicals? I am told many of them are hygroscopic (attract water) and so contribute heavily to rusting of the tubular frame members. Of course if yours was built and used exclusively for banner towing, that is not the problem. But do check to see what its history was.

[Piet Barber]

On Wednesday, January 14, 2015 at 11:16:25 AM UTC-5, wrote:
> Boxing the wake might teach essential skills but if it's doing damage to a tow plane, why on
> earth should we continue the practice. Develop other training methods to teach that skill set.

Students ask me "Why do we practice the box the wake maneuver?"
It takes all of my effort as an instructor to suppress the smart-alec answer:
"Because the FAA requires us to."
Which inevitably leads to the next question of: "Why does the FAA require us to?"
"Because the FAA requires us to."

Does it hone the skill of precise flying while on tow? Yes.
Does it teach people how to move around behind the tow plane? Yes.
Does it teach people "how much" they can get away with w.r.t. positioning behind the towplane? Yes.

When I went to Switzerland, I found that boxing the wake is not a required item for their flight instruction. It was more done as a demonstration to understand the limits of how far a glider can get out of position.

They also didn't practice forward slips on final to lose altitude. They saw this practice as out-of-touch for use with modern gliders. "Sure it's a useful skill... if you're flying old museum pieces like you do in the United States!" I think that might be a jab against Schweizers.

How many other countries, besides the US, require the box-the-wake maneuver?

[[email protected]]

Piet, I don't know where you got your information, but forward slip and also boxing the wake (called "extreme Schleppfluglagen") are both required maneuvers in glider training in Switzerland.

[Andrew[_14_]]

On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>
> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>
> What are your experiences:
> 1- with Pawnee tail fatigues
> 2- cause of repeated cracks, method of usage
> 3- methods of fixing them better next time
> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> Many Thanks,
> C1

Thanks for sharing this info. I imagine these cracks are present on many other Pawnee glider tugs without the knowledge of the operators...

I'm a little confused about the location of one of the cracks. For the crack that's between the bottom and middle rudder hinges, is the crack next to the bottom hinge weld or directly in the middle of the tube between the two hinges? Note, I'm assuming it's in the vertical stab tube that the hinges attach to, correct me if I'm wrong...

Also, is the crack opening facing aft, port, starboard, etc?

How did you guys discover the crack? I'm hoping it's easy to spot even with the covering on.

Where are some of the other cracks too? I'm getting at the ones not near the rudder hinges.

We don't have these cracks as far as we know. Although, we've seen failure in tailwheel bolts. One of them being the bolt that goes through the leaf spring. Another was nearer to where the leaf spring attaches to the fuselage. I'm having a hard time picturing the exact bolts at the moment...

P.S. I think it's unlikely that loads on the tow hook are contributing to the crack considering how the hook attaches to the fuselage and how small tow loads are when compared to other loads, like you've mentioned. Unless the wake boxing is done very aggressively... Worst case scenario is maxing out the weak link to 2500lb with a 30deg rope angle causes a 1250lb side load at the hook which should not happen during normal boxing... Most of that is quickly absorbed by rotational inertia and the sideslip angle quickly reducing from that maximum value. For a more reasonable steady state case of a 15/1 L/D and 1250lb glider banking 15deg and a 20deg rope angle would give about 354lbs.
1250/15*tan(20deg) +1250*sin(15deg)

[Dan Marotta]

Aggressive or sloppy? Some students are barely noticeable when boxing
the wake while others yank the tail around so hard they exceed the tug's
rudder (and elevator) authority. Of course, they're the same ones who
swing high and wide on every turn. What CFIs need to teach is that
minor corrections will get the glider into position much more quickly
than using large control inputs.


On 1/14/2015 10:15 AM, Andrew wrote:
> On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
>> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>>
>> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>>
>> What are your experiences:
>> 1- with Pawnee tail fatigues
>> 2- cause of repeated cracks, method of usage
>> 3- methods of fixing them better next time
>> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
>> Many Thanks,
>> C1
> Thanks for sharing this info. I imagine these cracks are present on many other Pawnee glider tugs without the knowledge of the operators...
>
> I'm a little confused about the location of one of the cracks. For the crack that's between the bottom and middle rudder hinges, is the crack next to the bottom hinge weld or directly in the middle of the tube between the two hinges? Note, I'm assuming it's in the vertical stab tube that the hinges attach to, correct me if I'm wrong...
>
> Also, is the crack opening facing aft, port, starboard, etc?
>
> How did you guys discover the crack? I'm hoping it's easy to spot even with the covering on.
>
> Where are some of the other cracks too? I'm getting at the ones not near the rudder hinges.
>
> We don't have these cracks as far as we know. Although, we've seen failure in tailwheel bolts. One of them being the bolt that goes through the leaf spring. Another was nearer to where the leaf spring attaches to the fuselage. I'm having a hard time picturing the exact bolts at the moment...
>
> P.S. I think it's unlikely that loads on the tow hook are contributing to the crack considering how the hook attaches to the fuselage and how small tow loads are when compared to other loads, like you've mentioned. Unless the wake boxing is done very aggressively... Worst case scenario is maxing out the weak link to 2500lb with a 30deg rope angle causes a 1250lb side load at the hook which should not happen during normal boxing... Most of that is quickly absorbed by rotational inertia and the sideslip angle quickly reducing from that maximum value. For a more reasonable steady state case of a 15/1 L/D and 1250lb glider banking 15deg and a 20deg rope angle would give about 354lbs.
> 1250/15*tan(20deg) +1250*sin(15deg)

--
Dan Marotta

[[email protected]]

On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>
> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>
> What are your experiences:
> 1- with Pawnee tail fatigues
> 2- cause of repeated cracks, method of usage
> 3- methods of fixing them better next time
> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> Many Thanks,
> C1

I highly doubt that boxing the wake has anything to do with the problem you are describing. The rope loads are not that high as to cause additional load.
I'm not sure why one would ever bang the rudder hard against the stops. Seems like a poor technique.
The most likely cause, in my experience would be the beating the structure takes doing 7-8 landings an hour.
Rather than repair, it may pay to replace the rudder post with new.
Boxing the wake is a useful training exercise and should not be reduced or eliminated because of a tail post issue.
42 years instructor and tow pilot.
UH

[Piet Barber]

On Wednesday, January 14, 2015 at 12:03:10 PM UTC-5, wrote:
> Piet, I don't know where you got your information, but forward slip and also boxing the wake (called "extreme Schleppfluglagen") are both required maneuvers in glider training in Switzerland.

Granted, I wasn't going for a rating there, so I didn't go through the whole training program. Maybe the instructor was just de-emphasizing the concepts.

[Bill D]

On Wednesday, January 14, 2015 at 9:16:25 AM UTC-7, wrote:

> Boxing the wake might teach essential skills but if it's doing damage to a tow plane, why on earth should we continue the practice.

Because it teaches ESSENTIAL skills.

[Bill D]

On Wednesday, January 14, 2015 at 10:15:02 AM UTC-7, Andrew wrote:

> Thanks for sharing this info. I imagine these cracks are present on many other Pawnee glider tugs without the knowledge of the operators...

No doubt. These are VERY old airplanes and maintenance requirements tend to rise exponentially with age. All steel tube airframes suffer rust, corrosion and fatigue with the lowest areas suffering most. If your AI doesn't know to check this, get another AI.

I once saw an old Piper (PA-20, I IIRC) siting in the weeds with its nose pointing higher than it should. It appeared the tubes forward of the tail wheel had failed from the weight of the parked airplane.

[Charlie M. (UH & 002 owner/pilot)]

On Wednesday, January 14, 2015 at 12:36:01 PM UTC-5, wrote:
> On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
> > Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
> >
> > As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
> >
> > What are your experiences:
> > 1- with Pawnee tail fatigues
> > 2- cause of repeated cracks, method of usage
> > 3- methods of fixing them better next time
> > 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> > Many Thanks,
> > C1
>
> I highly doubt that boxing the wake has anything to do with the problem you are describing. The rope loads are not that high as to cause additional load.
> I'm not sure why one would ever bang the rudder hard against the stops. Seems like a poor technique.
> The most likely cause, in my experience would be the beating the structure takes doing 7-8 landings an hour.
> Rather than repair, it may pay to replace the rudder post with new.
> Boxing the wake is a useful training exercise and should not be reduced or eliminated because of a tail post issue.
> 42 years instructor and tow pilot.
> UH

I agree, I can't see very high loads from "boxing the wake" as you will turn the towplane 1st.
I CAN see the abuse from the tail hitting the ground (on landing), rough surface banging the tailwheel, tight "lock" on the tailwheel putting bending/twisting loads when turning on the ground, etc.

As to whether or not to teach "boxing the wake", I also think it's worthwhile to do. Better in "training" than "learn as you go" if you get out of position.

[[email protected]]

On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>
> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>
> What are your experiences:
> 1- with Pawnee tail fatigues
> 2- cause of repeated cracks, method of usage
> 3- methods of fixing them better next time
> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> Many Thanks,
> C1

After my first reply and thinking more:
It seems that the problem is a bit beyond the end of the fin where it plugs into the tail post. If the brace wires are not doing their job(tension set correctly), the tail post could be seeing a lot of bending it was never intended to see.
Certainly another thing to look at.
UH

[John Ferguson[_2_]]

There are a number of ADs for the Pawnee, one specifically for corrosion
issues in the rear fuselage structure. You might just be seeing these
problems coming to light.

[bumper[_4_]]

On Wednesday, January 14, 2015 at 1:45:04 PM UTC-8, John Ferguson wrote:
> There are a number of ADs for the Pawnee, one specifically for corrosion
> issues in the rear fuselage structure. You might just be seeing these
> problems coming to light.

Adding to what Fred said re corrosive and hygroscopic chemicals in their former life, many Pawnees live outside where they are often subject to large temperature and humidity changes. Any condensation within the tubing runs downhill. The tail post cluster is a likely first victim.

The horizontal stab spars have an AD too.

[Bill T]

It's hard to believe that boxing the wake and slack line recoveries damaged the Pawnee. I fly both ends of the rope, tow and CFIG. The tubes holding the Schweizer hook and bolts would show damage before the lower tube weld cracks. I'd suspect hard tailwheel first landings on pavement, or pilots that land short in gravel and roll up onto a paved runway "over a lip" would cause more damage and flat tail wheels.

Our Pawnee saw crop duster service for 20+ yrs before converting to glider tow. The records show the entire lower fuselage frame has been rebuilt from corrosion over the years. It has been in a dry climate for the last 15 yrs..

Why do we box the wake? Why do we teach our teenage drivers how to parralle park. Because it shows you know where the corners of the car are and that you can "put it where you want it". Same with boxing the wake, same with boom limits when air refueling, you know where the limits are, you can control your aircraft throughout the entire envelope.

BillT

[Bob Pasker]

teach them to hold the stick 6-8" below the top, and explain to them what "milking the mouse" means

On Wednesday, January 14, 2015 at 12:32:47 PM UTC-5, Dan Marotta wrote:
> Aggressive or sloppy?* Some students are barely noticeable when
> boxing the wake while others yank the tail around so hard they
> exceed the tug's rudder (and elevator) authority.* Of course,
> they're the same ones who swing high and wide on every turn.* What
> CFIs need to teach is that minor corrections will get the glider
> into position much more quickly than using large control inputs.
>
>
>
>
>
>
> On 1/14/2015 10:15 AM, Andrew wrote:
>
>
>
> On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
>
>
> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>
> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>
> What are your experiences:
> 1- with Pawnee tail fatigues
> 2- cause of repeated cracks, method of usage
> 3- methods of fixing them better next time
> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> Many Thanks,
> C1
>
>
> Thanks for sharing this info. I imagine these cracks are present on many other Pawnee glider tugs without the knowledge of the operators...
>
> I'm a little confused about the location of one of the cracks. For the crack that's between the bottom and middle rudder hinges, is the crack next to the bottom hinge weld or directly in the middle of the tube between the two hinges? Note, I'm assuming it's in the vertical stab tube that the hinges attach to, correct me if I'm wrong...
>
> Also, is the crack opening facing aft, port, starboard, etc?
>
> How did you guys discover the crack? I'm hoping it's easy to spot even with the covering on.
>
> Where are some of the other cracks too? I'm getting at the ones not near the rudder hinges.
>
> We don't have these cracks as far as we know. Although, we've seen failure in tailwheel bolts. One of them being the bolt that goes through the leaf spring. Another was nearer to where the leaf spring attaches to the fuselage. I'm having a hard time picturing the exact bolts at the moment...
>
> P.S. I think it's unlikely that loads on the tow hook are contributing to the crack considering how the hook attaches to the fuselage and how small tow loads are when compared to other loads, like you've mentioned. Unless the wake boxing is done very aggressively... Worst case scenario is maxing out the weak link to 2500lb with a 30deg rope angle causes a 1250lb side load at the hook which should not happen during normal boxing... Most of that is quickly absorbed by rotational inertia and the sideslip angle quickly reducing from that maximum value. For a more reasonable steady state case of a 15/1 L/D and 1250lb glider banking 15deg and a 20deg rope angle would give about 354lbs.
> 1250/15*tan(20deg) +1250*sin(15deg)
>
>
>
>
>
> --
>
> Dan Marotta

[[email protected]]

Corrosion. Boxing the wake is not the problem. The energy is not transferred in that way to crack them.

[[email protected]]

Boxing the wake causing cracking of frame structure in a Pawnee is just nuts. The impact of the tailwheel on the pavement during landings has to be much more significant.
So...we are to illiminate a basic flight competency, boxing the wake, because the tow planes are so underengineered that they are getting ruined by the soft lateral loads imposed by boxing the wake?
Why not. Spins are obviously dangerous and very stressful on the airframe so we have to elliminate them.
Loops involve 3.5-4 Gs which is obviously a great stress on an airframe so those must be illegal.
My G meter has registered 5 Gs from flying through rough air so flying through rough air must be made illegal.
My G meter has registered 10 Gs from trailering so trailering a glider is obviously stressful to an airframe so that must be made illegal.
How do we survive?

[2G]

On Wednesday, January 14, 2015 at 7:35:43 AM UTC-7, mt wrote:
> Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
>
> As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
>
> What are your experiences:
> 1- with Pawnee tail fatigues
> 2- cause of repeated cracks, method of usage
> 3- methods of fixing them better next time
> 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> Many Thanks,
> C1

Metal fatigue is caused by the REPEATED application and release of stress. All stress is not the same, so certain types of stress will result in faster fatigue than other kinds. I think it is relevant to note that Pawnees were never designed to be towplanes, so their structure wasn't engineered for that type of duty. To blame one particular task as the cause is pretty much a fool's errand barring a detailed engineering structural analysis. Even putting in a poorly analyzed "fix" to strengthen the structure might just make matters worse by increasing loads somewhere else. Just repair the damage and move on.

Tom

[[email protected]]

Ueli,

slipping is not part of the instruction syllabus in Switzerland, except for FCL aerobatics.
However, it is still a very useful skill and could have saved the odd DuoDiscus during outlandings.

[Ian Strachan]

On Wednesday, 14 January 2015 15:58:40 UTC, wrote:
> On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
> > Our 235 hp Pawnee has again some cracks in the tail tubing. One of them is on the bottom of the vertical member where rudder hinges are welded. The crack is between the lowest and the middle hinges.
> >
> > As a glider instructor and tow pilot (over 35 years) I don't see why we should keep "boxing the wake", as part of glider pilot training. Having said that, contrary to some opinions in my club, I don't believe aggressive boxing the wake is the only contributing factor in our costly maintenance issues. FYI, our Pawnee has been hangared at least in the past 20 years!
> >
> > What are your experiences:
> > 1- with Pawnee tail fatigues
> > 2- cause of repeated cracks, method of usage
> > 3- methods of fixing them better next time
> > 4- what contributtes to more stress on the tail tubing: hitting rudder stops in everyday operations, boxing the wake, hard landings, or rope breaks (weak link about 1250 lb).
> > Many Thanks,
> > C1
>
> Boxing the wake is essential to
> learning how properly control a glider on tow.
> I box the wake on virtually every tow, just to keep my skills sharp.

Reply from Ian Strachan, UK glider and power pilot.

I was a glider and power (civil and military) instructor for 40 years, now retired from instructing but still flying gliders and tow planes at Lasham in the UK. In my gliding career I was Chief Instructor at two UK clubs and in the military instructed on single, twin and four engined types.

When I started instructing in the 1960s there was no such thing as "boxing the wake". Before sending someone solo on aerotowing you ensured that the guy could get back to the central tow position from being out of position left and right, up and down.

This was done by the instructor flying gradually and smoothly to the out-of-position position and handing over to the student to recover to the "central" tow position. The emphasis was on smooth, gradual and safe use of the controls, not rough and unneccessary control applications. The dangers of overcontrol leading to overshooting the central two position and the risk of oscillation were discussed and demonstrated. In the UK the standard tow position is "high tow" above the wake and part of pre-solo instruction was to show the wake and make sure that the pupil could get back into high tow position from a wake encounter. We did not deliberately teach the "low tow" position itself, at least until a guy had already been solo on aero tow.

When the fashion started for so-called "boxing the wake", I was horrified because many instructors took it as a licence to be rough with the controls and IMHO took it too far. As a tug pilot I looked at what was happening behind me as a demonstration of poor airmanship and probably off-putting to many pupils. A long-term instructor often forgets that some pupils are quite nervous. Pilots who have been instructors for many years need to be reminded of the basic principles such as gradual and sympathetic demonstration and then student practice of the various skills, without taking things too far because the instructor has lost the ability to put him/herself in the place of the student.

When instructing, I refused to Box the Wake but continued as I had done before. I don't think my aero tow students had any problem when they went solo on tow.

Clearly C1's claim that boxing is "essential", is not right. Unless you regard what I describe above as "gentle boxing".

I guess it all turns on what you mean by "boxing".

The problem was that once it started, there was far to much "aggressive boxing" by instructors who maybe were trying to show how clever they were (and annoying tow pilots like me) and had IMHO fogotten one of the basic tenets of instruction which is "not to do the advanced course before the basic", or not to demonstrate running before the pupil can walk, if you see what I mean. I have seen instructors take it too far, for instance breaking the rope/weak link or even arriving just off the tug wing tip with a huge loop in the rope.

I would hope that we could agree that "aggressive boxing" during pre-solo aero tow instruction is unneccessary.

IMHO it is a poor instructional technique which is not necessary before safely sending a student solo on tow. Even on post-solo check rides, I see no need for it and suggest that a less "agricultural" approach should be used.. An aero tow is not an aerobatic and controls should be used gradually, not over-used when it is not necessary.

Ian Strachan
Lasham Gliding Centre, UK

[[email protected]]

I have been instructing gliders for about 27 years, and for me the boying the wake excercise is essential during pre-solo training.
Part of it is to show the student the limits of possible positioning behind the tug (and on the lateral positions of the box, the tug pilot will have to use quite some rudder to keep going straight), and especially to show the point beyond which immediate release is mandatory on high positions.
Low position (well below the wake) is something the student needs to learn for descent and approach on tow anyways.

Having said that, there is no aggressive maneuvring involved at all, with me talking the students through the excercise. Changing positions is done gradually all the way through the excercise, with constant tension on the rope.

It usually is an excercise which is flown once with the student, and at some point when he is at a level where I don't have to interfere anymore on a normal tow.

Bert TW

[Don Johnstone[_4_]]

At 09:43 21 January 2015, Ian Strachan wrote:
>On Wednesday, 14 January 2015 15:58:40 UTC, wrote:
>> On Wednesday, January 14, 2015 at 9:35:43 AM UTC-5, mt wrote:
>> > Our 235 hp Pawnee has again some cracks in the tail tubing. One of
>them=
> is on the bottom of the vertical member where rudder hinges are welded.
>T=
>he crack is between the lowest and the middle hinges.
>> >=20
>> > As a glider instructor and tow pilot (over 35 years) I don't see why
>we=
> should keep "boxing the wake", as part of glider pilot training. Having
>sa=
>id that, contrary to some opinions in my club, I don't believe aggressive
>b=
>oxing the wake is the only contributing factor in our costly maintenance
>is=
>sues. FYI, our Pawnee has been hangared at least in the past 20 years!
>> >=20
>> > What are your experiences:
>> > 1- with Pawnee tail fatigues
>> > 2- cause of repeated cracks, method of usage
>> > 3- methods of fixing them better next time
>> > 4- what contributtes to more stress on the tail tubing: hitting
rudder
>=
>stops in everyday operations, boxing the wake, hard landings, or rope
>break=
>s (weak link about 1250 lb).=20
>> > Many Thanks,
>> > C1
>>=20
>> Boxing the wake is essential to=20
>> learning how properly control a glider on tow. =20
>> I box the wake on virtually every tow, just to keep my skills sharp.=20
>
>Reply from Ian Strachan, UK glider and power pilot.
>
>I was a glider and power (civil and military) instructor for 40 years,
now
>=
>retired from instructing but still flying gliders and tow planes at
Lasham
>=
>in the UK. In my gliding career I was Chief Instructor at two UK clubs
and
>=
>in the military instructed on single, twin and four engined types.
>
>When I started instructing in the 1960s there was no such thing as
"boxing
>=
>the wake". Before sending someone solo on aerotowing you ensured that
the
>=
>guy could get back to the central tow position from being out of position
>l=
>eft and right, up and down.
>
>This was done by the instructor flying gradually and smoothly to the
>out-of=
>-position position and handing over to the student to recover to the
>"centr=
>al" tow position. The emphasis was on smooth, gradual and safe use of
the
>=
>controls, not rough and unneccessary control applications. The dangers of
>o=
>vercontrol leading to overshooting the central two position and the risk
>of=
> oscillation were discussed and demonstrated. In the UK the standard tow
>p=
>osition is "high tow" above the wake and part of pre-solo instruction was
>t=
>o show the wake and make sure that the pupil could get back into high tow
>p=
>osition from a wake encounter. We did not deliberately teach the "low
>tow"=
> position itself, at least until a guy had already been solo on aero
tow.
>
>When the fashion started for so-called "boxing the wake", I was horrified
>b=
>ecause many instructors took it as a licence to be rough with the
controls
>=
>and IMHO took it too far. As a tug pilot I looked at what was happening
>be=
>hind me as a demonstration of poor airmanship and probably off-putting to
>m=
>any pupils. A long-term instructor often forgets that some pupils are
>quite=
> nervous. Pilots who have been instructors for many years need to be
>remin=
>ded of the basic principles such as gradual and sympathetic demonstration
>a=
>nd then student practice of the various skills, without taking things too
>f=
>ar because the instructor has lost the ability to put him/herself in the
>pl=
>ace of the student.
>
>When instructing, I refused to Box the Wake but continued as I had done
>bef=
>ore. I don't think my aero tow students had any problem when they went
>sol=
>o on tow.
>
>Clearly C1's claim that boxing is "essential", is not right. Unless you
>re=
>gard what I describe above as "gentle boxing".
>
>I guess it all turns on what you mean by "boxing". =20
>
>The problem was that once it started, there was far to much "aggressive
>box=
>ing" by instructors who maybe were trying to show how clever they were
>(and=
> annoying tow pilots like me) and had IMHO fogotten one of the basic
>tenets=
> of instruction which is "not to do the advanced course before the
basic",
>=
>or not to demonstrate running before the pupil can walk, if you see what
I
>=
>mean. I have seen instructors take it too far, for instance breaking the
>r=
>ope/weak link or even arriving just off the tug wing tip with a huge loop
>i=
>n the rope.
>
>I would hope that we could agree that "aggressive boxing" during pre-solo
>a=
>ero tow instruction is unneccessary.=20
>
>IMHO it is a poor instructional technique which is not necessary before
>saf=
>ely sending a student solo on tow. Even on post-solo check rides, I see
>no=
> need for it and suggest that a less "agricultural" approach should be
>used=
>.. An aero tow is not an aerobatic and controls should be used
gradually,
>n=
>ot over-used when it is not necessary.
>
>Ian Strachan
>Lasham Gliding Centre, UK

I agree completely with Ian, over my 50 years of instructing I have seen
some crazy ideas introduced and "boxing" has to be one of them. The
procedure is not required to teach recovery from out of position. I have
never yet flown with a student who did not get out of position naturally
giving the opportunity to learn the skill of recovery.
We are now starting to use motor gliders as tugs and my club uses a Rotax
Falke. The Rotax Falke is a standard Falke airframe fitted with a more
powerful engine and a "proper" undercarriage. It was never ever designed to
be used to tow other aircraft, which is of course the case for most of the
aircraft used as tugs. Who knows what stresses and strains out of position
flying puts on the rear fuselage of a Falke, I suspect we will only find
out when a failure occurs, which will be of more than academic interest to
the tug pilot.

[[email protected]]

I don't understand the logic of boxing the wake as a training exercise. Why teach students how to move from one undesirable out of position scenario directly to all the other possible out of position scenarios ? When is that going to be useful in real flying? It makes no sense to me.

John Galloway

[[email protected]]

On Wednesday, January 21, 2015 at 3:49:48 AM UTC-8, wrote:
> Why teach students how to move from one undesirable out of position scenario
> directly to all the other possible out of position scenarios ? When is that going
> to be useful in real flying? It makes no sense to me.

The 4 corners of the box are where one will be to initiate a steering turn in high and low tow.

Flying a smooth box with a pause at each corner allows the student to practice and demonstrate mastery of flying on tow.

Drop into the wake then move to the side until the ride smooths out. Turns out it's not very far and puts minimal strain on the tow pilot's foot.

Again, boxing the wake is to be a demonstration of precise control of the sailplane on tow, it's not something to be rushed.

-Tom