Re: Spindelberger towout bar is CRAP, PU vs. gel coat for repairs

[howard...@gmail.com]

On Thursday, August 24, 2023 at 7:32:46 AM UTC-4, Moto Hot Sauce wrote:
> My glider was damaged a few weeks ago when the auto tow out bar pin disengaged from my tail wheel dolly locking mechanism. I was using the Cobra/Spindelberger towout bar system that uses only half a cap screw head width (<3/8" lip) mechanically lock out the system. I hit a small bump and it came loose. I never liked this system, but it never failed till it did. I should have used a nylon strap as a backup. My plane smashed into the back of my car at about 5 kph and cracked my wing trailing edge, not the aileron or rudder thankfully.
>
> https://postimg.cc/yDFVFkLS
> [url=https://postimages.org/][img]https://i.postimg.cc/P57PnDZK/20230813-102410.jpg[/img][/url]
>
> My plane was repainted completely in Schwabbellack back in 1998 is 8/10 condition with some small cracks in the usual places (spoiler box etc.). The repair shop suggested painting the repair area with a color matched PU ( w/ base primer) paint so it would not be as visible as new white gel coat. I was told the gel coat would be brighter and first, then it would even out over the years. I don't think my gel coat would do another 10-20 years to reach that match. I am opting for the PU, but I am not sure if this is a good choice.
>
> Question: Has anyone have any experience or comments on how a PU paint repair matches the gel coat, is it a bad/good idea, or how it last over time?

Get a Mocho tow bar. Safe. Secure. Great design that actually works and is really well made.

[stephen.s...@gmail.com]

There is no reason why the gelcoat can’t be colour matched too. The PU will be colour matched today but as the gelcoat continues to age, not so much.

[Papa3]

On Thursday, August 24, 2023 at 8:38:10 AM UTC-4, stephen.s...@gmail.com wrote:
> There is no reason why the gelcoat can’t be colour matched too. The PU will be colour matched today but as the gelcoat continues to age, not so much.

Yup. A single drop of yellow tint in a 4 oz batch of gelcoat (for example) will get you close. And blending gelcoat into gelcoat will be a lot easier. There are other folks who will chime in who have a ton of experience in this, but I just did this over the winter on a small repair and it's almost impossible to find now...

[Moto Hot Sauce]

On Thursday, August 24, 2023 at 2:38:10 PM UTC+2, stephen.s...@gmail.com wrote:
> There is no reason why the gelcoat can’t be colour matched too. The PU will be colour matched today but as the gelcoat continues to age, not so much.

The shop told me the gel coat and PU will age almost similarly? Not sure about that. thx

[Moto Hot Sauce]

The shop told me they could try to match the gel coat too, but they told me the results are better with PU since they can measure the current gel coat color and then create a custom PU. Both options are still possible, and I have some weeks to decide after getting some feedback from others.. thx for your response.

[John Sinclair]

I can give you one data point, after I made extensive repairs to my LS-6, I spot painted several areas with gel coat tinted to a perfect match. I saw that ship about 20 years later and all the spot painted areas were clearly visible! They were brown and stood out like a sore thumb! I’d recommend going with polyurethane which does not fade with age as far as I have seen.
JJ

[Moto Hot Sauce]

Thank you for your feedback JJ. It's very helpful to hear other pilots long term experiences with tinted gel coats to make an informed decision. I would be happy to get another 8-10 years out of the 1998 gel coat. A new PU paint job is 14K in France.

[2G]

Your link didn't work, but this one did:
https://i.postimg.cc/P57PnDZK/20230813-102410.jpg
I have seen another failure as well - one of the screws holding the plate with the attachment tube broke allowing it to swivel which ran the elevator into the tow vehicle. I had that plate welded onto the caster to prevent this. I will look at some kind of backup clamp to keep the tow bar secured.

Tom 2G

[Mark628CA]

> I have seen another failure as well - one of the screws holding the plate with the attachment tube broke allowing it to swivel which ran the elevator into the tow vehicle. I had that plate welded onto the caster to prevent this. I will look at some kind of backup clamp to keep the tow bar secured.

Some of the earlier tube/plates that fit on the tail dolly caster only had two holes through the dolly cradle and caster. They were prone to shearing one bolt under load, causing the plate to rotate. Later versions have a larger plate that captures all four bolts. Check yours and modify/replace if needed.

[Dan Marotta]

Why don't you guys just drive out of the way when the tow bar breaks
rather than sitting still and waiting for the glider to hit the car?

Dan
5J

On 8/26/23 02:47, Rick Deckard wrote:

> I got very lucky! The tail traveled forward on the left side of my car. The elevator barely cleared the top of my car roof. I was going to install my Thule storage trunk and rails before leaving on my trip, but decided not to since it was a hassle. My elevator would have hit the car trunk first and destroyed the tail. Other pilots told me a story where something similar happened and the elevator got sheared off and the tail was broken.
>
> Tow out bar options:
> I am thinking of buying the IMI or the SoaringXX towout bar. The IMI has the tail hoisted in the air, the Soaring XX is tail one the ground and uses a bolt head and slot to mechanically lock out the bar. I read pros/cons of both designs.
> Which tow out system do you all use or recommend?
>
> http://www.imi-gliding.com/products/tow-bar-light-gliders.html
> https://soaringxx.com/product/soaringxx-tow-out-bar/
>

[Dan Daly]

I use the IMI with an SZD-55 and have been very happy with it.

[Chip Bearden]

> > > Which tow out system do you all use or recommend?
> > >
> > > http://www.imi-gliding.com/products/tow-bar-light-gliders.html
> > > https://soaringxx.com/product/soaringxx-tow-out-bar/

One hazard that I haven't seen mentioned is the risk of scraping the nose of the fuselage belly. You can see this in the IMI photo where the forward fuselage is relatively close to the ground when the tail of the glider is higher. This is more pronounced in gliders with less ground clearance, of course.

From experience, two danger situations are (i) towing through a low spot in the ground and (ii) towing off a paved runway onto the grass or gravel alongside. In both cases, the glider's main wheel can drop into a low spot, scraping the belly. Conversely, having the tail too low using the IMI approach can touch the tail dolly wheel to the ground and dislodge the towbar where it hooks over the tail dolly axle and/or the tail skid resting in the towbar.

Before using my Spindelberger-supplied towbar (which resembles the IMI version), I swap in a ball mount with the drop and ball size (1 7/8") dedicated to the towbar. Yeah, it takes 30 sec. to make the swap at each end of a towing run but it's my best chance of avoiding future scrapes. That said, I've been using my towbar for 30 years with mostly (!) good results. I keep the towing speed down fairly low, especially on grass.

Chip Bearden
ASW 24 "JB"

[Moto Hot Sauce]

Chip, thx for your feedback. I saw on the IMI website a picture of the belly low to the ground when the tail is up. A lot of the airports I fly at have dirt/grass runways, and parking areas so that chance of scrapping is high. I am leaning towards the SoaringXX design (tail on the ground). I also tow slowly by not pressing on the accelerator and putting it in 1st gear with the motor idling.
The failure point was between the dolly attachment and the tow bar. https://postimg.cc/cg9NdBbH

[2G]

A bungee could be used as a backup securing mechanism. All that needs to be done is to drill a .25-inch hole in the web welded to the cap screw. Attach one end of the bungee at that point, wrap it around the tail dolly, and hook it to one of the toggle clamps. Adjust the length of the bungee for the appropriate tension.

Tom 2G

[2G]

I actually asked that question of a pilot who had exactly that happen. He replied that he heard a noise and instinctively braked in response; it is counter-intuitive to accelerate at this point (it is very likely that you will end up compounding the damage).

Tom 2G

[Moto Hot Sauce]

The plane is about 1-3 meters from the car when towing after it releases. At 3-5 kph, that's about 1-3 seconds (3 kph = 0.833 m/s) of reaction time to hear a strange noise, check if the wing wheel fell off, main gear collapsed, or the tow bar came loose. By the time I looked in my rear view mirror it was too late.

[Dan Marotta]

It has happened to me twice. The tow bar that came with my Stemme is a
telescoping affair that had a steel square welded to the inner tube at
(only) one corner. When the weld failed, the tow bar separated. I
welded two corners and went merrily along until it failed again.

This time I welded it around all four sides. Since I'm a rank amateur
at welding, it'll last about a year now.

Since I pull my glider with an open 4 wheel ATV I can hear the scraping
sound when the tow bar lets go and I just don't stop. I turn around,
watch the tow bar, and stay out of its way.

Sympathies to the man who instinctively hit the brakes!

[2G]

An ATV or golf cart gives you better awareness of what is happening. You have better vision and are in a totally open vehicle. But those may be unavailable and you have to use your normal tow vehicle. I also have my wife sitting in the back to keep an eye on the glider, but many pilots don't. Preventing equipment failure is still the best option.

Tom 2G

[Mark Zivley]

Just curious, do you have a picture that shows what broke? Or are you suggesting that somehow the cap screw didn't catch on the lip and the whole assembly was able to slide sideways out of the receptacle on the tail dolly?

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

On Tuesday, August 29, 2023 at 8:45:50 AM UTC-4, Mark Zivley wrote:
> Just curious, do you have a picture that shows what broke? Or are you suggesting that somehow the cap screw didn't catch on the lip and the whole assembly was able to slide sideways out of the receptacle on the tail dolly?

My guess is, either it wasn't captured or it hit enough of a bump to unload and disengage. Does not sound like something broke.
Yes, a strap/arm to allow more vertical towbar movement without disengaging would be nice but I have never seen an issue with this type rig.

As to finishing the repair, almost any method will show color mismatch either new or aged. Question is, do you want a "1' finish" or a "5' finish"?