Brass/Bronce hinge sleeves in steel brackets duration test

AchimEngels · 18 February 2005, 11:31 AM

Hello Folks,

I thought the following would be interesting for some of you replica builders.

Darkangel and Franzkait brought up a very interesting topic with repect to brass and/or bronce sleeves soldered into steel brackets.

The idea was that because of the difference of materials an electrochemical corrosion will take place that will destroy the steel bracket.

Basically Franzkait and Darkangel are correct with the claim, but to my knowledge the effect is negligible in this context and will not very much effect the structural integrity of a rudder hinge made that way.

The matter is different in the case of plumbery where a complete system of water tubes are conected and are electrically earthed.

However the idea is interesting and I would like to check it out.

The idea of this test is not to proof that brass/bronce sleeves have not been used during WW1, but to examine whether there is a technical reason for using steel sleeves instead of brass/bronce, because of the potential destruction of the sleeve or the holding bracket due to electrochemical corrosion.

My pertsonal opinion is that there will be no such a reason and that the use of steel sleeves was nothing but a neccessity because of the shortage of brass/bronce.

The first image shows the new made late Fokker style strap along with an earlier style Fokker hinge. The erlier one is about 15 years old and showed no sign of severe corrossion where the brass sleeve is brazed to the steel strap. Admittedly this hinge was never exposed to the elements and was stored in our workshop
The other hinge is the new made piece for the experiment. The sleeve is of brass

This image shows the experimental hinge prior to soldering the sleeve in place. The file marks I set as to no one may claim in the end I exchanged the hinge.

This photograph shows the experimental hinge after it was partially soft soldered. I did the soldering only partial to give water the better oportunity to get into the small corners of the connection. Also note how the soldered brass sleeve got almost the same color as the steel strap.

To study the effect I decided to put a dummy rudder spar in place as well.

The experimental hinge will be exposed to the elements whithout oil and whithout paint, just to check the effect the electrochemical corrosion taking place in such a design.

My prognose is that the effect will not be very noticable (whithin a reasonable frame of time).

Just to make things clear: The test is to find out what happens to the soldered connection between sleeve and holding strap.

I will occassionally report about this test.

Enjoy!

Achim

Dan_San_Abbott · 18 February 2005, 01:44 PM

Achim:
I agree with you that steel sleeves were used in control surfaces hinges. They are called out in the Allied studies of the Fok.DR.I and Fok.D.VII.
Also brass and copper were in critical short supply.
Blue skies,
Dan-San

Machinbird · 18 February 2005, 09:46 PM

Great experiment Achim! From a practical viewpoint, the most significant point of corrosion in an aircraft would be between the fixed bushing and the moving control surface. Binding controls could be very annoying! Perhaps you could measure the torque required to rotate the dummy rudder spar and keep track of that over time.
While we are waiting for something to happen in the experiment, perhaps we can chat about the possibility that any sort of surface treatment other than paint was used to prevent corrosion. For example, electroplating was developed in the early 1800s. Does anyone have any examples of plating used to prevent airframe component corrosion in use by either side during WW1 (WK1)? After 80+ years any existing plating might not be very obvious.
I don't think we will have to worry too much about the wood components.

AchimEngels · 18 February 2005, 11:09 PM

Hello Machinbird,

The idea of meassuring the torque is a good one, but I assume there won´t be much of a difference. Brass and steel are relatively far apart in the scale which is bad as long as the pieces are joint, but intented in the use of hinges and bearings, since they wont stick together easily.

This is the reason for the use of brass and bronce, not just because they should wear instead of the steel.

I agree with you that galvanic and galvanic matters have been well known already at the time of the First World war and I could well imagine that you are right with the use of other surface treatments for corrossion prevention. I know of some "ancient" methods, but don´t know right now how they are called in English and neither whether they have actually been used in aircraft design of that time.

I will have to look into my "Baubeschreibung für Flugzeuge" (design reqirements for aircraft" of that time to see what type of corrossion protection they request. I assume the British, French and Americans did have some semiliar collection of requirements for aircraft design? Perhaps we can learn something from there as well?

I do not think that corrossion was a true matter of WW1 aircraft. These planes have not been designed to live comperatively long.

Using steel sleeves in ruder hinges is a dangerous thing and must have only been done as a result of a coercive situation because of material shortage. Not only corrossion is a problem with these sleeves, but also silting. Not only could this be tiring for the pilot, but also dangeraous for his live.

It is basicall knowledge in aircraft design that steel sleeves require a carefull and regular maintenance. Brass/bronce is much more gracefull here.

Enjoy!

Achim

nomma · 19 February 2005, 12:54 AM

Again a real life experience:

My hangar is not good at all - water dripping from the roof makes it really humid (moist?). Anyway, I left my toolbox in the hangar for two weeks. That was a mistake, most of the steel tools looked terrible, partly covered in a "sludge" of corrosion.

So how is it possible the Cub survives this environment? Some of the steel parts (like the seats of the rudder bushings I mentioned before) have no surface treatment at all, and have been like that for decades.

My conclusion is that the grease and oil is a really good corrosion protection, probably better than most "hard" coatings, because it doesn't wear and get scratched.

So, isn't doing the "weathering" experiment without grease/oil a step too far away from real conditions? The hinge will soon be covered by a layer of corrosion, and it will be hard to draw any conclusions from the outcome. Measuring the torque is interesting, but only if you have conditions similar to reality. On a real aircraft you would not have a "dry" joint like that.

Wouldn't it be more interesting to see how it behaves with grease/oil as in a real aircraft?

Best regards,

Magnus

AchimEngels · 19 February 2005, 03:23 AM

Nomma,

I agree again! In my eyes paint and oil are enough to protect the design.

The test is just a worst case scenario to detect whether Franzkait´s and Darkangel`s argument could have been the cause for an technically intented shift from brass/bronce bushings to steel bushings.

I could have done the test as well with a simple sheet of brass and a simple sheet of steel soldered together and exposed to the elements, but this way is more fun and we can study the effect on a untreated replica piece.

If we want to be exact we could not even use the outcome of this test to judge what happened back then, since for sure neither my steel nor my brass is of the same composition as the material was back then. Apart from that todays rain in our region is certainly more acidic than the rain back at that time. This without doubt makes the electrochemical corrosion implemented by Darkangel and Franzkait even worst in our little experiment.

I decided to make another hinge which will be painted and oiled regulary just to compare both in the end. Furthermore I will make one with a steel bushing to see which of both designs is the poorer one.

This experiment is far from scientiffic and should be judged as a rather beasic thing only. However, my prediction is that it will proof that no replica builder must fear to use brass bushings which are soldered into steel straps for his aircraft.

Obviously there was a change at Fokker when steel bushings replaced bronce bushings. when this shift might have taken place is not certain and requires to be examined closer for those who want to create an authentic (note the missing inverted commas!) reproduction of one certain airplane.

I find nothing that speaks again the fact that early D.VII´s might well have still had bronce bushings.

Enjoy!

Achim

Langdon · 19 February 2005, 11:57 PM

Quote:

Originally Posted by AchimEngels

Nomma,

I find nothing that speaks again the fact that early D.VII´s might well have still had bronce bushings.

Enjoy!

Achim

Except that the Dr.I rudders in England and the E.V rudder in the USA all use steel bushings and as these aircraft bracket the D.VII in the time they were built, it is reasonable to expect that all D.VII aircraft have similar bushings irrespective of what was intended.

I do not think you need to do the experiment above to work out if it is feasable to use bronze. Engines are full of bronze and steel parts and where oil is present there is no problem. Often steel (mild) wears faster than bronze when they are used in combination. This is the problem with the connecting rod shoes on my Oberursel, the steel shoes wear faster than their bronze bearing surfaces on the thrust block.

Langdon

AchimEngels · 20 February 2005, 12:08 AM

So we agree that electrochemical corrossion is nothing that could be judged beeing the reson for the use of steel bushings?

AchimEngels · 20 February 2005, 06:54 AM

Hi Langdon,

I might have been more specific with my reply above.

I agree that Paul Leaman has seen steel bushings in the Dr.I Rudder. I have not received an answer from him yet that he can cofirm this to me.

I have asked Dave Watts as well and he also could not yet positively confirm that steel was used on the E.V rudder.

The Munich D.VII has bronze bushings. This I checked out for myself. If they told Franzkait it were steel bushings, they are either wrong or Franzkait missunderstood something.

The point is, however, not whether steel sleeves were used or not, but whether the mentioned reason of electrochemical corrosion could be the reason for the use of steel.

I think we all agree that bronce or brass bushing are the intented and safest way to go for.

I also would like to explain the above note in which I said that I do not find anything that speaks against the use of brass/bronze bushings in early D.VII´s. If the IWM rudder and the E.V rudder indeed have steel bushings than you are right that D.VII´s certainly used the same material.

On the other hand we have the bronce bushings of the D.V given in the factory drawing. This was 1916/17, so the shift to steel sleeves due to material shortage must have happened at some point in time.

It is speculative, of course, but it is possible that early D.VII´s which have been built along the late Dr.I´s might well still have had the intented bronce bushings. Of course, provided that both examined rudders of the Dr.I in England are of late production models.

So, even from the historic point of view I see no real reason to replace the rudders I made so far.

I certainly will replace the rudder of my 228/18 with one of steel bushings once I am convinced, but with respect to longevity and safety I will not change Wulffo´s or the other ones rudder bushings.

This of course I will reconsidder in case the test subject to this post will reveal, that Franzkait and Darkangel are right.

It is true fun to figgure out all that! And I am pretty happy that such minor details are subject to open discussion here.

Enjoy!

Achim

AchimEngels · 21 February 2005, 08:57 PM

Machinbird,

in response to your question about other methods of corrossion prevention I promissed to look up into my "Baubeschreibung für Flugzeuge".

The methode to prevent corrossion for all metal parts, including welded joints in this official document is either.

- one coat of rust protection base (Bleimennige) + one coat of paint if possible oil paint.

or

- one coat of rust protection base covered with one coat (better two coats) of laquer.

Other methods of galvanic protection are:

- Zinc plating of all metal parts which are not welded or soldered after treatment.

- Cadmium or Chrome are allowed.

- parts that are covered with zinc, chrome or cadmium shall be covered with one coat of paint in addition.

I hope this is of interest.