Hasse

Hi Rick, This is an Amazing experiment! In my wildest Dream I wouldn't have expected this dramatic result with thinner on the stressed lexan and particularily the difference on the heat treated piece of lexan. How dramatic was the experiment with petrol? So, it turns out that the key factor for the fuel induced cracks is a question of rate of heat loss and only in places where the lexan sheet is under stress. That fits! I can also imagine that when during flight there is a spill of fuel that hits the lexan the heat loss is considerable as the wind flow will certainly increase the rate of evaporation. I agree, I would love to destress any new installed lexan in Aircraft if I only knew how. For instance, what temperature and how long? Also, should I treat both sides of the sheet? Once again, many thanks for the video. This is a great forum!

Hi xair, What I've Heard is that PETG isn't very UV resistant and shouldn't be used at temperatures more than 60 degrees centigrade

Hi again SDQDI, I may have been too Quick when I turned down your proposal about fuel spill. No spill during refuel but a lot of spill siphoning out overfilled tanks via the vent tube during flight. I wouldn't be surprised if that spill especially from the left tank came in contact with the Lexan on the pilot side where I now have the cracks.

Hi Mark, Your cracks are nice but not much to boost about compared to the Swedish Viking Cracks. Nevertheless, and seriously, I now start to Believe that they do originate from fuel spill (even though drilling holes etc may weaken the strength of the lexan). If this is correct then a lot of precautions should be made to prevent fuel coming into Contact with the lexan material. Not only during filling the tanks but also during siphoning because siphoning will be very hard to avoid. The vent tube should either be much further back of the wing away from the lexan or perhaps even better, on top of the wing. btw, who is Holy guacamole batman? Couldn't find him in the Holy Book.

Yes Rick, I had a pretty heavy spill of fuel during my last flight, siphoning fuel out via the venting tube under the wing. For some stupid reason, don't ask me why, before flying I tested if the wing pumps of the extra tanks could fill up the main tanks. They could and the main tanks got overfilled and spilled it out during flight. It was quite a lot of spill and as matter of fact it seemed as if the left wing was more active and indeed I think I saw some fuel even hit the left wing root close to where there is a crack in the window. It is not unreasonable to think that the fuel fumes also could have hit the left door. Hmm, I think we are coming close to the answer. How fast will a crack appear on lexan after hit by fuel?

Thanks Rick, That's hopeful. It's just so disappointing having to replace the door and window after only one year.

Thanks SDQDI! Good information. I'll have plenty of material for testing when I replace the lexan and yes, I may have painted too close.

Hi Dennis, and thanks for the help posting the Pictures of the cracks.

Interesting SDQDI! Tell me more about paint fumes and cracks. I'm a bit sensitive to this as I did all the painting myself, as an amateur.

I don't think that the ambient temperature as such is any key factor. The Lexan sheets has been sitting on my aircraft for over a full year now during a Swedish winter (not very cold though) and a very warm summer without any obvious cracks untill yesterday. Nevertheless, who knows, small cracks may have risen early on without me seeing them and then suddenly matured when circumstances were optimal. Perhaps at big differences in temperature. It is fall in Sweden with some temperature variation between morning and day time. Still, it seems that this is too small temperature variation to hurt the lexan.

Well Rick, The cracks I've got now are beyond salvation. I will try to post some Pictures when I know how. Most likely I have to replace the window and the doors (at least the left door) pretty soon. Was it difficult to install a new window? Did you also replace the roof even if it was ok?

No, no nuts and bolts overtightened but perhaps too small rivet holes in the Lexan sheets.

Yes, it may have to do about tension. Most of the cracks starts from a rivet hole. A few of these cracks run as a single paths and end after a couple of cm or so. However, there are cracks that start as single for 5 cm and then spread like a feather. There are a couple of those at the sharp bend where the windscreen meets the left wing root (nothing on the right hand side). Same type of cracks can also be found on the left door (there are no cracks on the passenger door). Perhaps it's all about tension and too tightly drilled holes as you say Mark. The tension around the holes in the left door may arise when the door is closed and secured i.e. squeezed against the door frame. By the way, my passenger door hasn't been used much as I am still doing the 50 hours of flight testing. So the remedy should include oversized Lexan holes (perhaps smoothly sanded) and carefully made doors that fit the frame without tension when closed and secured. Right?

No, no fuel spilt.

Hi, This is a mystery but I have got severe cracks in the Lexan window and one door of my Savannah S. As far as I know, for no reason. These are no small scratches and some of them are almost 5 inches long and runs through the whole sheet as if after a bird crash. It's one year now since I build the aircraft and and I have been flying approximately once every week and there has been no problems with the Lexan before until today when I noticed the disaster. Has anyone come across anything similar or should I expect that this is a sabotage.

Thanks Andy, I'll do the parallell first. No problems theoretically. In practise however my instrument panel is not easy to deal with. There are a lot of threads that pop up when you open it. Reminds me of the Pandora's Box.

Thanks Andy, Ok, now I've got several options. I will try them one by one and let you know. Hans

W

pmccarthy: Well according to the youtube instruction "bouncing tachometer" provided by fly_tornado the resistor is just cut into the lead thread in series. Hans

Hi Graeme, I don't know, but why not have a go? It's not a big job to connect a small resistor in series with the yellow/blue thread and see what happens. Not much that can go wrong. Hans

Hi Scott, You're a mind reader! Yes, I have an Aviasport tacho and it looks like you described it. The idea of resonance at a certain frequence also makes sense. It's great talking to you Scott! Thanks Hans

Great input Scott, I will sure try this asap. Not that I understand why this flutter only appears at a certain range of rpm. Still I will try your medication and report the outcome. Thanks Hans

Hi, I am doing the first tests with a new Rotax 912 engine in my Savannah S and the engine runs very smooth at all speeds. However, the tachometer behaves very awkvard and the instrument needle flutters markedly at a specific range (3100-4200 rpm). Very strange because the flutter is not correlated to any irregularities of the engine rpm. What may be the cause of this anomaly? Do I have a defect tachometer or may there be some kind of disturbances that can interfere at a specific range of speed? Below 3100 rpm and over 4200 rpm up to max (5400 rpm) the tachometer behaves normally and the needle is as steady as is the engine. I have separate tachometer and hourmeter instruments and not the standard combined Tachometer/Hourmeter. Any ideas from you guys or anyone who have had the same experience? I hope to fly soon Kind regards Hans Marchner

Ok, thanks Nev. I will try this scheme. Starting with something less preciaous. How durable? Well, time will tell. Anyway, painting need not be top quality - wing assembly should. Hasse

Sorry Dennis! Couldn't keep away from the Engine. Some kind of magnetic itch :-) Anyway, the chinese version of Scotch brite has arrieved. Thanks. But you know Dennis, the amount you ordered for me is enough to clean a fleet of B-757. So, you've decided on the D-motor. Was it the weight, efficiency, reliability or cost that made you to take the D-motor and not the Rotax? See you soon Hasse