EA 81 - Douglas Redrive

[NiqueNaque]

At the risk of another one of Ozy's chook attacks, here is a little progress made after I told everyone to go and get ...... while I fix my gyro:When you are welding around / on your gyro this is a precaution I used. The seat tank bleed line is plugged off as shown, I also filled the seat tank up with argon out of the mig welder bottle to 'inert' the fuel tank, ie, there should be no oxygen in the tank after a purge with argon (they do this at the RAAF base when working on the FA 18's. Always have an extingusher on hand when welding on your gyro, lest your dreams go up in smoke:Image Insert: 71.32

[NiqueNaque]

A few pointers I forgot to mention:Pipe was from "General Mufflers" - is just 44mm exhaust tubing - 1.2mm galvanised tube.The bends in the pipe are cut from a 'donut' which you can buy from General Mufflers, it is literally a donut shaped piece of exhaust pipe which you can use to make nice tight radiused bends as you see here, they have to be welded along the inside seam when the pipe is welded.It took 6 hrs to work out where to run the left side manifold and tack / weld it up, there was a lot of time wasted cutting twice or thrice to make things fit. The right side only took two hours including the 1/2 hour spent cursing the welder for the porosities and grinding them out. The left side served as template for the right side, so making the right side was much easier, just cut the pipe and elbows the same as for the left side and mirror it on the right side. I used a tube cutter for the pipe, and a 5" grinder with those ultra thin 1mm cut off discs to cut the donut up, worked a charm.The hot dog is going to be left out initially, if the machine is noisy as I expect it to be, I'll put a couple of them in.Cheers,Nick.

[NiqueNaque]

Now all I have to do is fix the throttle quandrant and replace the fuel pump, remount the fule pump and fuel meter, charge the battery and it should be right to go, but there is always something not done... looking, looking..Nick.

[asra]

Hi Nick now you'v lowerd the tail section how much rock will you have to balance machine on the mains.This all looked like a lot of work I fly a Rossco single & the clt is much worse than your machine with redrive before mods & it flys great so how dose clt affect my time in the sky?

[NiqueNaque]

Butch,In the order of 5 ~ 6 " of rocker in the mains. The fortunate part with the design of the gyro was that the tail wheel was on an extension, now it is recessed into the tail boom with about 1" hanging out.As to the Rossco Machine, I know of a few and they seem to fly well, certainly Ross Bannerman's gyro flies well, you along with Birdy might fly for thousands of hours and not suffer a mishap, the odds are usually not stacked so in my favour, let me tell you that the only raffle, lottery or game of chance I've ever won was a tray full of cooked prawns, but by the time they got to me, they were off, so I don't gamble with a view to winning, most usually the gains aren't worth the outlay. The one question to ask about non CLT and HTL machines is, 'When do they bunt over?'. I don't honestly know when / how it actually happens, but what I am doing is attempting to eliminate the chance of it happening with me in the hot seat. If I fix it as best I can to CLT or Neutral thrust line I can be 'self assured' of the machine's ability to mitigate the chances of a bunt over, so the mods are for my peace of mind.Cheers,Nick.

[asra]

Good work Nique Naque ! On your welder You might try dusting talc like baby powder on the wire and wire feed orfice.... Don't use WD-40 ofcorse... but talc or graphite should help the wire feeder stop jumping on ya ... I had a realy nice Mig welder when I was in Reno NV. many years ago , to my dismay I discovered I needed a garadge or inside place to weld without problems...any breeze at all blew the argon away easily.... turning up the argon pressure helps some but not much ... finally I sold it and bought an AC -DC 230 amp stick welderand have been quite happy with it . in the event that the wier feed caseing gets wore out they can be replaced fairly cheeply you'll know its wore out when the thing keeps giveing you 1/2" pieces of wire at a time in a jurking motion .... realy hard to weld like that HAHAHHAHHA ! good luck to you .... Nice job on your gyro by the way ! Bob....." Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[Ken Watson]

The problem is rarely the welding machine but usually operator technique.Porosity can come from oxygen contamination either from a lack of shield gas or moisture in the metal being welded. There is always a contaminate. Surfaces must be clean and dry.Nozzle angle and closeness is critical, but any d-head should be able to use a MIG. Mate, that plumbing looks wild. Didn't you worry about tuned length? We found that hp is critical to length. Pipe diameter is critical to torque and mid range aswell. Often smaller diameter will give more torque. My experience only, take it or leave it. Ken

[NiqueNaque]

Bob and Ken,Thank you, and for your advice. You're right, any dh can use a MIG, only this time it was me, not just any dh but the dh... one hell of an operator.The issue with this one was that every time you stopped welding, you release the trigger, everything is supposed to stop then, right? Not this time Olly.. the gas stopped and the wire kept going as did the amps, result - instant porosity! The weld 'on feed' was in the order of 0.5" to 1.5" of wire, I had to learn to modify my technique, but that was still not good enough as the wire run on was unpredictable... grrr. What was most annoying was that I had everything so neatly cut and the ends butted up perfectly, do a weld and then *bzzzzzzzzzt - poof* hole in the pipe, sparkels here, sparkles there, sparkles everywhere!.. arrg! I'm having a look at a Kempi 170 with the view to avoiding this problem in the future.Ken,If you could be so good as to describe how you would calculate tuned lengths it would be most informative not only for me but for others reading same. I don't recall any prior postings on this matter on the forum. Everything that I've done on the machine will stay as it is if it works... if not it will be reworked until it does work.Out of curiosity the engineering that is done in relation to exhaust systems relates to their use in motor cars with a requirement for an exhaust system, these days a gyro is not too different because we a forced to fly so close to the ground through regulation, ie, 300 to 500' AGL, we may as well have a car exhaust to keep the neighbours happy. However, if the engine is not required to meet 'car' requirements, then the exhaust system can be modified to do anything. Is your experience based on this 'car' engineering or is it specifically centred on gyros? I've used 44 mm tube as that is what matched the head exhaust manifold size, no other criteria was considered as I am ignorant of the vaguaries of exhaust system engineering. If you make it big, you can always throttle it to make it small, not the other way around.If you have a look at a Lycoming in a cessna or what ever, it appears to be more or less a straight pipe from the manifold, no consideration other than to get the exhaust out of the cowling in the most direct way possible, why don't we do the same?Look forward to your response.Cheers,Nick.

[asra]

Nick pulse wave length of 14-15 inches in inlet manifold gives best midrange torque it apears you have achieved this & a 32-36 webber is tops good choice as for your exhaust looks a bit busy also with a smaller dia torque will increase for ea81 which is helpfull for over square motors as for low reving long stroke high torque low power to displacment air cooled motors different kettle of fish completly

[asra]

Noise for one ... its loud doing it that way ... Pluss there is the risk of melting vlaves .if memory serves me correctly the size of the pipe in length is determined by the cubic inch displacement of the cylinders times 2 ... for a 4 stroke engineusing the same diamator pipe at the head through out the pipe ... I may well be off here so don't start cutting pipe ! conferm it first.another words figure out the c.i.d . of the 2 cylinders and figure out how much c.i.d is in the pipe .... make the pipe 1.5 to 2 times as long as the numbers say. this will give you a exhost pipe that helps pull out the exhost of the next stroke before exiting into the air . the improvement in horsepower can be alot or just a little bit ... but usually its arround 10 to 15% increase in hp. I have done this type of exhost on auto's and have had great luck with it .... never on a gyro. its been my experience that if you increase the diamator of the pipe after the head outlet... to say .5 " or 1.5" and do the same calculations for the length the increase is better yet .... and the biggest increase is in furl economy ... for reasons I don't understand completely .... I went from a 2" ehxost pipe on a 36 pasanger bus 1foot from the headder inlet into a 4" pipe that ran the length of the bus... the fuel economy doubled by just doing that ! .... I guess it could finally breath better ! it went from 8 mpg to almost 20mpg just by changeing the exhost pipes from 2" to 4" pipe are gyros the same ? they share the same basic principals of the internal combustion engine , however they do produce alot more HP than other engines but i would say that the same IDEA can be used on gyros yes. Short headder pipes or exhost pipes that exit to the open air within inches of the engines head worry me ... I never have liked them for a few reasons, I have seen melted valves on VW engines useing short pipes... split heads and other nasty things.... and the noise just plane hurts its so loud ... weather or not the short headder pipes were a direct cause of the dammage I cannot be sure , but other engines that had the stock muffler on the vw 's didn't have the same problem at all and they were being used doing the same thing in the same conditions .... I think the chances of the short exhost pipe being the cause of the problem were very good . In the Lycomeing engines where the exhost is exited with short pipes they have extreamily hard valves in the head and can withstand the torture... unlike automobil engines .... However... with the advent of alchol into the fuel the nesisity of all auto makers sense the 1980's was to have sodium filled valves or extreamily hard faced valves incorperated into the engines stock from the factory .... in almost every case . I am sure there are exceptions somewhere , there alwayse is ! so chances are you could run a short exhost pipe now and have no ill effects ... its hard to say ! it realy depends on the engine you have and the kind of valves it has in it I probly didn't help any but I tried good luck to ya !Bob......." Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[asra]

PS Nick I am curently building 2 dominator type gyros 1 two seat 1 single this is because I believe in clt but would not have worked as hard as you to achieve it. another question you have some sort of shock absorbing material at end of axel what is it & hows it work got better pics thanks butch

[asra]

by the way ... I was wondering what a chook was .... now I know.... thanks..... I think a few chooks could render a gyro useless in no time at all just pecking the bugs off the tail ! .... bet one could feed a whole tribe in the outback though ! ...be a mighty tough abarigineeee that goes after chooks i bet , I don't think I'ed wann'a tackel him with a pointed stick ! ....noooo sir ! not me !hehehehe Bob......" Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "

[asra]

Also the pipe your trying to weld is coated with aluminum & is bloody hard to do neat welds on try welding 2 bits of clean black steel this will tell you if its the mig or the **** exhaust tube also if you oxy over or tig over the top without to much grinding it should fix it sorry if I'm telling you what you already know as you are a plumber who welds for a living butch

[NiqueNaque]

Yeah Bob,They're killers mate, the ones we have over here have got teeth, descended from raptors from back in the dream time when the world was Gondwanna land. The one walking around on the lead is a genetically engineered toothless domesticated one, if it were a wild one it would have pecked his eyes out.. thats to start, can't tell you the rest, too gruesome.Goodnight,Nick.

[asra]

Hay ! I hurd dat Ausstrailia was Behind the times a bit but good greef ! I didn't think they ment Jurassic times ! WOW . Now I KNOW where them little Wombats get their attitude from .... they come by it Natural like ! I guess that puts the wild life in USA back to the tame side ... ! heheheheheheheI don't think I hurd of any Chooks trottin arround over here.... but I hurd tell of a critter they call Big foot ... and Hogzilla ... and worse yet .. the city Wolves ... I tell ya ... its not safe to go anywhere ! we're even supposed to have egles that are as tall as a man and have a 20 ft wing span ... and take sheep fer food or the unwarey camper ! .... But man anything that has a taste for Gyros is destened for the extension list ! no sir ...ain't puttin up with any holes in me gyro for no species ! c ya !Bob....." Momm'a alwayse told me , Son the impossable is only a little bit Harder... and ya know I do believe She was RIGHT ! "