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Guest fly

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Greetings to all!


I would like to know the main wheel base dimensions, OD to OD of a


Thruster TST-E or T500.


Tyre size 15x600-6


At the moment,


My wheel base OD to OD is 2300 mm or 90.5 inches


The plans I have for a factory built trailer gives 1980 mm or 78 inches as trailer width


I have 3 leaf heavy duty springs


Have my springs sagged this much that I have gained a foot or so in width, they dont appear to have ?


Are the 15x600-6 standard?


Thanks for all replies........ FLY



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Guest TOSGcentral

Hi Fly,


I will give you a somewhat complicated answer to your question – because there is no defined answer to it. I am also not sure exactly for what purpose that you need the information – so will cover most bases but also broaden into a general information document.


Historically (with the two seaters anyway) you are looking at an expansion of track from the original factory models (say 1985-1990 serial numbers) that was considerably narrower than what most of these aircraft now carry.


There a couple of reasons for this: Length of the springs and width of the tyres.


Track was widened to improve ground stability and quality of taxi ride as where tyre sizes. When the factory effectively ceased producing springs then these were sourced from a variety of professional spring manufactures and widths did vary.


Tyre size increased and basically stabilised at the ‘standard’ tyre dimensions that Fly has given and are also standard on the Drifter and other types. They are a very good tyre.


OK here are some actual measurements that I took this morning off some of my own Thrusters (Outside of tyre to outside of tyre),


  • Glasshouse. 1880 mm
  • TST. 1875 mm
  • T300. 2110 mm
  • T500. 1935.
  • (I do not have a Gemini here at the moment so could not measure that)



Notes: From the above the Glasshouse and TST may be regarded as ‘original’ dimensions – particularly the TST as the Glasshouse is very wide anyway and would be wider as it is on ‘special replica’ tyres while the TST has the same later standard tyre sizes and hubs that you have on yours Fly so would have had a narrower track on the original tyres.


The T300 can be taken as a modern ‘datum’ as she is on current standard TOSG springs and these are from the (free) technical drawings that you may have from TOSG.


The T500 (that I am currently using at the moment) has slightly longer springs and is on aviation tyres that are much the same width as the new ‘standards’ but have a slightly less footprint area.


In training I used 8†balloon tyres that made landings a lot more comfortable for students (and particularly the airframe) and these were much wider – but gave chronic wheel balance problems (that could have been solved with wheel brakes after take-off).


So I would deduce Fly that your springs are slightly longer than normal. We will look at some of the implications of that.


The longer springs do give a more comfortable taxi ride and landing. However they exhibit signs of fatigue earlier and can begin sagging. The narrower track springs gave a harsher ride and landing but lasted longer. For perspective I normally got 2000 training landings out of a set of springs and then threw them away – but I log every landing so that I can keep track of life duration.


As we have to have our own springs made for us these days then you have to be very careful. The basic spring and leaves are standard BHP automotive spring material. This is good material for getting a satisfactory temper of the metal – difficult to get wrong (but believe me it can be got wrong!). The important trick is to get the geometry right in all three axis of the spring!


If you have toe in or toe out (which is very easy to do by a car spring manufacturer) then the former is like having the brakes on all of the time and the latter splays the undercarriage like you would not believe. It either of these are happening then you have to fix it! Fixing it will involve the springs going back in a furnace, being trued and then correctly re-tempered, re-protected etc!


I would add a further (very pointed comment) for those that feel like leaping up and down that springs have to be ‘factory produced’ then I will not argue with the ethic but strongly suggest that you grow up a bit.


I had FOUR brand new, un-flown, un-run, ex factory aircraft here that were all unairworthy and I had to re-build to get them kosher. Every one of them had deformed undercarriages as a result of them being (presumably) made by the cheapest sub-contractor the factory could find! What do you do? Write off a $20,000 aircraft because of a sagging spring that you can no longer get from the factory and may have been worthless anyway. I would believe this compliance crap a lot more (because I do happen to believe in it very firmly) if very obviously required checks and balances had been applied. They were not so applied and there were plenty of complaints to justify them being applied (want to see the videos that I have?) OK rant over but let us get on with life responsibly please!


Normally the aircraft should be standing with the wheel sides vertical. That is not always the case! If (for any aircraft) you have hoisted to change a wheel then the wheel(s) will be standing with the top of the tyre leaning outwards a great deal.


This looks alarming but is easily rectified. Simply lift each side of the aircraft via the upper lift strut brackets so that the wheel is clear and then set it down again. The wheels will true up, but certainly will after the first taxi.


This is not always true on brand new springs and they will take maybe two or three landings before they bed in. If the spring has been made true then you will have normal vertical wheels. If you panic and get new springs re-trued before use then they will splay after the first few landings!




Never mind the ins and outs of Thruster undercarriage geometry per se! Where it really bites is when you come to put one on a trailer.


The approved conveyance is the ‘Thruster Universal’ trailer that will take any of them other than the nosewheel ‘600s. Makes you feel comfortable eh? Bollocks!


This trailer is original design for the original factory Thrusters and had the mainwheel support pads for the original track. The trailer came out in two forms – what I have designated as the ‘early’ model and then the more refined ‘later’ model (you can get original factory constructions drawings of both free from TOSG).


Try and put a later enhanced model on and they do not fit! This may be exceedingly depressing when you find out about it way beyond the Black Stump, in darkness and you need some engineering, equipment and materials to fix it. Been there and done that!


This is an image of the extension required from the factory original. Even this was not broad enough and needed to be a three inches wider for a good fit. Damn! That was a helluva night – but it worked and I got the BMW T500 Thruster home on it with no damage.


Y’all be careful out there eh? But I will answer any more questions that anyone has.











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Mine measures 2200mm (no wings, on trailer)


Hi Fly,


Just ran down the shed and measured mine, it's a T500 (25-0294) .


I have the long floppy springs.


Wheelbase outer edge to outer edge of tyre is 2200mm, when on the trailer , this is with 6" wide tyres (Kenda 15x600-6) on aluminium rims . (I think I got my wheels from Airborne here in Newcastle, they are fairly standard aircraft tyres). The measurement would be slightly wider sitting on the ground, with wings attached, and fuel in the tank, (after pushing the aircraft forward a bit), probably close to your 2300mm then. I'm guessing we have the same springs.


I originally welded some squares of angle onto a 5x8 tandem trailer to pick up the aircraft when first purchased. Then I built a custom trailer to carry it.


Went to take the Thruster home a couple of years ago (after Cooranbong airport closed:crying:), and forgotten I had put wheel pants on ! Had to take them off before getting it onto the trailer again aargh 088_censored.gif.2b71e8da9d295ba8f94b998d0f2420b4.gif!!!


Originally my springs had sagged, and I took them to Dumbrells springworks, and they annealed them, re-bent them, and hardened them. As Tony says, there's nothing special about the springs, and the springmakers can make you a custom set to suit your preferences (and to a better standard than most of the Thruster OEM springs.) The axle bolts used by the "factory":clown: can be dodgy too, and the hole in the spring they attach through can be malformed, you may need to file the faces flat and deburr the edges of the hole (need to anneal the springs first).


Check where the springs bolt onto the rectangular through beam too, if this connection is not rigid (ie the springs rock back and forth) then you may get fatigue failure on these bolts.


Cheers, BobT


PS I've uploaded some pictures, so you can see if yours looks the same front on, just click on "Thruster Bob" on the left side, select "view profile" and click on "album" , I've also uploaded a picture to the Thruster section of the gallery.



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Hi Tony:


First of all , thanks for info on springs, as usual you take the time to impart all the relevant aspects. For this I am grateful.


The reason for my initial inquiry, was regarding finding a suitable trailer for the beast as my rebuild is nearing the end.


I now understand that "standard'' can have many concepts regarding Thrusters.


I think after reading your advice, and also Thruster Bob's, I will take my springs and get them rehardened and re set., Thanks again....FLY




Have just received my TOSG bulletin,


Just finished reading about your TST/ Canberra adventure, you have all the fun !....


If you intend to sell the Thruster Universal trailer, I would be very interested ...... once again Thanks..FLY



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Hi Thruster Bob!.... greetings.


Thank you for your reply and advice!..... appreciated.


My 2300mm measurement is minus wings and fuel ,


so might take your advice and have my springs reannealed and hardened, I'd say they may have spread a bit !


by your photo's your T500 springs look identical to mine, thanks for those.


I like the look of your blue Thruster, nice aircraft, where are you at Cessnock? airport ?


Thanks again.........FLY



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Hey Thruster Bob, I just looked at your photo's and saw your rego. Last year I actually bought a T-500 and finished a rebuild on it that was rego 25-295 so they must be sister ships! My one had a Rotax 532 on it and was very low hour but unforntuatly I couldn't keep it and is now for sale once again and is sitting in a hangar in Watts Bridge next to my Glasshouse.


Small world.





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