C18 upside down

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stuart fields

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The JT300 has a T63-A-700 Allison engine installed upside down. One reason for this installation was to enable relatively easy alignment of the tail rotor drive with the aft end of the free wheeling unit. However, there is a problem created here. The oil drain on the sprag unit is now on top which causes the unit to be constantly flooded with lube oil. A design manual I found on sprag units doesn't like flooding the sprag. Further, the Bell design uses the same turbine oil in the gear boxes and engine which enables the sprag to be lubed off the same source, pumps, filters and sump. The JT300 main rotor gear box is a unit from a Ford 4wd car and needs gear oil with the EP additive. Sprag clutch design manual doesn't like the EP additive in the sprag unit. In an attempt to have just one lube system, a separate experiment has been reported where turbine oil was used in the main rotor gear box (Ford 4wd unit). Heavy gear wear was noted in a short period of time. At the present time, I'm designing and building a separate oil supply for the sprag unit. Adapting to the the engine oil system would leave the sprag un-lubed during any lengthy engine off auto rotation. Also the separate lube system would keep the engine oil from seeing any particles generated by the sprag. Also the sprag system does not want to see oil pressures that exceed 10psi.
Experimental aviation is designed to create a learning environment. There is also a small amount of actual aviation in there somewhere.
 

TFF

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Allison designed the engine the way you are running it for 500s. Bell wanted it the other way. Enstrom runs the engine " the correct way" too. The Enstrom has a self contained clutch. The design can have problems pushing the oil out into the engine and going dry. They have a reservoir kit that vents the clutch and holds extra oil that fixes the problem.
 

D Hillberg

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very low low low earth orbit
TTF the Hughes 500 installation and the FH 1100 has the engine tilted up inlet first NOT upside down the Bell installation has the engine level. the Hughes 300 and 330 the engine is inverted - the sprages in the 500 is sealed unit no oil circulation. the Bell is pumped from the main gearbox.

There is no correct installation for the engine as it's also a turboprop. The installation manual from Rolls Royce (Allison) has the data.
 

stuart fields

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May 30, 2008
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Well it is a little bit of a "Biggy" The Bell manual shows the oil return from the sprag gravity flowing to the tank. Not on this bird the tank is uphill from the sprag oil exit. Also the sprag seals don't want to see much pressure..e.g. 7psi max on some of the seals I've seen in the catalogs. That is handleable but... Also on engine shut down the oil supply would quit while the sprag system continued to drive the tail rotor. An engine out auto from some high altitude would have no lube oil flowing to the 6,000 rpm shaft bearings. Would it do much damage to have no oil flow for 15 minutes? Without a rotor brake maybe as high as 18 minutes. Have you tried it on a helicopter that you own?
Also the Hughes 500 has the C20 engine and evidently a different sprag clutch assy. Are they grease lubed? Different bearings and seals than the Bell unit?
 

D Hillberg

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Nov 23, 2010
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very low low low earth orbit
The main gearbox doesn't have a scavenge element to pull the oil from the freewheel unit, the flow from the gear box just circulates the oil and is under the head pressure of a gallon and a half of txsn oil. and a low flow doesn't hurt a thing. and those bearings spinning at 6,000 rpm only have the preload of the t/r adapter bearing. very little load on them. the Hughes unit is oil filled and has no t/r adapter, in early ones it just slipped over the splines and the housing bolted to the pto studs, the bell system is twice as big. the same style bearings are used in the t/r gear box and they carry more loads...
 
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