748 - Supercharger Removed

[HS-748 2A]

Can anybody tell me if it's OK to run a 748 with the cabin supercharger removed and the shipping / blanking cover installed in its place?

The reason I ask is that there is an oil supply line that feeds the supercharger from underneath the GB. Does the GB rely on oil flow from said line to feed bearings in the rear end or can that line be capped off and the GB run with the blanking cover in place of the S.C.?

The reason I want to know is simply for contingecy. I once, afew months ago had an S.C. leak oil really badly from the vent hole in the front. Several options were discussed in order to complete afew short flights at low alt, VFR. One of those options was to intall the blanking plate and fly that way.

Anybody familliar with C-GLTC at Wasaya should be able to answer this as I belive it is running around without superchargers.. (I reserve the right to stand corrected if I am wrong about this)

Thanks.

'48

[Strega]

Does the GB rely on oil flow from said line to feed bearings in the rear end or can that line be capped off and the GB run with the blanking cover in place of the S.C.?

simple answer is:
no and yes..

Wasaya must have an LSTC to run the machine you speak of without it.. as you will need to do the same.

[HS-748 2A]

Strega, thanks.

Lets say hypothetically I get a ferry-permit; OR maybe I do want to purchase the STC - Or maybe I want to MEL the SuperCharger, install the cover plate and not tell anybody.

I didn't need an answer from a lawyer; I want to know how it works.

[Strega]

operationaly, there should be no problems with installing the blank plate, and plugging the oil lines. Its been a while since Ive looked at the DART engine, but from my memory, the oil feed line simply pulls oil from the "galley" in the pressure lube system.

Whats the deal anyway? why dont you just fix the roots blower, and keep the pressurization operating? Im certain this would be cheaper than going the LSTC route. (or just blank it off, dont tell anyone, and fly below 10k with no o's)

[HS-748 2A]

It has been a while Strega; the G.B. on a 748 is about 7' from the engine an they don't share oil. I suspect you're right though. I'd still like to hear from sombody familliar with a machine configured that way. My concern is that the gears in the back of the G.B. use the oil after it makes its way forward through the supercharger. I don't want to risk starving those bearings / gears.

'48

[Strega]

if your worried about it, why dont you just adapt the oil line to install sans the blower?

What engines are in the 748? I thought they had RR Darts..

[moniker]

.

[Goodwrench]

I remember long ago, back in my apprentice days working in the component shop. (Ya, I was the parts cleaner guy) After repair or O/H of the gearbox (748) one of the big checks on the test bench run was to ensure the bearing oil jet spray pattern using clear blanking plates. This may help with the oiling question.

[HS-748 2A]

Thanks GoodWrench and that is interesting and must have been neat to watch. It would be great to find out if the gears in the rear of the GB are lubricated by spray-oil from the inside only or if they require return-oil from the supercharger.

'48

[Strega]

I have my doubts that it needs the oil from the blower as well,, what if you wanted to install that specific engine/reduction in something that didnt require pressurization?

[HS-748 2A]

Strega, the gearbox is driven by a driveshaft. The gearbox then goes on to drive the hyd pump, tach gen, alternator, DC gen, prop sync tach, and the roots-blower (supercharger). You still pretty much need the GB, though I have flown the airplane on a ferry permit with the driveshaft removed.

[Goodwrench]

From what I remember, the gearbox was operated for several hours at normal operating speed during this bench run, using a big electric motor driven rig in place of the driveshaft. All accessory pads were covered with the clear blanking plates. There were no accessories mounted on the gearbox at that time. I seem to remember that the oil pressure and temps were charted on this run also. I don't recall there being any external oil lines, other than possibly what was used for the pressure indication. As I haven't been around that stuff in many years, I probably should leave it at that.

[HS-748 2A]

That is very interesting Goodwrench. I appreciate it; thanks,

'48

Oh, PS, not sure if you were involved with the O/H of the superchargers as well but I've been told that when they run those things on the test stand, the noise is absolutely unbeliveable. The guy who told me that said he figured half of the noise a '48 makes must come from those things... Just an aside.

[Strega]

Strega, the gearbox is driven by a driveshaft. The gearbox then goes on to drive the hyd pump, tach gen, alternator, DC gen, prop sync tach, and the roots-blower (supercharger). You still pretty much need the GB, though I have flown the airplane on a ferry permit with the driveshaft removed.

I know,

My point was I doubt the engine/reduction gear box needs the blower to function, the blower is an airframe specific accessory.

[ettw]

I concur regarding the racket the blowers make. I was out at Carp one time when First Air still had the hanger and component shop out there. Leo was running a blower in the test cell in an ADJACENT building and you knew there was a blower running in that building....the noise is unbelievable. I agree as well that a disproportionate amount of the Hawker noise is from the blower.

It's amazing. Even in July peoples ears are apparently very cold when we taxi by. LOL!!

Cheers,

ETTW

[HS-748 2A]

I know,

My point was I doubt the engine/reduction gear box needs the blower to function, the blower is an airframe specific accessory.

Its not about the blower; its not about the airframe! The oil supply!

Does the gearbox need the oil that it feeds the supercharger with to come back through the rear and lubricate the geartrain or can you remove the supercharger, plug the hole and cap that line???

By the description from Goodwrench, of the GB being tested without any accessories, it think it likely that that oil supply line is not required for lube of the GB if the supercharger is removed.

I should have titled this thread "C-GLTC" and maybe I'd have gotten an answer from somebody who's worked on an aircraft in that configuration.

-'48

[HS-748 2A]

I concur regarding the racket the blowers make. I was out at Carp one time when First Air still had the hanger and component shop out there. Leo was running a blower in the test cell in an ADJACENT building and you knew there was a blower running in that building....the noise is unbelievable. I agree as well that a disproportionate amount of the Hawker noise is from the blower.

It's amazing. Even in July peoples ears are apparently very cold when we taxi by. LOL!!

Cheers,

ETTW

It was one of your 7F brethren who relayed a near identical story to me several years ago..

Maybe it was you?

Never been party to that performance myself.

I really liked Leo. Understand he's retired now? Too bad. A Guru he is.

-'48

[ettw]

Ya Leo is retired. Not sure who took his place.

Cheers,

ETTW

[6ftsnipe]

sweet jeebus strega! Have you ever been privy to getting any 'hawker slime' on you? Have you worked on them, or have any first hand experience? The more you type, the less I am impressed.

Perhaps we should find a 'ring-bearing engineer' to figure this problem out.

I do have one question for you though. I am questioning if you do indeed have any HS 748 time, so can you tell me where the hyd. reservoir is on them?

[casey]

Note if you look closely 6ftsnipe has included a hint in his post for the location of the hyd res.Just does not indicate port are stbd.

[HS-748 2A]

Note if you look closely 6ftsnipe has included a hint in his post for the location of the hyd res.Just does not indicate port are stbd.

Very witty, both of you.. 6'snipe you're full of allusions I see..

Strega - Why the silence pal; asking your lawyer where the hyd res is?

[6ftsnipe]

I've finally had enough of strega's mindless drone chatter. It's mostly inane, but sometimes he does have good points.
I am just curious, why contribute to a topic, when you have no first-hand experience?

I've kept quiet for a long time watching you tell us that we are not 'engineers' according to your standards.

This is one topic that I finally had to speak up about.

My contribution to this topic that I have heard people do a flight or two without a supercharger and blanking plate installed.
I'm sure Leo would know the answer.

[HS-748 2A]

Yeah, Leo would. Anybody around Carp there should pour him a cup of coffee some afternoon and find out for me....

'48

[AAAME]

As long as the blanking plate does not leak , the line is caped and you have approval to run with out it . There will be no damage to the gear box.
I have 25 years of Maint experience on the plane to back up my claim.

[HS-748 2A]

Right on AAAME, thanks. That's what I thought. So you've worked on aircraft approved in that configuration?

'48