Experimental setup with turboshaft 3

[frotojk]

Hello,
I am designing an assembly to test a twin-prop propulsion system using a Lycoming T53 turboshaft engine. There will be a a custom T-gearbox mounted to the front of the engine that will take the engine power and distribute it to two shafts coming out at 90degrees on either side, which in turn will power the two separate props.
I am not sure whether i can directly couple the engine output shaft with the gearbox, or a coupling of some kind would be necessary to make up for misalignment. The problem being the space constraint and that we'd have to go with an overly large industrial size coupling to handle the torque.
The gearbox mount will be CNC precision machined, though I don't have the exact dimensions of the mounting face on the T53, and may have to machine in multiple steps to obtain an accurate fit.

An image of the CAD geometry with the large coupling is included. Any input highly appreciated. Thank you.

 

[rb1957]

i think typical design (see PWC 121 engines, on a DHC8) has the gear box rigidly attached to the engine carcass and so they don't need a coupling between the engine and the gearbox (as they are well controlled in relative position).

if you don't do this, then i think you'll need a coupling between the engine and the gearbox.

i suspect you'll need couplings where the prop shafts (from the gear box) attach to the props.

just out of curiousity, is the engine mounted along the line of flight (so the prop drive shafts have 90deg elbows) or across it (so you'd have a pusher and a tractor) ? will the props be rotating in the same sense, or opposite ?

 

[frotojk]

Thanks. Yes we were planning on using couplings at the two prop shafts.
The engine is mounted along the line of flight with 90deg elbow gearboxes at the props as you guessed, with the props counter-rotating.

 

[MikeHalloran]

Don't those engines grow in length, a lot, as they warm up?


Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

frotojk-

I'd definitely recommend getting a hold of a copy of an installation drawing/spec for your T53. I'm not familiar with the T53, but most aircraft turboshaft engines have very specific requirements for mounting.

The engine PTO is usually a female involute spline and your gearbox input would be similar. The shaft connecting the two would have a crowned male involute spline on each end, and these splines would have a major diameter fit. The input shaft's crowned splines allows some angular misalignment between the engine and gearbox. The splines would also need to have a recirculating lube oil flow to flush out debris. The T53 installation drawing/spec will give the dimensional details of the splines and the lube oil flow requirements.

As for the mounting of the engine, the requirements of the T53 installation drawing/spec should also be followed to the letter. Aircraft turboshaft engines have very lightweight structures and very tight clearances between the blades and cases. Thus they have very little tolerance for excess strains/loads. The engine is designed with a determinate mounting arrangement that provides the proper DoF at each mount, allowing for thermal growth as well as directing torque reactions and dynamic loads to the proper engine structures.

Lastly, you will also want to pay close attention to the dynamic characteristics of your drivetrain and any possible modal coupling with the T53. Once again, the T53 installation drawing/spec will give you guidance on this.

For tech info on your engine, give Honeywell a call with the specifics of your engine. I'm sure they'd be happy to help you out.

http://www.honeywell.com/sites/aero...3E9_H83893473-B789-5F81-6A79-06E32B29AD0D.htm

I hope that helps.
Terry

 

[thruthefence]

Seems to me you are going to require the propeller drives to change direction twice. While the forces generated by a prop are pretty well understood, you are going to be adding a bunch of moving parts between the powerplant and the propeller. I can see the harmonics of the drive train causing some problems.

 

[rb1957]

this might be interesting ...

http://www.geversaircraft.com/ac/propdrive.htm

 

[berkshire]

rb1957 (Aerospace)
That is an interesting design.
I have one question, what happens to those engines in the event of a crash?
They look like they would go straight through the passenger compartment.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[kontiki99]

I'm curious how moving the engines around affect the aerodynamic performance.

Typically rotating air mass impacting control surfaces and fuselage at various points has a significant effect on how it handles.

Seems like it could get a lot more complex with the engines repositioning.

I don't believe anyone will ever build these. It's like all the beautiful concept planes you see in AWS&T. No one ever builds them and survives.

In theory, there is no difference between theory and practice; experience suggests that in practice, there is.

 

[jd750ace]

The UH60 engine and tail drive shaft installations use stacked members in a "flex pac" as it was called, to help isolate resonance in the powertrain. The engine is attached rigidly to the transmission input gearbox with a hollow tube that bolts directly to the swirl frame on the front of the engine, and the gearbox casing around the input flange. The high speed output shaft floats longitudinally and is splined at the ouput shaft of the motor, and the flex pac is a 3 bolt attach to the ouput shaft of the engine, and the input flange of the gearbox. The attach bolts at the flex pac are where balancing provisions, via weighted washers, is accomplished. You may look into how the T53 is connected in it's helicopter applications for guidance on your design.

 

[frotojk]

Thank you all, this is very insightful. I'm in the process of getting some more data.

Best Regards,

Jon

 

[Sparweb]

The UH-1 / Bell 205 helicopter would be a good reference, too. Has a T5317A engine and a flex-coupling to the main rotor tranny. 90 degree turn inside this tranny done with a bevel gear on the input quill, to a bevelled ring gear. Dual planetary gears reduce speed 20:1 (to ~300RPM) to drive the main rotor. I think the input quill gear is about 8" diameter.

STF

 

[tbuelna]

frotojk,

Here's a link to the front section of the manual you will need for the T53.

The manual number is TM 55-2840-229-23-1.

Terry