Third homebuilt, Fleet model 7

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

mullacharjak

Well-Known Member
Joined
Nov 5, 2010
Messages
155
Location
Peshawar Pakistan
The drive looks fine.The prop pulley having no front support would not be a problem I hope.What size prop does the fleet use? I am thinking of using the L13/15 engine because of availability with the stock ignition/fuel system.I need info on the Guibo or the crankshaft flex coupling.Is it a car driveshaft part? Can you provide a part number or car spec. I need to swing a 72 42 prop at approx 2000rpm for an aircamper. Thanks and keep up the good work.
 

Sonny Furman

Member
Joined
Feb 23, 2011
Messages
14
Location
Punta Gorda FL
Your assumption about prop pulley is incorrect. The main output 1 1/2" shaft goes thru the pulley & extension to the end and supported by collars internally, so there is no possibility of flexation at that point. The prop I will be swinging will be a custom Culver of approx. 76 X 38 and with the redrive should not be a problem reaching desired RPM
 

rhbelter

Member
HBA Supporter
Joined
Mar 9, 2015
Messages
9
Location
Carmel CA
Ahoy, Sonny,

Nice looking PSRU, but I see no sign of a guibo to afford torsional 'softness'. I suggest that you go to http://www.epi-eng.com/, and see all about the subject by Jack Kane, THE foremost PSRU designer of-all.
Enjoy /s/ Bob
 

Sonny Furman

Member
Joined
Feb 23, 2011
Messages
14
Location
Punta Gorda FL
To respond to Bob's message, yes there is a "guibo" unit, actually a stock Mercedes unit with the stock drive shaft cut down and fitted to the input of the PSRU, just a bit difficult to see in the photo and resides at the flywheel. Bob was kind enough to send a link on guibo's, but trust that I spent quite a bit of time engineering the entire PSRU and nearly wore my lathe out. Do not buy a Chinese built lathe - they just don't hold up well and parts can be very hard to source.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,133
Location
CT, USA
Nice, my only questions are will the round standoffs that you're hanging the redrive from be stiff enough to keep the entire redrive from twisting due to torque, and is the front plate (looks like 1/2"?) be stiff enough to take the gyroscopic loads on the prop? Replacing pairs of standoffs with rectangular plates would make it a lot stiffer, unless there's additional structure that's not visible in the photos.
 

spaschke

Well-Known Member
Joined
Oct 24, 2012
Messages
236
Location
Denver, CO
In airplanes, belts are reliable much higher than 100 hp. airplanes don't need the instant high torque & accelleration for drag racing, etc. We open the throttle relatively slowly. The Blanton psru design using a 4" belt is good for at least 350 hp. Modern belts also can be made with much stronger materials.
 

litespeed

Well-Known Member
Joined
May 21, 2008
Messages
1,557
Location
Sydney
Also about belts and bikes...

They are much stronger on a aircraft engine. The bike has massive torque pulses when gears are changed and that is what does the big damage. Bikes go to a lot of trouble to ensure they don't rip apart the drivetrain and gearbox when changing gear.
When launching they have a huge pulse of torque trying to propel a heavy object from a standing start.

The gearbox has a clutch and sometimes other anti destruction devices in big power bikes. Slipper clutches, anti spin, anti highside etc on many new bikes.
The Chain or belts and drives get a lot of wear esp chains.
The wheel itself has a cush drive that is soft inside the wheel and transmits the drive from the chain/belt drive to the wheel.
Some bikes limit hp dependant on the revs, gear and speed to save destruction.
The slack of the chain/belt drive changes with suspension movement.
They have movement in the tyre as well to absorb the shock loads of torque.
Every gear change can be push the system towards its limits, mutliply times 100? for a lap of a track and it illustrates the problems.

When all that is combined- they can still be unreliable in big power bikes or when drag or track racing. Even just from user abuse. Having seen many a bike box/clutch/drive gear/belt/chain etc self destruct and cause huge mayhem.

In reality the failure modes and potential for catastrophic failure on a bike is high. A broken chain can lock a wheel in a instant and that can easy kill- it normally happens when the horizon is rushing at you and even worse when changing down entering a corner.

But in the normal world they are proven and safe in use unless abused or badly designed.

Both systems have harmonics to deal with. But the bike has a whole level of other problems to deal with.

The aircraft running a redrive has far lower needs, so can handle much more power reliably. Belts and chains should not be feared just done correctly.

They are a great solution to the redrive problem.
 
Top