I am building a tractor, side by side, engine behind pilot gyroplane.

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Sabine

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Hi Sabine,

You have done an excellent job on your tractor gyro, what HP are you looking at using.

Your design is very much like my design from 2002; which I never got around to build.

View attachment 95580
Oh goodness, that looks amazing- I built a previous itteration which had a dual vertical rudder and chucked it because of wanting to reduce complexity. i think by going to a single rudder i eliminated 18 parts. I would settle for 125hp but i guess there is never enough power is there.
 

wsimpso1

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The next unknown is the long carbon fiber prop-shaft (1500mm+-) to the propeller that goes through a kevlar tunnel in the cockpit. It would seem that torsional vibration has historically been a problem here. Molt Taylor and others rectified this using a Flexidyne coupling and my thoughts are, surely today there is something out there that is lighter and possibly better (motorcycle slipper clutch?). I really would appreciate your thoughts on these.
Besides the already mentioned thread on torsional behaviour, you might find this one useful;


Next, I can tell you that I helped some folks with a Jabiru four cylinder engine, a 44" long shaft, and prop, all in direct drive, tame their vibration. An elastomeric coupling at the engine helped with the shaft alignment issue and allowed the engine to deflect and vibrate on its mounts without overloading the shaft. This also allowed the system to operate without any lash in the system. The shaft was the primary torsional compliance having an adequately low spring rate that, when combined with a substantial increase in engine flywheel inertia, drove resonance down near engine idle rpm, and tested adequately. I modeled their design and adjusted inertia using SolidWorks and was also able to find all other nearby modes were significantly above operating input vibrations. The system tested well, and we verified no hazardous vibrations using Rotec Munich measurement system and laser tachometers pointed at targets applied to engine and both ends of the prop shaft.

Your system with a high revving outboard head will require a prop reduction system somewhere with considerable attention to torsional vibration management, particularly toward driving :
  • If you run the shaft at engine speed and make it a lashless system, you may need a substantial flywheel at the engine end, allow the shaft to be small diameter (engine torque) and relatively torsionally flexible, then the gearbox at the prop hub can operate in a vibrationally clean area. This is the Allison/Airacobra system, and it worked. This system must have the shaft designed for a specific spring rate to put resonance above cranking speed and below idle speed;
  • The alternative is to run the gearbox at the engine end. UGH. First you will need a significant flywheel on the engine, then a soft element such as a clutch disc center spring set or a rubber giubo or other compliant element to prevent the gearbox seeing all of the engine vibe. Then you need a U-joint of some sort to the shaft, then the shaft has to be sturdy enough to carry prop level torque and speed.
Both systems require a bunch of design and analysis work to be even close to being right when you build the first copy. The first type will be lighter and simpler, and thus easier to to make work. The second type will be more difficult to make work as you must isolate torsional vibration of the engine in a small package, then the speed reducer, then a beefier shaft, then the prop. Oh, besides Hertog's book or other ME vibration text, you should look up critical speed calcs for shafts. Whirl mode must be prevented, with several ways of preventing it, including increased shaft diameter (and concurrent increased torsional stiffness), breaking the shaft into more pieces with U-joints and supports (like are done with many trucks), and a system of support bearings as is seen in helo tail rotor shafts.

You did not pick an easy one...

Billski
 
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Toobuilder

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Tractor gyro- no porpoising. Engine behind cockpit -awesome visibility
In aircraft design, we often list pilot visibility in terms of angular degrees as a design requirement. Did you define that angular value and find that the firewall engine interfered with that requirement, or was your goal simply to have "more" visibility?
 

saini flyer

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Besides the already mentioned thread on torsional behaviour, you might find this one useful;


Next, I can tell you that I helped some folks with a Jabiru four cylinder engine, a 44" long shaft, and prop, all in direct drive, tame their vibration. An elastomeric coupling at the engine helped with the shaft alignment issue and allowed the engine to deflect and vibrate on its mounts without overloading the shaft. This also allowed the system to operate without any lash in the system. The shaft was the primary torsional compliance having an adequately low spring rate that, when combined with a substantial increase in engine flywheel inertia, drove resonance down near engine idle rpm, and tested adequately. I modeled their design and adjusted inertia using SolidWorks and was also able to find all other nearby modes were significantly above operating input vibrations. The system tested well, and we verified no hazardous vibrations using Rotec Munich measurement system and laser tachometers pointed at targets applied to engine and both ends of the prop shaft.

Your system with a high revving outboard head will require a prop reduction system somewhere with considerable attention to torsional vibration management, particularly toward driving :
  • If you run the shaft at engine speed and make it a lashless system, you may need a substantial flywheel at the engine end, allow the shaft to be small diameter (engine torque) and relatively torsionally flexible, then the gearbox at the prop hub can operate in a vibrationally clean area. This is the Allison/Airacobra system, and it worked. This system must have the shaft designed for a specific spring rate to put resonance above cranking speed and below idle speed;
  • The alternative is to run the gearbox at the engine end. UGH. First you will need a significant flywheel on the engine, then a soft element such as a clutch disc center spring set or a rubber giubo or other compliant element to prevent the gearbox seeing all of the engine vibe. Then you need a U-joint of some sort to the shaft, then the shaft has to be sturdy enough to carry prop level torque and speed.
Both systems require a bunch of design and analysis work to be even close to being right when you build the first copy. The first will be lighter and simpler, and thus easier to to make work. The second will be more difficult to make work as you must isolate torsional vibration of the engine in a small package, then the speed reducer, then a beefier shaft, then the prop. Oh, besides Hertog's book or other ME vibration text, you should look up critical speed calcs for shafts. Whirl mode must be prevented, with several ways of preventing it, including increased shaft diameter (and concurrent increased torsional stiffness), breaking the shaft into more pieces with U-joints and supports (like are done with many trucks), and a system of support bearings as is seen in helo tail rotor shafts.

You did not pick an easy one...

Billski
Billski, how does things change if you have an electric brushless motor instead of the ICE? I understand something needs to be done with a zillion pounds of battery for an electric plane and sorry for the thread drift but the same reasoning for a very good visibility in this design holds for fixed wing too. There can be two options: one with only battery power and the other with a serial hybrid generator.
 

wsimpso1

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Billski, how does things change if you have an electric brushless motor instead of the ICE? I understand something needs to be done with a zillion pounds of battery for an electric plane and sorry for the thread drift but the same reasoning for a very good visibility in this design holds for fixed wing too. There can be two options: one with only battery power and the other with a serial hybrid generator.
Yes, this is thread drift from the OP, but I will bite for a little.

All motors exhibit some cogging and that vibration can be a vibe input that may need to be managed. Even turbines have blade passing frequencies that show up as vibration inputs. Much of the early vibration theory was developed around steam powerplants, first steam piston engines, then steam turbines. The important thing is still the range of vibration frequencies and keeping the range of resonant modes away from the range of input vibrations. That is how you avoid exciting resonant vibrations.

If you want to talk more about this, please open a thread with your questions, etc.

Billski
 
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Blackhawk

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Oh goodness, that looks amazing- I built a previous itteration which had a dual vertical rudder and chucked it because of wanting to reduce complexity. i think by going to a single rudder i eliminated 18 parts. I would settle for 125hp but i guess there is never enough power is there.
Reducing the complexity of the tail feathers may cause you some dissapointment in handling for the sake of the 18 parts you saved.

All gyrocopters draw air up through the rotor blades for lift; they also draw up air from the prop thrust; tractor gyros have a greater distance between the prop which lose considerable prop thrust being drawn up through the rotor baldes before it gets to the rudder.

Pusher gyros don't suffer this problem anywhere near as bad because the prop to rudder distance is very close together

Tractor gyro air movement.jpg
I would use twin rudders on any tractor gyro and with my design I could even mount three rudders.
 
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wsimpso1

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Blackhawk,

You went from prop in the front and air motion through the rotor to needing two or three tails, and that leap was way too big for me, maybe for the rest of us too. Please explain how the configuration ends up making multiple tails more desirable than a single tail. Seems to me that one would require a lot of justification to tolerate the downsides of multiple tail planes...

Billski
 

Blackhawk

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What I said above even looked confusing to me.

Just pointing out that you need good rudder authority in a tractor gyro and I would always use a H tail to get the rudders clear of the fuselage for cleaner airflow.

I also said I "could" put triple rudders if I wanted to.
 

Blackhawk

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This is the Jukka Tervamäki 2 seat tractor gyrocopter concept.

I don't like the PSRU up front having a shaft spinning about 6000rpm between me and my passanger; I'd prefer the PSRU back in the engine compartment and have the shaft spinning at about 2500rpm

He has information on the shaft: JT-11 Autogyro

Controls1.jpg JT11kab2side.jpg Controls3.jpg
 
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Blackhawk

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Rear wheel car you can pull over on the side of the road in the event of a problem and also, the shaft is under the car; not at hip height in a confined space like a gyrocopter.
 

wsimpso1

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At engine speed, it carries engine torque. Slow it down to prop speed and it carries several times engine torque. Both take being designed for their loads and speeds.

The high driveshaft between the seats exists in a lot of cars, all Corvettes up until the current one, many Euro sports cars, Cobras, and so on. Yeah, the tranny comes back past your knees, but it is shaft from there back.

Maybe a driveshaft loop or two would make sense. In a composite airframe, it could be a couple beefy Kevlar rings laminated in. That was the racecar rule to keep drivshafts out of the cabin or the ground.

Billski
 
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