Project Ladybug

[Asker]

I have collected all the materials I required for the next blade making attempt, hoping for it to be the final one that nails it. Just honing my hocus pokus skills aka the making process, at the moment.

 

[Asker]

Hello folks,

I have taken my time to prepare to cast a blade and I am all set to go for it now but I still want to wait to see if there needs to be a requirements change. If I can make a larger blade I will make it larger without wasting money just to test my blade making skills.

 

[Asker]

Hi,
I have gotten into exploring the coaxial design a little further before I push the buttons to start building the Ladybug for the Gofly. As my choice of single top rotor is mainly for better autorotation capability and better ground clarence for safety purposes which do not have any meaning for the competition prototype, so I am equally considering a coaxial design and I am looking for insights regarding the merits and demerits of

1. A 25cm rotor separation: This is important as I make the distance longer I will have to make the bottom rotor smaller as I have to meet 8.5ft size requirement.
2. Bottom rotor 8 cm smaller in diameter: Again the dimensional constraint.
3. 4 blade top rotor and 3 4 or 5 blade bottom rotor
4. No teetering, with somewhat flexible composite and elastomeric elements

I am also thinking if I go very simple with the most basic gear arrangement it will be simpler to build than the top and tail rotor arrangement. Which is only one gear rather than with and additional tail gear.

@btd1982 and others

 

[btd1982]

I personally think coaxial or intermeshing is the choice most likely to succeed. Coaxial's can autorotate just like conventional's can but you obviously need blade feathering for that.
You will be able to use a single stage gear reduction easily as your rotor will be spinning fast, that will help with weight and friction losses and synchronous belts can be up to 98% efficient. Another option is poly 'v' belts and belt tightening pulleys instead of the heavier centrifugal clutch needed for synchronous belts.

 

[Asker]

I personally think coaxial or intermeshing is the choice most likely to succeed. Coaxial's can autorotate just like conventional's can but you obviously need blade feathering for that.
You will be able to use a single stage gear reduction easily as your rotor will be spinning fast, that will help with weight and friction losses and synchronous belts can be up to 98% efficient. Another option is poly 'v' belts and belt tightening pulleys instead of the heavier centrifugal clutch needed for synchronous belts.

Tighten your belts, we are taking off!

Absolutely, I will use belt tightening and not a clutch.

When I say autorotation I refer to the rotors ability to keep turning due too its higher inertia when the engine power is cut off and not the auto rotative maneuver of a classical helicopter that requires feathering of blades and a skilled pilot. This autorotation is a short lived one but it will be enough if it gives like 5 seconds of time for an electric motor to take over the engines load.

 

[Vance]

Tighten your belts, we are taking off!

Absolutely, I will use belt tightening and not a clutch.

When I say autorotation I refer to the rotors ability to keep turning due too its higher inertia when the engine power is cut off and not the auto rotative maneuver of a classical helicopter that requires feathering of blades and a skilled pilot. This autorotation is a short lived one but it will be enough if it gives like 5 seconds of time for an electric motor to take over the engines load.

In my opinion what your describe is not autorotation and it my opinion any value of what you describe will be very short lived.

 

[Asker]

In my opinion what your describe is not autorotation and it my opinion any value of what you describe will be very short lived.

Helicopter pilots have around 2 seconds of time to react to an engine out situation. If they react in time to an engine out they can hope to have enough energy left to feather a landing. 5 seconds is very short lived too, I am thinking. However in the case of an 8.5ft rotor the inertia of the blades will be very low unless additional weight is put on the blades which is again out of question in this case. I am not relying on autorotation as a safety measure, I am relying on redundancy of engines. The question is do I run a second engine in parallel the whole time of the flight or do I start that engine when a power failure of the main engine is detected. And if I start the backup engine on failure of the first one how much time do I get to bring that motor to full power. Electric motors can rev up to full power in a few seconds. Maybe I just keep the motor on idle and engage when I detect the outage.

 

[Mayfield]

Helicopter pilots have around 2 seconds of time to react to an engine out situation. If they react in time to an engine out they can hope to have enough energy left to feather a landing. 5 seconds is very short lived too, I am thinking. However in the case of an 8.5ft rotor the inertia of the blades will be very low unless additional weight is put on the blades which is again out of question in this case. I am not relying on autorotation as a safety measure, I am relying on redundancy of engines. The question is do I run a second engine in parallel the whole time of the flight or do I start that engine when a power failure of the main engine is detected. And if I start the backup engine on failure of the first one how much time do I get to bring that motor to full power. Electric motors can rev up to full power in a few seconds. Maybe I just keep the motor on idle and engage when I detect the outage.

Which is simpler and lighter, a separate drive motor, or a rotor pitch change mechanism?

 

[Asker]

Which is simpler and lighter, a separate drive motor, or a rotor pitch change mechanism?

I my case because I am restricted with only 8.5ft of rotor diameter it won't help with autorotation even if I had a pitch change mechanism. When size restrictions do not apply I would still go for an electric motor backup and keep the rotor simple. Whichever is actually simpler to achieve for a given person and conditions. Remember the Gen4 fixed blade coaxial helicopter, it relies on multiple engines too.

I am also looking for simplicity and low cost of building the thing too as I am not fully funded.

 

[Mayfield]

Thanks for your response. Best wishes for your success.

 

[Vance]

Helicopter pilots have around 2 seconds of time to react to an engine out situation. If they react in time to an engine out they can hope to have enough energy left to feather a landing. 5 seconds is very short lived too, I am thinking. However in the case of an 8.5ft rotor the inertia of the blades will be very low unless additional weight is put on the blades which is again out of question in this case. I am not relying on autorotation as a safety measure, I am relying on redundancy of engines. The question is do I run a second engine in parallel the whole time of the flight or do I start that engine when a power failure of the main engine is detected. And if I start the backup engine on failure of the first one how much time do I get to bring that motor to full power. Electric motors can rev up to full power in a few seconds. Maybe I just keep the motor on idle and engage when I detect the outage.

It reads to me like you do not understand how an autorotation to the ground is done in a helicopter.

The seconds you mention are to get the collective down after the engine stops making power.

There is no time limit on an autorotation to the ground.

There are many video’s on the internet showing what is involved.

Pulling collective at the end is part of an autorotation to the ground.

I feel a better understanding of how autorotation woks will be helpful in understanding your challenges.

 

[Asker]

It reads to me like you do not understand how an autorotation to the ground is done in a helicopter.

The seconds you mention are to get the collective down after the engine stops making power.

There is no time limit on an autorotation to the ground.

There are many video’s on the internet showing what is involved.

Pulling collective at the end is part of an autorotation to the ground.

I feel a better understanding of how autorotation woks will be helpful in understanding your challenges.

I do know, I have read the pilots training manual and I have seen many videos.
There is absolutely no time limit before you can touch down as long as you are at an altitude or you have a never ending headwind.

I mean pilots have 2 seconds to lover the collective then how much more time would I have to add to that before I rev up the motor and resume power. It will depend on how high I am and what the sink rate of the helicopter is.

 

[btd1982]

If using a second engine as a fail safe it would have to be running at the same rpm as the primary engine and ready to give full power when it's needed. It's not an option to have the secondary engine switched off or even at idle. Two stroke engines don't like idling and could very well stall when it's needed.
Electric motor is the solution to an engine failure I think and needs to cut in automatically, you just have to incorporate it into the belt drive, driven with a one way bearing, the same as the engine.

With my low inertia blades even weighing 2.6kg each and fixed pitch, there is very little time between shutting off the throttle and decent. Yours could well be worse and a near immediate power replacement would be necessary.

 

[Asker]

If using a second engine as a fail safe it would have to be running at the same rpm as the primary engine and ready to give full power when it's needed. It's not an option to have the secondary engine switched off or even at idle. Two stroke engines don't like idling and could very well stall when it's needed.
Electric motor is the solution to an engine failure I think and needs to cut in automatically, you just have to incorporate it into the belt drive, driven with a one way bearing, the same as the engine.

With my low inertia blades even weighing 2.6kg each and fixed pitch, there is very little time between shutting off the throttle and decent. Yours could well be worse and a near immediate power replacement would be necessary.

Exactly my thinking.

The question now is what do I do to to keep the electric motor consuming the least amount of battery power while also being on standby to engage in the quickest fashion possible. This allows me to have a smaller battery and possibly a smaller motor which can exert a high power for a small amount of time like 10 seconds which will allow me to land safely. The amount of time this system allows will dictate my flight altitude as well. There are motors that allow seconds to minutes in their highest powers and the right choice of motors+drivers and batteries will mean the ideal amount of weight and safety factor. There is also the possibility of using several electric motors together on the same belt.

 

[Asker]

I am also revising structural elements for easier and cheaper contruction and in a way to distribute weights for a more comfortable seating of the rider. This may introduce some more weight but I will see the ups and downs and chose between comfort and lower weight. I may simply introduce a joint to bring the shaft off of the axis of the rotor so that the rider can sit closer in to the center of gravity.

 

[Asker]

I am also wondering if a one piece tail rudder will do the job of a two piece one.

 

[btd1982]

I'm sure the motor or speed controller specifications will tell you how quickly it will go from zero to full rpm. I would have thought it would be quick enough. The Hungaro copter is developing an electric back up system

Electric Rescue System

hungarocopter.hu

Difficult to say how much tail fin area you will need. By comparison mine has 0.5m2 total area and provides good authority at 1.7m radius from centre. It's only the wind that causes issues, in a still environment I could have half that area and it would be effective enough.

 

[Asker]

From what I know the time required to rev up a brushless electric motor is around 1 second when not under load. This time would probably be around the same at the moment when the petrol engine is taken out as the belt is still turning fast.

 

[Asker]

I want to build the Ladybug as an electric only machine that will only fly a person for around a minute and test it out and move on from there. This will bring down the cost of first manned flight to around $4k if it all goes to plan. I am actually wondering how long it can fly on electric power alone.

 

[Asker]

Hello folks,

I am preparing for an investor presentation but I have not been able to find details of a good coaxial gearbox design for my coaxial type helicopter. I am looking at Nolan, AirScooter and Gen4 and similar designs. There are some others too but I don't see very legible visuals of them. I need to know which one is robust and reliable and to see details which can be copied, please.

Fixed pitch blade, counter (contra) rotating, coaxial.

My own webpage showing links to similar designs

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