Project Ladybug

Asker

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Hi, my name is Murat,

I want to make a small helicopter and enter it in the Gofly Prize.
The main requirement of the competition is that the rotor can not be any bigger than 8.5ft.
I have no clue if my rotor will lift the 400lb MTOW that I want it to lift.
Looking for any thoughts while I am designing my single main rotor.
 
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Asker

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Hello again,

I am still recovering from a cold and I had little time with calculations.
Below is the relevant part of the spreadsheet and we need some modifications.

My rotor is 4 blades and it is fixed pitch. I can increase the blade count to five or six.
Blue numbers are entered by hand and green ones are calculated.
Numbers in rectangles are not entered by me.

I am more interested in 30mph and 63mph speeds as my design is a Part 103.
So, how do I factor in my number of blades, if I can?
What are the numbers telling?

rotor.png
 

Mike G

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This looks like Chuck Beaty's autorotating gyrocopter spreadsheet, I'm not sure it's applicable to a helicopter.
Mike G
 

Asker

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There must be some calculation approach that will at least give some rough approximations.
I guess treating rotor blades like fixed wings will produce some numbers.
 
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XXavier

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I guess treating rotor blades like fixed wings will produce some numbers.

This is a question–and–answer internet site with lots of useful information on aviation: https://aviation.stackexchange.com/

For example, on rotor blades treated as wings:

 

Asker

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This is a question–and–answer internet site with lots of useful information on aviation: https://aviation.stackexchange.com/

For example, on rotor blades treated as wings:

Muchas gracias mi amigo.
 

Jean Claude

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Hi,

I want to make a small helicopter and enter it in the Gofly Prize.
The main requirement of the competition is that the rotor can not be any bigger than 8.5ft.
I have no clue if my rotor will lift the 400lb MTOW that I want it to lift.
Looking for any thoughts while I am designing my single main rotor.

Even if it is possible, you need to know a lot more to do it.
- How much power is required?
- What chord to give the blades?
- What is the optimal twist?
- How many revolutions per minute?
- What sink rate in case of engine failure?
- What amplitude to give to the collective pitch?
- Stability?
- Etc...
There must be some calculation approach that will at least give some rough approximations.
I guess treating rotor blades like fixed wings will produce some numbers.
The blades of a helicopter are almost like wings, but they do not work in the same environment at all: Think that in hovering flight they fly in the air stream deflected by their own previous passages.
This changes radically the results
 

Asker

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Even if it is possible, you need to know a lot more to do it.
- How much power is required?
- What chord to give the blades?
- What is the optimal twist?
- How many revolutions per minute?
- What sink rate in case of engine failure?
- What amplitude to give to the collective pitch?
- Stability?
- Etc...

The blades of a helicopter are almost like wings, but they do not work in the same environment at all: Think that in hovering flight they fly in the air stream deflected by their own previous passages.
This changes radically the results
There are many aspects I need to address to make a helicopter but the main problem is what kind of a rotor system will keep the machine hovering out of ground effect. I have actually already designed the machine and it is not a regular helicopter with cyclic and collective controls but a basic 4 blade fixed pitch rotor. It is one of the unknowns for me how it will handle the dissymmetry of lift issue. I am thinking of using some elastomeric elements to enable flapping and give a tilt to the mast to compensate for lift difference.

I also want to make it a hybrid with electric and gas engines working together and electric will basically help keep the rotor turning until landing in case the main piston engine fails.

The machine is meant to be a very simple helicopter to build and it may be a little lacking in its handling qualities.
I am hoping that it will have some degree of innovation in it and what it will bring to the table is not the highest quality but affordable quality.

At this point I want to make an announcement:
I AM LOOKING FOR FUNDING PARTNERS TO MAKE THE PROJECT FLY AND WIN THE GOFLY PRIZE.
EVERY 1000 DOLLARS GET 1% OF THE SHARES OF THE COMPANY AND I NEED 20.000-30.000 $ TO MAKE IT HAPPEN.
THE GOFLY PRIZE IS 1.000.000 $ AND THE DEADLINE IS SEPTEMBER 26 2022.
THE PRIZE WILL BE AWARDED TO THE FIRST TEAM THAT WILL FLY ACCORDING TO THE COMPETITION RULES AND THERE SEEMS TO BE NO OTHER COMPETITOR STANDING AFTER THE FINALS HELD LAST YEAR.
 
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Jean Claude

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A few preliminary elements to evaluate the power required to lift 400 lbs with a rotor of 8.5 ft diameter.

Without any air friction losses, or blade stall, the induced speed at the disk in hovering flight is given by Froude's theory:
Vi = √(T/2ρS)
(in M K S units), which gives here 16.75 m/s
The power required in these ideal conditions is therefore already worth Vi * T = 30 Kw (i.e. 40 hp) at sea level, to which you must add a further ascent power worth 11 kw if Vz = 600 ft/mn (½*Vz*T).
The whole gives you 48 kW (i.e 65 hp) when you have 15% of various losses by friction and turbulences
 

Asker

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A few preliminary elements to evaluate the power required to lift 400 lbs with a rotor of 8.5 ft diameter.

Without any air friction losses, or blade stall, the induced speed at the disk in hovering flight is given by Froude's theory:
Vi = √(T/2ρS)
(in M K S units), which gives here 16.75 m/s
The power required in these ideal conditions is therefore already worth Vi * T = 30 Kw (i.e. 40 hp) at sea level, to which you must add a further ascent power worth 11 kw if Vz = 600 ft/mn (½*Vz*T).
The whole gives you 48 kW (i.e 65 hp) when you have 15% of various losses by friction and turbulences
Thank you Jean Claude for the insightful analysis.

65 hp is on the high side of the power sources that I can fit in the weight budget but on the other hand the competition does not actually have a requirement for hover and climb. It does not have to go straight up but it has to be able to touch down and take off from an imaginary landing pad of the shape of a cylindrical bucket sitting up.

So I guess it will take some experimentation and a way of combining powers of several motors into one shaft.
I will need a two stroke piston engine and make it work together with one or two electric motors to augment and backup power sources.

However the above calculation is with some ideal propeller of which shape we do not know.
I have sketched a propeller from a Clark-Y airfoil.
When I apply the basic airfoil lift calculation to the rotor it gives me 885 RPM at 68F sea level with 8deg average pitch angle.
Considering some losses I guess I will have to be able to provide up to 1000 RPM to the rotor.

rotor.png
LadyBug.png
 
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Jean Claude

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When I apply the basic airfoil lift calculation to the rotor it gives me 885 RPM at 68F sea level with 8 deg average pitch angle.
In hovering flight, when the thrust is 400 lbs, the flow crosses the disc at the speed Vi. It is in this flow that the blades work and it is thus necessary a much larger pitch setting to obtain a sufficient A.o.A.
 

Asker

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perf25.png

This is a calculation made with the Jukka Tervamaki software.
The limitation here is the software only takes 10ft as the smallest rotor diameter value while my rotor diameter is 8.5ft. So I have plotted 3 lines on the same graph: the bottom one is 12ft, next one up is 11ft and the top one is 10ft which may give an indication to where the 8.5ft line will fall.

perf25b.png

On the rate of climb graph the top plot is 12ft, the middle one is 11ft and the bottom one is 10ft.
 
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Asker

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In hovering flight, when the thrust is 400 lbs, the flow crosses the disc at the speed Vi. It is in this flow that the blades work and it is thus necessary a much larger pitch setting to obtain a sufficient A.o.A.
I see, that's why I will not simply take the 885rpm calculated value as accurate but would take it to 1000rpm for good measure. It would be nice if we knew how much the lift at like 20 miles forward speed is compared to hover flight. I think the image in my previous post sheds some light to it.
 

Asker

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Another consideration about my configuration is the tail is a short one. This is again because of the dimensional constraints of the Gofly Prize competition. Hence the tail rotor falls totally under the rotor footprint and even a little further in than the tip of the blades. This will mean more of the engine power will go to the tail rotor than the typical 10%. I took it as 15% in the calculations.
 
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Jean Claude

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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
A few preliminary elements to evaluate the power required to lift 400 lbs with a rotor of 8.5 ft diameter.

Without any air friction losses, or blade stall, the induced speed at the disk in hovering flight is given by Froude's theory:
Vi = √(T/2ρS)
(in M K S units), which gives here 16.75 m/s
The power required in these ideal conditions is therefore already worth Vi * T = 30 Kw (i.e. 40 hp) at sea level, to which you must add a further ascent power worth 11 kw if Vz = 600 ft/mn (½*Vz*T).
The whole gives you 48 kW (i.e 65 hp) when you have 15% of various losses by friction and turbulences
Sorry, it's Vi = 11.7 m/s instead of 16.7 m/s, as I had found by mistake.
 

Asker

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perf26.png

This software gives the best approximation when I set it to the metric system when I can set the rotor diameter to as low as 2.95 meters (10ft in US option) while the actual diameter is 2.59 meters. I can also increase the blade count to 5 but the software only allows up to 4. What benefit can come from having 5 blades, any comments?
 
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Asker

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A different calculation with a smaller engine combination

perf27.png

I am looking for a good way to combine piston engine and electric motor powers into one shaft that will not add too much weight, any ideas?
 
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