Post by wildflyer on Aug 28, 2023 19:14:40 GMT -6
I was hoping to copy the Schubler WIKI The Power to Weight Ratio, for info for you. But some how the formulas will not copy and it would take a math major to understand them anyway.
You can look at the full deal here, www.schubeler.com/the-power-to-weight-ratio/?v=7516fd43adaa
There is some high level math that they don't really explain and I didn't make it through calculus
One time I put an EDF unit in a prop jet, expecting hi speed, it just barely stayed in the air. I sure didn't get it right.
For us really only the bottom chart will give you the possible results for an EDF plane. hope this helps a little, I put an EDF unit in a prop jet, expecting hi speed, it just barely stayed in the air.
Case Study: Minijets Stinger with DS-51-AXI HDS and HET 700-68-1125kV
In order to avoid a disappointment due to unexpected flight behavior or insufficient performance of the planned model, we would like to take the opportunity to present some substantiated criteria enabling the realization of the favored characteristics for the model.
A simple calculator is sufficient for all the indicated formulas. The required data are easily definable with the manufacturer information or by means of a scale (weight).
An important point when choosing the right fan unit for the model is the power/weight ratio. In contrast to the thrust/weight ratio this also considers exhaust speed (all calculations refer to max. battery voltage).
Power/weight ratio:
refers to the output power,
refers to the overall model weight. This is determinable with a scale or can be calculated after having chosen the fan system.
can be calculated with thrust and exhaust speed data which are available in our measurement diagrams.
In order to get
it is also important to consider the efficiency factor of the channels of our model.
from exhaust speed and thrust:
The efficiency factor of the channels
at the extreme could reach values of about 65%. Such an extreme case could occur for example with high velocity models at standstill.
With these fast models and an advantageous design of the ducted fan the efficiency factor will increase remarkably during the flight due to more beneficial inlet flow and a more effective flow around the blades.
Consequently, the efficiency factor of the channel adopts different values depending on the model and flight phase.
In the following you can find estimated factors which occur during the flight:
Short Airliner nacelle, large intake lip radius (e.g. models like Airbus A-300, Boeing 737) ----95%
Long straight nacelle (e.g. ME-262)----90%
Very long, but straight channels (e.g. MiG-15 etc. but also SU-27)----85%
Curved channels with small cross-sections, small intake lip radius (e.g. Vampire, F-16, Pampa etc.)----85%
These values are considered as approximate indications for informational purposes about the different flow conditions according to the model.
In order to incorporate it is necessary to simply multiply with the corresponding value for
.
e.g.: My F-16, 485watts on a wattmeter x curved channels , 85% = 327 watts effective ( if I under stand the math correctly)
The resulting value (P abges) now has to be plugged into the first equation and then divided by the model weight (e.g. Minijets Stinger 3,7kg).
That way we receive a parameter for our model which enables us to estimate its flight performance with assistance of the following table.
Model type:
high speed model: 500 – 800 W/kg
sporty Jet, Trainer: 300 – 500 W/kg
moderate speed Jet (Me-262, A-10 etc.): 200 – 300 W/kg
Airliner, Transporter: 150 – 200 W/kg
The values indicated in the table above refer to battery peak voltage; they are on the high-performance side and are well-achievable with our propulsion systems.
You can look at the full deal here, www.schubeler.com/the-power-to-weight-ratio/?v=7516fd43adaa
There is some high level math that they don't really explain and I didn't make it through calculus
One time I put an EDF unit in a prop jet, expecting hi speed, it just barely stayed in the air. I sure didn't get it right.
For us really only the bottom chart will give you the possible results for an EDF plane. hope this helps a little, I put an EDF unit in a prop jet, expecting hi speed, it just barely stayed in the air.
Case Study: Minijets Stinger with DS-51-AXI HDS and HET 700-68-1125kV
In order to avoid a disappointment due to unexpected flight behavior or insufficient performance of the planned model, we would like to take the opportunity to present some substantiated criteria enabling the realization of the favored characteristics for the model.
A simple calculator is sufficient for all the indicated formulas. The required data are easily definable with the manufacturer information or by means of a scale (weight).
An important point when choosing the right fan unit for the model is the power/weight ratio. In contrast to the thrust/weight ratio this also considers exhaust speed (all calculations refer to max. battery voltage).
Power/weight ratio:
refers to the output power,
refers to the overall model weight. This is determinable with a scale or can be calculated after having chosen the fan system.
can be calculated with thrust and exhaust speed data which are available in our measurement diagrams.
In order to get
it is also important to consider the efficiency factor of the channels of our model.
from exhaust speed and thrust:
The efficiency factor of the channels
at the extreme could reach values of about 65%. Such an extreme case could occur for example with high velocity models at standstill.
With these fast models and an advantageous design of the ducted fan the efficiency factor will increase remarkably during the flight due to more beneficial inlet flow and a more effective flow around the blades.
Consequently, the efficiency factor of the channel adopts different values depending on the model and flight phase.
In the following you can find estimated factors which occur during the flight:
Short Airliner nacelle, large intake lip radius (e.g. models like Airbus A-300, Boeing 737) ----95%
Long straight nacelle (e.g. ME-262)----90%
Very long, but straight channels (e.g. MiG-15 etc. but also SU-27)----85%
Curved channels with small cross-sections, small intake lip radius (e.g. Vampire, F-16, Pampa etc.)----85%
These values are considered as approximate indications for informational purposes about the different flow conditions according to the model.
In order to incorporate it is necessary to simply multiply with the corresponding value for
.
e.g.: My F-16, 485watts on a wattmeter x curved channels , 85% = 327 watts effective ( if I under stand the math correctly)
The resulting value (P abges) now has to be plugged into the first equation and then divided by the model weight (e.g. Minijets Stinger 3,7kg).
That way we receive a parameter for our model which enables us to estimate its flight performance with assistance of the following table.
Model type:
high speed model: 500 – 800 W/kg
sporty Jet, Trainer: 300 – 500 W/kg
moderate speed Jet (Me-262, A-10 etc.): 200 – 300 W/kg
Airliner, Transporter: 150 – 200 W/kg
The values indicated in the table above refer to battery peak voltage; they are on the high-performance side and are well-achievable with our propulsion systems.
