Modeling propeller aircraft in heliciel
Tutorial design of a propeller plane (2/2) optimize

Following the tutorial propeller aircraft design (1/2)


The parameters available to us to optimize our propeller are:

At the imposed rotational speed (8000 rpm) and 7 blades, we obtained (tutorial propeller aircraft design(1/2)) thrust a little low 22 N instead of 30 N necessary to compensate the drag:

propeller performances

To increase thrust without increasing the speed we could use what we have seen on the shape of the profiles, and increase the camber of our profile. Under the tab 2.2 "profile law" we see that the profile used for our blade is naca 1408

blade profile naca1408

Click on "choose another profile" to display the database profiles, under the tab "database" grid profile data can be sorted by clicking the column header.The header cz_f_max indicates profiles lift coefficients at the best lift/drag ratio.Click ont this header to sort the grid according the best CL. lift at best lift drag ratio

In this database choose the profile with better Cz (lift coefficient): The naca6412 . Note that the camber is more pronounced than the naca 1408

naca 1408

To apply this new profile to our propeller click "Default Profile (profil law)"

profile blade propeller

Restore the rotational speed of 8000 rpm, and then click "rebuild twist at the operating point": construcion vrillage pale helice , the new performances of our propeller are displayed:

propeller performances

thrust (60 N) has actually increased due to the increase in lift, but torque also (3.7 Nm), while our engine can provide only 1.9 Nm
To reduce torque without changing the speed we could go back to the database and find a profile with a lower Cd (The drag coefficient is largely responsible for the torque) , the same way that we have done to look for a lift coefficient stronger. But we are in a tutorial, so we will choose to reduce the number of blade to explore other levers.
As the thrust is more important than what we need, take off a few blades, 7 is a bit much , and it will save money: Tab 3 "Optimize" we can change the number of blades:

number blades propeller

apply 5 blades and rebuild:vrillage pale

propeller performances

The thrust is inow 45 N and torque 2.5Nm, the thrust and torque decreased but not enough to our goal of 30 N for 1.9 Nm,

so let's apply to 3 blades and rebuild: reconstruire vrillage , résults:

propeller blade performances

Resistant torque of our propeller fell below 1.9Nm, but the thrust is only 28 N
A blade more? no, too expensive, and we understand how changing the number of blade varies our performance, so let's try an other lever:
Modify slightly the geometry of our blade: to increase thrust, we can increase slightly the surface of the blade by modifying the chords distribution:

blade distribution chords

This slider controls the equation, distribution of cords, he is sensitive, if youcan't find this equation, click " linearize " to restart from a linear cord, and repeat the operation:

blade chord distribution

cette nouvelle distribution de cordesi a pour effet de gonfler un peu la pale:

blade shape

and rebuild:vrillage helice

propeller thrust

The thrust is now 32 Newton with a couple of 1.7 Nm This propeller is adapted to our specifications.
We have seen here how to adapt our propeller to operating conditions imposed, but the propulsive efficiency of our propeller is 0.76. A profile can work on, perhaps, slightly increase the efficiency..

The levers are multiple, to optimize a propeller.There is no magic formula, because the specifications are as varied as the goals. HELICIEL combines the functions to test hypotheses optimization we want to follow, but the choice of compromise is infinite and yours.

see: multiple analysis, a tool for editing curves to test the propeller

return to Tutorial design propeller plane (1)