# Starling 2 Max payload capacity and flight time impact

Source: https://forum.modalai.com/topic/3732/starling-2-max-payload-capacity-and-flight-time-impact
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2024-08-21 02:01:21 UTC by GL Lim
Replies: 2 · Views: 1428

## GL Lim · 2024-08-21 02:01:21 UTC

Hi, may I ask what's the flight time of the Starling 2 Max Outdoor GPS-denied Development Drone without a payload? It is stated as 55+ minutes flight time [here](https://www.modalai.com/products/starling-2-max?variant=48172375310640) and >35 minutes [here](https://docs.modalai.com/starling-2-max-datasheet/).

Would also like to ask what would be the estimated impact on flight time on Starling 2 Max suppose I have a 500g payload that draws ~30W.

Thanks!

## Reply by Alex Kushleyev (ModalAI staff) · 2024-08-26 19:04:19 UTC

@GL-Lim ,

Here is a plot from a PX4 log that was collected during a Starling 2 MAX flight endurance test.

![2c9c2cb8-2fb9-47ed-a4a5-20a97c80736f-image.png](https://forum.modalai.com/assets/uploads/files/1724697325177-2c9c2cb8-2fb9-47ed-a4a5-20a97c80736f-image.png) 

and zoomed in to show the total current draw
![a6137e44-9178-4f5d-8a5a-bb16603dc304-image.png](https://forum.modalai.com/assets/uploads/files/1724697373886-a6137e44-9178-4f5d-8a5a-bb16603dc304-image.png) 

The vehicle is about 500g during the test, and it looks like it drew 4000mAh in the test before the battery was discharged completely.

If you add 500g of payload, your weight will increase 2x, so in ideal world, the flight time will be cut in half. However, motor and battery efficiency will decrease with 2x higher load. When doubling the thrust (2x thrust from each motor), the overall motor/propeller efficiency will decrease around 25-30% (roughly, based on some prior test data).

It looks like at hover the vehicle draws about 55-60W, so that is consistent with discharging 4000mAh (~60Wh) battery, in just under an hour. 

For flight with 2x mass without extra power draw, we would calculate:

60W * 2 * 1.33 = 160W (1.33 correction factor for 75% motor efficiency = 1/0.75)

adding 30W that the payload would draw,
160W + 30W = 190W

take original 60Wh battery, divide by the new power consumption:
60Wh / 190W = 0.32h = ~19 minutes (very roughly, to full battery discharge)

without extra 30W power draw (by payload), the flight time would be appriximately:
60Wh / 160W = 0.375h = 22.5 min (very roughly)

This is not taking into account the battery efficiency loss and assuming hover flight (any maneuvers will cause higher power draw from motors, obviously)

I hope this gives you some idea how to estimate the flight time for different loads. I will double check to see what data we have for loaded flights on the Starling 2 Max. Please let me know if you have additional questions about the calculation.

Alex

## Reply by GL Lim · 2024-08-29 00:54:17 UTC (in reply to Alex Kushleyev)

@Alex-Kushleyev Thanks for your insightful reply!!