<p>You're right that the physical limit is the reduced density of air at altitude, but it's a little more complicated. As density decreases planes have to fly faster to generate the same amount of lift. They can do this because drag also reduces with density - so really the limit is Mach number. If you go high enough, your stall speed approaches the speed of sound and shockwaves cause extra drag.</p>
<p>Most aircraft are also limited by air-breathing engines. Propeller powered planes are limited by the speed of the propeller tips. These are going faster than the rest of the plane and will hit Mach number issues first.</p>
<p>The absolute altitude limit will be an optimisation problem rather than a hard number, but I think it's safe to look at the best NASA has been able to do:</p>
<blockquote>
<p>Pathfinder raised the altitude record for solar-powered aircraft — as well as propeller-driven aircraft — to 71,530 feet (21,800 m) on July 7, 1997</p>
</blockquote>
<p><a href="https://en.wikipedia.org/wiki/NASA_Pathfinder#Flight_testing_and_records" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/NASA_Pathfinder#Flight_testing_and_records</a></p>
<p>I suppose the theoretical limit is the <a href="https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line" rel="nofollow noreferrer">Kármán line</a> at 100km, which was originally intended to be the point where the air is too thin to provide meaningful lift - but that's largely theoretical.</p>

CC BY-SA 4.0
2022-02-07T09:26:57.997Z
2022-02-07T09:33:04.110Z
2022-02-07T09:33:04.110Z
Robin Bennett
<p>Assume I programmed my drone to fly on it's own.  How high can it fly?  (Again, ignore laws).  Is there a physical limitation due to amount of air?  Is the answer the same if it is was part glider?  (ie very large wings)?</p>
<p>If I wanted it to take pictures every so often and give its position on a twitter account.  I assume I have to use a satellite phone.  What is the cheapest/best worldwide satellite phone to use?</p>

CC BY-SA 4.0
2022-02-06T05:44:28.590Z
It's quite possible you could connect to a regular mobile phone network. The range of cell towers can be up to 45 miles, so since you'd only be flying under 10 miles up (roughly airliner cruising height, which is way higher than a small (<2m) drone could reach), you'd probably have connection. However, even ignoring the airspace limitations, it might be illegal to have a cell phone emitting that high in the air. Apart from FAA laws, I think your biggest issue would be building a craft that has enough battery capacity to drive a powerful motor for long enough to reach cruising altitude at all.
ThatCoolCoder
CC BY-SA 4.0
2022-02-06T12:56:26.057Z
I said ignore all laws.  This will be over the ocean, so regular mobile phone won't work.  I will be building a solar plane (part glider).
Markis Gardner
CC BY-SA 4.0
2022-02-07T09:37:47.690Z
This site's format doesn't work well for asking multiple questions because we won't be able to vote for the best answer. I think you'd be better to move the second paragraph to a new question.
Robin Bennett
<long-range-drone>
For an autonomous propeller drone plane, what is the absolute highest it can fly (disregard any laws)?
Markis Gardner
# For an autonomous propeller drone plane, what is the absolute highest it can fly (disregard any laws)?

(Asked by: username_0 on 2022-02-06)

Assume I programmed my drone to fly on it's own. How high can it fly? (Again, ignore laws). Is there a physical limitation due to amount of air? Is the answer the same if it is was part glider? (ie very large wings)?

If I wanted it to take pictures every so often and give its position on a twitter account. I assume I have to use a satellite phone. What is the cheapest/best worldwide satellite phone to use?

**Tags:** long-range-drone

> **Comments:**
> **username_1**: It's quite possible you could connect to a regular mobile phone network. The range of cell towers can be up to 45 miles, so since you'd only be flying under 10 miles up (roughly airliner cruising height, which is way higher than a small (<2m) drone could reach), you'd probably have connection. However, even ignoring the airspace limitations, it might be illegal to have a cell phone emitting that high in the air. Apart from FAA laws, I think your biggest issue would be building a craft that has enough battery capacity to drive a powerful motor for long enough to reach cruising altitude at all.  
> **username_0**: I said ignore all laws.  This will be over the ocean, so regular mobile phone won't work.  I will be building a solar plane (part glider).  
> **username_2**: This site's format doesn't work well for asking multiple questions because we won't be able to vote for the best answer. I think you'd be better to move the second paragraph to a new question.  

---

## 1 answers

### Answer by username_2 on 2022-02-07. Score: 2

You're right that the physical limit is the reduced density of air at altitude, but it's a little more complicated. As density decreases planes have to fly faster to generate the same amount of lift. They can do this because drag also reduces with density - so really the limit is Mach number. If you go high enough, your stall speed approaches the speed of sound and shockwaves cause extra drag.

Most aircraft are also limited by air-breathing engines. Propeller powered planes are limited by the speed of the propeller tips. These are going faster than the rest of the plane and will hit Mach number issues first.

The absolute altitude limit will be an optimisation problem rather than a hard number, but I think it's safe to look at the best NASA has been able to do:

> Pathfinder raised the altitude record for solar-powered aircraft — as well as propeller-driven aircraft — to 71,530 feet (21,800 m) on July 7, 1997

<https://en.wikipedia.org/wiki/NASA_Pathfinder#Flight_testing_and_records>

I suppose the theoretical limit is the [Kármán line](https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line) at 100km, which was originally intended to be the point where the air is too thin to provide meaningful lift - but that's largely theoretical.


---

