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EDF or Prop for high altitude?

#1
Hello all!
I was recently gifted the X-29 for the holidays and need to obtain the electronics to make it fly. I live at 7000ft altitude and have been flying a simple scout with no issues at all (power pack B). I plan on buying the power pack C. I am wondering what will work better for high altitude, an EDF or a prop? Also, will a lower Mah battery weigh less? Thanks in advance.
 

d8veh

Well-known member
#2
At 7000ft everything weighs less! Your planes must weigh about half a gram less than mine if you built them the same.

Air density is less though, so your plane will have to fly faster than mine. It's only about 20% difference, so shouldn't be anything to panic about.
 
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Hai-Lee

Old and Bold RC PILOT
#3
Hello all!
I was recently gifted the X-29 for the holidays and need to obtain the electronics to make it fly. I live at 7000ft altitude and have been flying a simple scout with no issues at all (power pack B). I plan on buying the power pack C. I am wondering what will work better for high altitude, an EDF or a prop? Also, will a lower Mah battery weigh less? Thanks in advance.
When flying at altitude the air is thinner and so in order to move the same weight of air you either need to either make the motor turn at higher speed or increase the pitch of the prop/fan. So with an EDF you would need to run it using a battery a cell higher and on a prop driven ship either a larger dia prop or a pitch greater.

In addition it is wise to try to keep the plane as light as is possible because you will need to fly a little faster to gain the same lift as you would at sea level.

Generally smaller capacity batteries weigh less.

Have fun!
 
#4
I am almost leaning towards using a prop because I have had difficulty with EDF planes at this altitude in the past. The airplane I tested was never able to get enough air speed while hand launched to stay flying. I attempted to make the F-22 but I think it was under powered, used a 20amp esc and 3cell battery. I tried both a prop and EDF. It could have been a combination of too much weight and was under powered. I just dont want to make the same mistake. I currently fly the simple scout on a 3 cell battery with no issues.
 

Hai-Lee

Old and Bold RC PILOT
#5
I am almost leaning towards using a prop because I have had difficulty with EDF planes at this altitude in the past. The airplane I tested was never able to get enough air speed while hand launched to stay flying. I attempted to make the F-22 but I think it was under powered, used a 20amp esc and 3cell battery. I tried both a prop and EDF. It could have been a combination of too much weight and was under powered. I just dont want to make the same mistake. I currently fly the simple scout on a 3 cell battery with no issues.
Your attempts using an EDF where doomed to low thrust unless you were able to make it spin a lot faster. A simple fix for your fears is to use the specified motor/ESC/Battery and increase the prop pitch by one!
If you cannot source a higher pitch of the same diameter you could try a larger diameter of the same pitch or even try a 3 bladed prop.

Whatever you use make sure you post your results for others in a similar situation!, (We don't ll live at sea level.\!).

Have fun!
 

quorneng

Well-known member
#6
As other have said the important thing is to recognise that flying at altitude is aerodynamically a bit more difficult.
So what might just work at sea level will struggle the higher you go but a plane capable of 'unlimited vertical' will probably manage fine.

Although, unlike IC, an electric motor is unaffected by altitude (it will produce the same power at the same revs) but the prop it is driving is. To produce the same performance it will have to spin faster, have more pitch, diameter or a combination of all three!
Remember brush less motors are constant speed devices and produce a specific power at a specific rpm. Thus with the same prop the power produced at sea level will be greater than an altitude.
Put another way, as Hai-Lee suggests, when at altitude you will have to fit a bigger prop to get the motor to draw the same current as at sea level but make sure you use a Watt meter to check you are not over doing it!

Going back to your original question an EDF is much less efficient (about 50%) at converting Watts into thrust than a prop so when flying gets a bit more 'difficult' guess which is the better choice.!
 

IcedStorm777

Well-known member
#7
@nightmode

I also live a altitude (7400ft) and am currently building a scratch build 70mm EDF so i will let you know how that goes. Where do you live at such high altitude?
 
#11
Oh wow! small world. I am downtown Colorado Springs. There is a small group of us here that fly electric on Saturday mornings at a local church parking lot. Usually only 3 of us fly and the rest just show up to watch. They arent very active in the cold weather. Me and my buddy are the ones that fly the most. There is a valley by the garden of the gods that we fly at frequently as well. I'm sure you know about the gas club here out east.
 
#13
Its at heart of the springs church. Its not a club, just a casual meet up place that the church lets people fly at. It has a parking lot with a painted runway and a decently large field.

2726 N Union Blvd, Colorado Springs, CO 80909
 
#14
Greetings nightm0de, IcedStorm777 from another Coloradan! I am up north flying out of Arvada Aeromodelers (https://www.arvadamodelers.com/weather/).
Picking up on Quorneng's post...
As other have said the important thing is to recognise that flying at altitude is aerodynamically a bit more difficult.
So what might just work at sea level will struggle the higher you go but a plane capable of 'unlimited vertical' will probably manage fine.

Although, unlike IC, an electric motor is unaffected by altitude (it will produce the same power at the same revs) but the prop it is driving is. To produce the same performance it will have to spin faster, have more pitch, diameter or a combination of all three!
Remember brush less motors are constant speed devices and produce a specific power at a specific rpm. Thus with the same prop the power produced at sea level will be greater than an altitude.
Put another way, as Hai-Lee suggests, when at altitude you will have to fit a bigger prop to get the motor to draw the same current as at sea level but make sure you use a Watt meter to check you are not over doing it!

Going back to your original question an EDF is much less efficient (about 50%) at converting Watts into thrust than a prop so when flying gets a bit more 'difficult' guess which is the better choice.!
I discovered a formula referred to as the propeller loading factor.

PLF = (diameter^3)*pitch*(number of blades-1)^0.5

It is useful if you want to convert between 2 and 3 blade propellers where you want the same performance.

I decided to use it as a rubric for how much I could out of different props. In my experience with a UMX Timber and a Turbo Timber, I've found that a 40% increase in PLF works well.
BUT, as was said above, you must use a watt meter to see what the current draw really is.

I received all the bits, including the Power Pack C, for my Edge today. I am expecting to try 10x6 and 10x7 props which are 33% and 55% increases respectively from the 10x4.5 stock props.

(As an aside, I've talked to folks at my field flying the Viper and Avanti and they have had no complaints flying EDFs at altitude.)