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Author Topic: Is an EDF a 'reaction motor'?  (Read 403 times)
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billdennis747
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« on: October 11, 2019, 02:54:52 AM »

Can't find a definition. I would have thought no but am happy to be told otherwise.
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cvasecuk
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« Reply #1 on: October 11, 2019, 05:49:55 AM »

No. It is simply a propeller within a shroud, albeit a rather long one!
Ron
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Bredehoft
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« Reply #2 on: October 11, 2019, 07:20:26 AM »

definition:  https://en.wikipedia.org/wiki/Reaction_engine

EDF = Electric Ducted Fan

i'd say no.

--george
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Viperkite
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« Reply #3 on: October 11, 2019, 07:49:02 AM »

I always thought a 'reaction' meant something changing it's properties in some way.
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billdennis747
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« Reply #4 on: October 11, 2019, 07:57:46 AM »

No. It is simply a propeller within a shroud, albeit a rather long one!
Ron

Thanks all - it isn't, is it.
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strat-o
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« Reply #5 on: October 11, 2019, 10:58:45 AM »

The definition of a reaction motor excludes ducted fans but includes turbojets.  I'd argue, from a black-box perspective (and maybe a pair of earplugs) that there is little kinetic difference between a turbojet and an EDF, other than in a turbojet the eflux is hot, but temperature difference doesn't seem to be part of the reaction motor definition.  The use of electricity is not a disqualifier either because ion engines meet the reaction motor definition

As an interesting side note, I believe that the mathematical models for reaction motors mostly apply to EDFs as well.
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FreeFlightModeller
Russ Lister
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« Reply #6 on: October 11, 2019, 11:17:23 AM »

As I see it, an EDF motor still acts as an airscrew so does not qualify as a reaction motor.
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TimWescott
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« Reply #7 on: October 11, 2019, 12:43:49 PM »

As I see it, an EDF motor still acts as an airscrew so does not qualify as a reaction motor.

Don't overcategorize.

A turbofan engine is basically a ducted fan powered by a gas turbine.  A high-bypass one is going to pretty much act like an EDF (albeit a really big EDF).

There's a lot of engineering problems where you'll take something that could belong to more than one category (like an EDF being a reaction engine) and either put it in that category or not, because it makes the problem easier to solve.

So unless there's some competition rule involved, call your motor a reaction motor or not.  Or call it a reaction motor in some circumstances, but not others.

If there is a competition rule involved, then no matter how stupid you think the rule is, call your motor a "reaction motor" if it fits the rule's definition.
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FreeFlightModeller
Russ Lister
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« Reply #8 on: October 11, 2019, 02:23:45 PM »

I didn't think I was over- categorizing?
I would only regard a "pure" reaction motor as a reaction motor ie. One expelling reaction mass only.
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SP250
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« Reply #9 on: October 11, 2019, 02:51:36 PM »

Bill

My take on it is a reaction motor has no air inlet, whereas an EDF or a gas turbine does have an inlet.
So Newton's 3rd law applies for a reaction motor to be categorised as such - burning a supply of on-board fuel, not just accelerating a column of air.
In agreement with Russ.

An EDF should be in the electric class.

John M
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TimWescott
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« Reply #10 on: October 11, 2019, 04:14:27 PM »

I didn't think I was over- categorizing?
I would only regard a "pure" reaction motor as a reaction motor ie. One expelling reaction mass only.

I would have, too, but Wikipedia defines jet engines as reaction motors, and they need air coming in.

I think that you have a spectrum, with propellers (essentially spinning wings) on one end, and rockets on the other.  In between there are ducted fans and turbofans and turbojets, which may or may not be categorized as "reaction motors" depending (apparently!) on who's talking.
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FreeFlightModeller
Russ Lister
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« Reply #11 on: October 11, 2019, 04:38:51 PM »

True, but as I see it, the intake of air in a jet is to enable the burning of the reaction mass to be expelled .... it's an "ingredient ", rather than the medium through which the airscrew works. Sorry if I'm not explaining myself too well!
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wms
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« Reply #12 on: October 15, 2019, 06:29:22 PM »

How About Pulse Jets? Kind Like? Maybe
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charlieman
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« Reply #13 on: November 26, 2019, 10:42:34 PM »

Is a toy balloon a reaction motor when the filler end Is released and it rockets about the room?
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lincoln
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« Reply #14 on: November 27, 2019, 02:15:19 AM »

True, but as I see it, the intake of air in a jet is to enable the burning of the reaction mass to be expelled .... it's an "ingredient ", rather than the medium through which the airscrew works. Sorry if I'm not explaining myself too well!

An awful lot of "jet" engines have a fairly high bypass ratio, making them as much ducted fans as jets.
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