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Outdoor Free Flight Forum => EDF, Jetex or Rapier Powered Free Flight Jets => Topic started by: billdennis747 on October 11, 2019, 02:54:52 AM



Title: Is an EDF a 'reaction motor'?
Post by: billdennis747 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: cvasecuk on October 11, 2019, 05:49:55 AM
No. It is simply a propeller within a shroud, albeit a rather long one!
Ron


Title: Re: Is an EDF a 'reaction motor'?
Post by: Bredehoft on October 11, 2019, 07:20:26 AM
definition:  https://en.wikipedia.org/wiki/Reaction_engine (https://en.wikipedia.org/wiki/Reaction_engine)

EDF = Electric Ducted Fan

i'd say no.

--george


Title: Re: Is an EDF a 'reaction motor'?
Post by: Viperkite on October 11, 2019, 07:49:02 AM
I always thought a 'reaction' meant something changing it's properties in some way.


Title: Re: Is an EDF a 'reaction motor'?
Post by: billdennis747 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: strat-o 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: Russ Lister 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: TimWescott 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: Russ Lister 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: SP250 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


Title: Re: Is an EDF a 'reaction motor'?
Post by: TimWescott 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.


Title: Re: Is an EDF a 'reaction motor'?
Post by: Russ Lister 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!


Title: Re: Is an EDF a 'reaction motor'?
Post by: wms on October 15, 2019, 06:29:22 PM
How About Pulse Jets? Kind Like? Maybe


Title: Re: Is an EDF a 'reaction motor'?
Post by: charlieman 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?


Title: Re: Is an EDF a 'reaction motor'?
Post by: lincoln 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.