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EDF advice


Frank Day
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Hi,

 

A newbie to EDF,

 

Looking for some advice. I have a Robbe Concorde 1/32, courtesy of Ebay and a jolly nice chap who despite only offering collection posted it to me.

 

The original 400 cans and paddles have been replaced with some brushless items and it has good power. As a tinkerer and with winter approaching I have decided on EDF propulsion and some functional retact landing gear. However as a newbie to edf im confused as hell with the inconsistant data.

 

Model currently weighs in at 790g was at 1050g new,  but old school nicads, full size servos, snakes etc have all gone. I guess with some LG etc it will get back up around its original design weight. 

 

I thought of 4x 30mm edf but I dont think they will offer enough shove. A pair of Dr Mad Thrust 40's or similar, not sure they will have enough either so im looking at a pair of 50's. I would like the smaller items but I want good performance and not to be at full beans for the duration of a flight.

 

Im aware of roughly 100watts per LB/500g etc but have got myself confused with the edf stuff.

 

Plain English advice very welcome, please don't hit me with formulas etc unless they are very basic.

 

Also as I intend to refurb it I am looking for scale decals 1/32, I found a supplier in the US but I think he makes up a figure and adds a zero.

 

Thanks in advance and sorry if this is covered elsewhere.

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From what I have found out about the Robbe Concorde as a newbie you might well struggle to fly it with EDFs.

If you look at the diameter of the original props and then compare it to the area of even two 50 mm EDF you are going to need something like 8 times the thrust density (g/sqcm). To create that sort of thrust is going to need a lot of power which means significant motor and battery weight. It can be done but not really the sort of thing to learn about EDFs

I have built a Concord out of Depron, it is a bit bigger than the Robbe and it just about manages on 4 x 40 mm but it is lighter. To save weight and drag it has no undercarriage so is hand launch & belly land.

 Complete.JPG.106f265832601b45558a02444ae06e00.JPG

My advice would be to go for a simpler ready to fly EDF so you can get to understand what it is like. Convert the Robbe only when you have some EDF experience.   

Edited by Simon Chaddock
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Hi Simon,

 

Thanks for the reply.

 

I have a couple of Freewing lippisch P15's with 64mm. but have never had the problem of working all that out for myself. I looked at the Tony Nijhuis Concorde it seem to be about four times the weight and runs on four 50mm. So im floundering around and dont want to waste time and money with the wrong purchases

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Wishing to spend my day "productively", I managed to do a bit of a thrust test on the Robbe Concorde.  It has unknown small brushless motors, glued behind all sorts so left it untouched for now. 6x4.5 counter pushers

 

3s 2200 30c battery it lifts vertically from hand.

 

With the aid of some particularly good kitchen scales (returned to exactly where i found them) I did a horizontal test i.e  flat surface on  some wheels pushing againt the scales:

result 850g of thrust.

 

Next scales on the floor model nose down fully charged battery, Concorde weighed in at 790g, zero the scales, full beans on the throttle 875g thrust.

 

I looked on the 4Max site, they have FMS 50mm items as follows: 3s setup 620g  & 4S at 1086g static and Powerfun 50mm at 3s 640g & 4s at 765g static. Per unit.

 

I may have it completely wrong but it seems any pair of these would give me more thrust than the current pusher paddles.

 

Current 875g,

 

Pair of Powerfun 50's  on 3s 1240g to FMS 50's on 4s at 2072g  (lowest and highest)

 

Advice/lesson welcome

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32 minutes ago, Frank Day said:

....................................................

I looked on the 4Max site, they have FMS 50mm items as follows: 3s setup 620g  & 4S at 1086g static and Powerfun 50mm at 3s 640g & 4s at 765g static. Per unit.

...................................

Advice/lesson welcome

I have the 50mm FMS fan from 4Max running on 4s.

It might give 1068g thrust in the open, but installed in a TN Gnat I get 680gm thrust measured on a similar "scales" test rig to yours.

Even with the losses in a model it does sound like a pair would give you more thrust to the present setup.

 

Dick

Edited by Dickw
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Hi Dick,

 

Thats quite a loss, Hence the extra holes in the underside of the Freewing Lippisch.

 

I'm tempted to go for the FMS on 4s or similar, I'll check ot some more figures.

 

I'm guessing I should push the fan units as far forward and as open as possible or set back and open up the nacels as much as possible.

 

Thanks for the reply

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Frank

Two 50 mm sounds about right but you need to take into account the amps each motor will be taking. It is likely to be about 40A each. Even with a 3000 mAh 3s that's a 27C discharge rate which gives 2.5 minutes max, 2 to be safe. With throttle management you will get a bit longer.

So 3000 mAh 3s 240 g, 2 x FMS 50 mm EDF 150 g, 2 x 60 A ESC 100 g. Even the weight of the wire is not insignificant. It quickly adds up.

I agree with DickW the quality of the EDF ducting is important.

Finally the Concorde wing was intended for supersonic flight. Efficient at slow speed it is not. ? 

Edited by Simon Chaddock
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I admire your pluck ? but my honest advice would be leave it in the box, at least for now. Use it as a third or fourth EDF model once you have more experience of the power train calls, speed and skills needed - going ahead at this stage may lead to tears before bedtime…

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Hi Simon, Quite a bit to consider, at 790g inc 2200 3s the Robbe is about 300g below its original spec it had NiCads, 2 fullsize servos with very long control snakes etc, it has 60g of lead in the nose as well due to the removal of the old servos, I'm hoping to come in under original weight, the earlier conversion wasnt planned well with cable running around like spaghetti, rx and a bunch of cable up front, 2x esc under hatch in top of fuzz, battery in bottom of fuzz directly below and two long runs to the motors. The Robbe has wings that look ok from the top but viewed from the side they are like a cargo plane wings. 

 

5 hours ago, Simon Chaddock said:

From what I have found out about the Robbe Concorde as a newbie you might well struggle to fly it with EDFs.

If you look at the diameter of the original props and then compare it to the area of even two 50 mm EDF you are going to need something like 8 times the thrust density (g/sqcm). To create that sort of thrust is going to need a lot of power which means significant motor and battery weight. It can be done but not really the sort of thing to learn about EDFs

I have built a Concord out of Depron, it is a bit bigger than the Robbe and it just about manages on 4 x 40 mm but it is lighter. To save weight and drag it has no undercarriage so is hand launch & belly land.

 Complete.JPG.106f265832601b45558a02444ae06e00.JPG

My advice would be to go for a simpler ready to fly EDF so you can get to understand what it is like. Convert the Robbe only when you have some EDF experience.   

 

6 minutes ago, Simon Chaddock said:

Frank

Two 50 mm sounds about right but you need to take into account the amps each motor will be taking. It is likely to be about 40A each. Even with a 3000 mAh 3s that's a 27C discharge rate which gives 2.5 minutes max, 2 to be safe. With throttle management you will get a bit longer.

So 3000 mAh 3s 240 g, 2 x FMS 50 mm EDF 150 g, 2 x 60 A ESC 100 g. Even the weight of the wire is not insignificant. It quickly adds up.

I agree with DickW the quality of the EDF ducting is important.

Finally the Concorde wing was intended for supersonic flight. Efficient at slow speed it is not. ? 

 

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Hi Matty,

 

I'm currently playing with a Freewing Lippisch on 3s its small and fast but glides quite well fortunately, still in one piece with a few bruises.

 

I'll probably carry on with the refurb and conversion whilst getting more experience, no rush.

 

The Robbe motors have quite a down thrust angle so more research into whether I need to maintain that angle with the edf's

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A bit more detail from my Gnat with its FMS 50mm on 4s which may help your planning.

I think Simon may have a good point about the relative flying characteristics of the Concorde v the Gnat, as the Gnat seems to have an amazing ability to wizz around on very low power to the point that I always fly for 5 minutes on the 2200mAh pack without ever pushing it to the limit.

 

A couple of charts attached, one showing a typical full throttle at launch in detail, and the other showing power and consumption throughout the (maiden) flight with 5 minutes from 1200 mAh (with more spirited later flights I usually land at about 1800mAh). As you can see I rarely need to use full throttle once it is away, but the Concorde may be very different.

 

Dick

Gnat typical launch V-A.jpg

2020-05-28 maiden flight W.jpg

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Try experimenting with a couple of small fan units , they are not expensive. Also check up on balancing them as any out of balance saps power really badly. Have a look through YouTube about balancing EDF fans. Plenty of stuff on there but beware of the idiots . There are plenty on there as well. A good entry lip on the fan housing and a smooth efflux tube with the correct taper will increase thrust enormously.

Let us know how you get on .

Ps the advice re saving the concorde for a later EDF is good advice.

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Many thanks for all the advice, I'm probably guilty of running before Ive got the walking fully sorted. I haven't done RC flying for decades and found that I missed the boat regarding interest items so have been picking them up when I can. It was 2 stroke, tissue and dope when I was younger so electric and edf are a steep learrning curve.

 

I'll spend more time with the Freewing Lippisch before the Concorde. Although from the top it looks Concorde the profile reveals a very thick wing  stretched into a delta shape and produces lift very easily,  its more Globemaster C17 than Concorde. I think the other Concordes out there are much more scale and need a certain atitude to fly well. I'll try and post a good image, owners say it actually glides quite well if balanced out correctly.

 

I also noticed on the Robbe that the motors are set with quite a down thrust angle, and am not sure if this should be replicated in a conversion.

 

RC Turbines had ready made thrust tubes but they seem to be unavailable.

 

Aliexpress seems a good source of test items.

 

Thanks again for all the info and advice.

 

 

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  • 2 months later...

Spent £10 on a 12 month subscription to ecalc and you can play with all the fan, thrust, battery, airframe and esc combinations under the sun - that will tell you what will work and what wont.  It will also get you through 90% of the EDF learning curve too without wasting money on buying the wrong components.  https://www.ecalc.ch/calcmember/signup.php

 

John M

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Frank

Just a bit more info.

I have a PowerFun 50 mm EDF and it is supremely well balanced, sounds fantastic and produces quite a bit of thrust but on a fully charged 4s it takes a whopping 52.5 A that's 752 W.

https://www.youtube.com/watch?v=iznMsOgNAdo

You will need quite a bit of battery to supply those sort of amps without risking damaging it.

A single 2200 mAh 4s would be able to supply just one 50 mm PowerFun at full power for less than 3 minutes and it would then be exhausted and rather warm.

High power EDFs are thirsty beasts!  

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