By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

New EDF Mini Jets- Sabre & MiG15 RCM&E 2018 Special

All Topics | Latest Posts

Search for:  in Thread Title in  
Nigel R09/07/2019 10:37:44
avatar
2935 forum posts
470 photos

I would probably go for a couple of skids on something this size.

If you use a central balsa rail, try curving the underside a little and fixing a length of steel wire to it. I'd put it over the CG position with most of it in front of the CG.

A couple of very light tip skids would prevent it leaning over and scraping wingtips.

David Clark 1809/07/2019 12:28:31
3 forum posts

Thanks. It's looking like skids are the way to go. Would you putskids on the wing tips as well?

Edited By David Clark 18 on 09/07/2019 12:30:10

Edited By David Clark 18 on 09/07/2019 16:26:38

Daithi O Buitigh09/07/2019 15:58:46
avatar
1354 forum posts
49 photos

An alternatrive (I've used it on foamies) is fibreglass tape .

A couple of strips on the belly and each wingtip should work

Steven Shaw09/07/2019 22:06:13
avatar
308 forum posts
164 photos

I used "Crystal Clear Gorilla Tape"

Gorilla Tape

Colin Bernard23/07/2019 15:55:30
avatar
478 forum posts
81 photos

Well my Sabre was finished and ready for its maiden - and failed miserably, getting effectively a 30' powered glide with its FMS 50mm fan.

During my testing I am getting nothing like the thrust others are reporting with their fans so looking for ideas!

Stats: AUW = 21oz

LiPo: Dynamic 2200 3S

At WOT I got 32A, 378W

Holding the Sabre over the kitchen scales I got a max of 460g (~16oz) thrust but that soon dropped to around 350g.

I tried the same using a brand new identical fan and still got the same - 470g.

Interested in any thoughts so I can get this bird flying as at the moment it is putting me off trying any other of Tonys mini jet projects.

20190616_112933.jpg

BTW - safety tip. If you have to hold an EDF unit to test it, hold the shroud at the motor end. I held it at the other end and got a cut. When at speed the blades stretch and almost close the gap between tip and shroud. Although I was using a very light pressure to hold it was enough to close the gap so that the blade tip sliced through the shroud and the side of my thumb! An EDF test mount is now being designed!

 

Edited By Colin Bernard on 23/07/2019 15:56:36

Alan Gorham_23/07/2019 16:33:40
avatar
868 forum posts
95 photos

Tony's website listing for the Sabre quotes a 16oz AUW and minimum thrust requirement of 600g.

I would look to lighten the model if you can, but failing that I would be checking the timing setup of the ESC, checking the ESC endpoints are calibrated so that it is delivering full throttle at full stick and then maybe check the voltage of your Lipo with a wattmeter at full throttle. If your Lipo is tired or isn't a high enough C rating then it will struggle to deliver enough amps.

I'd also confirm that the duct and cheater inlets aren't obstructed.

Tim C23/07/2019 16:35:13
avatar
484 forum posts
253 photos

Not enough air to the fan, I got nearer 700gm on my kitchen scales in a raw open test, if the the motor is being starved of air, or the thrust tubes restrictive you will loose a lot of thrust, your amp draw looks about right.

Colin Bernard23/07/2019 16:48:43
avatar
478 forum posts
81 photos

Thanks for the quick replies - but already thought along these lines.

As to the AUW this is down to my using a 2200 rather than the 1500 Tony uses in his lighter version. Can't take any more wood out - sanding through in a couple of places as it is! And there is no paint on it other than the flashes. Having said that, the AUW does not affect the thrust.

ESC has been calibrated, and the LiPos were giving 12v or more on the wattmeter.

I thought about the 'C' rating and tried with an almost new 45C graphene. That simply gave me an extra 10g of thrust, as did testing it with the cockpit cover off in case not enough air was getting through.

Re duct obstruction, all wires have been hot glued out of the way so the only wires to be seen looking down the nose are those from the LiPo.

And don't forget I did test another fan in the open and got much the same, (hence the plastered thumb), so airflow is not an issue.

I'm sure you can understand my bewilderment here. I already use the FMS 70mm fans and they are superb but am starting to doubt these.

I do have the AEO fan, so I guess the next step is try an open test with that, but need to get it soldered up first.

Alan Gorham_23/07/2019 17:04:17
avatar
868 forum posts
95 photos

If your thrust was a constant value then upping your weight 5oz over the designers prototype will certainly help you to achieve a powered glide.

You just have some fantastic 3s Lipos if they are showing over 12V under full throttle load! I wish any of mine would do that.

I suspect the 12V you have read is the off load value which is pretty meaningless.

Mark Elen23/07/2019 17:14:31
338 forum posts
585 photos

Quick question..

Are you sure you have the 3s version of the fan/motor set and not the 4s one?

Specs from FMS:

Description:
Brand Name: FMS
Item Name: 50mm 11 blades Ducted Fan 
Motor: 2627 KV4500(4S)/ KV5400(3S) (Optional)

Weight: 75g

Cheers

Mark

Edited By Mark Elen on 23/07/2019 17:16:51

Geoff Gardiner23/07/2019 17:20:37
avatar
370 forum posts
645 photos

Just a thought - you have got the 3S version of the FMS fan and not the 4S version?

Geoff Gardiner23/07/2019 17:21:15
avatar
370 forum posts
645 photos

Mark beat me to it - whilst I was typing.

Edited By Geoff Gardiner on 23/07/2019 17:22:59

Colin Bernard23/07/2019 17:55:54
avatar
478 forum posts
81 photos

Cant check the fan in the model without chopping up the fuselage but it was certainly a 3S order!

The other fan is definately the 3S version.

As to the voltage, yes that was the off load voltage to stop someone wondering if tbey were fully charged or not. They were and showing 98%.

When running i focus on amps and watts. But i did note the voltage on running which started at 11.8V, dropping quite quickly to around 11.2V.

Edited for typos...

Edited By Colin Bernard on 23/07/2019 17:57:09

Alan Gorham_24/07/2019 05:21:27
avatar
868 forum posts
95 photos

I've looked up the 3s fan specs on the 4-max website and it quotes 32A and 358W, so your batteries seem healthy to me and your fan is up to spec.

Piers Bowlan24/07/2019 06:53:12
avatar
1804 forum posts
44 photos
Posted by Colin Bernard on 23/07/2019 16:48:43:

Thanks for the quick replies - but already thought along these lines.

As to the AUW this is down to my using a 2200 rather than the 1500 Tony uses in his lighter version. Can't take any more wood out - sanding through in a couple of places as it is! And there is no paint on it other than the flashes. Having said that, the AUW does not affect the thrust.

'The AUW does not affect thrust' Whilst this is true the extra weight will require extra lift which can only be generated with a higher A of A (at launch) = more drag - requiring more thrust. Without that the model won't accelerate and with the thin wing section the model needs speed to fly well (in my view). I don't know the difference in weight but I think it might be worth trying a 1500mAh LiPo for comparison and see if it improves on the 30ft powered glide. Light models fly better!

You have built a cracking looking model Colin, I am sure you will get it sorted.

Update: I just had a look at the HK website and a 40C 3s 2200mAh LiPo weighs 205g whilst a similar 1500mAh weighs 129g, so a 76g saving. I suggest that weight is probably fairly critical with this type of model.

Edited By Piers Bowlan on 24/07/2019 07:11:06

Ron Gray24/07/2019 07:06:31
1425 forum posts
358 photos

Your cheater ducts look to be too far forward?

Alan Gorham_24/07/2019 07:12:41
avatar
868 forum posts
95 photos

Have you installed the Lipo in a "pannier" under the fuz/wing as per Tony's proto?

Steven Shaw24/07/2019 11:47:40
avatar
308 forum posts
164 photos

My FMS 3S fans tested at:

559 grams thrust

33.8 amps

351.5 watts

10.4 volts

dscn2912.jpg

I found that a 2200 battery had a very very large frontal area and blocked too much of the airflow, even a 1800 is big.

I think his newer designs with the large side inlets and the battery out of the airflow will be a much better design.

Edited By Steven Shaw on 24/07/2019 11:50:59

Colin Bernard24/07/2019 19:46:35
avatar
478 forum posts
81 photos

Thanks to all for your thoughts and suggestions.

Piers - appreciate the compliment, thanks! (Not looking quite so good now I've ripped the wings off to get at the ESC for testing!)

I agree with you, and the others in that swapping to a 1500 would pay dividends - I just didn't have any at the time.

Ron - yes my cheater holes are further forward than the plan due to servos. I wanted to put them as far back as possible to give me more room in the cockpit area. It's cramped enough in there. The position should not make much difference though - the main thing is the amount of inflow available in front of the fan.

Interestingly, all my testing has been with the cockpit lid off the fuselage and the battery hanging down the outside of the fuselage in an attempt to get the best reading possible. This gained about 10% over the fuselage closed with the battery inside - not as much as I thought.

Alan - the model is built as per plan. If you have a look at the mag you can see the LiPo sitting in the bottom of the fuz. The 'pannier' is a hand hold to assist hand launching - unless I have missed some pics somewhere.

Steven - your results are interesting. I see it still falls short of the 620g FMS claim and the 700g some have reported. With you using a proper test setup I trust those figures more than simply upending over some kitchen scales which is what I do currently.

So next steps - compare the AEO; get some 1500 LiPos; stick the wings back on; try again!

Ron Gray24/07/2019 20:42:03
1425 forum posts
358 photos

Colin - the cheater holes should be immediately in front of the fan, I’ve played around with these on other edf models and it makes quite a difference!

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E! 

Support Our Partners
Addlestone Models
CML
Pepe Aircraft
Wings & Wheels 2019
Gliders Distribution
Cambridge Gliding Club
electricwingman 2017
Slec
Advertise With Us
Sarik
Latest "For Sale" Ads
Does your club have a safety officer?
Q: Does your club have a safety officer, or is the emphasis on individual members to each be their own safety officer?

 Yes we have a SO
 No, it's down to everyone

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us