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        Discussion Can it be done??

#1 Chuchuf Nov 12, 2012 07:56 PM

Can it be done??
 
Alright guys, I'm looking to the braintrust of this forum to see how you think the Tomahawk L39 2.7m could be set up as an EDF model.
http://tomahawk-design.com/produkte/...ros-l39-270cm/

I have some ideas of my own and am trying to get some answers from Schubeler of the upcoming DS-215-HST.

I'm open to any and all ideas no matter how radical.

The goals are to keep it light and have reasonable flying speeds like the turbines do.
Jet Power: Ali Machinchy flies the Tomahawk L-39 (5 min 25 sec)


Thanks,

Terry

#2 Double E Nov 12, 2012 08:37 PM

Terry,

Let's start with an estimated thrust to weight ratio that you think would be needed to fly the plane. The video said the plane weighed about 20kg which is about 44lbs. In the smaller EDF's we're usually shooting for something close to 1:1 but I would assume that anything .75:1 would probably fly reasonably well. That means you are looking for something with 33lbs of thrust or better. That shouldn't be too difficult. Tam will tell you that well designed and efficient ducting will be critical in getting the most out of whatever fan you do choose to use. On a side note, I've seen Tam fly one of his 1:12 scale F-16's on a Jetcat P-20 which produces about 5 1/4lbs. My understanding is that the efflux speed from the turbine is much higher than the EDF and that is why a 5 lbs thrust turbine would outperform a 5lbs thrust EDF. The other issue is that as turbines burn off their fuel, they get lighter and their performance improves. With EDF, they take off and land at the same weight and performance reduces as the voltage drops in the battery. I recently saw another video where Tam was flying a big BVM F-86 on one of is 90mm EDF setups. It's amazing what he has been able to pull out of a 90mm EDF. So let's start looking for EDF's with thrust in the 33+ lbs range.

#3 Double E Nov 12, 2012 08:53 PM

So here is a video of a 127mm Dynamax fan from Extreme Power Systems that is putting out nearly 30lbs of thrust and flew this 33lbs Skymaster Viper at close to 200mph.

video-2011-08-27-12-24-11.mp4 (1 min 9 sec)

#4 Double E Nov 12, 2012 08:59 PM

Maybe aluminum is the way to go. Check out this 120mm fan from Easy Tiger that they claim can handle 100k RPM. I'm pretty sure this fan is just a private label of something that is already available on the market.

http://easytigermodels.com/index.php...2vutv5e8m7boh5

#5 Double E Nov 12, 2012 09:05 PM

Tamjets has a Dynamax conversion that produces 5.4kw on 12s.

http://www.tamjets.com/original/prod...roducts_id=669

#6 Ron101 Nov 12, 2012 09:05 PM

2 Attachment(s)
That's a huge plane at 1:3 scale

So it would really come down to the inlets... but Tam had great succes doing a large Comp ARF hawk with twin TJ -100 on 10s each fan....very smart ducting setup

If I was doing that plane I would check your inlet FSA and tail pipe....

I would think as big as that plane is you could do a twin 128mm Tam Jets Dynamax conversion... giving you a total of a 256 mm fan

Run each fan on 12s 35c 8300 neu motor packs for just over 6000 watts per fan...
Should put you right around 36 pounds installed thrust

Here is what Tam did with the large Comp ARF hawk on twin TJ 100's...
if the 128mm was to large you could work down to 120mm or 110mm fans
but I think two is the way to go on that beast

Tams twin hawk thread: http://www.rcgroups.com/forums/showt...ht=carf+s+hawk

CARF'S HAWK twin TJ100 conversion (5 min 25 sec)

#7 Double E Nov 12, 2012 09:09 PM

A twin fan setup looks like a great option.

#8 Double E Nov 12, 2012 09:23 PM

Okay Terry, I think I found the single fan solution.

http://www.schuebeler-jets.com/en/ne...er-2012en.html.

This new giant Schuebeler fan is suppose to produce close to 54lbs of thrust.

#9 Gamalier Nov 12, 2012 09:24 PM

Quote:

Originally Posted by Chuchuf (Post 23253129)
Alright guys, I'm looking to the braintrust of this forum to see how you think the Tomahawk L39 2.7m could be set up as an EDF model.
http://tomahawk-design.com/produkte/...ros-l39-270cm/

I have some ideas of my own and am trying to get some answers from Schubeler of the upcoming DS-215-HST.

I'm open to any and all ideas no matter how radical.

The goals are to keep it light and have reasonable flying speeds like the turbines do.
http://www.youtube.com/watch?v=lBvccb_uigI

Thanks,

Terry


If you use the Schuebeler DS-94-DIA HST with DSM6745-700 which produces 29.1 lbs of thrust at 14S the plane will have a .83:1 power to weight ratio which is not bad but given the weight of the plane it can be tricky to fly once you start to loose power in the batteries. The DS-215 will be a different type of beast here but like Ron 101 said the inlet will be the key factor here. If you can get the measurement of the inlet from Tomahawk or a owner of the jet you can submit the info to Daniel or Christian @ Schubeler and they can guide you in the right direction. Good luck in the project!

#10 Double E Nov 12, 2012 09:59 PM

That's one of the big issues with EDF jets, they usually have to increase the size of the intakes to accommodate the amount of air the EDF needs to perform properly. RC jets designed for turbines usually have way smaller intakes than their EDF counterparts. The next issue will be the strength of the intake ducting. I assume any fan capable of producing 54lbs of thrust is going to generate a lot of negative pressure on the intake ducting that will need to be incredibly strong to avoid collapsing.

#11 Jack G Diaz Nov 12, 2012 10:13 PM

Quote:

Originally Posted by Chuchuf (Post 23253129)
Alright guys, I'm looking to the braintrust of this forum to see how you think the Tomahawk L39 2.7m could be set up as an EDF model.
http://tomahawk-design.com/produkte/...ros-l39-270cm/

I have some ideas of my own and am trying to get some answers from Schubeler of the upcoming DS-215-HST.

I'm open to any and all ideas no matter how radical.

The goals are to keep it light and have reasonable flying speeds like the turbines do.
http://www.youtube.com/watch?v=lBvccb_uigI

Kirk Sonnier is evaluating doing this. You might want to connect with him and pick his brain. He was taking measurements at BITW

Thanks,

Terry


Kirk Sonnier is evaluating doing this. You might want to connect with him and pick his brain. He was taking measurements at BITW

#12 Gamalier Nov 12, 2012 10:14 PM

Those Schuebeler fans pull a lot of pressure! Mine the first time I flew it closed the gear doors completely and the pneumatic cylinder were not able to keep them open while the fan was running. Also the cover in top of the fan collapsed, I ended up placing a wood former to avoid the collapsing of the cover while the fan is running. I ended up removing the gear doors, cylinders.

#13 Christian W. Nov 13, 2012 01:09 AM

Hi Terry,

I have problems sending you emails. They are always coming back. Hopefully you received my PM I sent you a few minutes ago.

Christian

#14 jofro Nov 13, 2012 01:43 AM

Quote:

Originally Posted by Chuchuf (Post 23253129)
Alright guys, I'm looking to the braintrust of this forum to see how you think the Tomahawk L39 2.7m could be set up as an EDF model.
http://tomahawk-design.com/produkte/...ros-l39-270cm/

I have some ideas of my own and am trying to get some answers from Schubeler of the upcoming DS-215-HST.

I'm open to any and all ideas no matter how radical.

The goals are to keep it light and have reasonable flying speeds like the turbines do.
http://www.youtube.com/watch?v=lBvccb_uigI

Thanks,

Terry

Sounds like great challenging project, but for that size of model I would rather select model to take twin 127mm set up then single uncharted territory of that caliber. It would give you more chance to bring it down if the worse happened then single EDF unit. Good luck, keep us informed with your progress, J.

#15 erh7771 Nov 13, 2012 02:30 AM

Quote:

Originally Posted by Chuchuf (Post 23253129)
Alright guys, I'm looking to the braintrust of this forum to see how you think the Tomahawk L39 2.7m could be set up as an EDF model.
http://tomahawk-design.com/produkte/...ros-l39-270cm/

I have some ideas of my own and am trying to get some answers from Schubeler of the upcoming DS-215-HST.

I'm open to any and all ideas no matter how radical.

The goals are to keep it light and have reasonable flying speeds like the turbines do.
http://www.youtube.com/watch?v=lBvccb_uigI

Thanks,

Terry

Use two fans, one for each intake with a Y intake ducting...

More thrust and 20 - 30% less watts if you're in the fans sweet spot and if they'll fit.


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