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Old May 21, 2015, 07:14 AM
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question on Stumax 110-47 fan unit

Hi all, I will be using a Stumax 110-47 for the first time, and I want to seek some advice on how best to install this fan.

As you see from the photo below, the intake ring of my plane (JTM L39) is larger than the fan unit itself. Can I push the fan forward a bit so that it sits inside the intake ring, without sealing off the gap between the ring and the fan? I assume the way to maximize the fan's power/thrust is by sealing off the gap entirely. But, since this fan has a 9+kg thrust and the plane will have an AUW weight of only 6-6.5kg, I'm ok with some loss of power/thrust as long as it's not too significant.

Would love any thoughts/advice from those who have used and installed this fan. Thanks!

Kevin
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Old May 21, 2015, 07:54 AM
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The right way to do it would be to make a short adapter, that on the fan end has the same inside diameter as the fan shroud, for best performance you do not want any ridges or sharp edges inside the duct, and keep it sealed as well. The upside to spending a little bit of extra time on this is you get the most out of your fan, I know you have more performance available than needed, but you can throttle back and get longer flights this way.

Do a hack job of the fan install and you will have to be on the throttle more due to loss of fan performance. Your choice really.

Kind of strange this JTM plane did not include a intake adapter to fit a Stumax 110mm fan, my xXx had one that was a perfect fit. Are you sure it's not just something they forgot to include in the box?
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Old May 21, 2015, 08:14 AM
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Thanks Arngeir - yup that's what I figured. I just asked JTM and confirmed that they didn't include a ring for 110mm - only for 120mm.

Another reason I'm thinking about leaving the gap unsealed is, given how powerful this fan is, I'm concerned the air sucking would collapse the ducts at full power. This was an issue with the BVM EVF fan that I have on my JTM Viper, and I ended up having to cut a few cheater holes on the intake ducts to lessen the suction effect that was collapsing the ducts.

Kevin
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Old May 21, 2015, 08:22 AM
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Quote:
Originally Posted by Arngeir Blakseth View Post
The right way to do it would be to make a short adapter, that on the fan end has the same inside diameter as the fan shroud, for best performance you do not want any ridges or sharp edges inside the duct, and keep it sealed as well. The upside to spending a little bit of extra time on this is you get the most out of your fan, I know you have more performance available than needed, but you can throttle back and get longer flights this way.

Do a hack job of the fan install and you will have to be on the throttle more due to loss of fan performance. Your choice really.

Kind of strange this JTM plane did not include a intake adapter to fit a Stumax 110mm fan, my xXx had one that was a perfect fit. Are you sure it's not just something they forgot to include in the box?
+1
Make a proper adapter, will be worth it in the long run. My large Viperjet only came with an adapter for a120mm fan. I split it and cut a chunk out, then filled the edge. The smoother the better. You'll enjoy the 110-47, it's an awesome fan

Chris
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Old May 21, 2015, 09:12 AM
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Easiest is as Chris suggests and try to cut and get the 120mm adapter to fit, or if you want to run it open you will need a bellmouth on the fan. But I'm not sure anyone makes one for the SM-110. Maybe the one Schubeler makes for the HDT-75 fits? That's also a 110mm fan.

I'm waiting on a 110-47 myself for my xXx, I thought about installing a 110-52 I have but decided I wanted a bit more power, and also be able to keep on using the 14S batteries I already have for the plane ( I have 2 x 14S 6000). Will be using a 780kV motor and I hope it will give me around 6kW.
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Old May 21, 2015, 09:15 AM
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Kevin another option might be to make an inlet ring to fit the fan. Then place the fan so the inlet ring about two inches behind the termination of the ducting. But I personally would make the adapter and then reinforce the ducting if needed.
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Old May 21, 2015, 11:39 AM
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Installing it just the way it's sitting in the picture won't be that good primarily because I don't see that there is a thrust tube installed. One very important component that I've not seen anyone mention is the installation of a thrust tube. Are you planning on installing one on this project? Performance greatly depends on the thrust tube. Others can chime in on this as well. From my understanding, a good thrust tube is one that is 80% the size at the tail end compared to the size where it connects to the EDF unit. A while back, I saw a youtube video of a Habu 32 losing it's thrust tube in mid flight, which it lost nearly all it's thrust when this happened.
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Old May 21, 2015, 12:31 PM
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For sure it'll have a thrust tube...
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Old May 21, 2015, 01:00 PM
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Yes it'll have a thrust tube The fan is just placed temporarily inside the fuselage for the sake of illustration.

Interestingly, though, I spoke with JTM today and they say the best way to install this fan, even without a bellmouth, is to place it about 2 cm (1 inch) behind the duct ring - in other words, a 2-cm gap between the fan and the duct ring. That's how they test piloted this L39's prototype, using a fan without a bellmouth that only had a static thrust of around 5.5kg.

I may do as JTM suggested and see what the performance is like before deciding what, if any, alterations should be done. After all, this Stumax fan pumps out 9.1kg of thrust at about 140a. Even if performance is limited to, say, 7 kg thrust at 100a, that is still way more than enough performance for this light, sleek plane.

Here's a more specific data point. My JTM XXX has the Ramtec 127MM fan installed pretty much exactly the way JTM suggested - see photo, which illustrates a small gap between the fan and the intake duct ring. With this setup, this fan performs as expected, churning out about 8 kg of thrust at around 118A. See the video below for the XXX's 100th flight, during which it was clocked at 272 kmh/169mph during the second low pass. It is hard to imagine that this isn't maximizing that fan's performance.

So, I guess, the only way to find out for sure is to do some experiments on the L39.

Kevin

JTM XXX 100th flight (4 min 37 sec)
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Old May 21, 2015, 01:49 PM
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Quote:
Originally Posted by kchen95 View Post
Yes it'll have a thrust tube The fan is just placed temporarily inside the fuselage for the sake of illustration.

Interestingly, though, I spoke with JTM today and they say the best way to install this fan, even without a bellmouth, is to place it about 2 cm (1 inch) behind the duct ring - in other words, a 2-cm gap between the fan and the duct ring. That's how they test piloted this L39's prototype, using a fan without a bellmouth that only had a static thrust of around 5.5kg.

I may do as JTM suggested and see what the performance is like before deciding what, if any, alterations should be done. After all, this Stumax fan pumps out 9.1kg of thrust at about 140a. Even if performance is limited to, say, 7 kg thrust at 100a, that is still way more than enough performance for this light, sleek plane.

Here's a more specific data point. My JTM XXX has the Ramtec 127MM fan installed pretty much exactly the way JTM suggested - see photo, which illustrates a small gap between the fan and the intake duct ring. With this setup, this fan performs as expected, churning out about 8 kg of thrust at around 118A. See the video below for the XXX's 100th flight, during which it was clocked at 272 kmh/169mph during the second low pass. It is hard to imagine that this isn't maximizing that fan's performance.

So, I guess, the only way to find out for sure is to do some experiments on the L39.

Kevin

https://www.youtube.com/watch?v=TK68YGvCtq4
Pretty impressive video, but unfortunately I take everything coming from China, including video footage, with a grain of salt.
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Old May 21, 2015, 02:03 PM
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Originally Posted by YokohamaSoGo View Post
Pretty impressive video, but unfortunately I take everything coming from China, including video footage, with a grain of salt.
I'll take it as a compliment that you thought the video/my flying was impressive enough to warrant a grain of salt - meaning it was so impressive that it is slightly unbelievable in your eyes

But FYI the video didn't come from China - I'm an American living in Taiwan, and the video was shot in Taipei. Feel free to search through my YouTube channel ("mrkchen95") for a whole bunch of other flying videos, including other videos of this exact XXX plane. Think it would be hard for me to fake all those other videos too

Kevin
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Old May 21, 2015, 03:02 PM
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Originally Posted by kchen95 View Post
I'll take it as a compliment that you thought the video/my flying was impressive enough to warrant a grain of salt - meaning it was so impressive that it is slightly unbelievable in your eyes

But FYI the video didn't come from China - I'm an American living in Taiwan, and the video was shot in Taipei. Feel free to search through my YouTube channel ("mrkchen95") for a whole bunch of other flying videos, including other videos of this exact XXX plane. Think it would be hard for me to fake all those other videos too

Kevin
You could very well be lagit. However, not all are, and I've seen plenty burned. Enough that I take everything from that general local with a grain of salt. If you're as lagit as you say you are, you too would agree.
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Old May 21, 2015, 03:41 PM
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Pleae take the time to do your research and then decide if Kevin is legit or not.

If you don't have the time to do that then you could at least refrain from hinting that he is a fraud just because he happens to live in Taiwan. Couldn't someone mistake this type of b ehaviour as insulting?
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Old May 21, 2015, 05:20 PM
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Originally Posted by anlucas View Post
Pleae take the time to do your research and then decide if Kevin is legit or not.

If you don't have the time to do that then you could at least refrain from hinting that he is a fraud just because he happens to live in Taiwan. Couldn't someone mistake this type of b ehaviour as insulting?
Ok now, what's the problem here? I commented that I take it with a grain of salt. You want to fill in a spin and rework it to include words like "fraud". As I simply stated in my reply, he may be lagit, but that doesn't mean everything/everyone is lagit. So what's the problem with saying this? It's discussions like this that makes me realize I need to leave this so called hobby altogether, aint worth the drama anymore.
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Old May 21, 2015, 06:53 PM
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Kevin, the best solution would be to cut the original inlet back to the intersection between left and right, then roll up an adapter to connect that with the fan. Otherwise, move the fan aft so you have enough space for an adapter which isn't too conical.

An easy way to make an adapter is to roll it from Mylar or even thin card which is glossy on one side (glossy side in!) and tape it in spots. Then lay a couple of layers of 200gm (6oz) glass over it. Leave the Mylar or card inside, no need to remove it.

Do take the time to get it right, the fan performance will suffer tremendously without any inlet, the air just can't turn around the sharp edge of the shroud without getting all messed up. You'll find that current draw will drop by about 20% and thrust will drop by about 30-40% without an inlet on the fan. Don't follow JTM's suggestion, that won't work very well, you need to guide the air into the fan otherwise the outer section of the rotor won't be doing anything for you except making nice jet sounds.

Stu.
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