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Old Oct 16, 2014, 09:37 AM
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V-Man's Avatar
Canada, QC, Montreal
Joined Dec 2009
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Quote:
Originally Posted by oldsneakers View Post
I have'nt flown it yet but I'm a little disappointed. The thrust to weight ratio being less than one surprised me. I guess that motor is pretty heavy being all alloy. Am I missing something or is what I got with the new components to be expected?
There's a rather large difference between the theoretical thrust and the actual thrust, and I think that's where you should focus your efforts. Did you:

1) Balance the fan?
2) Add a thrust tube behind the fan?
3) Add a feeding tube behind the intakes (the stock design just dumps air into a cavity above the wing, creates lots of turbulence)?
4) Add a proper lip to the fan? (Might not be needed if you have done 3) above)

Basically, the power is going in, but it's not being converted to thrust.

P.S. Also notice something weird with the RPM. 63640 at 14.8V would be a 4300KV motor, not 3300KV. How did you measure that number?
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Old Oct 16, 2014, 01:06 PM
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oldsneakers's Avatar
United States, CT, Hamden
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Thanks for answering V-Man. I've flown EDF's for a while but am just now trying to learn and improve my planes.

1. The EDF unit said it was dynamically balanced so I didn't mess with it. It sounds super smooth.
2. I will give a thrust tube a try. I think I saw a template for one earlier in this thread.
3. Another great idea. I will try it.
4. The fan has an alloy case with a lip machined in. I saw that the stock did not when I removed it.

I read that RPM = Kv x measured volts. That's where I got that.

Thanks again.
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Old Oct 16, 2014, 01:12 PM
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United Kingdom, Derbyshire
Joined Aug 2011
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3300kv @ 63,000+ rpm would mean your voltage is around 20V.

I would guess that the "max thrust" figure they quote is based on a free-standing unit, not fitted into a model. the thrust would be affected by the efficiency of the inlets & outlets (the t45 being terrible in stock form on both these fronts).

edit:
you might bet better figures (or at least, less sag) with a higher capacity lipo. fwiw I run a 4000mah 4S in my t45.
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Old Oct 16, 2014, 01:32 PM
nom
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Oldsneakers, have you tried newer lipos?
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Old Oct 16, 2014, 02:42 PM
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V-Man's Avatar
Canada, QC, Montreal
Joined Dec 2009
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Quote:
Originally Posted by oldsneakers View Post
2. I will give a thrust tube a try. I think I saw a template for one earlier in this thread.
3. Another great idea. I will try it.
I have a hunch this is the source of your thrust issues. The T-45 has terrible ducting front to back (though thankfully, easy to remedy).
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Old Oct 16, 2014, 03:26 PM
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Ha. Back to school for me on the RPM math. 4000mah. That's pretty big. I have one from a ME262 that had a very short life. I'll give it a try after I maximize my thrust. I buy mostly HK NanoTech batteries and lately I've been getting the 60C or 65C ones.

Thanks for the help all.
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Old Oct 16, 2014, 05:26 PM
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You will only get about 0.7 to 0.8 of the V x KV. eg When the fan is loaded.

You also only need 0.5 : 1 for a "jet" to fly... though poorly, lol.
"Jet" meaning one with at least reasonable lift - like this T-45, or an Me-262, even some high lift body's like F-22.
0.7 : 1 is about where it begins to fly 'properly' (not nose up like landing all the time!)
It can't hurt to have more.... nice to have 0.8 : 1 or more.

The main issue with the lower thrust ratios is then it needs a runway like a real jet too! To get it up to a flying speed.
So for hand-launch you need more thrust available - the more the better.... or a very good throw! Again, to get it close to flying speed 'instantly' then.

You are 'losing' too much thrust, it should at least be 1000g by the look of your numbers, if not a bit more. If your AMPS were down, then less thrust would be expected, but they are not down (much). 'Normal" amps, but low thrust, is usually the exhaust side restricted.
Take the wing off and test - to get more inlet air - if you can. That is the quickest and easiest thing to do, and that will then give info on whether it is the inlet side or the exhaust side that is stifling it. eg If you get 1.0Kg or 1.1kg then you know it was at least inlet restricted.
For 70mm it is both ends that need improving..... but I am not sure for 64mm's.... but that is a pretty good power level fan you have there, so it might also be restricted on both ends anyway.

Unless you bench test the fan, to get the TRUE maximum ability it has, with your battery and ESC you use, you won't know what it truly would do - though 'Lander' are usually reasonably true numbers. So if they got X thrust from 68A, then you should too, fairly closely (just a fraction lower usually). And with your Amps being a bit lower, your 'raw' number is probably 1.3kg, or even a bit lower (1.25Kg?). Then remove losses and 1.0Kg could be the max you could ever get in a plane anyway.

I think I would do the 'wing off' test... to find that it improves it a bit. If so, add a naca duct under the wing ahead of the fan - that can be easily covered over again with plastic/PET-C later if you need/want to. Then go and fly it !! But even the 900g is enough anyway, so that is not going to stop it flying - it will just need a better throw!
I would do this order because if 'wing off' shows it is the exhaust side restricting it, that is messier to do and will also lower top speed. So by flying it first you can get an idea if it is really ok just at the 900g, or whatever any inlet cheater can gain.
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Old Oct 16, 2014, 06:38 PM
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kevinkal's Avatar
United States, CA, Gilroy
Joined Nov 2013
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Quote:
Originally Posted by oldsneakers View Post
Sorry FireHawx. That sucks.

I went to 4S with a new motor & esc on my T45. When I originally tested the stock plane, I got these results:

With 3S NanoTech 2200 45C - 90C
---------
Amps = 41
Watts = 453
Volts. = 10.9
RPM. = 47,730
Weight = 955 gms
Thrust. = 640 gms

I bought a Hobby King 10 blade EDF combo with these specs:
Kv: 3300kv
Max Power: 1000w (continuous)
Max Voltage: 14.8v (4S)
Max Amps: 68A
Max Thrust: 1.40kg
Weight: 236g

And these guys:
Hobby King 80A ESC
NanoTech 2250mah 4S 65C - 130C

Specs with new motor, esc & battery
------
Amps = 65.6
Watts = 968
Volts. = 14.5
RPM. = 63,640
Weight = 1168 gms
Thrust. = 905 gms

I have'nt flown it yet but I'm a little disappointed. The thrust to weight ratio being less than one surprised me. I guess that motor is pretty heavy being all alloy. Am I missing something or is what I got with the new components to be expected?
Quote:
Originally Posted by V-Man View Post
There's a rather large difference between the theoretical thrust and the actual thrust, and I think that's where you should focus your efforts. Did you:

1) Balance the fan?
2) Add a thrust tube behind the fan?
3) Add a feeding tube behind the intakes (the stock design just dumps air into a cavity above the wing, creates lots of turbulence)?
4) Add a proper lip to the fan? (Might not be needed if you have done 3) above)

Basically, the power is going in, but it's not being converted to thrust.

P.S. Also notice something weird with the RPM. 63640 at 14.8V would be a 4300KV motor, not 3300KV. How did you measure that number?
If you haven't already done so, it might be a good idea to enlarge your exhaust diameter and use a thrust tube as V-man suggests.

For my 64mm CS-12b unit, I had to open the HK/Sapac T-45 exhaust diameter to 100% FSA, or 57mm minimum diameter through a smooth thrust tube in order to get the fan to stop stalling and produce decent thrust. Doing this bumped my thrust up from about 600g to 800g on 4S with the wing on. If I took the wing off, the thrust would go up to low 900's.

It's quite possible that the Dr. Mad Thrust 10blade unit would have too much back pressure and thus produce poor thrust with the stock exhaust diameter.

I also have the same Dr. Mad Thrust Alloy 10blade EDF with 3300kv motor and fairing. I have run in on the bench an noticed that it is not balanced as well as I'd like it. The balance on these things is hit and miss. Some are good, some are bad.
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Old Oct 19, 2014, 04:35 PM
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Spain, GA, Ourense
Joined Apr 2014
5 Posts
First Edf

Hi guys, after a quick research I've decided to be this T45 my first edf plane, I already ordered from HK (EU warehouse). Also I ordered TURNIGY TRUST 55A SBEC and I plan to do the rudder mod as I have seen in this thread, and perhaps in the future also add retracts.
I have a few questions:
How do I manage to take out edf, to balance fan? I've seen some pics and it looks like it is glued at the bottom. Is it hard to take off?
What is the shaft size of the original fan? I want to order a replacement one but I don't know what and where to buy it. Does this one fit http://www.hobbyking.com/hobbyking/s...F_7blade_.html? I plan to stick with stock motor, for the moment.
Any special advice for the maiden?
Thanks in advance. I hope making her first flight review soon.
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Old Oct 19, 2014, 08:02 PM
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USA, MD, Frederick
Joined Jan 2010
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Sounds like you bought the PNP/ARF version.

If you plan to keep the fuselage intact when you remove the fan, then yes, it is a challenge.

An alternative is to carefully split the fuselage along the seams.
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Old Yesterday, 07:04 AM
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Spain, GA, Ourense
Joined Apr 2014
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Quote:
Originally Posted by fredmdbud View Post
Sounds like you bought the PNP/ARF version.

If you plan to keep the fuselage intact when you remove the fan, then yes, it is a challenge.

An alternative is to carefully split the fuselage along the seams.
Yes I got the pnf version. You say split the fusalage underneath, taking appart all the edf unit and the fragment of cut fuselage all together?
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Old Yesterday, 03:46 PM
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oldsneakers's Avatar
United States, CT, Hamden
Joined Jul 2011
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I managed to get the stock EDF unit out working it with a wide flat screw driver, wedging it down each side alternately. It eventually worked its way out and wasn't damaged.
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Old Yesterday, 05:25 PM
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USA, MD, Frederick
Joined Jan 2010
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The edf wasn't damaged, but how did the foam make out?
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Old Yesterday, 05:47 PM
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oldsneakers's Avatar
United States, CT, Hamden
Joined Jul 2011
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Minor scuffing. And it was covered up with the new engine. The original EDF is glued in with the rubberized stuff you see a lot on RTF planes.
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Old Today, 06:28 AM
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oldsneakers's Avatar
United States, CT, Hamden
Joined Jul 2011
307 Posts
I didn't have time to make a thrust tube before I went flying with my upgraded T45, HK EDF unit, 80A esc and 2250mah 65C 4S. It was quite a bit faster than the stock configuration. The surprise upon land was the battery. It had ballooned up as if it were going to pop. Doing the math(as I understand it), I didn't expect it.

HK motor max amps are 68 amps. I tested it with this battery and it drew 65A.

The battery can supply (2.25 x 65 = 146) amps continuously.

So I though the 146 amps would be fine even if I flew wot the whole flight. I guess not. Not sure where I went wrong.
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