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Old Jan 25, 2008, 08:02 AM
Texas Buzzard
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McAllen,Texas
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Selecting an EDF/motor for 1st "JET"

EDF power is new to me, although I've been flying RC ( glow & electric) for many years.

I am trying to select an EDF power unit that has between 12 and 20 ounces of thrust. I estimate my scratch-built "trainer jet" will weigh 17 to 20 ounces ready to fly.

I have been looking at Hobby-Lobbies Fan EDF 60/15 Mk2 3 blade spun by a Jetscreamer MMH550 w/ extention 3500 kv.( inrunner) ( about $105)

Also HL has an outrunner 3500 kv MT2235 mated to Fan MT1028 66mm fan. (about $85)

Are these units made to just sell, or will they do the job of pushing my 18 ounce/230 sq. in. airplane with reliability? I just want to fly a ducted fan powered job at maybe 45 to 55 mph.

Yes I have looked at "Ducted Fans.com ". Any advice is welcome, thanks.
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Old Jan 25, 2008, 08:16 AM
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orlando fl
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what size is the inlet area?

Depending on that you should get the largest size fan you can that will fit the plan (i am assuming an interal fan not a pod)

you are shooting for inlet area about the same as the area of the fan.

outlet area should be about 90% of inlet area

Smooth ducting (not hard turns, gradual changes in tapers, no junk in airway) is important and can make or brake a jet performance.

If not using ducting, the the fan should have an inlet lip installed to at least smooth the flow into the fan.
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Old Jan 25, 2008, 09:41 AM
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welcome, another Texan to EDFs, I been flying propeller planes for a long time, pick up EDF last year and never look back on my air screw plane again.
I have not tried the one you mentioned, but I seen my fellow club member fly a EDF wing with the HL duct "ETH550 "XF-Fan" 56mm Ducted Fan ..... $ 24.90" with this motor ETH5512 XF-Fan 5100 Inrunner Brushless Motor ..... $44.90 Introductory Special! ..... $ 34.90" and I have the same fan and motor for my HL lynx which is still in the box, I think this set up should be good for you 16~20 ozs trainer type ducted fan plane, how is your fan mount onto the plane, is this going to be external or it will be internal with ductings. I did a hotliner sailplane with an external fan mounted on top of wing and it is simple and do well. One thing you need to think about is how to launch your trainer, do you fly off hard surface, are you planning ROG, or this is going to be hand launch or bungee launch, all these need to be considered.
IMHO, EDF is still marginal in power/weight or thrust/weight ratio, so you need to watch the AUW, I think your 230 sq.in wing area is on target, for the set up I mention, you will need a 3s 1800 to ~2200 mah good quality lipo pack cause you are looking at 20~22 amp current draw.
If you are comfortable with scartch build, that the way to go, I scatch build most my plane, even I buy ARF, i change almost everything.
good luck!!
Kong Ho
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Old Jan 25, 2008, 10:25 AM
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EDFs fly like jets when you can manage about 200 watts per pound.
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Old Jan 25, 2008, 12:31 PM
Texas Buzzard
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McAllen,Texas
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Good Stuff. THANKS

DAVE, The inlet dia. of fan is 56mm ID and 71mm OD. Since I will design and build my EDF plane Scratchbuilt I will take note of your comment. The proposed power unit weighs close to 3 OZ. Thanks.

Hokonging, I see that the notor you told me about is OUT OF STOCK until Feb 22. Thats the ETH5512 X-fan motor. I will be designing a plane that looks like (sorta') a L-39 but with the wing placed up on the top of the fuse.
The Germans had a Jet in the early days that will look like mine.

The EDF will be externally mounted up over the wing...slightly back of the center of lift. The fuse will be boxy for ease of construction, will use a 12% airfoil for lift. Ailerons & elevator used ( maybe rudder later if needed.) With the EDF mounted externally I can get to it easily, also can change the thrust line if needed. Want to keep it simple and lightweight. That heavy Lipo will need a solid mount too. So probably will build everything up to three inches forward of the L.E. of wing then balancing with Lipo, finishing with closing in around that Batt. Do noit want to have to add nose weight.

It's not as complex as it might sound. Maybe I can shoot for about 7 ounces for the empty airframe. !/8th sq. spruce covered w/ 1/64 ply for fuse has worked for me earlier. Depron ships I have built (scratch) have been durable at 12 to 14 oz. But where I fly Depron gets scratched up.

Homgkong, do you have a shorter name? TELL ME about your planes and equipment - I am all ears. Tell me about what you have seen flying in Houston, I am in the Rio Grande Valley and no Ducted Fan here...nust lots of War Birds and Trainers on .46 glow.
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Old Jan 25, 2008, 01:11 PM
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Hello, TB, oh, what am I saying. I go by Kong.
I think you are on the right track, for the first jet, I will not sink a lot of money into the fan, you can spend $100~$200 on the big name fans. for smaller plane, the Wattage power fan, the Xf, the alfa fan are all good for 15~20 ozs beginner's plane, I started with a $20 wattage fan with my scratch build vampire and that time, some people tell me it won't work get a "real" fan, I built it and it just doing fine not great but for a beginner like me, the power fan just do fine, goto Balsa product, I think they have some smaller fans.
After the Vampire, I did a lippisch P20 this is powered by a wm 480 and I did a hotliner and a Mig 15, now I have a Huckebein, a F16 on my work brench. Do a search under my name, you will find some of my planes.
For the plane you want to build, I suggest you do a "V" tail if you mount the fan on top of the wing this way the exhaust is not directly blow on the elevator and cause some ill effect.
You will find it very rewarding building and flying edfs.
Kong Ho
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Old Jan 25, 2008, 04:41 PM
Texas Buzzard
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McAllen,Texas
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Kong, looing Spiffy.

Your pics show a planform very close to my idea of a first ducted fan ship. Your aspect ratio is a bit higher than I was thinking about. But I bet you have a sembalence of a glide,huh? Hey, Kong that is a meat looking set up plane and catapult. I envisioned a catapult too. I have flown Sailplaanes off a UPSTART ( boost )

Looking at you fan unit could it be an X-Fan or a 66mm DF MT1028?

I do apperciate you answering me. About an hour ago I went to Hobby-Lobby and ordered the ETH550 X-FAN + Acessories,(56mm or 2.20 inches) Got the Little Screamer " Jetscreamer" w/ extention which fits the fan. I have had excellent luck with two Little Screamers ( Purple Peril) w/ 6X4 prop on a scratchbuilt job looking like hobby-lobby's V-Diamond ARF. Mine is a w.s. of 34" 180 sq. in. sweptback. In Depron, a bit heavy at 14 oz. But defeats the winds we have here...very few days the wind is below 10 mph.

This hobby is always turning up new things to learn. My first RC was in 1958 ( rudder only) on Citizen's Band - 27.225 . And we had to build our transmiters. Thanks - Later
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Old Jan 25, 2008, 06:38 PM
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Houston
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TBU, the fan in the Hotliner is a Wemotec Mini 480, motor is a cheap 3900KV motor from Hobby city, I used 4S A123 cells on that plane, it is heavy, almost 38OZs ready to fly, but do well with about 300 sq.in of wing area, I like those high speed low passes.
Kong Ho
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Old Jan 25, 2008, 09:25 PM
EDF rules... :)
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The Alfa 60/15 3 blade and Little Screamer Jet Scream will work adequately for your plane, the thrust in a podded setup is ~14oz on 3s, and 20oz on 4s. The Xfan and LSJS is similar but smaller diameter fan will produce a bit less thrust for the same power in with a higher efflux speed proportionate to the difference in size. The GWS 55 is also adequate with 20mm 4200kv motor on 3s ~16oz at 250watts. Good luck with your design.

Kong Ho,
Wil you be out tomorrow, if the weather is good I might try the maiden of the little 40mm fan?

Eric B.
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Last edited by AirX; Jan 25, 2008 at 09:26 PM. Reason: added info
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Old Jan 25, 2008, 10:03 PM
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Eric, you have PM
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Old Jan 26, 2008, 10:45 AM
EDF rules... :)
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Answered it this morning...

Eric B.
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Old Jan 26, 2008, 12:12 PM
Texas Buzzard
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McAllen,Texas
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Excellent , Thanks AirX

Quote:
Originally Posted by AirX
The Alfa 60/15 3 blade and Little Screamer Jet Scream will work adequately for your plane, the thrust in a podded setup is ~14oz on 3s, and 20oz on 4s. The Xfan and LSJS is similar but smaller diameter fan will produce a bit less thrust for the same power in with a higher efflux speed proportionate to the difference in size. The GWS 55 is also adequate with 20mm 4200kv motor on 3s ~16oz at 250watts. Good luck with your design.

Kong Ho,
Wil you be out tomorrow, if the weather is good I might try the maiden of the little 40mm fan?

Eric B.
.................................................. ...................................
This is what I wanted. Some real life data. So, from your post my 55mm X-Fan will produce about 55/60ths of the thrust as the 60mm dia Fan ( of course with same power in).

So 11/12th of 20 is =18.3 oz thrust. But alllowing for "slop" it may actually be 16 oz.
The diagram is a 1st drawing of the proposed plane for this 55mm Fan on a LS JS on 3S to start. Hope to come in under 17 oz AUWt.
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Last edited by Texas Buzzard; Jan 28, 2008 at 09:48 AM.
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Old Jan 26, 2008, 01:23 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
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Cool design, get a thread started on it and lets see how she progresses.

The problem with some of these small fans is the 3 high aspect ratio blades require a lot of rpm to make the fan work well. Blade density(coverage of the swept area) is the key to efficiency in fans for ducted installations where a podded install like yours wont be that much of a thrust killer for a 3 blade fan. I have the Alfa fans both the 60/15 and 60/25 and the 25(5 blade rotor) outperforms the 15 all day long, the LSJS is installed in mine too and I can vouch for the numbers, I have seen some good video on the Xfan in the Alfa jets with the LSJs but have not used it myself.

Eric B.
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Old Jan 26, 2008, 03:29 PM
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Houston
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TexasB: just want to cautious you about the exhaust blowing onto the elevator, in your design , when the high speed exhaust pass the top of the elevator it create a low pressure zone, so at take off, when flying speed is low, there will be a nose down moment from the high speed exhaust, it make it more tricky to launch, but once you are on the "Step", you will be OK.
Just come back from flying my Lippisch, it turn out a beautiful day here in Houston. Eric you have to see this thing flies.
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Old Jan 28, 2008, 09:44 AM
Texas Buzzard
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McAllen,Texas
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Kong, Automatic Stall Recovery ??

Thanks Kong,
Understand the "automatic DOWN ELEVATOR due to fan's blast going over top of elevator.

GO BACK to post 12 ....see modification of elevator.

My (movable) elevator will extend 1.5" out of fins. Maybe if in clean air this extention will help. But, say Kong, if the fan blast causes a down elevator effect only at low airspeeds then it would act as an automatic stall correction, eh? But I can expect this auto Down during the bungee launch.

I got some new 1/4" dia bungee at Lowe's yesterday, Got 15 feet ( all they had)...I stretched it to twice it's length in Lowe's. Estimate a 4 pound pull by hand. 4 Pounds accelerating a 1 pound plane near horizontal gives : F=m x a.
Or Force = mass x Acceleration .
Force divided by mass being accelerated = acceleration

So to use metric for convience;
Plane's mass = 1 lb = 454 gm or 1.0 Kg
Average force = less than 4 lbs, estimate 3 lbs during first part of launch. So using 3 lbs of force we get 3 x 454gm or 1362 gm or 1.362 kg.....we must multiply the mass x accel of gravity or 1.362 kg x 9.8 m/sec^2. This is called NEWTONS , (a force unit).
This gives 13.35 meters per second squared for ave. acceleration.

So this 1 lb plane will accelerate at about 40 feet per second squared. At end of first second it will be moving at 40 ft/sec. 21 ft/sec = 20 mph. so at end of 1 sec it will be moveing at about 39 miles per hour. Don'tcha' think this is well above stall speed?


Conclusion: The 1/4" Lowe's bungee will be good for a plane of maximun flying weight of 1 lb to 1.5 lbs with margin of safety.
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