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Old Apr 05, 2007, 10:13 PM
United States, GA, Columbus
Joined Mar 2002
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EDF Intake Lip Question

I'm about to finish up the EJF/Sapac Red Arrows Hawk and I need to install the fan.

I was wondering how to attach the lip to the fan. Is simply snapping on good enough? Doesn't seem an extremely tight fit. Is it normal to glue the intake lip to the fan? How do you normally secure the lip to the fan?

Thanks, Jim
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Old Apr 05, 2007, 10:24 PM
SoCal, Year Round Flying!
bmiller's Avatar
Newport Beach, CA
Joined May 2002
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I've used silicone to secure intake lips on some of my other fans with no probs.
I was afraid that using CA would etch the plastic and the silicone helps quell vibration/noise too.
Bruce
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Old Apr 05, 2007, 11:50 PM
United States, GA, Columbus
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Thanks, I'll give that a try.

Jim
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Old Apr 06, 2007, 06:19 AM
Kat Builder
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Bellflower, Calif.
Joined Apr 2004
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Hi Jim...

You are right in being concerned about securing the intake lip, because, if it has any roundness at all, it will supply a very measurable amount of the total "THRUST".

I learned this, when I first fired up the ducted fan modules for a balsa TomKat, and the intake lips SHOT across the room, against the incoming airflow (WOW !!!).

I have spent a lot more time designing my intake lips since then, with much improved static thrust. But also keeping in mind, what design feature improves static thrust, can, and often does, get in your way as high speed drag.

Life and airplane design, is all a bunch of give and take...

Bob Reynolds
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Old Apr 06, 2007, 09:44 AM
EDF rules... :)
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Inlets with a rounded intake will provide 20-30% more thrust than a fan without it, one thing I found interesting is the size of the inlet in area can be pretty large in relation to the scale of the plane for the speeds we are capable of. Inlet pressure recovery is mostly consumed by the needs of the fan till it reaches 155% of FSA so using an inlet that is 120% FSA will not detract from the speed of the aircraft and will enhance the flow thru the fan for our needs.

Eric B.
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Old Apr 06, 2007, 12:06 PM
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Jim I'm suprised you found room to that inlet lip inside the Sapac Hawk, the stock tunnel size in front of the fan is about 65mm, if you're using the smaller XF fan (I can't recall if it's 60 or 55mm) then I see why you need it. If foam removal become necessary to fit the lip (and it may end up not being a great fit near the outside of the lip because the lip goes past the front and then speeps back again going outward and back because it's kind of designed to fit an A-10 type nacelle), a dog collar/lamp shade type of transition adapter made from photo paper or card stock may make for a cleaner installation. You'd have to cut a former/bulkhead out of lite play or balsa to sit against the face of the fan and have this say one or two inch long transition piece glued to the inside of the ducting and the inside opening of the bulkhead (the purpose of the bulkhead being to help form the paper piece). Hope that makes sense without out pictures. Even with a less than super clean installation (airflow wise), the plane with only go so fast with fixed gear plus the aileron servo and linkages sitting in the ducting and the lack or area ruled ducting...with all that, being super critical on the inlet in front of the fan is not critical. The biggest reason my EJF Hawk (see the thread in the foamy edf section) was able to hit 70mph level and 84 out of a dive was the 500 watt MF480 and Mega 16/15/2 setup, shear power. Ducting mods didn't seem to make much difference if any, it would have been nice to get more than one flight in with the new mods but my damn FM receiver glitched and killed the plane.

One thing I'd do for sure on your setup would be to use and exhaust tube, I even used one on my MF480 setup, the stock opening is too big for the stock fan and especially a smaller fan.
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Old Apr 06, 2007, 07:46 PM
United States, GA, Columbus
Joined Mar 2002
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Quote:
Originally Posted by Ed Waldrep
Jim I'm suprised you found room to that inlet lip inside the Sapac Hawk, the stock tunnel size in front of the fan is about 65mm, if you're using the smaller XF fan (I can't recall if it's 60 or 55mm) then I see why you need it. If foam removal become necessary to fit the lip (and it may end up not being a great fit near the outside of the lip because the lip goes past the front and then speeps back again going outward and back because it's kind of designed to fit an A-10 type nacelle), a dog collar/lamp shade type of transition adapter made from photo paper or card stock may make for a cleaner installation. You'd have to cut a former/bulkhead out of lite play or balsa to sit against the face of the fan and have this say one or two inch long transition piece glued to the inside of the ducting and the inside opening of the bulkhead (the purpose of the bulkhead being to help form the paper piece). Hope that makes sense without out pictures. Even with a less than super clean installation (airflow wise), the plane with only go so fast with fixed gear plus the aileron servo and linkages sitting in the ducting and the lack or area ruled ducting...with all that, being super critical on the inlet in front of the fan is not critical. The biggest reason my EJF Hawk (see the thread in the foamy edf section) was able to hit 70mph level and 84 out of a dive was the 500 watt MF480 and Mega 16/15/2 setup, shear power. Ducting mods didn't seem to make much difference if any, it would have been nice to get more than one flight in with the new mods but my damn FM receiver glitched and killed the plane.

One thing I'd do for sure on your setup would be to use and exhaust tube, I even used one on my MF480 setup, the stock opening is too big for the stock fan and especially a smaller fan.
Thanks everyone for your input.


Ed, I am using the xf fan and I will use a thrust tube as you suggested.

I have flown edf's before but not any that needed a thrust tube. Could you please tell me what would be appropriate to use for this plane. Something strong and light-weight. I know its just plastic sheet rolled up by what do i need to go look for at the store to purchase?

Is it best to secure it to the exhaust end of the fan with clear packing tape?

Also does the tube need to be centered within the ducting of the plane or can it just rest on the floor of the ducting secured by tape or epoxy etc....?

Thanks for your help, Jim
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Old Aug 31, 2008, 11:59 AM
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United States, NJ, Trenton
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Jim,
Going through some old threads and came upon this one. Did you actually put the lip within the fuselage? I asked a similar question recently regarding the Sapac Gripen. It has a huge intake chamber ahead of the fan and I thought that a lip might work there. Any thoughts and comments on how it worked out for you on the Hawk?
Mike
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Old Aug 31, 2008, 10:25 PM
United States, GA, Columbus
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Quote:
Originally Posted by CarreraGTSCS
Jim,
Going through some old threads and came upon this one. Did you actually put the lip within the fuselage? I asked a similar question recently regarding the Sapac Gripen. It has a huge intake chamber ahead of the fan and I thought that a lip might work there. Any thoughts and comments on how it worked out for you on the Hawk?
Mike
Yes, I did use the intake lip. As far as if it helped or not I really do not know.

Problem is, I did use a thrust tube but it is not at the correct exit diameter and I am losing thrust there. Pretty much the same diameter as the fan,

The Edf's I built prior to this jet already had the correct intake/exhaust diameter built-in so I was kind of learning on this one.

Since then, I have gone edf crazy and that is almost all I fly now.

I know you saw my post about the Sapac Gripen where I am getting 1000 watts with the JS 1400 where I feel the watts should be higher.
The exhaust is the perfect diameter on the jet so something else is not efficient.
It should worth trying to add a lip, the extra weight at the rear would be welcomed.

James
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