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        Discussion FMS Dassault Alpha Jet - 70mm

#1 Prowler901 Mar 29, 2012 09:16 AM

FMS Dassault Alpha Jet - 70mm
Howdy folks,

Can anyone tell me how the edf unit is mounted in this plane? I need to remove the fan so that I can balance it. I've got the bottom cover plate off, but the edf unit won't come out. I can't see any screws that are holding it in. I don't know if it is glued in, and I don't want to damage anything by forcing it out.


#2 JGuilty13 Mar 29, 2012 10:39 AM

If you dont see any visible screws, then it is most likely glued in by the factory. Pull lightly and slowly! Can you fit an x-acto blade in there to try and separate the glue from the foam?

#3 clinth01 Mar 29, 2012 05:33 PM

They usually use fairly cheap and nasty glue. Try dribbling a little de-natured alcohol/white spirits down the shroud/foam joint to soften it a bit before trying to remove the fan.

#4 Prowler901 Mar 29, 2012 11:24 PM

Thanks guys. That did the trick. There wasn't really much glue there. Thank goodness. Now, when putting the unit back in, what is the best way to fix it there?


#5 clinth01 Mar 30, 2012 12:45 AM

To re-install, some people use double sided tape, I generally use dabs of silicone bcause I have always got an open tube of it somewhere.

Whatever you do, choose a method that will allow you to remove it easily in the future if the need arises.

#6 Prowler901 Mar 30, 2012 08:29 AM

Thanks Clint. That sounds like a plan to me. :)


#7 Prowler901 Mar 30, 2012 10:51 PM

2 Attachment(s)
Is there any reason I can't mount the fan unit to the bottom/removable cover plate? The model comes with the unit glued to the inside of the fuselage. The cover plate then 'sandwiches' the unit from the bottom. Could I mount it to the bottom instead? It would be easier to remove for maintenance that way.


#8 clinth01 Apr 01, 2012 06:51 AM

It could, but it is more usual to have it fixed to the airframe rather than the cover because most (well, a lot) of these foamies mount the ESC in the roof of the duct just in front of the fan for cooling. With the fan fixed to the airframe, it is usually much easier to route the wiring from the motor to the ESC in its' groove in the foam. If you fix the fan to the hatch it becomes much more difficult to keep the wiring tidy and out of the airflow, and also more difficult to connect/disconnect the wiring bullet connectors for maintenance.

Remember, you want to keep the ducting before and after the fan as smooth as possible with minimal obstructions/things dangling in the breeze.

#9 Prowler901 Apr 01, 2012 07:33 PM

Gotcha. Thanks for the advice Clint. That helps a lot. :)


#10 Prowler901 Apr 14, 2012 09:25 AM

Maiden Success!!!
I competed assembly during the week (not that it's real hard ;) ). However I added two spars between the center section and the outer wing panels. A simple glue joint just makes me nervous. :eek: I took the fan out and balanced it. She runs real smooth now. I did a run up with my watt meter to check the power plant. I don't recall the numbers right now, but I was pleased with what I saw. And, the 'jet blast' was blowing things down across the room. :D Then last night I got the CG all set at 178mm. The weather report for the morning was for calm winds. Perfect day for an early morning maiden.

I did a hand launch because I don't have a decent field to take off from. Winds were 2-3 knots. She left my hand at a good up angle, but she was a bit squirrely until speed built up. I managed to keep the wings level enough and she climbed out beautifully. There's nothing quite like the feeling on that first climb out. :) Acceleration was decent enough. As others have reported, she is no speed demon. But, the speed is nice and scale and low passes were really cool to watch. I flew most of the time between 50-90% throttle. Handling is crisp. The rolls are very clean with little to no loss in altitude. Approach to landing was nice and easy. She sets up in a glide real well. But, you do have to keep some power on as she'll slow down pretty quick. I only flew for 3 minutes because I was only using a 2200mah 4s. It is a 20c battery and was warm when removed. I'd recommend not using a 20c battery at all. A 30c will be much better. I have one but the winds started picking up. And, I don't like to push my luck on maiden days. But, I'm really psyched. She was a real blast to fly. $100 well spent. :)

More fun to be had!


#11 clinth01 Apr 15, 2012 04:31 AM

Congrats on the successful maiden !!

There's nothing quite like the feeling of getting your pride and joy back in one piece after its' first flight, is there :D

I generally use 2650mAh batteries on my 70mm jets to get decent flight times, and now that I know, 30C is the lowest rating that I will use. It keeps the heat down as you're not working the pack to its' maximum all the time.

Not sure about the smaller one, but on my 90mm the nose-gear opening let lots of cooling air in for the battery, but I had to make a couple of openings to let the warm air out into the ducting in front of the fan. It seemed to keep the battery a bit cooler.

#12 Prowler901 Apr 15, 2012 10:35 AM

Thanks Clint. Yeah, I had a huge grin on my face the rest of the day. Silly as it may seem. But, this is my first edf. I've been dreaming of flying an RC jet since my Dad and I flew 2-stroke props back in the 80's. I think that was when the 2-stroke ducted fans were coming out. But, it was just too much money for us. So, yesterday was a dream come true for me. :)

My other battery is a Blue Lipo 2650mAh 30C. I look forward to trying that one out. Today we have T-storms moving in so the wind is grounding me. Next weekend perhaps.

This 70mm version doesn't have any venting to the battery compartment. There isn't an opening for the nose gear. I don't plan on using the gear. Perhaps if I remove the block that the gear protrudes from I can set up a vent through there. I'll have to see how I can address that.


#13 clinth01 Apr 15, 2012 05:28 PM

With foamies, I usually get a length of 5/16 landing gear wire, heat it up with the small gas torch, and poke holes in the foam with it. it gives a nice clean hole with smooth edges which makes it easy to touch up with paint afterwards if you want to.

#14 Prowler901 Apr 15, 2012 11:03 PM

Hmmm... Good idea. Thanks.

#15 PsicoPete Apr 18, 2012 12:01 PM

Hi there,

I have a 70mm AlphaJet and I'm probing what the best radio mixes are for her.
What mixes do you have set up for acro flight so you can take the most out of the flight?

Thank you.

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