Martin Taylor Posted August 30, 2007 Share Posted August 30, 2007 Hi Guys, I have a problem witha lack of power for my BAE Hawk. The Hawk comes with a 64mm 6 blade fan unit, the flying weight is around 620g and I am using a 11.1v lipo and 40A ESC. I thought I could use the motor from my now deceased Phase 3 Fantom (not crashed by me!!). I fly off tarmac and thought I should be able to ROG easily but when the throttle is opened up the Hawk just trundles along the runway but doesn't build up enough speed to take off. My questions are: Could the Kv rating of the motor not be enough?Is it simply a case of getting a motor with a higher Kv rating to turn the fan quicker? Any help or thoughts would be appreciated. Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted August 30, 2007 Share Posted August 30, 2007 Oh, the dark art of EDF.....potential problems are, high kva motor might improve performance but then draw silly current. You don't say what kva/size the motor is, and what C rating the lipo is?Many fan's are of a very poor design and just don't really work very well. EDF are only around 50% efficient as a prop, and personally, I agree with the guy from Greenair designs I spoke to at Cosford.....pusher prop set up's on jet's are so much better. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted August 31, 2007 Share Posted August 31, 2007 But look naff First question is, what motor is the supplied 6 blade fan supposed to be paired with ?second one.... why not use that one Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted September 3, 2007 Share Posted September 3, 2007 Yeah, they look naff.....but go very well! I keep going with EDF, but it is a minefield for sure. Reccomended power set up's are the only way to go for a particular model....and even then...they don't always work that well....you have to choose carefully. Quote Link to comment Share on other sites More sharing options...
Tazz Posted September 10, 2007 Share Posted September 10, 2007 Can u install a 75mm fan??? If u can then buy one from BRC with motor £20.00!!! Th interesting Use a good 4s battery and a 60 Amp ESC.Lastly throw the model like a Javelin. If u dont know how then ask somebody with a large motorised glider to show u. A slightly windy day helps! Forget the ROG and the undercarriage. EDF's like to fly fast. The fans actually work better in fast air currents. I fly regularly a firebird with a cheap 68 mm fan and 3s battery and very small 25 amp OUTRUNNER motor. Boy does it fly and fast!!I am now slowly building three more EDF's because they teach u everything about electric power trains. Connectors, ESC's, Batteries, Motors, Ferrites etc. etc. Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted September 10, 2007 Share Posted September 10, 2007 Er, to be honest, that isn't entirely correct, I have fitted fan unit's that look better than o/e....only to find they are pants. Put it this way, recent experiment, F-16, try a 6 blade, fancy pants unit with a top drawer 4800kv motor.....total rubbish. Used a Mega 55, 3 blade, cheap as u like unit with a DX-9 in-runner, 4600kv but upping from 3s to 4s......oh my lord....seriously quick. The Hawk in question will ROG quite easily [although all EDF's seem to need to get up a fair amount of ground speed], chucking it under-powered may result in a very messy crash! I have owned one, original fan/motor in it, flew nice but not seriously fast, when the motor burned out, I replaced it with a 68mm Airpower unit and reccomended motor....result? Rog.....struggled...then hit the deck due to being under-powered. If you find a fan that works [relative to model weight] fantastic....personally.....I have given up on 3s set up's, and use only 4s in EDF.....they fly like a jet! Oh, and I only use Opto ESC's, and have just switched to 2.4ghz as I got so sick of glitching. Finally....EDF peace of mind! Quote Link to comment Share on other sites More sharing options...
Tazz Posted September 11, 2007 Share Posted September 11, 2007 Scott u r right about throwing an underpowered edf model but u can easily measure thrust of the unit with any scales. Just point the nose at the scales holding the model reasonable upright. Now note the weight and then open the throttle and note the weight. I have flown edf's with as little as 30% thrust i.e. the thrust is 30% of the total weight. The provisos for such a models are 1. The wing loading not to exceed 65 gms/sq.dm.2. The model is reasonably clean aerodynamically. ( servo covers, sanded foam or better sanded and covered with film/decals etc.)As Isaid before u need to get it to flying speed by a good throw or a catapult or bungee. In fact a bungee is quite easy to make. We are not talking 4m. 5kg glider bungee.Once the plane starts to fly the clean aerodynamics really pay as the speed from even a 30-35% thrust plane is phenominal. For yr reference my Firebird develops 33% thrust and it flies right out of my hand and flies so fast that i always back off on the throttle to something estimated to be half power. I repeat it flies on 3S.The airpower 68mm fan is a good one but u need to find the right motor. One of the best motors is the HET 2W-20. It is seriously powerful. Quote Link to comment Share on other sites More sharing options...
Derek Posted May 4, 2008 Share Posted May 4, 2008 I have just moved into edf with the fly-fly 1.4m sabre, not easy to put together but with the std. 90mm fan and a 1600kv Taiwanese motor,49 quid, 5 li-po cells,3800ma, weight with air re-tracts around 2.5 kg, power output after resetting the s/c via card programmer and whatt meter(invaluable pieces of kit), 700watts at 38 amps, will rog with ease and achieve a good 6 min.flight, plenty fast enough and aerobatic, great fun and looks great in the air, a doodle to land as well, Scott at electric flight cumbri is the person to talk to, very helpfull. Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted May 5, 2008 Share Posted May 5, 2008 Derek - I love that Sabre but how has the undercarriage stood up to things....? Quote Link to comment Share on other sites More sharing options...
Derek Posted May 5, 2008 Share Posted May 5, 2008 David, after the initial problems, no not problems, challenge, it is working well, plenty of lube and set the legs up using the grub screws to minimize play, i put a bit of lead on the nose leg to give it more momentum on the way down, no effect on c/g, this model is not c/g sensative.How have you got your Sabre set up etc?Derek Quote Link to comment Share on other sites More sharing options...
David Ashby - Moderator Posted May 5, 2008 Share Posted May 5, 2008 Haven't got one Derek, just like the full size and those larger EDF's have always caught my eye. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 5, 2008 Share Posted May 5, 2008 Are you flying from grass - and did you modify the mountings, because if not, then I cant believe the retracts have survived. Quote Link to comment Share on other sites More sharing options...
Derek Posted May 5, 2008 Share Posted May 5, 2008 No not off grass, we have the luxury of a 600 acre site with tarmac, spoilt aren,t we?Slight mods, as in a touch of epoxy at the weaker section of the mains as i had one nearly collapse , think i caught a stone at take off, obviously ditched the kit retract valve, it is useless, replaced with a Robart unit, i see that Graupner do an electronic retract unit, do you know anything about it? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 5, 2008 Share Posted May 5, 2008 A few guys in the US have fitted them I believe, but not without issues - they do take a fair bit of power via the receiver sockets which could be an issue if not allowed for. Most have done the ply plate mods for mounting, and ditched the flyfly valve for a decent one, or used springair 602s. Grass strips are proving nigh on impossible in handling the crummy metal oleo connectors - even decent piano wire replacements are not working - this bird was NOT designed for grass strips, and light glassing and hand launch / bungee seems the best option. Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted May 5, 2008 Share Posted May 5, 2008 The electric retracts have all sorts of issues, main one for me [flying 2.4ghz] is current drain, then people have had regulator failures but more commonly.....stripped gears...er, which kind of defeats the object?! You can pick up decent air systems for jet's now for pretty reasonable money, even for the very smallest EDF [X-Flight systems for instance, complete leg assembly's are 10g each!]......so I just don't see the point in all honesty.Tell you what I did with the Sabre [grass flyers], I installed "bogey" wheels in the wing tanks, they worked ok-ish for take off [but you have to get the wheels in exactly the right place], but I suspect bungee launch, and landing on the tanks would be better. Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted May 6, 2008 Share Posted May 6, 2008 Nice one! I'll go and have a look. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 6, 2008 Share Posted May 6, 2008 2.5lbs ? and skinned ?? Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 6, 2008 Share Posted May 6, 2008 It could be better. Cant fathom out the graphing at all - I have other issues with it though. I still dont see how you achieved 2.5Lbs AUW with glassing and a paintjob too! I am expecting closer to 5lbs + Are you sure ?? If so, I am going to have look really hard at how I glue things together !! Quote Link to comment Share on other sites More sharing options...
scott cuppello Posted May 6, 2008 Share Posted May 6, 2008 So, 5.5lbs pretty well, which is smack on for 6s, still in the power to weight ratio zone.....that's what matters! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted May 6, 2008 Share Posted May 6, 2008 Thats bettter, I KNEW something other than my heavy handed use of the epoxy botttle was wrong Quote Link to comment Share on other sites More sharing options...
Laurence Naylor Posted July 18, 2008 Share Posted July 18, 2008 Re: Martin Taylors foamy Hawk. Mine came fitted with motor and all the gear apart from the receiver. It will definitely not take off from even very short grass. It has to be firmly hand launched by a.n. other since there are no finger holds for a self launch. I have smoothed out the inside of the fuselage with self adhesive plastic to improve the airflow. Battery choice is limited by the size of the tray, although the length can be increased by careful removal of a small amount of foam at the front of the compartment. I can fit a Flightpower Evolite V2, 2500mAh 3s LiPo. Once airborne it flies quite well. Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 18, 2008 Share Posted July 18, 2008 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
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