|Feb 13, 2013, 05:09 PM|
Mine is a Sky Angel 50mm EDF . To make a long story short , it was difficult to hand launch because I had to hold it by the tail cone and support the nose with my left hand. I was the only guy at my field with the right technique. Someone else would take the Tx, I'd throw, then take the Tx back.It did ROG off of asphault on the short landing gear but I dont always fly off a paved runway
And even with an up graded fan it was no speedie flyer. The only way to get it properly balanced was to put the 1000ma 4s 40c li-po behind the cockpit in the area of the intake splitter. On a AEO 8 blade fan I got 2.5 min. flight time.
It's now been a pusher for a week and what a difference . I legthened the landing gear, modded it with rudder, installed a Suppo 2212 06 2200Kv w/ a 6x4 APC prop on a ply bulkhead in the exhaust cone. And fly it on 1600ma 3s 40 c Sky li-po.
It's like a whole different plane. 60 -70 MPH looks jet like , flys jet like , and gets 8 min. flight time . It went from a P O S to a great piece of plane.
Here's how it flew as a EDF YAWN
Here's the 2nd flight as a pusher
|Feb 13, 2013, 05:49 PM|
This one is the latest one ive done it uses a 2200kv ( could be 2700kv) with a 5.5*5 in apc prop ( its not the same setup in the photo ) this gets the motor hot im gonna go down to a 4.75*4.75
Im using a 12amp esc and a 3s 460mah nano tech flight times are around 6min
I think it weighs around 220gr maybe 240gr i forget!
I have more pictures in my attachments for some reason its telling me the file are to large?
|Feb 14, 2013, 08:14 PM|
Just a just a few thoughts from a Pusher speed freak ...
I note that posts mention torque ... this is a problem that besets pushers in that you have NO prop-wash over surfaces to help ... until the model reaches flight speed ... you are at mercy of prop diameter.
Note : Diameter.
Most Pushers you will note have small diameter but high pitch props, high KV motors - this is for very good reason. One of the biggest reasons being torque rolls.
A Tractor prop can be bigger and slower as the wash over main wing and surfaces will assist in early stages.
A Pusher needs thrust but is always risking that torque roll if over pressed before flight speed. So pitch up for drive, diameter down to reduce that flywheel effect. Many sizeable models - bigger than the 50mm EDF series run 5 x 5 ... 6 x 5 or similar props ... The only reason that an EDF convert to pusher may need a 6" prop is if fuselage blankets the prop. Obviously if the duct can be kept reasonably clear to feed the prop - then you can come down to smaller props and still get good drive.
Launching - ROG is usually no problem as long as prop has clearance to have model rotate on wheels ... full throttle can get her up and flight is from lift off .. so Torque is not so bad. But hand launch - is another ball-game and why many pushers are launched at part throttle ... in fact some are even launched NO throttle ...
It is also why I advoacte the bungee catapult system ... I can get 113kph at exit of rails guaranteeing no torque roll because the model is already well over minimum speed before it leaves the rails.
So my thoughts are HIGH kv motor, small diameter but high pitch prop.
Look at the Parkjets ... 3000kv, 4.5x4.5 props ... some like me running 5x5 and higher KV ...
|Feb 22, 2013, 08:20 AM|
This one was not popular as a twin J Power EDF but as a pusher it was my all time favorite
|Mar 17, 2013, 02:56 AM|
A club mate at my home field had a J Power Sky Blazer 64mm F-86 converted to pusher today.
It weighed in at 27 ounces, had a 2700 Kv in runner mounted in the fan housing, Then he took a 3 mm "music wire" used it as the motors shaft and extended it about 12 inches out the exhaust of the jet . Where he had a gear drive bracket with a bearing mounted as a carrier bearing.
He ran it with a APC 6x4 prop on a Gens Ace 2200ma 3s 65c li-po . I don't know esc or Watt meter readings but it really woke this plane up and we estimate it's speed between 80-90 MPH And that's with the canopy blowing off at launch
|Mar 17, 2013, 04:19 PM|
That's an awesome flying conversion Carl. I like it . Nice and big too.I've been having fun with a scratch built copy of a 50mm Sky Angel Screamer . It's a simplistic effort at a copy done with Readie board foam board and pool noodle fuse but for a few $s they are a hoot
|Mar 18, 2013, 04:22 AM|
OK ..... not one to shy away from a try at something ...
I have a cracked up T45 50mm job that sits there looking at me ... beaten up but saying - for all the faithful service and tests I did for you - I'm now left on the side forgotten !
Nose is crap ... after 4 replacement DIY noses ... wings look like rats have been nibbling at them ... fuselage needs a few fillings ... control rods need replacing, servos etc.
So I've considered a tractor prop on the nose ... but now the subject of pusher arises.
So a standard Jpower T45 ... what motor ? I have a 1400, 1800 and 3700kv ... I have various props from 4.1 up to 7" diameter ... If I did a tractor - it would be the 1400 + 7" prop I think ... as a pusher ... this is where the fuselage bulk comes into play ... a 4.5 diameter prop is going to be masked by it ... but a high KV motor will not like anything over that sort of size. How much would the ducting help her ?
Will take a few photos and see what I come up with ........
|Mar 18, 2013, 09:18 AM|
Thats wonderfull news Nigel.
The Hawks large inlets are a concern. It will be a good idea to allow max air flow thru the fuse. I closed the tail pipe of the Gripen with a firewall motor mount bulkhead and it caused a wobble from the compressed air escaping out alternate sides of the inlets , untill I closed the inlets with streamlined covers. I'm using a stick mount into a verticle vane on the Mirage.
The most popular motor for pusher park jets is a Suppo ( or equivalent ) 2200 06 2200 Kv
on 3 cells and a 6x4 prop. in the Sky Angel jets it's equal to the 5 and 6 blade fans on 4 cells with nice speed, unlimited verticle and about 7 min run time WOT on a 1600ma 3s 40c li-po. The elevator servo might have to be moved back to fit a 1600 li po in the Hawk.There is a little prop tork but it's not more than what can be handled .
Hand launching is another issue with low wing flat bottom fused jets . Grasping behind the wing is close to the prop.
More thoughts when I look at my T-45
|Mar 18, 2013, 01:21 PM|
Here's the sorry T45 ..
Cut a slot in upper inside of duct ...
Set up a beam mount for the slot ..
Extend motor wires to ESC at front of model ..
Motor is a 250 Heli motor ... 3700kv ....
Tests with 1800mAh 3S Zippy Compact. My Fuselage was modified up front for such LiPo's when it was an EDF ...
The voltage sag is excessive and LiPo is being hammered ..... so either a higher C rated LiPo is needed or use a lower kv motor.
The motor is one of the pair I had fitted to my infamous Parkjet Twin ... the power draw then was over 110A and too much for the PKJ Twin set-up.
BUT - the set-up shows substantial thrust capability ... while holding the model - she was pushing VERY hard against my hold. She would be quick I'm sure.
Trouble is the motor mount then had problem ... the rivets holding the L plate to the bracket worked loose with the thrust. The mount will need replacing, but I set the beam so that I could do this if necessary.
Balance ? Perfect with the 1800 3S and servos in original positions ... ESC pushed into the upper area immediately behind canopy.
I'm really looking fwd to fitting a new mount and getting her in the air ...
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