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Old Jun 10, 2008, 12:50 AM
Registered User
Michigan
Joined Jul 2007
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Eflite F-15 does not fly

I assembled my Eflite F-15, took it to the field, and much to my consternation it just will not lift off the smooth surface I normally fly from. The motors screem, but there's not enough speed to get it to lift off. I am using two 2200 3S Thunder Power Extremes too. I let it roll for about 100 feet and still it did not want to lift off. Has anyone had this problem? I am wondering if anyone has tried another motor-fan combination to get it to have more thrust.
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Old Jun 10, 2008, 01:42 AM
SoCal, Year Round Flying!
bmiller's Avatar
Newport Beach, CA
Joined May 2002
5,745 Posts
what motors and ESCs are you using?
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Old Jun 10, 2008, 01:47 AM
Switching to guns
BpwrJet's Avatar
Joined Dec 2006
1,297 Posts
Quote:
Originally Posted by airider
I assembled my Eflite F-15, took it to the field, and much to my consternation it just will not lift off the smooth surface I normally fly from. The motors screem, but there's not enough speed to get it to lift off. I am using two 2200 3S Thunder Power Extremes too. I let it roll for about 100 feet and still it did not want to lift off. Has anyone had this problem? I am wondering if anyone has tried another motor-fan combination to get it to have more thrust.
got your CG right??
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Old Jun 10, 2008, 02:46 AM
A-4 nut!!
skyhawk's Avatar
Vancouver B.C.
Joined Apr 2002
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Are your batteries good?
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Old Jun 10, 2008, 07:56 AM
Member 120mph Club
ATIS's Avatar
New Bern, North Carolina, United States
Joined Oct 2004
12,445 Posts
Quote:
Originally Posted by airider
I assembled my Eflite F-15, took it to the field, and much to my consternation it just will not lift off the smooth surface I normally fly from. The motors screem, but there's not enough speed to get it to lift off. I am using two 2200 3S Thunder Power Extremes too. I let it roll for about 100 feet and still it did not want to lift off. Has anyone had this problem? I am wondering if anyone has tried another motor-fan combination to get it to have more thrust.
My friends required 250 feet to ROG... you need a little more then the recommended throws (elevator) to get her to rotate. Even in the air the stock throws left him with very little elevator control. Also check to make sure at WOT that 1 motor isnt shutting down... I had that happen on my F-22.
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Old Jun 10, 2008, 10:00 AM
Checking CG is for NERDS!
Smokescreen38's Avatar
Joined Jun 2005
5,347 Posts
This F-15 is sounding better and better.

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Old Jun 10, 2008, 10:11 AM
Official Boat Bum
Eddie P's Avatar
United States, NV, Reno
Joined Mar 2000
7,392 Posts
F-15 does not fly!!!!

I'm sure you'll get it worked out here with the guys and some good suggestions. Stay patient and remember, with EDF, the little things add up, either positively or negatively.
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Old Jun 10, 2008, 11:16 PM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
7,933 Posts
I'd first check the power the plane is making with a wattmeter to see if your batteries are "putting out" enough power. I don't recall what the stock setup pulls amp wise but I'm thinking it's about 225 to 250 watts per motor.


If the batteries check out ok, try this technique: let the model accelerate for a while without holding in any up elevator (less drag, might help), then when you think you have enough speed, pull back on the elevator and hold some up, maybe not full but half stick, and quickly pull back on the power. The thrustline being above the ground will tend to push the nose of the airplane downward. Cutting power reduces this downward force which means that the downforce on the tail will have less to fight so it just may make the difference you need to get the nose rotated. Once you get the nose up the wing is making a lot more lift and the plane can lift off. Once rotated and climbing, the power needs to be back on. You have to be really quick doing this because you don't want to lose a bunch of speed/energy and you'll be climbing so the speed will want to drop anyway. Accelerate, wait, wait, pull back on the stick about halfway, pull power quickly, then immediately add it back in, total time of powering down and back up about a second, just a blip, just long enough to remove that downforce on the nose and give the tailerons more authority. BE CAREFUL NOT TO OVER-ROTATE the airplane and pitch up to 45 degrees. That will kill your speed and energy and it can happen so quick that you can't get the nose down again. You probably don't want to hold full up elevator the first time you try this.

Try extending the length of the nosewheel strut to get the model sitting at a higher angle of attack. I don't know if that's possible, I don't know what the retracts look like or if there's any extra wire. If the wire is too short perhaps you could replace it with a longer wire, or extend it with some more wire and short section of brass tubing for a coupler.

If raising the nose isn't possible, maybe bending the main gear forward a bit would help. That would slightly lower the rear end of the airplane and would reduce the amount of downforce needed on the tail to raise the nose. If the main gear are set too far back behind the cg, the elevators/tailerons have to provide more downforce to get the nose up and so the rotation speed increases. My scratchbuilt twin MF480 F-22 has the maingear in the scale location and it's takeoff rolls are longer because of it. When I built the larger 120mm F-22 I moved the gear forward and extended the nosegear so the model sits at a positive angle of attack. The big one takes off on it's own at a certain speed, I don't even feed in any up elevator!

The ideal placement of the main gear for easy rotation is for the main wheel to rest on the ground at an angle of about 15 degrees downward and behind the cg. Draw an imaginary line downward, perpendicular (90 degrees) to the ground, and then project a line backwards that's 15 degrees from the first line and where that line intercepts the ground the main wheel should be placed. The angle can be increased, I think my small F-22 is about 30 degree. That can make for longer takeoffs but at long as the model has enough power (6 lb airplane with 1100 watts) and enough runway it's fine. The nice thing about having the gear farther back is the model doesn't sit on it it's butt with the nosewheel in the air when the battery is pulled out. I realize this is an ARF and changing the maingear placement probably isn't necessary, I just wanted to relay the thinking behind gear placement. Bending the main gear forward a bit is an easy way of changing the placement. I have no idea what the angle of the maingear reference the CG is on the airplane.

Lastly, more power is a cure for many ills, as long as the airframe can hold up. I wouldn't trust HS65 servos on the tailerons if I was putting 1000 watts in this thing. Mini digitals (Hitec 5245s I think) are what I use on my 90mm and twin MF 480 planes on the tailerons.
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Old Jun 10, 2008, 11:37 PM
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lavochkin's Avatar
Mokena,Illinois -United States
Joined Oct 2006
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I flat out cant stand that thing! Seen it at SEFF and it flew well, but on 4s. I dont remember if they took off that golf course grass or not. The 3s one horizon had there that flew also was a pud. It needs 4s for sure. That one penetrated the 15 mph winds pretty good.
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Old Jun 10, 2008, 11:53 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
22,444 Posts
they hand launched it. they said over the loud speaker it was on 3s..but i heard the horizon guys talking before the show...they said it was 4s. i could tell it was on 4s too.
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Old Jun 10, 2008, 11:56 PM
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EDF30's Avatar
Mercer Co. PA
Joined Mar 2008
825 Posts
Solution: Get yourself the GWS and make it look the Eflite with iron-on covering. With CF used in the build, it will be much stronger. This plane takes off quite easily on ail/elev.

Bill
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Old Jun 11, 2008, 02:21 AM
Doing it in the Lateral Axis
modfly's Avatar
USA, OH, Akron
Joined Dec 2006
15,360 Posts
Post(s) removed because instead of debating this topic like men,(ie- good buddies) have chosen instead to conspire and complain to the moderators because I have made them mad with my opinions
I normally do not concede like this (deleting posts)but the points are adding up (5) from this thread. So it looks like they win this round. However..I am patient and will post my thoughts one way or another.

these two individuals have gotten together and are playing "point tag" with my posts..
Quote:
Originally Posted by usmc_VTOL_mech
2112
we flying today or what bro???
And there are others doing the same in this thread. Wow...what a cowardly way to try and shut somebody down because you don't like their opinions
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Old Jun 11, 2008, 12:45 PM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
7,933 Posts
Buying a gws is not the solution, unless you're going for more cartoon scale

3S setups on 2100 packs just don't have the power of 4S setups.

If I were building this thing, I'd use one 4S pack of 5000 cells and two 3200 kv outrunners, that's probably pull 900 watts total. Or a 5S setup with different motors.
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Old Jun 11, 2008, 12:59 PM
Checking CG is for NERDS!
Smokescreen38's Avatar
Joined Jun 2005
5,347 Posts
The GWS Eagle was clearly modified for the sake of flight...but Eflite one doesn't look right to me either.
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Old Jun 11, 2008, 01:10 PM
Doing it in the Lateral Axis
modfly's Avatar
USA, OH, Akron
Joined Dec 2006
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removed.
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Last edited by modfly; Aug 22, 2008 at 02:10 PM.
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