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Engine For Kwik FLi Mk. III

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Old 02-25-2011, 04:17 AM
  #76
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Default RE: Engine For Kwik FLi Mk. III

Ben,

What motor/prop combo are you currently using? I'm currently flying my Hangar 9 P-51 .60 with a .90 size elec motor and 16 in prop. Really enjoying it, but obvioiusly the prop is way too big for a vintage pattern bird.

BTW, I had 3 Kwik Fli's back in the day. I know for a fact that Mr. Kraft's scratch-built KF III's used a DuBro 14 in. canopy which hasn't been available for decades. The one in the Graupner kit was too small. Don't know about the TF kit canopy. Maybe someone at Du Bro still has the mold?
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Old 02-25-2011, 08:41 AM
  #77
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Default RE: Engine For Kwik FLi Mk. III

Good Morning,

I am using a AXI 4130-16 with a 13/8 prop. That is what I also used in my Hangar 9 Miss America and a Hangar 9 P-40. The Miss America has long since crashed and the P-40 has been upgraded to the E-flite 90. It has a long enough landing gear to handle the big prop and, like you say about your P-51, it flies great.

But the landing gear on the Quick Fly (Graupner called it the Kwik Fly - I call it what ever comes to mind at the time!) is too short for a big prop but it is indeed working great with the 4130-16 and that prop.

Last summer I built and flew an Astro Hog from an old Sig Kit. I initially tried a 4130-16 with the 13/8 and it worked fine but since it was so heavy I tried a E-flite 90 in it. It has such a low rpm/volt number that the biggest prop that I could get on it wouldn't load it enough. I even went to a three blade prop but it still didn't work. It actually flies better on the .60 sized 4130-60.

But of course the P-40 can use a big enough prop that it really works nicely - fast and vertical lines, etc.

I always thought the QF looked funny with the little canopy perched on the top of the flat part of the fuselage. I had doubts about the bigger canopy I am using now but once I got used to the looks (and the wild lady pilot with the big hair inside) I am happy with it. It certainly brings more fuselage side area over the wing where it is needed to get rudder effectiveness. I think my canopy came from a Hangar 9 P-51. It does wrap around the side - kinda, just a little - but my upper hatch is a cut at 45 degrees to the horizontal right at the intersection of the canopy and the fuselage.

It is held down with really big magnets (pick up the airplane with it, almost) and when it is removed you have room for both hands and batteries. I put the batteries on the sides of the fuselage and right up against the bulkhead at the wing LE and the airplane balances fine and flies great. I use what looks to be a very strong velcro with no other fastening straps, etc. The batteries are held in place with velcro only - it works fine. It might be different if it were a gas/glow motor.

Ben
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Old 02-25-2011, 09:17 AM
  #78
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Default RE: Engine For Kwik FLi Mk. III

Gents,

A picture of a Kwik Fly MK3, a picture of RCU member Holderlin Germany, 7/30/2008.
There is some distortion in the background of an ugly plane, sorry!
(Mäxi I did fly myself).
Cees
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Old 02-25-2011, 10:26 AM
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Default RE: Engine For Kwik FLi Mk. III

Now that's a pretty Kwik Fly!
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Old 02-25-2011, 08:33 PM
  #80
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Default RE: Engine For Kwik FLi Mk. III

Thanks for the info Ben. I have one of the Home Hobby Solutions kits for the Mk III and I'm giving some consideration to electric power. Maybe what's needed for vintage pattern is more like an EDF motor that could turn a smaller prop at higher rpm. BTW, Phil Kraft, in the original article in M.A.N. and on the plans, called it the "Mark III Kwik-Fli", so that is the form I try to stick with when I can remember. Thanks again for the inspiration.
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Old 02-26-2011, 01:28 AM
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Default RE: Engine For Kwik FLi Mk. III

Hi,

Is there any reason why you can not cut some off the tips on the prop on electric driven pattern plane to get better clearance to the ground/surface? The proptips do not help that much to move the plane through the air anyway.

/Bo
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Old 02-26-2011, 03:01 AM
  #82
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Default RE: Engine For Kwik FLi Mk. III

Ben omitted an important part of the equation, he didn't specify the battery used. Actually, you could use a smaller prop at more rpm by adding a cell to the battery (as long as you don't overburden the motor).

I don't have a Kwik-Fli, at least not a real one, that is. But it might be equipped with an AXI 4120/14, a 12x8 prop, and a 5s2p 6000 mAh LiPo battery (or equivalent 6s A123). The prop size is no problem (see picture). This drive weighs about 44 oz, which is of course a bit more than an old .60 drive with engine, prop, tank, fuel, and so on. Remember the old .60 engines were lightweight, but today's R/C equipment is much lighter than the old one, so it should be still possible to stay within the 6 to 6.5 lbs AUW range.

With this drive the model is a bit slower than with the glow drive but has more pull. For me, electric is a more pleasant and even better flying, but I'm so weird to be happy with the old, "normal" drive power and don't need a .90 in a Kwik-Fli. Flight time is about 10 minutes.


By the way, usually Graupner modified model designs for a reason. They "enhanced" (as they called it) several details on their KWIK FLY MK3, compared to Phil Kraft's original version. For instance the nose landing gear is symmetrical with two wires. Now they might have chosen the smaller canopy to avoid the Kwik-Fli dance. I don't really know, but might be the reason.
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Old 02-26-2011, 08:36 AM
  #83
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Default RE: Engine For Kwik FLi Mk. III

For this time forward it will be the Kwik Fli :-) As far as battery power I use a 6 series 4000mah lipoly pack. I do like the dual strut nose gear that the Graupner kit has. It might be a little draggier but it keeps the loads symmetrical on the system. In general I have been impressed with all of the Graupner kits I have.

Bem - About propellers - there is a good summary in the March issue of Model Aviation, Page 137, it says - Thrust is proportional to the square of the rpm, and the fourth power of the diameter.

So the more diameter you can get the more thrust you can get. It also turns out (and fly flights with the Astro Hog proved it) that the number of blades has no real input to the thrust.

The greater the pitch you can get the more speed you can get. An approximation is - the propeller pitch in inches times its rpm in thousands equals the maximum speed (in mph) through the air that can be achieved. In other words 5 inch pitch times 10K rpm (10,000 rpm) equals 50 mph mazimum speed.

So when I went to the three blade prop it is no wonder that I didn't really see any results.

Increasing the diameter or increasing the pitch does require an increase in power so there may or may not be an advantage to running one of the inrunner brushless motors. I don't know. I do know that as mine is set up now it is very fast and has good vertical pulling power. Of course it won't prop hang but I think it might be close to the original Kwik Fli in terms of speed, etc.

I do have a Hangar 9 T-34, fixed gear, 57 inch span, 555 sq. in area, 7 lb weight giving about a 28 to 29 ounce/stft wing loading. For this airplane I use a AXI 4120-18 motor driving a 13/7 prop and using 6 series 4000mah lipoly pack. It gives good flight times, is very fast and groovy and just plain fun to fly.

I am totally happy with electric power - easy to start, relatively quiet, consistent, and no mess at the end of the flight. The biggest problem is that you have to dust the airplanes now and then to keep them clean!! The only down side is the cost of the batteries and storage of them. Mine reside in fire proof locking Brinks boxes and those sit in the hall right under a fire alarm. I keep a fire extinguisher just a few feet away in a closet.

Ben
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Old 02-26-2011, 08:49 AM
  #84
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Default RE: Engine For Kwik FLi Mk. III

you can't really bang the cost of batteries. Noticed the price of glo fuel lately. I am using a 3350 3S pack in an ugly stick (Great Planes ARF with the suggested Rim Fire Outrunner) and I love flying it. No fuel costs and when the batteries give out, the cost will be very small compared to what I would spent for fuel.

John (electric convert)
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