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Old Nov 02, 2014, 06:01 PM
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Discussion
Thoughts About Hand Launching a 50mm EDF Foami

Well the summer has finally ended and so has my initial experience of flying edf foamies. My first 50mm foamie edf was a Viper from the Banana Man. Nice plane but was eventually destroyed. Chalk that up to my learning curve. The maiden flight was piloted by an experienced edf pilot in my club and a veteran of 20+ years to rc hand launching. The first flight saw the edf "fly" about ten yards, flip upside down with a full power nose dive into the ground snapping off the front half of the fuse! A little CA and we were back in action with no further incidents. Don't get me wrong, I am very skilled at crashing a plane, but there is something that warrants observation. First off the plane barely weighs a pound and as it says in fine "Chinglish" in all the manuals, launch into the wind. Duh? But after a few flights at the field the wind direction may change just a bit so as to launch in the same direction, without paying much mind, you may have a cross wind be it ever so slight. Given the weight of the edf, and the initial launch speed of the edf, the ever so slightest cross wind will pick up a wing tip, there by having the edf dip into the ground. I don't find the headwind has that much and effect on lift as opposed to the negative effect of even a slight crosswind lifting a wing tip. It all makes sense once I get my head around that this is not prop driven plane with lots of prop wash and greater launch speed. I believe that the hand launch of a 50mm edf is the most vulnerable time of flight. So what I do now, before launch, is check the wind direction, no matter what the weather report says and even the windsock at the field, being that the wind can swirl in different directions because of buildings, trees, etc. I find the feel of the wind on my face, at the point of launch, is about the best indicator of wind direction. Since my Viper has come to an unceremonious end despite the several rebuilds (thanks for EPO foam) I am now flying a F-86 50mm foamie. Thanks to following my own advice, launches are much more successful and I'm also more discerning on whether to launch or not. Like to hear you thoughts. Thanks.
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Old Nov 03, 2014, 11:06 AM
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Quote:
Originally Posted by bachynski View Post
.
.
Given the weight of the edf, and the initial launch speed of the edf, the ever so slightest cross wind will pick up a wing tip, there by having the edf dip into the ground.
.
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With my limited experience with the 50mm fans. I assume You used a
3S battery and You did not check how much thrust You got.

Most of these cheap RTF/ARF EDF are low thrust, increase thrust
and get a much easier hand launch plane.

I know some will say don't bother with thrust it's the exhaust air speed
that matters, but if You look at the physics (impulse formula) thrust is
dependent on the speed ... and thrust is easy measure (digital kitchen
scale).

This thrust You measure here will be almost the same at a hand
launch (the fan thrust will be reduced at the very moment the plane moves)
so it's important to give it a good throw too or bungee launch.

For planes with small inlets cheater hole helps a lot. Again the speed
freaks will "frown" oh no it destroys top speed ... who cares as long You get
the plane in the air without crashing that is the goal at this level!
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Old Nov 03, 2014, 07:27 PM
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Quote:
Originally Posted by bachynski View Post
Well the summer has finally ended and so has my initial experience of flying edf foamies. My first 50mm foamie edf was a Viper from the Banana Man. Nice plane but was eventually destroyed. Chalk that up to my learning curve. The maiden flight was piloted by an experienced edf pilot in my club and a veteran of 20+ years to rc hand launching. The first flight saw the edf "fly" about ten yards, flip upside down with a full power nose dive into the ground snapping off the front half of the fuse! A little CA and we were back in action with no further incidents. Don't get me wrong, I am very skilled at crashing a plane, but there is something that warrants observation. First off the plane barely weighs a pound and as it says in fine "Chinglish" in all the manuals, launch into the wind. Duh? But after a few flights at the field the wind direction may change just a bit so as to launch in the same direction, without paying much mind, you may have a cross wind be it ever so slight. Given the weight of the edf, and the initial launch speed of the edf, the ever so slightest cross wind will pick up a wing tip, there by having the edf dip into the ground. I don't find the headwind has that much and effect on lift as opposed to the negative effect of even a slight crosswind lifting a wing tip. It all makes sense once I get my head around that this is not prop driven plane with lots of prop wash and greater launch speed. I believe that the hand launch of a 50mm edf is the most vulnerable time of flight. So what I do now, before launch, is check the wind direction, no matter what the weather report says and even the windsock at the field, being that the wind can swirl in different directions because of buildings, trees, etc. I find the feel of the wind on my face, at the point of launch, is about the best indicator of wind direction. Since my Viper has come to an unceremonious end despite the several rebuilds (thanks for EPO foam) I am now flying a F-86 50mm foamie. Thanks to following my own advice, launches are much more successful and I'm also more discerning on whether to launch or not. Like to hear you thoughts. Thanks.
I agree that launch is the most critcal phase of flight for a hand launched model.

Did you launch your 50mm Viper overhand or underhand? Where did you hold it at?

Again, are you launching your F-86 overhand or underhand and where do you hold it?

I had many problems launching a 50mm T-33 overhand while holding it behind he CG. Launching it underhand allowed me hold it ahead of the CG, and it made a world of difference yeilding nearly problem free launches. It was the only jet that I had been holding aft of the CG to launch. Holding a model aft of the CG when hand launching is prone to inadvertent uncoordinated flight upon release.. such as side slip resulting in roll or possibly a stalled wing.
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Old Nov 03, 2014, 08:19 PM
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Thanks to both Floey and kevinkal for your responses.
.
Floey you are very right about the amount of thrust you can provide yourself with the hand launch. I have also noticed, when experimenting with the bungee, launches were very successful. Hadn't thought about it, but it makes sense now, that the fan thrust will be reduced at the very moment the plane moves. Thank You for that thought. I have avoided the bungee launch only because of the hassle of extra equipment set up. But it certainly gets the plane up safely.

To answer kevinkal's questions, I have been doing an overhand launch with my hand aft of the CG and in very close proximity to the fan for both the Viper and F86. Your comments make so much sense when you note that the hook for bungee launching is forward of the CG thus providing a more directed launch. I have not thought about the underhand launch except once because I assumed I could get more power by launching overhand. Will definitely consider your suggestion.

Thanks again to both for taking the time to comment.

Its interesting to note that with prop aircraft, I am very comfortable with the take off and nervous about the landing. With these 1 pound foamie edfs the reverse is true.
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Old Nov 04, 2014, 07:13 AM
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Quote:
Originally Posted by bachynski View Post
.
.
Its interesting to note that with prop aircraft, I am very comfortable with the take off and nervous about the landing. With these 1 pound foamie edfs the reverse is true.
Nervous? It depends on the plane (condition) ...

Wicked prop planes: HK Ju-87 (685mm), E-flite/Art-tech P-40 (650mm),
Sonic Model Hurricane (680mm) ...

Wicked EDF's: Kyosho A-6, Sky Angel F-8...

Have just bought (sale) a J-Power F-18 ... looks very fragile ...
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Old Nov 10, 2014, 05:40 AM
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we can take off without that
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I am exlusively a hand-launcher of 50mm and smaller edfs.
As Floey says static thrust to weight ratio for the plane is very important in deciding how to hand launch.
Most planes will fly with a thrust to weight ratio as low as 0.5 to 1. For such planes you should launch them overhand, as flat as possible and be very carefull not to impart any spin or twist to the plane as you release the plane. As the plane leaves your hand, a low thrust plane will sink down before it gathers speed, during this part try no to touch the controls, especially elevator, if you apply elevator you will kill speed and stall and crash. Just let the plane sink down and gather speed, then gently apply elevator to avoid hitting the ground.
A lot depends here on how true the surfaces are (ie if they are warped) and if the plane has been properly trimmed and has correct COG. If any of those things are not set up correctly it will force you to apply controls immediately after lanuch and it will reduce your speed likely resulting in a crash. However as you get more experienced you should be able to launch even a wrong COG and incorrectly trimmed plane. Case in point JPower 35mm Mig 15 has wrong COG right out of the box (tail heavy) and elevators fixed in a nose-up position and very low thrust, 50g thrust for a 95g all up weight. Yet with a little care it can be hand launched successfully.

A plane with close to 1:1 thrust is different, you can be more relaxed when hand launching it, with a less forceful throw (sometimes almost no throw, it will just leave your hand) and a steeper upward throw will also work. All this also relies on the plane being trimmed out, correct COG and no warped surfaces. Any of these coupled with the higher thrust can make the plane bank hard, flip over or do any number of horrible things on lanuch.

Another option, if you have very long soft grass, is to do glide tests with no power. This should reveal if the plane is out of trim, wrong COG or if you are imparting any twist to the plane during lanuch.

Good luck, and have fun.
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Old Nov 13, 2014, 02:29 PM
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Thanks green_flyer - good "rule of thumb method", my motor is supplying about 400g of thrust at best and the f86 foamy is about 450 grams. Almost a 1:1 ratio. Perhaps a more gentle hand launch will improve things. Temperatures in Canada are about -5 degrees Celsius now which is a bit discouraging for heading out. Either I'll muster up some courage and go flying or whimp out and wait for spring.
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Old Nov 13, 2014, 10:16 PM
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I'm launching overhead with a strong but smooth arm motion. The important thing is to launch flat, and not panic when the plane dips down close to the ground. It will eventually rise as it gains speed.

Quote:
Originally Posted by bachynski View Post
Temperatures in Canada are about -5 degrees Celsius now which is a bit discouraging for heading out. Either I'll muster up some courage and go flying or whimp out and wait for spring.
I stopped flying my 50mm EDF Mig-15 a couple weeks ago because the cold (near freezing) made my battery sluggish. Very poor thrust, shortened flights. It'll fly again next Spring!
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Old Nov 14, 2014, 04:06 PM
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My first(sucessful) ducted fan, was a Berkeley Crusader, from the fifties. I used a Wen-Mac .049 and the stamped aluminum rotor given. Very low thrust. But, handlaunching it was a breeze. I was able to get a perfect level throw, from holding on the CG. It would go about 200' in a gradual decent.

I switched the stamped rotor to a 3 blade Wen-Mac prop, and a can of Fox Missle Mist, allowing it to actually climb. If RC small systems were available it would have been controllable, from each and every hand launch.

What I'm trying to say is, The crusader was a light frame, able to hold on the CG, and proper throwing and attitude of the plane. Success in hand launching, is only throwing as hard as needed to obtain lift, just above minimum. And, not throwing into a stall. And success can be achieved even with low thrust.

Anybody wanting to be good at hand launching can easily learn, with a simple profile glider. I have one I made from the Guillows plans. Trimmed for strait flight, I can get 150' by pointing it at place on the ground 200' away. It will teach smoothness and attitude needs, plus speed needed. Later you will be good at throwing level on the EDF version.

I have some jets(RBC kits) that are not easily hand launched. Safer to bungee. High wing loadings, even with high thrust, can still have erradic or failed launches. Anything over 20oz sq ft WL gets bungeed. And of course, size of the frame is important. Smaller models do not fly as well as larger ones, even if kept very light. Surfaces need to be thicker or different airfoil. We can change the scale of a model, but we can not scale the air to match.

I'm an old free flight modeler. Hand launching was and is a way of life.

Fuzz
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