Power to Weight
03-01-2003, 06:45 PM
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It really depends on the airplane. Recreation means alot of different things to different people, so I can't really make a judgement on that. On something like a Cub, it wouldn't be nearly as high as Bill Hemple's 50% Edge 540. What plane are we talking about?
03-02-2003, 12:56 AM
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Power to Weight
I'm not really sure what a Cessna's would be. I personally like to overpower scale models so that I can throttle back to a more scale like RPM. I would guess that a typical Cessna model would have about the same power to weight ratio that most Cubs do. That is, 1/2 throttle to take off, and 1/3 to cruise. All the Cubs I've seen will almost hang on the prop, but not quite, meaning that they have a slightly less than 1:1 power to weight ratio. It's probably about 9:10 power to weight.
03-02-2003, 09:06 PM
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a 1/2 SCALE, AND YOUR PROFILE SAYS YOU ARE A BEGINNER[img]i/expressions/face-icon-small-shocked.gif[/img] You sure are a fast learner. Good Luck, but you will have to be more specific. Do you want your power suggestion in displacement, horse power, watts, torque, or what?[img]i/expressions/face-icon-small-confused.gif[/img]
03-02-2003, 10:25 PM
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I wouldn't advise it due to cost... but you could build a 1/2 scale Cessna 152 and use that as a primary R/C trainer. (if you could keep it under 55 lbs... as they won't give you the waiver if you aren't a proficient pilot.)
It is true that bigger gives more time for responding to the aircraft's needs... But there's such a thing as going too far. [img]i/expressions/face-icon-small-wink.gif[/img]
It is true that bigger gives more time for responding to the aircraft's needs... But there's such a thing as going too far. [img]i/expressions/face-icon-small-wink.gif[/img]
03-04-2003, 02:01 AM
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Power to Weight
Yup, its gana be a big one. I'm really just doing it for the fun. It wont be too fancy, so hopefully that should cut down on price and time.
<blockquote>Quote
<hr>Do you want your power suggestion in displacement, horse power, watts, torque, or what? <hr></blockquote>
Bill, I was thinking hp or watts.
<blockquote>Quote
<hr>Do you want your power suggestion in displacement, horse power, watts, torque, or what? <hr></blockquote>
Bill, I was thinking hp or watts.
03-04-2003, 01:47 PM
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Forget watts. Electric power systems that size will be very, very expensive - probably hundreds of dollars for a battery pack, plus a few hundred more for something to charge it with.
If you just want something huge why not a really big motor glider? That would use a much smaller engine for a given wingspan and the servos will be cheaper. It won't be the most aerobatic thing even with ailerons but then a Cessna isn't exactly a 3D plane.
I don't have any experience with planes even close to that size but I think you're looking at several thousand dollars.
If you just want something huge why not a really big motor glider? That would use a much smaller engine for a given wingspan and the servos will be cheaper. It won't be the most aerobatic thing even with ailerons but then a Cessna isn't exactly a 3D plane.
I don't have any experience with planes even close to that size but I think you're looking at several thousand dollars.
03-04-2003, 05:32 PM
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OK. I'm going to show you just about exactly what it will cost to get it into the air without shortchanging anything. I'm not trying to cut you down, just show you what you are getting into. There are some things you can do to cut the cost down a little, but I'm showing you what I would do to feel safe.
On a tipical 50% airplane, you will need AT LEAST 3 high tourque metal geared servos per control surface just to fly it. Some of the aerobatic ones have 4 on the ailerons, and I saw one with 3 on each elevator half, and 4 on the rudder. Chip Hydes Ultimate at the TOC had 8 on the ailerons alone. That was a bipe, however. A Hitec 5945 has 180 ounces of tourque on 4.8 volts. You need to run a 35-50% on 6 volts to give you more tourque. On that Cessna, you will have a 18 foot wingspan if it were exactly half scale. You will need 3 servos on each aileron, and 3 or 4 on the flaps. Thats 6 or 7 servos at around $90 a piece.
The airplane will also be a little over 4 feet tall. I'm not sure how much it will weigh, but that will be the deciding factor on your engine. Most 50% aerobatic planes have somewhere between a 200 to 240 CC engine on them. Now, these planes have better than a 2:1 power to weight ratio. Just so long as your plane weighs less than 55 pounds, you could probably fly it with a 150CC engine, but a 200 would be better if you fly from grass, or a short field. There is no rule that says you cant throttle back. A 3W 150 is about $1,250, and a 3W 240 is about $2,300. A DA 150 is about the same as the 3W, maybe a bit more, but they don't make an engine for a 50% yet. They have a prototype 200 4 cylinder, but it isn't available yet. Mufflers for the 3W are anywhere between $165 to $240 per pair. The prop depends on wood VS carbon fiber. A wood one will be cheaper than a carbon fiber.
You will probably need 3 elevator servos per side, with a total of 6. That's six more $90 servos. Your rudder will need more than all of them to be effective. I'd say you could use 2 or 3 Hitec 5735's on the rudder. You might be able to use them on the flaps too. They are much larger, and a little slower, but they are more powerful. They are about 100 bucks each.
As for the battery system, you need 4000 mha packs for the 2 recievers, and a 2000 pack for the ignition. You can use Nicads or Nickel Metal batteries, but those are heavy, offer less redundancy than a Lithium Ion, and by the time you get the batteries and the charger, you might as well get the Powerflite System 4000. It is a 7.2 volt battery system with 6 volt regulators. It has the 2 reciever packs, ignition pack, charger, 1 amp volt meter load, and the 3 regulators. One of the regulators is 4.8 volt for the ignition system on the plane. This system is about $450.
I said 2 recievers. On a plane with 15 to 16 high tourque, high speed servos you will burn up one reciever. I think a JR 9 channel PCM is right about $200. I would also run a power buss of some kind to run the servos without ever having to run the power through the recievers. EACH servo can draw up to 1 amp if fully stalled out. That will probably not happen in a Cessna, but that's another reason why you should use enough servos per surface. They don't draw anything near that when they aren't stalled out. You MUST have PCM recievers for the signal quality, and the fail safe. If you loose contact with this monster, you have to have the engine throttle back. A 23 HP engine swinging a nearly 3 foot prop can kill someone easily.
Then, you will need all the wiring extensions. Those make you loose lots of voltage. In the 4 foot extension running to the elevator servos on my 40%, I lost .5 volts. So, that 6 volts is now down to 5.5. It would 4.3 with 4.8 volt. I bought some adjustable regulators from Powerflite so I could step this up. They were about $40 each, and I used 2 of them.
This, total $4,835 for the 240CC engine, and most of the radio gear. This isn't exact, but it gives you an idea. You now need lots of covering, paint, prop, spinner, wheels, titanium 4-40 pushrods, Rocket City links, metal control arms, fuel tank, fuel tubing, wiring extensions, heavy duty switches....
Like I said, I'm not trying to shoot you down, just to give you an idea of what you are getting into.
On a tipical 50% airplane, you will need AT LEAST 3 high tourque metal geared servos per control surface just to fly it. Some of the aerobatic ones have 4 on the ailerons, and I saw one with 3 on each elevator half, and 4 on the rudder. Chip Hydes Ultimate at the TOC had 8 on the ailerons alone. That was a bipe, however. A Hitec 5945 has 180 ounces of tourque on 4.8 volts. You need to run a 35-50% on 6 volts to give you more tourque. On that Cessna, you will have a 18 foot wingspan if it were exactly half scale. You will need 3 servos on each aileron, and 3 or 4 on the flaps. Thats 6 or 7 servos at around $90 a piece.
The airplane will also be a little over 4 feet tall. I'm not sure how much it will weigh, but that will be the deciding factor on your engine. Most 50% aerobatic planes have somewhere between a 200 to 240 CC engine on them. Now, these planes have better than a 2:1 power to weight ratio. Just so long as your plane weighs less than 55 pounds, you could probably fly it with a 150CC engine, but a 200 would be better if you fly from grass, or a short field. There is no rule that says you cant throttle back. A 3W 150 is about $1,250, and a 3W 240 is about $2,300. A DA 150 is about the same as the 3W, maybe a bit more, but they don't make an engine for a 50% yet. They have a prototype 200 4 cylinder, but it isn't available yet. Mufflers for the 3W are anywhere between $165 to $240 per pair. The prop depends on wood VS carbon fiber. A wood one will be cheaper than a carbon fiber.
You will probably need 3 elevator servos per side, with a total of 6. That's six more $90 servos. Your rudder will need more than all of them to be effective. I'd say you could use 2 or 3 Hitec 5735's on the rudder. You might be able to use them on the flaps too. They are much larger, and a little slower, but they are more powerful. They are about 100 bucks each.
As for the battery system, you need 4000 mha packs for the 2 recievers, and a 2000 pack for the ignition. You can use Nicads or Nickel Metal batteries, but those are heavy, offer less redundancy than a Lithium Ion, and by the time you get the batteries and the charger, you might as well get the Powerflite System 4000. It is a 7.2 volt battery system with 6 volt regulators. It has the 2 reciever packs, ignition pack, charger, 1 amp volt meter load, and the 3 regulators. One of the regulators is 4.8 volt for the ignition system on the plane. This system is about $450.
I said 2 recievers. On a plane with 15 to 16 high tourque, high speed servos you will burn up one reciever. I think a JR 9 channel PCM is right about $200. I would also run a power buss of some kind to run the servos without ever having to run the power through the recievers. EACH servo can draw up to 1 amp if fully stalled out. That will probably not happen in a Cessna, but that's another reason why you should use enough servos per surface. They don't draw anything near that when they aren't stalled out. You MUST have PCM recievers for the signal quality, and the fail safe. If you loose contact with this monster, you have to have the engine throttle back. A 23 HP engine swinging a nearly 3 foot prop can kill someone easily.
Then, you will need all the wiring extensions. Those make you loose lots of voltage. In the 4 foot extension running to the elevator servos on my 40%, I lost .5 volts. So, that 6 volts is now down to 5.5. It would 4.3 with 4.8 volt. I bought some adjustable regulators from Powerflite so I could step this up. They were about $40 each, and I used 2 of them.
This, total $4,835 for the 240CC engine, and most of the radio gear. This isn't exact, but it gives you an idea. You now need lots of covering, paint, prop, spinner, wheels, titanium 4-40 pushrods, Rocket City links, metal control arms, fuel tank, fuel tubing, wiring extensions, heavy duty switches....
Like I said, I'm not trying to shoot you down, just to give you an idea of what you are getting into.
03-23-2003, 09:24 PM
#11
Senior Member
Power to Weight
Good information Jack........Somewhere in Australia an aeronautical university techer built a "Super Connie" 1/3 scale at an estimated cost of ower $ 15 000 with the help of his students. The plane is powered by four OS Gemini 5 cyl engines and two radio systems to make it function..
