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Thrust to weight ratio?

Discussion in 'Scratchbuild Talk' started by nblnckRV8, Jul 10, 2012.

  1. nblnckRV8

    nblnckRV8 Cadet

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    Ok this is really throwing me off. I have the F22V2 all built and it weighs about 1.5 pounds. I also have the Grayson hobby Supersonic V2. It produces up to 24 ounces of thrust which is like 1.4 pounds. while my airplane weighs 1.5. I'm sure the motor will do fine but i think it would struggle!

    I had an issue with it yesterday. It was possible that my ESC wasn't programmed for the motor. THe plane didn't even fly out of my hand, it stalled and crashed. The prop was going the correct directon it was spinning in the correct direction. It just wasn't giving enough power. I have a 1350 Mah battery. I have had this ESC for a while so im probably going to get a new one tomorrow.

    How much does your plane(any) weigh? What kind of motor are you using?
  2. Grey

    Grey Ace Pilot

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    Have you set your throttle range?

    The thrust won't make it the best plane in the world but it should still fly. Get used to the lower power to weight ratio and there's no reason it can't still be a lot of fun too.
    AccidentalStuntPilot likes this.
  3. rodrigo

    rodrigo Ace Pilot

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    excuse the ovious question... are you sure than your prop are facing at the front? the letters on the prop should be facing at the plane nose (forward direction)

    Enviado desde mi GT-I9003L usando Tapatalk 2
  4. nblnckRV8

    nblnckRV8 Cadet

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    Yup! It's in the correct direction. I am Probably going ot get a new ESC. I think the one ive had for a while has had it. PLus there is no manual to program it. and i have no idea what the amp range is. 20amp 25amp i do not know
  5. Jeriah

    Jeriah Ace Pilot

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    when I made my first plane (f22v2) it was really heavy!! I had the micro jet (less power) and I was worried it wouldn't fly :( . I tried and it flew great. your plane will still fly perfectly and way better than mine!

    programming speed controllers

    all speed controllers come programed unless they specify that they aren't. I have bought a lot of speed controllers from different brands and never had to program one and they don't come with manuals because you have to have special equipment and stuff to program them. probably 90% of people on this forum have never programmed one.

    Amp draw/rating

    Amp rating is the maximum amps the motor can draw, the super sonic v2 has a max amp draw of 28 amps so you want a speed controller with (AT LEAST!!!) 28 amps. you want a speed controller with 30 or 40 to be safe. the higher the amp rating the better and you can't go over kill on speed controllers. if you use an esc with less than 28 amps it can fry ur power system if you fly it long enough. this mite be your problem. also make sure ur battery has at least 20 c rating.


    throttle end points.

    before you fly you want to find your throttle end points. This shows your esc where ur high and low throttle points are. 1 plug everything together like your ready to fly. 2 take your propeller off for safety. 3 unplug your battery and move the throttle stick to full throttle. 5 plug in you battery while your throttle stick is on high (the motor will not start spinning). 6 wait till the esc stops beeping or has a same steady beep and put your throttle stick back down. 8 once it quits beeping the throttle end points are set!
    ScottLott likes this.
  6. MoTheG

    MoTheG Airman

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    No, you do not.
    usually the programming mode is entered by sending full throw to the controller on power up. It uses the motor to beep for feed back.
  7. LukeWarm

    LukeWarm Top Gun

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    There are some problem areas I've listed in the below URL that you can check. Some of these alone are not serious, 2 or 3 of them together will devastate your plane’s performance.
    http://www.rcpowers.com/community/threads/why-does-my-plane-fly-so-slow-info.12453/
    1) An incorrect prop: You must use a prop that has the correct length and pitch to take full advantage of the power the motor has to offer.
    2) A damaged prop: Damaged props have an unbalanced delivery, run at a lower RPM, are less efficient, and will damage the motor by compromising the motor’s bearings.
    3) The prop is on backwards: Some props (like APC props) must be mounted with the writing on the prop facing forward. If you incorrectly mount the prop, your plane will lose around 30% of the motor’s thrust.
    4) Bad, dirty, or inadequate motor: If the motor is failing, dirty, or too small, the plane will feel underpowered.
    5) An inadequate ESC: An inadequate ESC is not rated at a high enough amperage to let a sufficient amount of current flow to the motor. This will only cause poor performance, it will also cause the ESC to overheat and eventually fail.
    6) A misadjusted ESC: A misadjusted ESC will limit the motor’s RPMs, there-fore limit the motor’s thrust.
    7) The control surface trims are adjusted to compensate for an incorrect Center of Gravity : If the aircraft’s trims are adjusted to be straight in line with the wing, the aircraft is at its ideal Center of Gravity. If the aircraft is tail heavy, the control surface trims will have to be adjusted low so the plane will fly level; this is inefficient, takes more power, and will cause the plane to fly slower.
    8) A bad battery: Old, worn out, or damaged batteries have a diminished capacity (both in voltage and energy storage).
    9) An inadequate battery: The batteries C rating times the Amp hour rating will tell you the maximum amount of current the battery can supply. If the motor ask for more current than the battery has available, this will starve the motor and overheat the battery. A battery also must have a high enough S rating. A motor will run much slower with a 2s (2cell = 7.4volts) battery, than a 3s (3cell = 11.1volts) battery. Make sure you using the correct battery for the job you're asking it to do.
    10) A poorly charged battery: A poorly charged battery will start off at a lower voltage.
    11) An Incorrectly adjusted Transmitter: If the Transmitter’s throttle is adjusted to limit the throw, it will do the same thing a misadjusted ESC will do, it will limit the motor’s RPMs, there-fore limit the motor’s thrust.
    12) A blockage in the airflow: Anything that prevents the free flow of air across the plane or through the propulsion system will slow the aircraft down. With a battery mounted sideways right in front of the motor, you will see a noticeable drop in performance. The plane must have good aerodynamics to efficiently slice through the air.
    13) The plane is built way too heavy: Every option you add to your plane adds weight; Things like extra glue,*Spackling compound and sealer, *gyros,*more servos and the hardware that goes with them,*paint, fiberglass, varnish, tape and other coatings,* landing gear, * big batteries,* and too much use of heavy materials like wood and metal. It is easy to over build. Heavy wing loading will make your plane plow through the air. Plows are slow.
    14) Inadequate ventilation to the electronics: The motor, battery, BEC, and ESC do not function as well when they are hot. Vent the electronics to where you have air flowing pass them so that they don’t sit in their own heat and cook.
    15) Bad wiring: A cold solder joint on the connectors will limit current.
  8. LukeWarm

    LukeWarm Top Gun

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    I have a good test that you can use:
    With the plane ready to fly, hold the plane by its nose so that the nose points toward the sky, then go full throttle for a few seconds. A plane with a better than a 1 to 1 power to weight ratio will more than lift its own weight. If it does not, your plane has less than a 1 to 1 power to weight ratio. If a 20 oz plane with 24 oz of thrust does not lift and try to climb out of your hand, you're wrong about the 24oz of thrust. You have less than 20oz of thrust, and you need the troubleshoot the power system to find out why.
    This is also a good test for planes with less than a 1 to 1 power to weight ratio. Imagion that your plane is hanging by its nose on a on a hanging scale. A 20 oz plane with 18 oz of thrust will weigh 2oz on the scale when the plane is at full throttle. For this test, most people don't use a scale, they judge the weigh with their hand.
  9. The plane will still fly if it has less than a 1:1 thrust to weight ratio. It just wont have unlimited vertical.
  10. rodrigo

    rodrigo Ace Pilot

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    this is true but depends of the wing loading values.... motor gliders can fly with 1/3 thrust weight ratio but a heavy plane could be fly at high speed only....
    make a glide test to discart than your plane exceed the maximum weight of the airframe

    Luke spoke about the intake and clear air importance for a good performance of your power plant...this is really important. I proved this when a make the 3D nose for my first F35.... post photos of this and near the motor mount zone

    Enviado desde mi GT-I9003L usando Tapatalk 2
    Grey and ScottLott like this.
  11. LukeWarm

    LukeWarm Top Gun

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    Very true, but most of our planes are Jets. Jets need better than a 1:1 thrust to weight ratio to fly like a Jet. Anything less is not as fun.
    Grey likes this.
  12. Grey

    Grey Ace Pilot

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    I "liked" this comment but would just like to point out that I don't think it works as a blanket statement. The plane is more versatile with a better than 1:1 thrust ratio but it doesn't have to be less fun under that (within the limits of common sense of course).
  13. nblnckRV8

    nblnckRV8 Cadet

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    Would having a 40amp ESC with a 3cell 1350 Mah battery 15Wh matter? It should't right? Its should discharge at the same rate as another battery but a smaller capacity? My plane does infact weigh 24 oz

    I would just have to program the ESC to the correct throttle throws.
  14. Grey

    Grey Ace Pilot

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    Do you mean 1350mAh 3s 15C? That's too small. That's only 20.25 amps and you want 28. Could be your problem right there.

    The 1350mAh needs to be at least 20C (27A) and even then it's a little too small and you will be relying on the burst rate at the top end of the throttle. For a 1350mAh 3s battery I would be going 25C.

    But honestly..? For the F-22 V2, unless you are really hurting for money, get at least 1500mAh 3s 20C or 1600mAh 3s 20C batteries for that motor. 1350mAh 3s batteries are going to give you excessively short flights. The F-22 V2 is a draggy plane so it needs some throttle to maintain cruising speed and being so heavy yours will need a little more.

    And yes, you can get more flight time because the plane WILL fly slower than a nice cruising speed BUT you won't want to be flying that slow most of the time.
  15. nblnckRV8

    nblnckRV8 Cadet

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    Forgot to put in 25C Its a 1350Mah 3cell 11.1V 25C burst is (33.7A/67.5)
    But ill see if i can get a 1800Mah But the ones i found at my local hobby store are like 30bucks
  16. Grey

    Grey Ace Pilot

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    Cool. Those 1350's will work then, the only issue will be short flight times.

    At that price it's cheaper to order from hobbyking etc provided you buy more than one. Freight is a killer on single items from most online places.

    Here in AU I can get a pair of 1800mAh 3s 20C's (Zippy or Turnigy) for about $30 (freight included) ordering from the intl warehouse provided I'm willing to wait on registered air mail. At your plane's weight the 1500mAh and 1600mAh might be a better option tho.

    Of course they are cheap brands but provided you look after them (charge at 1C, don't run them down too far) they'll last you a fair while.

    Throw your new ESC in with the order while you are at it.

    The Turnigy Plush are popular and reliable (rebranded Hobbywing like RCTimer ESC's - programmable) available in both 30A (40A burst rate) and 40A. The 40A is an extra $8 tho.

    The TowerPro one from the RCP Master Parts list is also supposed to be nice (also with auto timing feature) but is only available in a 30A (which is enough for this motor except on really hot days).

    The entire order form the HK Intl warehouse is about $40-$50 for 2 batteries and your ESC but you'll need to get connectors for the ESC too (bullet and whatever you use to connect the battery to the ESC).
  17. nblnckRV8

    nblnckRV8 Cadet

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  18. Grey

    Grey Ace Pilot

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    The 1600 is the cheaper. I prefer these tho;
    http://www.hobbyking.com/hobbycity/...lightmax_1600mAh_3S1P_20C_USA_Warehouse_.html

    over a buck cheaper than the Turnigy 1600mAh 3s and 15 grams lighter (last time I weightd a pair they were both slightly heavier than listed but were still 14 grams apart).

    I wouldn't personally. It will be ok if you stick to cruising speed most of the time but honestly? I'd go for a 30A continuous minimum. You are better off having a little too much rather than not quite enough.

    And you'll have an issue if you order those; You've picked batteries from the USA warehouse and the ESC from the international (at least that's what it comes up for to me). It won't let you combine them for the order.

    If you are squeezing for money where every dollar counts? Get the Zippy 1600mAh 3s 20C batteries and use the saving to get a 30A ESC. I can't cruise the USA warehouse for long sorry, sooner or later it picks up on the Australian IP address and only shows me the AU and Intl warehouse stuff so I can't help on an ESC.
  19. nblnckRV8

    nblnckRV8 Cadet

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    Im not extremely tight on $$ I would like to keep it under $30 for sure.
  20. Grey

    Grey Ace Pilot

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    In that case you are probably looking at one battery and the ESC (and the required connectors) + freight.

    Out of curiosity what has made your plane so heavy? Is the next one likely to be heavy as well? If you are going to continue the "heavy" trend I'd favour the 1600mAh Zippy for the weight reasons. If your next builds are likely to be a lot lighter? The 1800 will probably be the go. A lot of people are happy with their F-22 v2 on the 1800mAh battery (weight vs performance vs flight time).

    Then just pick up an extra couple of batteries when the opportunity presents itself. Your 1350mAh 3s 25C's will fly the plane in the mean time. No sense in not using them if you have them ;).
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