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-   -   Actual weight of a model (http://www.Wattflyer.com/forums/showthread.php?t=74358)

FishHawk 08-25-2014 12:18 AM

Actual weight of a model
 
How does one determine the actual weight of a model? For example, if the flying weight is given say it's 37 oz do you subtract the weight of your own motor and battery to get the weight of the model? FishHawk

JetPlaneFlyer 08-25-2014 01:08 AM

The flying weight is the weight of the model including everything, ready to fly.

So to determine flying weight you physically weight the model with everything included, motor battery, the lot. Weighing is the only reliable method to determine the weight of your model, published weights are often not very accurate.

kyleservicetech 08-25-2014 01:57 AM

Quote:

Originally Posted by FishHawk (Post 955829)
How does one determine the actual weight of a model? For example, if the flying weight is given say it's 37 oz do you subtract the weight of your own motor and battery to get the weight of the model? FifhHawk

If you are looking for a reasonable priced digital scale, I've got this one. It's pretty accurate:
http://www.harborfreight.com/digital-scale-95364.html

Also have this one for weights under 1000 grams, or about 35 ounces.
http://www.harborfreight.com/1000-gr...ale-60332.html

FishHawk 08-25-2014 02:01 AM

This confuses me.
 
I understand about weighing everything. But if my motor or battery is lighter or heaver than the suggested weight is where I'm confused.
If the designer used a lipo battery and I'm using a Nicad battery that weighs more how do I determine what the designer says if the correct weight for the various components? FishHawk

Stevephoon 08-25-2014 03:03 AM

Lets see if I am following you. Lets say the flying weight for a plane is listed at 37 oz with the suggested equipment. You already know that one of the components you want to use (the battery) is going to weigh more. You are not sure how much more, but historically nicads weigh much more than lipos...

So the question is how to still try and hit the target weight, correct?

This can be tough if you do not have the plane yet. If you do, then just weight the plane (ARF?) and then you can calculate what weight you have left to play with. If not, it's usually difficult to get the individual weights of the parts... What I would do is to try and find the comparable components on a site like HeadsUpHobby.com and use their weights.

But in the end you are probably just taking an educated guess. Just by going to NiCads, you probably won't hit the target weight. Some planes don't care too much, others do....

Steve

JetPlaneFlyer 08-25-2014 06:47 AM

The only way would be to find out what the weight is of the recommended components, (which you can do by looking up the specs, most give weight) then add or subtract the difference between that and the component you want to use.

kyleservicetech 08-25-2014 06:50 AM

Quote:

Originally Posted by FishHawk (Post 955836)
I understand about weighing everything. But if my motor or battery is lighter or heaver than the suggested weight is where I'm confused.
If the designer used a lipo battery and I'm using a Nicad battery that weighs more how do I determine what the designer says if the correct weight for the various components? FishHawk

What is the wingspan and wing area of your model, or the make and model mfg?

The original Nicad batteries were kind of OK for electric power, years ago. The newer Nickel Hydride batteries got rid of the hazardous cadmium, but in the process, those Nih cells can't put out the same current at the same voltage as the original Nicads. At least, that's my opinion, having tried both in the years gone by.

Now, we've got the LiPo batteries, available in a very wide variety of sizes, from real tiny for models less than one ounce, to big enough to fly a 20 plus pound giant scale electric model. LiPo batteries do have a fire risk, but using a quality BALANCING type battery charger does a lot to reduce that risk.

If you're worried about fire hazards and LiPos, there is also those A123 cells. They can not ignite (Yeah, I tried it :oops:) but they weigh about 35% more, have lower voltage, and are about 30 % larger in physical size, compared to an equivalent LiPo battery pack.

That kind of rules them out for models of the size you're considering. I'm using those A123 battery packs in models ranging from about 48 inch wing span, up to two giant scale models with 82 inch wingspan, and 17 pounds. They are running between 2500 and 3000 watts. Nice thing about A123's, with a proper high powered charger, they can be recharged in 15 minutes or less, so you don't need a pile of batteries to fly for an afternoon. At our club fun fly today, I put on 8 flights on two different giant scale models during a period of three hours. With a bit of gabbing in between.

There are about 100 A123 cells in my various models, and so far, they seem to outlast the models they are installed in. After several hundred flights, they turn the same exact motor, same prop at the same exact RPM. And, do it with better than 90% of their original ampere hour capacity.

FishHawk 08-25-2014 10:24 PM

Skybench Aerotech
 
I am looking at either the Big Bird or the OlyIIS. Wing span is 100" on the Big Bird and 103" on the OlyIIS. Steve I enjoy building models so no ARF for me.
Thanks guys for your help. FishHawk

kyleservicetech 08-25-2014 11:16 PM

Quote:

Originally Posted by FishHawk (Post 955891)
I am looking at either the Big Bird or the OlyIIS. Wing span is 100" on the Big Bird and 103" on the OlyIIS. Steve I enjoy building models so no ARF for me.
Thanks guys for your help. FishHawk

I've not heard the Olympic II name in quite awhile. That was a very popular Rudder/Elevator/Spoiler sailplane years ago, and is likely still a very good model for conversion to electric power.

For other wattflyer readers, a bit more info on this model:
http://www.outerzone.co.uk/plan_details.asp?ID=5116

Stevephoon 08-26-2014 03:06 AM

I've heard good things about both those models. I almost bought the 2M Lil-Bird instead of my Chrysalis.

But in general you correct, subtract the weight of the suggested electronics from the total and you have a bare weight. If you have any specific questions, I'd email them directly. I've always had good luck with direct contact with the small kit builders.

Steve

road king 97 09-20-2014 09:20 PM

Fishhawk there is no desighner with plans whos planes are as light as Ivans plans . Mine seaplane is 99 inch wing span and 8 pounds with the two lipo packs but Ivans is around 7 pound cause he can build way lighter than i can . Iam building his bigger twin otter now at 85 inch wingspan and his came in at 6 . All the imfo plus scroll down for the videos here .http://www.rcgroups.com/forums/showthread.php?t=710485 One of his desighns the Martin mars at 130 inc wingspan i think . this is the video that got me to build his solent. joe http://www.youtube.com/watch?v=7sgM6-AmDhg


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