glow to electric weight gain,how much extra weight is too much?
hello builders of conversions,
so i placed everything into my rv 4-40 using the 4000mah 40c[a 3cell & 4cell]7cell count batteries and am shocked at how nose heavy these packs make this RV over the last RV 4-40 i built using 2 3cell 4000mah 20c packs to get 6cell. and a feather weight turnigy esc.
i also think the eflight power 60,and 100amp castle esc weighs a lot more than my cheaper hobbyking setup that failed and caused the fatal crash.
now i may have to scrap the location of the batteries that were easily accessible via a hatch in the cowls underside. if i leave them as is i will need to locate the esc at least 16" away from where i plug in the battery which is unacceptable,and the 3 esc to motor wires would also be 16inchs which would be ok. the Rx battery pack would get pushed to the tail area and basically out of reach except by a custom little hatch built in the tail section.
...........oh yeah,i forgot the reason for this post.the question is
so whats the weight gain others have added to their conversions?
.................................................. .................................................. ...
i really don't want to buy more batteries of lesser weight/mah/c rating,so right now I'm looking at relocating the batteries to be installed when the wing is off,change the rx battery out for either using the bec in the castle which i don't want cutting power to the motor if theres ever lvc ,or get a ubec like the castle 10 amp/6v. having to rework everything is annoying since i was building and figuring my design based on the previous RV-4 which i never weighed after completion and gain cg with everything pushed forward.
i would even consider moving the tail servos to the rear of the fuse and ditch the extra weight of those push rods.
sorry for the rambling i just need to go back and re-figure this bird a little.
Currently you can actually come out lighter with electric than glow, gaining power and performance at a modest (possibly none) loss of duration.
It requires a bit of work lightening the parts of the struture designed to deal with the cyclic stresses imposed by the internal combustion engine, but its not hard once you know what to do.
I think you have way, wayyy too much battery and motor for a model of that size.
The 4-40 was intended for a 40-52 glow motor. The Power 60 is a 60 size (1700W) electric.. so far too big and heavy. A 800-900W power system would be tons of power along with something like a 5s battery in the 2600-3000mAh range.
I'm a great believer that you can never have too much power, but you certainly can have too much weight. You need a much lighter power system. You can move stuff around as much as you like but that wont make it lighter.
I'm running those heavier, physically larger, lower voltage A123 cells in all of my models. Nice thing about these A123's, they do not have a fire hazard, and can be permanently installed in your model. They can be be recharged repeatedly in 15 minutes with a high powered charger. After 300 or 400 flights, they don't loose very much capacity. (I've got over 100 of them in my various models.)
"C" and what it is
Here's some more info on this subject.
Thread on 70 size glow engine conversion to electric
Hacker 6S2P A123 powered Models
Hangar 9 Kantana Model
Hanger 9 Twist 40 Model
AEAJR's Site on Electric Power
BEC Linear Current Rating
Forgot to answer your main question - every gas/glow to electric conversion I have done has come out lighter than the original design weight.
Here are a few ARF's Ive done that I have pics of. All came in under the normal gas/glow build weight - mostly due to savings in the power system. All had at least as good performance as the gas/glow originals.
Your power system weighs almost as much as my heaviest one - which was good for around 3000 watts and powered an 17 pound model!
i do believe you've talked some sénce into me....:D i will research a lesser size motor with higher kv and use the 4cell 4000mah 40c battery alone cutting out the 3cell. this will allow me to use the battery box i built and possibly get a smaller esc.
today is my birthday,so might just as well use the money for the RV-4.
what eflight motor to buy and esc....i really do want vertical to be impressive. what set up will attain my goal and not break the bank. the power 60 on 7cells packs a huge punch in the greatplanes extra 300s at 64" wingspan.she really tears up the sky with no hurting handling and i know it weighs more than its glow equal since a bud at my field has one.he was very impressed with the power from electric as were other watching
the same goes for the hog bipe from sig....and it defiantly flys like a pig with added weight compared to another bud at the field who flys his pig with glow.
ill look into some choices and post back Sunday . have a great night and thanks for the input. stu
Its a 40 size model... Power 32 will fly it for scale performance. Power 46 will fly it very well.
Happy party/plane day!! :D
The power 32 motor will work great on 5 cells, you need to use 5 cells because its a low 770KV motor, a 12x6 11x7 or 9x9 prop will make it Haul @@s :D a 60 to 80 amp esc will work great, I dont think you need more than a 4000mah lipo. but to keep the weight down, I think I would use 3000mah lipos.
power 32 motor on 5 cell lipo and a 9x9 prop
the weight of the RV by greatplanes is 5.5 to 6.5 pounds. i fear all up weight with the batteries will be 7+pounds.
research is showing the eflite power46 on 5cells would use a smaller prop than the 4cell option. seeing as the rv rolls very close to the ground ,the 14"prop is out. in fact a 12"apc e prop will be perfect. greatplanes says 11x6prop.
the motor weighs less and may be moved closer to the firewall, the esc can be a 80amp or still the castle moved forward inside the fuse. best of all the battery box will have space for cool air flow over the packs.
eflite power 46=$89, the 2cell 4000m 40c zippies to go with my 3cell 4000m 40c bats gives me 5cells,i'll need 4 of the at $20 each[that includes shipping]. this reduces the nose weight by 2 cells.and the motor will be lighter.
its late here,1:16am...i'll shift things around after church.
My conversions albeit in the smaller sizes - have all been lighter than the original glow ... plus the advantage that I could move weight around better than when glow. Major weights then were engine, Rx battery and Fuel tank. The only part then that could be moved significantly was the Rx battery.
i agree Nigel,my smalled 1/2a builds were all no gain as the smaller brushless motor automatically cut weight,and smaller battery made for easy balancing.
YIKES!!! chellie,you are a sweetheart to supply that video of the sundowner. i just watched it and ws amazed at its speed:D. i the checked out the spec's on the sundowner...60+wingspan and up to 7lb's flight weight.[popcorn]when i get home from Church the first order of business will be to order a new motor and a couple of 2 cell 4000mah 40c batteries to mate with my already existing 3cell pack to get five cells.I'm also considering using the turnigy 80 amp plush. they are in several planes and have been great to my birds like the towerhobbies uproar.
lastly,i am considering the power 60 and 100 cc esc for the wall queen f4u corsair,64 inch wingspan and weighs what a topflight fully sheeted kit would way...heavy!:cool:
i know absolutely 0 about glow motors and the weight of fuel. so if i could ask another question please. these are the spec's on the RV 4-40....when the manufacturer of kits give a 1/2 pound to play with does that include all up weight with fuel:confused:. i kind of wonder since fuel tanks come in different sizes and liquid isn't light. a guess is approx 770grams. motor with 10 0z filled tank
to go electric with all operating items like motor,rx,rx battery...ect...ect...it really adds up quick.
the added total weight of batteries,and speed control/motor=952grams[2 lb's]. this is on 5 cell 4000mah40c batteries using a power 46 eflite motor. i could use the built in bec with the castle esc since i trust it to work 4 servos and rx flawlessly.i', using the cc esc to eliminate the 147g rx battery.
total weight of RV-40 using the 7cell pack and the 60power motor.....way to much...lol:Q. same as aboves list and the total is 1168g[2.5 lb's]
this why i asked the question.....it weighs a ton and i wonder how everyone else is coming in under spec weight of a build. stu
Stock Number: GPMA0180
Wingspan: 54.65 in (1388 mm)
Wing Area: 631.6 in² (40.8 dm²)
Weight: 5.75-6.25 lb (2.6-2.8 kg)
Wing Loading: 20.9-22.8 oz/ft² (64.1-69.7 g/dm²)
Fuselage Length: 49.6 in (1260 mm)
Required: 2-stroke .40-.52 cu in engine or 4-stroke .48-.70 cu in (8.0-11.5 cu in); also required, 4-5 channel Radio with 5-7 servos (5-channel radio with 7 servos required to use optional flaps) Pilot figure not included.
Recommended: Pitts style muffler
http://www.greatplanes.com/images/pdficon-small.gifProduct Manual - Parts Listing - Accessories Needed
As for the numbers, Motocalc predicts following for the $89 E-Flite Motor, both based on a 5S 4000 Mah LiPo and a total model weight of 6 3/4 pounds.
1200 Feet per Minute climb rate
43Amps, 770 Watts into the motor, 570 Watts out of the motor (74% efficiency)
9700 RPM on a 12-6 Prop
As a comparison, the $115 Hacker A40-10L motor predictions:
2200 Feet per Minute climb rate
52 Amps, 900 Watts into the motor, 820 Watts out of the motor (89.9% efficiency)
8900 RPM on a 13X8 Prop.
I've got a Hacker A40-10L, those numbers are pretty close. As for the E-Flite motor specifications. Don't know, never used one.
The Castle Creations Switching uBEC's are pretty good. I've got several of them, but for models of this size and larger, I use dual receiver power, first, the ESC uBEC, and the second, the Castle Creations 10 Amp uBEC. These must be isolated from each other with two $2.50 10 Amp Shottky diodes. (I've got drawings and part numbers if desired.)
The kit's list expected weight does not include fuel.
I can't say for sure how my RV-40 will turn out regarding weight yet... I haven't started the build. I have 8 other airplane kits in the build que before I will get to it. I have no predictions as to what changes I will make yet.
I generally come out 10% below kit's listed weight for the ready to fly model when I am not making any modifications other than glue choice.
When I start making modifications, keeping the same power system type (glow/gas/electric) I tend to come out even lighter.
Then there's the changes I make when changing from glow to electric...
or 730 watts on 4 cells for an even lighter setup...
hmmm 1000w on 5 cells and a 12" prop.
thanks for the responses. so the 6.25 lbs of the RV spec listed above.....what does that include? glow motor,tank . will it be the target weight I'm supposed to achieve with motor,esc,batteries:confused:. it's going to weigh more than 6.25, i never did find time to go down and start changing weight ratios around.
by this weekend the eflite power 46 should arrive and with any luck the three 2 cell zippy 4000mah40c batteries i ordered from the USA hk warehouse will also arrive by next week.
one thing I'm also hoping for is after experimenting with weight relocating ,the battery box i built Will still be usable. it will be even more open for air flow to travel over the 5 cell compared to the 7cell fit.
when i get the smaller motor i can also build a battery mount out of standoff spacers and bring it in closer to the fuse. again offsetting some weight closer to the cg. have a good night all,i have work again after a nice week off. stu
The expected weight listed on the box includes equipment equal to the radio (RX, servos, battery,extensions), engine and fuel tank as suggested in the instruction, using the glues and covering as recommended in the instructions.
Often it includes an allowance for lead weights expected to be used to get the airplane's CG correct.
The list weight will be based on having actually weighed one or more models that are ready for flight, except empty fuel tank.
While "more power is almost enough"... you can add so much power that the airplane is just unpleasant to fly because its too heavy.
I use 6 cell LiPo in .60 to .75 glow conversions... and have used 6 cell in a .91 conversion. 4 cell is usually just fine for .40 conversions.
Part of your problem is your batteries. I know you said you didnt want to change them out, but you have a lot more battery than you need for that model = excess weight.
Your batteries are capable of putting out well over 2000 watts if they perform to spec. If your model weighs 6 pounds, then that works out to 333 watts per pound. Thats way way waaaay more than you need to fly that model very briskly. With that kind of power you could easily hand launch the model straight up accelerating all the way and it would be out of site in seconds :)
Its also waaaaay more potential power than your motor or esc can handle, so its kind of wasted.
The only reason to carry that much excess battery would be to fly long duration, but with this type of model you really need to think light weight.
Electrics can be a pain when your trying to figure out all these details,
your right Larry,
I've down sized the power system and battery size,this should put me at the 6.75 pound range using the power 46 and 5cell batt. with the power 60 and 7 cell i was just around 7.25pounds and it felt real heavy i realized it would fly like a brick with huge power.
i may also trim a few hundred more grams relocating the tail servos to the rear of the fuse.eliminate the pushrods inside the fuse and if need be I'll get a 80 amp opto esc and a cc ubec. i have confidence the rv will be very close to the 6.5pound range with plenty of power.
what you said about duration is why i use the 4000mah40c batts. i get 10+ min flights on the hog and gp extra with out depleting the packs and having plenty of juice left for go around if i have to wait to land.
so for the rv4 i will give up some aerobatic performance for duration.besides,the rv4 isn't a super high aerobatic bird but more for scale flight.
I'm glad i posted this question as it helped a lot to make a few changes straight off. thanks again gang,I've hit the thank button to every post here as everyones suggestions have been helpful. stu
|All times are GMT +1. The time now is 03:33 PM.|
Powered by: vBulletin
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright 2005 WattfFlyer.com
RCU Eflight HQ