Young Eagle Corsair A-7 conversion help. - RC Groups
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Jul 31, 2001, 10:49 PM
Time wounds all heels.

Young Eagle Corsair A-7 conversion help.

The Young Eagle is a 120g, 26.7" wingspan foam model. It it rumored that you can bash this into a EDF R/C model. I already ordered it. It looked too fun to pass up.

I posted on the open board, and got kinda bashed, for not doing my homework, and not being smart enough to post in the proper forum, so here goes.

I wish to power this EDF conversion with one of three EDF's.

1. Blue Blaster. Recommended by website I purchased kit from. 35 Watt, 143g with 5@270 cells. Static thrust, 3 oz. Reccomended wing area, 150-200" on a 16-20oz. model

2. Red Blaster. designed to run on 1-3 800mah batteries. 6 oz. thrust. 105g with 3@800 cells.

3. Knight and Pridham KP-44. I have no specs on this motor. I would like some.

I also wish to know if it would be possible to power one of these small, low draw?, light fans with a 2 cell Li battery.

I admittedly do not have the experience or knowledge to figure this out on my own. So what will probably happen ( unless I can get some good advice ) is I will end up with 3 DF units, and have to purchase a foam cutting setup to make some new DF models for my spare motors.
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Aug 01, 2001, 12:05 AM
EDF all the way!
bruff's Avatar
Do you have a web page for the Young Eagles. How does the A-7 compare to the Flying Styro A-7?
Aug 01, 2001, 12:26 AM
Blew out my flip flop
David Hogue's Avatar

That's the same kit.. Some sites list them as Young Eagle, but it's the same product line, as far as I can tell. You still cleaning out the garage, btw??

Aug 01, 2001, 12:59 AM
EDF all the way!
bruff's Avatar
Check out Electric Jet Factory they have a conversion of the A-7 to EDF. See for the instructions.
Bob Ruff
PS Still cleaning. ;-)

[This message has been edited by bruff (edited 08-01-2001).]
Aug 01, 2001, 01:15 AM
Time wounds all heels.
I saw the conversion page, great stuff.

I will follow it closely when my little A-7 arrives.

But the real kicker for me is can I shoehorn in those long-life Li batteries?

I would love to fly some long "missions" with this bird.
Aug 01, 2001, 01:37 AM
Time wounds all heels.
ok, i looked at the EJF turbo 200 and reg 200. the reg 200 makes 3.5 oz of thrust on 4@600AE cells. Thats a pretty sweet number

But I still want to continue discussing this project, and the optimum motor/battery configuration.

Quick run down on EJF 200 vs. Blue Blaster.

the EJF+4 600mahAE cells: 142.56g 3.5oz. thrust

the BFB+5 300mah cells: 142.9g 3.0oz. thrust

for .5oz more thrust, not considering the addition of one more 600mah cell (28g) the EJF is the superior mini DF. and its significantly smaller, the drawback or gain yet to be seen.

25 min flights would be all my heart could take, and better than Disneyland if it works.

[This message has been edited by watersharer (edited 08-01-2001).]

[This message has been edited by watersharer (edited 08-01-2001).]
Aug 01, 2001, 02:38 AM
Time wounds all heels.
More in the A-7 saga.

EJF sells this same plane. They claim 13-15oz all up weight. I believe it.

This complicates things tremendously, as I suspect 3, or even 6 ( Red Blaster ) oz of thrust may be insufficient to power 13oz of very careful built jet.

As EJF makes a EDF400 w/ 8 oz static thrust, this sounds much better, but the added weight+added battery+largerBEC/ESC+higher current draw.....

I calculated weights with the EJF 200EDF. With a fairly generous margin for building, I project 350g. 13oz. With a 3.5oz thrust powerplant. 27% power to weight. Sounds a little weak.

But to go to the 8oz thrust EDF400, I add an additional 132.3g of motor and battery. 18oz plane, 8 oz thrust. 5oz of weight to gain 4.5 oz of thrust. 44% power to weight.

Now if I could just run that EDF400 off of my 51g Li battery, I get back in line with my weight, saving almost 150g. More than the weight of my power upgrade! 61.5% power to weight.

Can 3 Li cells pull 10-12A?

[This message has been edited by watersharer (edited 08-01-2001).]

[This message has been edited by watersharer (edited 08-01-2001).]
Aug 01, 2001, 02:58 AM
Time wounds all heels.
Oh I just cant stop.

I saw a blurb about guys using their Tadiran Li cells at up to 3.5A draw, successfully. Long term effects unknown, but this really seems to me to be a crucial issue for many small electrics.

The general consensus around here seems to be, "Don't risk it." Good advice.

But does anyone have any experience running Li cells at higher draws?

5 oz of battery could make a lot of difference for a lot of planes. And if Li cells can be used at even, say 2.8A per cell... thats 8.4A. Speed 300 class power. Heck, properly propped, many planes could draw 8A, if they could just shed a little flying weight. And what about a 6 cell 1600mah Li pack? Properly wired, for 9v, thats 12A of draw@ 2A per cell. At 102g. About half the weight of a 800mah NiMh. Manufacturers recommended daily allowance of fun anyone?

Can someone please tell me if I am completely off my rocker here?
Aug 01, 2001, 09:42 AM
Dude, where's My Plane?
JasonJ's Avatar
Very interesting indeed. Well, I too have been told the Lion cells cant put out the current needed. But, I have some things that might answer some questions.
I have EJF EDF 400 fans sitting around.

I also have a good supply of Lion cells from old laptop packs whose smart circuits went bad, cells are fine.
I will have to wire some of them up to the EDF 400 and see what kind of current I can pull from them.
The problem with the low current is you will need to put the cells in parallel to get the cumlitive current form them. That means lower voltage and more or less you will need to double the cell count to get the voltage up. If you can in fact get about 3.5 A form them, than 2 cells in parallel will get you about 7 A but at nominal Voltage, about 1.5 V? I think this is why the Li Ion cells are not used, once you double up the cell count, your way to heavy. NiHh seem to be the better cells with around 20 - 25 A max current figures.
So the question is what type of voltage dose your motor need? It would take 4 LI Ion cells to get 7A at about 3V. 6 cells to go to 10A at 4.5V and so on. I am not sure how the Li Ion cells stack up against NiMh as far as weight, but you can bet that if they were a better mouse trap for EDF, they would be in use. I have not hered of anyone using them. They are used in laptops because of the high life capacity, the laptops do not draw much current so its not a problem.
Aug 01, 2001, 02:26 PM
Time wounds all heels.
according to motocalc the 4 and 6 battery set up are the most efficient.

Here's the poop, straight from the motocalc's mouth.

2 cells: 3.3A, 3.4oz thrust, AUW 8.8oz

4 cells: 7.3A, 7.9oz thrust, AUW 10.1oz

6 cells: 9.4A, 10.2oz thust, AUW 11.3oz.

this is what I plugged in to get these numbers.

Motor: AF brushless 010, weight 1.9oz (including EDF unit)
Battery: Tadiran Li 3.6v cells 2-6, .62oz
Drive: Red Flame Blaster
Speed Control: Astro 800 brushless
Airframe: basic Robart F-16 for coeff., the modded wingspan to 25.1" (680mm), 160 sqin area, and a empty weight of 5 oz.

I arrived at 5 oz weight for empty frame by taking shipped weight ( 120g) and adding 1.5 oz of glue, hinges, ect. This may end up being more, but without completed airframe, tough to accurately predict.
Speed Control:

[This message has been edited by watersharer (edited 08-01-2001).]
Aug 01, 2001, 02:31 PM
Time wounds all heels.
I do believe that your EJF EDF400 may pull to many amps for LI.

But the 010 pulls half the current of a 400, and still makes its power.
Aug 01, 2001, 02:53 PM
Registered User
Foxtrot's Avatar
How are you setting up your batteries in motocalc. You looking to do series or parallel packs? Which one do we normally use. I'm always getting these two mixed up.

series + to -
parallel + to + and - to -

Is that right? Anyway. Is their a way to tell motocalc which way you want your battery packs configured? Interesting thing is if you put 2 motors in series the amps drom to 3.5. Bet that'll get you thinking.

Actually, on an after thought. I don't think I have a clue as to what I'm talkng about.


[This message has been edited by Foxtrot (edited 08-01-2001).]
Aug 01, 2001, 05:39 PM
Dude, where's My Plane?
JasonJ's Avatar
I think that is the root of the confusion here. Ill try to brek it down quick and easy. First off, yup. + to - to + to - is series. In series, the cells will have additive voltage, that is 1.5 V + 1.5 V = 3V. Thats cool BUT, to max current will be the max current of ONE cell. So if the Li Ion Cells are 1.5 V with 2 amps max, with 2 cells in series we get 3V at 2 amps.

Parallel is + to + and - to - .
in parallel current is cumlitive wich means 2 of the above cells gives you 4 A,,,,, BUT voltage is = to V max of one cell. So we get 1.5 V and 4 Amps max.

So you can take your 8 cells and put them in series and get the 8V or so but still only get 2 Amps from the pack.
Put the same 8 cells in parallel and get 16 Amps but only 1.5 V . The 1.5 V may not even be enough to spin the fan.

The best solutioin for this low current cell, is a series / parallel combination pack. That means we make up say two packs of 4 cells in series, and put the two pack in parallel with each other and get a total of 6 V @ 4 Amps.
You can get 6 V @ 6 Amps by adding another 4 cells in series with each other by in parallel with the other 2 sets of 4. Thats not a bad voltage and current figure, but you now are up to 12 cells! . Like was said before in the post, if you can get it to fly, it will be up there a while as moto calc has suggested.

So you can see how even though you can get either the Voltage or the Amps you need but not both. You need to double or tripple the cell count to get the numbers you need.

You can get the numbers you need from the correct series / parallel combo, BUT, you now need to do the weight, space, and cost figures and see if it adds up.

Now, realize that as you start to push the Max current of a cell, the Voltage begins to drop and the cell can be damaged . Also, the nominal voltage of a cell differs by the material it is made from and nominal voltage is the voltage the cell maintains with NO LOAD. There is ALWAYS a drop in voltage when a cell is loaded.

Hope this helps, sorry about any misspelled stuff, I am a BAD speller .

[This message has been edited by JasonJ (edited 08-01-2001).]
Aug 01, 2001, 05:43 PM
Time wounds all heels.
what about if I use 3.6v cells?

6 cells wired as 3 parallel packs at 7.2v

would this work?

3@2A=6A which is real close to my target of 7.1A ( per motocalc)
Aug 01, 2001, 06:03 PM
Dude, where's My Plane?
JasonJ's Avatar
Yup, now your on to it, But, like I said, that 3.6 V will take a dive when and if you approach 2 A current. Running cells at their max current output is not efficient, loss of wattage, loss of cell life.