Brian Taylor Me109E

not sure if untiracts are available now, might be bale to get you some YT ones, from the 72inch 109, right angle, either air, or lekky

what would you suggest ? I am doing this as electric flyer

Ok, so, 11lbs, 100watts per lb will give you a fairly sedate flyer, let's go for 125w/lb so 1375watts minimum. Now, if we knew the required prop diameter?................

To 'Mike ' at Admin, Many Many thanks, I see the light LOL

Klip I'll see if I can find that out, would be useful LOL

Alan, think I'll go electric uni's, weight is my enemy, so I was thinking air = container for the stuff plus pipes etc, at least that's what one of my old one's had, whereas elec = all wired up, at least thats my logic, anyone feel free to interject as I'm no where near putting them in yet.

Mike

Klip, this is what one guy who's light years ahead of me used, hope he don't mind, I just copied.

Looks like it's going to be a 24-26 cell model (Aveox 1415-3y or the new sensorles equiv if it turns out to be more efficient), on my H-1000HD belt drive around 5/1 to swing a 20 x 11 "PUMA" 3 blade prop. (20" is scale)

This from a gent called Tom Hunt, many thanks sir

Hi Solo, the 23to 26 cells will be A123's or some such. My advice don't go there! Stay with lipo's, 2 x 3s in series will give you 20 volts when nearly flat and will be much cheaper than anything else!
Suppose we use a 60amp Esc, 20x60=1200watts. Ok, not enough!
2 x 4s = 25volts so 25 x 60 = 1500watts perfect.
We must stay away from pushing the envelope, otherwise it'll all end in tears! (Ask BB)
A gear train is going to be both noisy and expensive! Let's go for something like a 5 or 6 inch prop, It'll also be quieter!

Back later, dogs to walk!

Klipkopwildlife wrote: Let's go for something like a 5 or 6 inch prop, It'll also be quieter!

Back later, dogs to walk!

Isn't that a bit on the small side?

Old Fart wrote:

Klipkopwildlife wrote: Let's go for something like a 5 or 6 inch prop, It'll also be quieter!

Back later, dogs to walk!

Isn't that a bit on the small side?

Oops. that's pitch, silly me!

LOL even I thought that and I don't have a clue

Well lost an entire post, cooking fat jumped on the keyboard!

I'm going to revise my estimates a bit, the guys in the know say 90 to 110watts/lb for a fast scale model, this means looking at the high end 11lbs x 110watts = 1210watts
I've already said we'll go 6s or 8s for cheapness, so at 3volts per cell at close to flat we've got 18volts or 24volts, so 1210/18 = 67 or 1210/24 = 50. I still think a 60amp ESC will be Ok.
We're committed to a 20inch prop so let's decide what rpm we'll need. The F3A buys have been doing this for years and say that a tip speed of more than 400mph is too noisy, so, let's aim for 360mph, that gives us a bit of leeway as the prop unloads. Now how many rpm is that? First reduce the speed to minutes, that's 360/60 = 6miles/min, 1 mile is 5280feet, so that's 31,680feet/min that the tip has to cover.
It's a 20inch prop so diameter x pi will give us the circumference 20 x 3.142 = 62.84 inches. divide by 12 to give us feet 62.84/12 = 5.237feet per revolution.
We need 31,680feet/minute at the tip so 31,680/5.237 = 6,049rpm. This then is what we'd like to spin our prop at, tops.
Now, let's go back to the batteries, when flat we'll have 18 or 24volts, to find out what Kv of motor we need just divide the rpm needed by the volts, so 6049/18 = 336 or 6049/24 = 252
So, rounding the numbers a bit, a motor with a Kv of 250 to 350.

Are we all on the same page here?

:blink: my head hurts :woohoo: Fair play Klipi I know who I'll talk to about the electrics even though i don't understand a word of it hahahahah, Thank you sir.

Mike

Stick with Kippy, Mike , he DOES know his stuff, and whats more, knows how to explain it as well

Garry

Ok, so where were we? We know, Lipos 6s or 8s, prop size = 20 x 6, ESC 60amp and motor 250 to 350 Kv.
Time now to 'plug the figures in and check our sums.
There's a rather good calculator called ecalc, it's free and you'll find it here it'll even recommend motors and stuff.
What's immediately apparent is we have a problem!
Now I understand why large diameter props have such large pitches!

did a tiny bit more this morning

Congratulations to those who saw it coming, a 6" pitch at 6,000 rpm will give us a maximum speed of just over 30 mph! Here's the math, 6" = .5' multiply the pitch by the revs .5 x 6000 = 3,000 times it by 60 to bring it to hours is 180,000ft per hour, finally divide by 5280 to give us miles, = 34mph
Sorry Solo, can you give us any idea what the normal flying speed of this model is going to be?