General Misc Questions I Never Always Wondered About

mooserider

mooserider

Active Member
I originally had a question about batteries, but it evolved into a list of things I've always wondered about.

(flight batteries?) I often see helis or planes with more than one battery. Does that lengthen the flight time, or just speed up the motor? I learned at the los today that the mA rating is run time. I thought it was something that had to match the motor. Then he said it was based on the esc (mine is a bec and esc in one, 45a). My heli has no 'bec', just and esc. All this electrics stuff is so gd frustrating!

(nitro vs electric receiver?) To top it off, I bought a 4ch receiver (spektrum ar400) today for another airplane I am setting up (nitro 4ch). There's no battery slot (like, for a nitro plane bat). I read the instructions, which said to use the bind plug in batt/data, and the flight battery in any other slot. This seems to work, it seems to bind, but as soon as you re-power the receiver, it's bind is lost. Is it because this receiver is intended for electric use only? I read another article that said that you should always use 6ch receivers for nitro planes (which doesn't make any sense to me).

(satellite receivers?) While I'm at it (this turned into a rant, sorry), airplanes have no satalites, and helis do? Why? Or is it size, like on a 1.20 plane, you would want a satelite.

(fuel nitro %?) I think this is pretty much answered, but 10% vs 15 or 20 for nitro engines? Let's says I have these engines: OS 20, OS 46fx asb, OS 61 fx, YS110 (4-stroke). Can I just use 15% on all of them? Forget about tunning the engine if you change blends, I understand that. And I hear it makes the engine run cooler if you have a higher nitro content. Mainly, can I stick to 15% for all my engines?

(nitro breakin) Do you really need to run a nitro rich for the first few tanks before leaning it out?

Super bonus question: Why is it that nitro heli motors have square heads, compared to planes? Heat disipation or some such
 
Derek

Derek

Well-Known Member
WOW! I wasn't quite ready for this rant this early in the morning, lol. Let me go get my coffee and I'll be back.....

....Ok, I'm back...I'm no pro at any of this but I think I can help shed some light on some of this and hopefully I don't confuse you any more than you already are.

Flight Batteries...some heli's run 1 battery (my Trex 450 and my two Trex 500's) and some heli's run two batteries (my Trex 600 and 700). Some planes run 1 battery (all but 1 of my planes) and some planes can run two batteries. It just depends on the setup. 600 class and larger helicopters run two lipos packs in "series"...essentially doubling the battery voltage. Using two 6S 4000mah packs would then mean that you have a 12S 4000mah lipo pack on board (6S + 6S =12S). Doubling the voltage means double the power (grrrrr, love power!!!) In reference to planes, you can do the same thing with 6S packs and double the voltage for more power (like I am doing with a new scratch build) but I also have a few planes that run two 3S 2200mah packs and I connect them to the esc in "parallel" (meaning I'm doubling the MAH, or the capacity). So I'm getting the same 11.1v from the batteries but I essentially have a 3S 4400mah pack on board. I hope that makes sense.

Nitro vs Electric...I'll just give you what I know. I think I'll just leave this part to the people that know more about nitro's than me. I've never owned one.

Satellite receivers.....satellite rx's aren't always necessary in some cases but in other cases, satellite rx's are a MUST. In the cases where a sat rx would really be necessary would be in my small foam airplanes. Generally, the main rx will suffice and give proper reception. Now, if you get into larger helicopters (500 class and bigger), the frame has much more carbon fiber. Carbon fiber blocks our beloved radio signal. By using a satellite rx on the exterior of the heli frame allows for a better reception of signal. Some larger planes will use satellite rx's, placed far away from a mass of wiring, to allow for better signal. In some cases, it's just personal preference. In other cases, it's a MUST. Make sense?

Nitro fuel....again, I'm gonna leave that one to the nitro people.

I hope this helps!!!!
 
Tony

Tony

Staff member
The reason for multiple batteries is actually quite simple. Most of the larger ESC's are what is called OPTO, meaning they do not have a BEC in them to feed power to the RX. Because of this, you either have to run a separate BEC off the flight pack or you need to run what's called a Rx pack (receiver pack). Most receiver packs are 7.2 volt LiFe batteries and usually around the 2000mah range. This allows you to run 50+ Volts to the motor and ESC, but only run 7.2 volts to the Rx. It also allows you to use higher amperage servos than a BEC can allow in an ESC (usually 5a or so). But the biggest reason I would run a separate Rx battery is redundancy. If your flight battery drains out or if your ESC goes bad, you still have servo control because you are using a separate battery for the Rx and servos.

Most of the really cheap 4ch Rx's are made to use an ESC that has a BEC (didn't we just talk about this? lmao). And for this reason, they made the Rx smaller by getting rid of the battery port. However (are you ready for this), just go get a Y harness and plug the Y into the throttle port of the Rx, plug one end of the Y into the ESC and the other into the Rx battery. You see, the positive and negative are jumped on ALL pins across the ESC. They are exactly the same. It's the signal wire that changes. But with a flight pack, you are ONLY plugging into the red and black wires, not the white (or yellow). They do this because of the lightweight planes that are out today. They are made for planes with a < 30" wing.

Airplanes do have satellite Rx's and you SHOULD use them! Satellite Rx's are there for diversity. You point them in different directions so that if one Rx has a brown out, the other Rx should have already picked up teh signal and you keep flying. Always run a satellite if you can. I will also add, most Rx's that are made for planes are going to have to antennas. One short and one quite long. This is also for diversity but make sure the tips of those antennas are pointing in different directions (one to the back and one to teh side).

Nitro fuel is a blend of Methanol, Nitromethane and caster oils. The methanol is great fuel but does't have much power for our little engines. That is where Nitromethane comes into play. Nitromethane is what Top Fuel Dragsters run on to make the 8000+HP to go down a 1000' (used to be 1320') track in 3 seconds and change at over 300mph. It's the exact same fuel. Nitromethane will actually cause your engine to run hotter because it's going to make more power. Your question "can I use the same fuel in every engine", yes you can. In fact, I would always do that because the last thing you want to do is put the wrong fuel into an engine and damage it. This won't happen if you are running the same fuel in everything.

Breaking in an engine, no matter what kind of engine you are talking about is important. VERY IMPORTANT! Especially with nitro engines. You do need to run it rich for the first few tanks (I suggest 5) and do not go balls out on the throttle. On a plane, the first couple of tanks need to be at about half throttle on a bench just running static. Maybe some up and down on the RPM, but nothing crazy. Then, take it to the sky and just meander around the sky slowly. Next tank, lean it out on the top by about 3 clicks and to it again. By the time you get to the 7th tank, you can start ripping into her. What you are doing is putting a coating on everything inside the engine. This coating is protection and boosts compression. So yes, you really do need to do it. However, if you want your engine to last half as long, go ahead and dont' do the break-in. but I highly suggest you do.

Heli engines need more proficient cooling, hence the larger head. On an airplane, the engine is right out in the open right behind the prop in the prop wash. It is ALWAYS going to get good airflow. On a helicopter, the engine is tucked into the frame then it has a canopy put over it so when you are in Forward Flight, it gets NO air flow. Heli's depend on a fan that is bolted to the engine, behind the clutch to force air over the head of the engine via the air duct. Because of this, they need more surface area so that you can still make power out of them but yet still keep them cool. Square heads have more surface area than round. And also notice that the heli head is about twice as large as the same size nitro plane engine. It's all about cooling.

I think this answers all of your questions. If not, let me know and I will try again lmao.
 
RandyDSok

RandyDSok

Well-Known Member
Some additions/corrections...

The receiver battery packs actually start at 4.8v and go up from there. Which output you need will depend on the receiver and the servo's being used.

Engine break in... isn't to develop a coating as mentioned. It is so all of the parts seat with each other to help develop a better fit and seal. Primarily on the piston rings to the cylinder wall although the push rod seats ( if the motor has them ) also will develop a better seal. Because of the better machining and materials we use today, the break in time has been shortened... but read the instructions given for the motor in question and follow those since each may differ slightly. If you have no instructions, what Tony mentioned about running 5-7 tanks is close enough. The same also applies to any engine even the ones we get in a new car.


I'll just reword and generalize what was mentioned on the satellite receivers.... smaller aircraft typically don't have satellite receivers with a few exceptions where there are materials that may block the signal. The motors, engines, batteries and other metal objects can "shadow" the signal... carbon fiber also can block a signal and may end up requiring the use of a satellite. I would probably start considering a satellite on any plane much larger than say about 50"- 60" ( since I didn't see plane sizes mentioned yet ).
 
mooserider

mooserider

Active Member
This is great, thanks so much you guys! So it sounds like I need to bring that new receiver back and get one with a satellite. It's for a P51 with an OS 61 in it... fairly big plane I built years ago, but never flew. I told the guy at the hobby shop what it was for, but he assured me that I didn't need a satellite. It does have two antenas, as Tony mentioned. But I still can't get it to bind properly anyway. My flight battery is only 4.8v (it's not lipo, it's what came with the radio years ago). I tried what Tony mentioned (minus the ESC cause I don't have one for that plane)... it acts like it's bound, but then resets as soon as I repower it. I'll probably just bring it back and get the 6ch receiver with a satellite.

I'll make sure I do the break-ins still. I've heard some people say you don't need to on newer engines now, but it sounds like they probably don't know what they're talking about.

I think I'll also take back the 10% nitro and get 15% and just stick with that for everything. I assume this is also ok for 4-strokes.

The descriptions of how the lipos work was very helpful! It's really cool that you can put them in series and get a longer flight time.

Thanks again for the feedback everyone! I was up really late working on a plane to take out today, and of course now it's raining all day here in Seattle. I did take that Piper out yesterday though and got in a flight... first one in maybe 10 years. Felt great!
 
Tony

Tony

Staff member
Actually, putting them in parallel will give you a longer flight time (red to red, black to black). Putting them in series will double their voltage if you are using tow packs of the same voltage.

Are you removing the bind plug before powering the Rx off?

Yes, 15% will work in a 4 stroke as well. I'm using the same fuel in my F4U 2 stroke as well as my Decathlon 4 stroke. So you will be fine there.

Congrats on the flight! But next time, we must have some video. :biggrin1:
 
mooserider

mooserider

Active Member
Err, parallel, ugh. Read that too quick. I'll always have this thread to look back on though!

No, I don't remove the bind plug until I power off. I swear I've always done it that way... have about 4 spektrum receivers now. Figured you shouldn't be plugging or unplugging things in while the Rx is powered.

I should have taken a video. But I did bring my wife and she took a picture of the landing!

landing1.jpg

landing1.jpg
 
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