iron eagel

The real limitation as far as electric motors is their ability to dissipate the waste heat they generate.
This is similar to the problems of CPU's in computers, when the first generation of fast processors came out there was a problem with them cooking themselves. Back before the days of really fast chips many hackers (those who experimented with computers before this label was applied to troublemakers) used to overclock there chips and had come up with ways to cool them so they would operate fro longer than a couple of minutes. Some large mainframe type such as Cray and alike were actually cooled using cryogenics.
Now while cooling a motor in a model airplane with cryogenics is not a possibility there are alternative solutions that could be developed. Also as the prior post mentioned it is possible to exceed this limitations at least to a small degree. I have a smaller .40 size airplane powered with a motor rated for 450 watts continuous and 525 watts burst that has been run at over 800 watts continuous for the past year with no ill effects. The secret is a rather unique approach to cooling and heat dissipation which has kept the motor at close to ambient temperatures during operation at these elevated power levels, and these results have encouraged me to actually see how far this motor can be pushed. Now the downside to this is it did add a bit of weight to the airplane but it did enhance the performance to a point that the added weight was not really not an issue. As a matter of fact the electric speed plane I posted a picture of earlier has some of what I have learned about the heat issue incorporated in it's design. While it is based on Mike Connors original planeform the fuselage/center section is an adaptation of my cooling system into the original planeform. While my wing structure is very different than Mikes (it is an experiment to see if a thin airfoil can be built using wood and actual surpass the original Vne of 130 mph) the airframe is a second attempt at using a electric motor well beyond it spec limits.
The one point I am trying to make is this:
The specifications for electric motors are nothing more than a starting point, given close attention to cooling these limits are not written in stone.
Granted the end result could be a bright flash and a loud pop but if you are careful you can take close to that line without crossing it.

HighPlains

My Feedback: (1)

Unlike electric motors that speed depends on the KV rating and voltage applied, a nitro motor will unload in the air, depending on aircraft drag and exhaust system. My open exhaust racing .40's ran at about 22K on the ground, but were up 5K in the air. Ground rpm doesn't mean a whole lot.

The electric motor also unloads, but the effect is to lower the current not increase the rpm.

If they ever manage to create stable high temperature super conductors, then motors will shrink in size and weight.

jeffk464

I think thats about 150 miles faster then my brain can handle.

erazz

Lithium-XX has energy densities around 0.5-5 MJ/Kg
Methanol is around 20 MJ/Kg
Gas is ~50 MJ/Kg
Kero is ~40 KJ/Kg

Problem is efficiency. While Electric systems can reach 60-80% total efficiency IC systems are much worse. I believe that our engines operate at round 5%. Add to this the ability to tailor your prop to the speed and the improved aerodynamics and you can see why electrics can give a good fight. Unfortunately for IC engines it looks as though they can't get much more efficient. Batteries OTOH are getting better all the time. I think that when we get into nano-tech batteries and fuel cells the IC engines will be hopelessly outgunned.

FWIW I fly a nice 1.20 4C powered sport plane, and electric Yak and a turbine powered Falcon. They are all great fun. Each has it's advantages, the Yak is always ready to go, the sport plane has a wonderful sound and the Kero burner, while being really complex to operate is a total thrill to see and fly. I also don't think that all out electric speed planes are any less complicated to operate, they are just complicated in other ways.

HighPlains

My Feedback: (1)

I think they are slightly better than 5%, as most IC engines are about 25-35%.


This years update -

Thunder Power has 65 C batteries now with burst current of 130 C. Great for pulling 110 Amps for 1500 Watts (4S) in a 3 1/2 oz battery for 10 seconds. Not good for a speed application, but might make a great free flight with R/C assist.

daven

My Feedback: (1)

Yep, we'd race grocery carts through the supermarket...

freakingfast

My Feedback: (3)

Yup, that's pretty good "C" for batteries available(known) to the public, but man, you guy's aint seen nothin yet....not even close in your wildest dreams, both in current draw AND capacity LOL.

378

My Feedback: (4)

I will never drop glow. I went hobby grade to avoid charging batteries and to get the sweet wail of an engine at high speed. Electric may be faster, but I really don't care.
Actually...they can get MUCH more efficient. First of all, two strokes need to go. They may rev like crazy but they're a very inefficient design. This will be a harder transition for cars than planes. Then, we need to go EFI. EFI can perfectly match the fuel mixture to the conditions present where the engine is at that moment, carbs can only come reasonably close. Now to claw back the revs, throw DOHC heads on those four strokes.

You'll see a significant increase in IC efficiency by doing this.

combatpigg

My Feedback: (3)

Don't forget that you need an engine that is low profile.....it doesn't do any good to make an engine 25% more powerful if the engine itself creates twice the drag.

iron eagel

Cp,
That is why my first speed plane attempt, that you have seen the photos of, was built using an electric motor for power.
I wanted to keep the frontal area at an absolute minimum and not having the cylinder of an IC engine sticking up was a big plus.
I know that the battery setup I am using is minimal but it should prove an interesting experiment none the less.
I am just finishing up the servo mounts and linkage so you guys should see a post of the finished bird and it's maiden flight videos shortly.
I'd love to see how it worked with a 65 C 4 cell with around a 4000ma battery on board, but that clearly is not in the cards at the moment. I am going to have to settle for a 3 cell 3200ma 30C (1/2 lb) that I have on hand but it should provide enough power to get it at least past the 150mph mark for a couple of minutes.

378

My Feedback: (4)

If I had the machining equipment, supplies and sufficient time I could make a DOHC head for an OS four stroke that's no more drag inducing than the current OHC head. Better cooling, too, seeing as there won't be a rocker box and pushrod tubes in the air stream. With it I would have to machine a new crankshaft, back plate, and what would appear to car guys as a start shaft, because I would drive the cams from the back of the engine. It would be chain drive, because timing belts suck, and the chain would drive one cam which turns the second by means of a gear...wait if I used the FS26 or FS40 I could just grab the off-the-shell recoil start parts used in the car versions.

Think about it. Better cooling, more RPMs, more power, more efficient, better fuel economy, more revs, easier starting, better throttle response, less fiddling....it would literally be as plug-and-play as electric...and if someone like me can think it up I'm sure the likes of OS and Thunder Tiger can whip one out no problem.


Also, if you really want to drop the profile of the engine, there's no reason we can't run a skirted piston and have the counterweight on the crank coming quite close to the rings...just like they do in larger engines.

jjookkeerr

I work on industrial electric motors for a living. Eventualy electric motors will hit a wall with what they can handle amperage wise.  You'll need more copper and more iron, that means more weight.  Even if you have batteries that can expend huge amounts of amperage, you'll still have to have a bigger motor to handle it.  Engineers have electric motors down to the numbers. They will need some major advancement in motor disign, right now  the only thing that you can do is increase voltage to get around the amp draw problem, but that has its limits also.
As for glow the engines are not much different than they were 50 years ago.  In my opinion gasoline will be the leader.  The power that modern IC engines put out today as compared with 50 years ago is night and day. Model IC engines have a lot they can do to increase power.

iron eagel

Right now I have a 850 watt rated motor that weighs in at 4.2 oz, I do not think you can get even close to that as far as weight v power with an IC engine at the moment.
Right now I think one of the biggest limiting factors regarding electrics is the waste heat issue, if you can find a way to dissipate the heat you can pump a lot of power through an electric motor and the associated electronic circuitry.

jjookkeerr

Heat is the issue because you are pumping large amounts of current through a very small amount of copper and iron. There is only so much you can do to cool the motor. You have two choices you can put a cooling system on or you can use more copper and iron. Both options will raise the weight a lot.

iron eagel

You are right both of those options will raise the weight.
However with a pure speed plane there may be a third option of incorporating a cooling system into the structure of the airframe, my design is exploring this third option.
The actual weight gain was very minimal, but it took a lot of work to incorporate it into the airframe design.

jjookkeerr

How do you get the cooling into the motor? Is it liquid, gas, something else?

combatpigg

My Feedback: (3)

.40 sized 2 stroke engines weighing in at around a pound are doing 210 mph on pylon racers....so that's where the bar has been set for that size engine.

At some point, 4 strokes make more sense...but I'm not sure where that size / displacement is at right now.

iron eagel

I am using a pressure cowl type of setup that Andy Lennon described in one of his books. The cooling intakes, motor mounts nozzles and ducts are part of the airframe superstructure, at speeds over 100 mph a lot of air is forced through and around the motor. The sheer volume of air moving through the system should be enough to the motor to be safety run at least 50-75% above factory specs as wattage. I know that magnets in the neodymium family are fairly temperature sensitive, and these are the most common types used in today's brushless motors because of their maximum-energy product (MEP) is much higher than other types of magnets, so cooling was a consideration for me right out of the gate as far as the design. Hopefully the combination of intake, venturies, ducts and exhaust nozzles will move enough air through the motor to keep everything happy.
Test on the ground using vacuum to simulate airflow showed that the motor temp stayed well within the spec limits even though it was running at better than 1100 watts, not bad for a 850 watt motor.

iron eagel

CP,
What would you put that .40 type of engine at as far as peak HP?
I think my OS .90 df spec is something around 2hp at some insane rpm...
But I know that the tricked out stuff you run probably goes well beyond your typical .40.

jjookkeerr

Now the way I understand it, if you have a motor that pulls 850 watts, then you make it to pull 1100 watts it will put out more power, but it isn't a linear thing. You eventully get to the point ofdiminishing return. On very large industrial generators, ie power plants, they use windings that are hollow and they run coolant like liquid hydrogen through them. If you could miniturize this, this would probably be the max you'd ever get.

HighPlains

My Feedback: (1)

In airplanes, it is all about power to weight. While a 4C engine might pull a higher percentage of the available power from the fuel (due to the longer stroke with the exhaust still closed), the 2C engine can easily reach 7 HP/cu in. So a .40 sized engine can output 3 HP, more or less.

378

My Feedback: (4)

Four strokes support boost. You can easily supercharge a four stroke to the moon and back. The only real limit is the mechanical strength of the engine. BRM, waaaay back in the mid 50's, had an 800HP 1.6L V16 that they ran in F1. They got it there because they boosted the hell out of it, ~55 pounds or so. It sounded awesome, too. But anyways...I see no reason why we can't supercharge our glow four strokes either. Everyday modelers like myself will run with low boost setups, perhaps no more than 20 pounds, while hardcore racers who don't care how long their engine lasts as long as it finishes the race, can and likely will go absolutely bonkers.

With a boosted four stroke your only limit to power output is how strong the engine physically is.

HighPlains

My Feedback: (1)

Cooling is probably the most overlooked and least understood problem in any type of high speed model. For most GA air cooled airplanes, cooling drag can count for 10 to 30% of the total aircraft drag. So for a model we don't want the maximum amount of air we can push through the cowl or motor, we want the least amount that gets the job done.

High speed air flow is not the key to great cooling. High pressure is. You want to take the air in at the free stream speed, and slow it down by increasing the volume inside a plenum chamber while at the same time increasing the pressure. Now are there other things that could improve cooling? Sure, you could mist a volatile liquid into the air stream that would phase change from a liquid to gas and really remove large amounts of heat. This would require even less airflow, as steam cooling really was in vogue back in the '30s on some of the unlimited racers of the day.

Just saying that if your only tool is a hammer, then all your problems better be nails.

jjookkeerr

Really when it comes to supercharging engines you'd only need about 6-8 psi to increase output by around 50%. That seems to me like it could be done.
When it comes to cooling a motor no matter how good your cooling is, at some point you are going to have to increase the copper and iron to get more power. You may get to the point where a heavier motor will actually be faster than a light one with an advanced cooling system

378

My Feedback: (4)

Air is less dense the higher you go. You may want to overboost by a few pounds on the ground to compensate for that.