Mike Wiz

My Feedback: (2)

Really... If you want to follow the recipie then just stick a 2.cycle .61 on there and be done with it. Otherwise if your going electric then making it preform in a similar manor to the original is all that makes sense. An 11x7 at 15000 rpm is possible with electric power. It's just not the best way to get an electric power system to yeild the same performance as the old 2-cycle .61. Spin a bigger prop a little slower and your prop will get better traction and you will get to enjoy longer flight times and quicker acceleration.... but do as you will. If you like spinning an 11x7 at 15K, whose to tell you your wrong? Certainly not me.

Trisquire

You wouldn't get the same thrust without a duct, but we're not trying to reduce the prop diameter to that of a ducted fan rotor. We're just trying to get it down to 11 inches.

Back in the glow powered ducted fan days, you had to shoehorn an O.S. 91 into a "60 sized" jet, to make up for the duct's lack of efficiency; and those engines are not covered under the O.S. 2-year warranty, because your spinning them at such high RPMs.

Tom

daggets

An 11x7 at 15000 rpm is possible with electric power. It's just not the best way to get an electric power system to yeild the same performance as the old 2-cycle .61. Spin a bigger prop a little slower and your prop will get better traction


you are probably right...

stuntflyr

So I guess that based on what I've read here the compromise is to go to 12 inches and see how well the model trims out. I suppose for most of these Classics the gear length would be able to handle a 12 inch prop with minimal changes. I bet what Dean was saying about the big props with big pitch would be fine and work well on the bigger, later ships, like EU-1A. It's a massive brute with big surfaces.

Mike Wiz

My Feedback: (2)

You were the one that used a ducted fan as an example to prove a point, not I. So does the ducted fan comparison make your point or not? I'm confused.

People didn't spin their 11x7 props at 15000 rpm because that was the most efficent method of providing thrust for the plane. They did it because that's where these engines made their best power. That's not true of electric power systems. So, can you do it the old way and spin a little prop like mad with an electric motor? Sure but why?

cygnet

My Feedback: (33)

Here Here!

bjr_93tz

The bottom line is Mike, that my Curare just doesn't fly right with a 12" diameter prop. I get about 1.5lbs more thrust with a 12x6 APC as apposed to the 11x10 APC that I run on the IC engine thats in there but the plane flies like a bucket of horse droppings.

I believe there's no argument that bigger diameter props are more efficient at the slowflier speeds that planes fly at today, but most of the short coupled planes of the classic era were just not designed for high torque motors and large diameter props. Don't get me wrong, a fourstroke or electric in my Curare with a large diamater prop will do just as good of a job or better than the current screaming two stroke when it comes to pulling it around a schedule but the plane just won't be as "nice" to fly.

The planes of the Curare and Magic era need a small prop and plenty of revs to get the same feel in the air. You just can't put in a V8 and fat tyres on a Volkswagon Beetle and get the same driving experience as the original....

Trisquire

Maybe I'm hung up on cosmetics. You'd have to extend the length of the landing gear. That would alter the look of a classic pattern ship. I'm just saying that spinning a little prop like mad will not diminish performance all that much.

If performance is your sole objective, just build a 2/3rds scale F3A plane, and use the optimal motor/prop combination.

Tom

stuntflyr

This is the rub for the Classic guys as far as I can tell. These models need to fly well and in trim if electric is to be used. But the electric "crowd" get all into the big props and forget that the aerodynamics of the Classic model don't change. Dean seemed a bit hard-line on the big prop thing based on the efficiency of the electric motor, but you can bet he'd use whatever prop it took to make the model trim out if that was the airframe that was to be used.

My last post was a bit of a bridge to the big prop loving posters, because the newer Classics are longer and have bigger surfaces, but for the smaller, older ships the smaller props seem appropriate. Can't wait until someone gets some experience with this type of set-up. Then I could quit using poison paint!

Chris...

daggets

more simply, if you want speed, you need rpm.... example the racers... faster are electrics.. 30 000 rpm or more, make the speed..
classics are ballistic,they need needs rpm...

Dean Pappas

Hello BJR
You cannot change from an 11-10 to a 12-6 and say that this "experiment" tells us anything meaningful about diameter changes.
Your engine's running characteristics (torque curve) and how they play with the dramatic change in pitch swamp out any diameter comparison.
Many of us flew 21-11's and 12-12's on normal 60 sized pattern ships with no ill effect.

take care,
Dean P.

Mike Wiz

My Feedback: (2)

I have a hard time believing that 1" of additional diameter completely ruins the handling of an airframe like these. Also, why would the airframe care if the thrust came from a shallow pitch prop spinning fast or a deep pitch prop spinning slower. If the screw moves the air then it does.

MTK

It doesn't completely ruin it. In fact if the pitch was identical, the original poster probably would not see much difference.

A 6" pitch versus a 10" pitch does make a big difference in how the plane handles in the air.

As Dean stated it was common to run a 12x12 or 12x11 on 60s back in the day and hauled the planes around great, even when the planes got a bit larger than the Curare size

bjr_93tz

Hi Dean, I still fly a post turnaround ship with a Hanno and a 12.5x10 APC and while I prefer the 12x12 APC for sport flying it still flies the schedule better with a 12x11APC, however I need the extra oomph (and braking) that I get from the 12.5x10 when flying at proper turnaround speeds and I am prepared to live with the extra work it puts on me as a pilot. The plane is less pure to fly coupling wise and requires a lot more throttle management.

Where I will stick my neck out, is that anyone who puts a Curare or similiar pre-turnaround plane in the same category as any post turnaround plane, either hasn't flown both and doesn't know what their talking about, or has a very poor feel for their plane when their flying because they are two very different types of planes. Increasing prop diameter 1" (from 11"-12") is a big change and maybe my assessment of the change was a bit harsh but just as valid. From that experience I would try a 11" 3-blader on an electric before upping the prop dameter.

I'v seen people who should know better bring planes down after a maiden flight obviuosly fighting it all the way, proceed to tell every one how well it flew. I don't know why some people do that. Maybe they wear rose coloured sunglasses when flying, while I use various combinations of tints and mirrors.

I agree that small dameter and high revs is not the most efficient way to go but don't knock the bloke for wanting to go down that path. At the end of the day it's him that has to enjoy flying it whether I enjoy watching it or not.

Mike Wiz

My Feedback: (2)

Hummm.... Try a 3 bladed prop with an electric. I never considered that. I'll have to look into it.

Thanks for the idea!

NM2K

My Feedback: (14)

No, I'm afraid you fellers have missed the point of modernized classic pattern powerplants altogether. Why use props? Let's get the deed done and go directly to turbine powered Phoenix 8 and EU-1A models. No whiney two-strokes. No glorified food processor motors and most of all - no old fashioned propellers.


Ed Cregger