Selecting propeller for stunt plane..
 

Hi, i am building the Rascal stunt plane, there are propeller 7x5 recommented at the Rascal plan ,and i am planning to use the ASP 12. I has maked the carburator for C/L use, there are 5 mm venturi, works well. I shall take bench running the ASP 12 with miscellaneous propeller from 7x3 to 7x6 to find calculated speed and thrust with the program ThrustHP.

Are the speed or thrust neccesary to make stunts?

Jens Eirik

RE: Selecting propeller for stunt plane..
 

Speed and thrust are both good in proper relationship. Your airplane has a preferred speed at which it flies and maneuvers best. What you want is a prop which will maintain that speed through maneuvers, accellerating while going up and braking while going down. Generally more diameter and less pitch is good. The Rascal is not a big airplane and the lighter you build it the better it will fly. My guess is that you'll like the 7 x 4, but one has to fly and try.

What you want is the airplane flying at its happy speed on lines of a length which gives a slow enough lap time that you can comfortably stunt the airplane, while providing plenty of line tension. Give me some RPM numbers on your props and I'll recommend a starting line length.

RE: Selecting propeller for stunt plane..
 

7x3 16400 rpm 0,227hp 1,94 Thrust Lb 46,59 mph
7x4 14600 rpm 0,213hp 1,54 Thrust Lb 55,30 mph
7x5 14000 rpm 0,235hp 1,41 Thrust Lb 66,29 mph
7x6 12800 rpm 0,216hp 1,18 Thrust Lb 72,73 mph

I am using APC propeller.

Jens Eirik

RE: Selecting propeller for stunt plane..
 

I like the 7 x 4 still. The RPM numbers are similar to a TD 09 as I run them with a Cox 7 x 3.5. You need a lap time around 4.5 sec. Slower is better, but small airplanes need to truck along to fly well. I'd guess 55 ft lines will be about right with the 7 x 4. From experience, not calculated. I think you will find that the higher pitch props will load and slow down in maneuvers. Anyway, it will be interesting to fly and try and see how actual flight relates to your calculations.

Are you building the Rascal from plans or the German kit?

RE: Selecting propeller for stunt plane..
 

Thanks... i am building from plan :)

Jens Eirik.

RE: Selecting propeller for stunt plane..
 

Props are cheap.

I hope you test fly the airplane with all of the props you've bench tested. And then tell us how each performed. What speeds did the airplane actually fly with each prop. And how the airplane speed varied in manuevers like the square 8 or just consecutive loops.

Control line offers an excellent testing environment for just such comparisons. A stopwatch is perfectly accurate to clock speeds, and almost any pilot can easily judge how an airplane slows down in maneuvers.

It would be really nice to be able to put some realworld test results into the thread alongside the theoretical data just listed.

I hope you will report back for all of us.

RE: Selecting propeller for stunt plane..
 

I would also try an 8x4 also.

RE: Selecting propeller for stunt plane..
 

In the plan: For 1cc use 35-40 ft lines, for use 1.5 cc use 40-50 ft.. Maybe 55 ft are a bit long lines, will begin first with 40 ft to be sure.

Jens Eirik

RE: Selecting propeller for stunt plane..
 

Jens,

I am not familiar with the Rascal and don't have an ASP 12 so take this with a grain of salt. Older designs sometimes suggest engines that were made many years ago and do not reflect today's engine power. For example, the fabled K&B Greenhead made ~.25 bhp, if I remember correctly. Those engines flew planes on 45'-52' length .012 cables. Today's engines are much more powerful.

You might want to fly on 45'-50' lines initially until you get the plane/engine sorted out...especially if it makes you feel more comfortable. My guess is that you will eventually end up flying on the length that Jim suggested.

Is the ASP 12 1.2cc or 2.0cc?

George

RE: Selecting propeller for stunt plane..
 

Better to be sure test the plane first flight with 40 ft before increase linelength to 45-50 ft. Never had the stuntplane before.. then i am very careful man. :)

ASP 12 has a totalvolume at 1.96cc, it is same size as OS 10FP.

Jens Eirik

RE: Selecting propeller for stunt plane..
 

I would suggest a small amount of fuel for first flight as the airplane will have a fast lap time and you will get screwed into the ground, so to speak[:o]. My TD 09's turn a Cox 7 x 3.5 at 14-15,000. On a Jr. Flitestreak, I was getting 3.8 second laps on 55 ft lines. Quicker than I can fly stunts accurately. I have an OS FP 10 which I have run on the bench. It runs like the TD 09.

RE: Selecting propeller for stunt plane..
 

Ok, i take a try with small fuel first flight and see how it works.. :)