NE0

My Feedback: (9)

chipm,

Awesome idea... I think that would be fun. I'll look for the info but may have to take you up on your offer. I used an article like that to build a custom balsa cowl on my FourStar and it turned out beautiful. Those articles can be quite helpful in custom mods and builds.

Thanks,

Neo

Henri

The guy is Jukka Pikkusaari and is absolutely the best scale builder here in Finland! I have been watching him flying his LA5, thats just awesome...

pittsdriver

My Feedback: (7)

Check out clarkindustries.on.ca and go to engines and scroll down about halfway. He is developing a gearbox that will turn a scale four blade Spitfire prop. Looks awsome! Don

Skeletor-delete

Here is a couple solutions I ran across on this website.

Pelle Gris

Hi all...

Here is my solution to the problem of too small props. It´s a 35cc Webra Bully with a homemade 2:1 belt drive, which hopefully will be able to swing a 24x16 3-blader at about 4000rpm. I´m currently in the finishing process of the drive, and only need to fabricate a working tensioner for the belt.
I sure hope that it will work...

URL: http://www.nuserne.dk/tinus/

Skeletor-delete

Oops..... I guess I didn't save the picture of the other reduction gear/engine set-up. It looked real heavy anyway...I'm building my plane to fly, but the more I get done, the more scale I tend to try to make it. (I haven't got to sheeting the wings yet so the urge for panel lines and rivets hasn't hit me yet. A scale cockpit is planned for, maby even a sliding canopy, I just read a post for a electronic gear door sequencer, I hadn't planned on using wheel covers but now.......)
I doubt I'll go to a reduction gear and 4 blade prop. They do make them with replaceable blades and adjustable pitch.

Someone please send me the winning numbers for the next Texas lottery.

Skeletor-delete

Pelle, awesome CAD work!!!!!! Just slot the holes for the secondary drive bearing mount for when the belt stretchs and the motor mount holes too. (to lower the assembly so the prop shaft is back where its supposed to be.) When I was a auto mechanic, a new belt would stretch a bit when it is new but once the inner cords are tight, they dont have to be adjusted for a long time, by then its time for a new belt anyway. James

Skeletor-delete

And!!!!!! If the driven pully could be machined in the design of a turbine fan, theres some forced cooling for the jug.


Un-employed Industrial Instrumentation Technician, looking for job as rocket scientist,,,, will work for model airplane parts.....

Pelle Gris

I already have made a prototype of the tensioner. It´s rather hard to explain, but it consists of a needle bearing mounted off-center on a bushing which mounts to the upper left screw holding the front frame in place. That way I can set the tension without changing the distance between the wheels. And when mounting it right it will try to tighten itself when the engine runs... hopefully....
But your idea of slotted holes might be another alternative. Didn´t think of slotting the engine mounting holes too, so I decided not to use that design, because it might offset the spinner.
If it works out I will start making a similar drive for my G-62. Would love to see it swing a scale 34in 3-blade prop on my upcoming 1:5 Typhoon project...

Pelle Gris

Oh by the way... would love to make the upper wheel lighter by machining it like a fan, but thought that it would be a little too much for my first try at metal working.. Maybe next time though...

HalH

My Feedback: (12)

There are a couple of factors that have not been mentioned.
1. Almost all warbirds have constant speed props that are variable pitch. Model props are fixed pitch .

2. Most warbirds don't operate over 3500 rpm. Model engines operate at up to 7 times that rpm. Even 4 stroke engines run 2 1/2 times that rpm.

Forgues Research

My Feedback: (7)

For scale props, you don't increase the size of the engine, but rather reduce the RPM on the propeller via a prop drive.

Here is an exemple.

Forgues Research

My Feedback: (7)

Here is another Hamilton standard

Forgues Research

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Here is one for the ZDZ 40

F106A

My Feedback: (2)

Grampi,
I think you're talking about the all aluminum P-51 that was advertised years ago. He had great ad's that showed the "progress" of the prototype. It was to be powered by 4 (I think) 120 4 cycles.
He took advance deposits and after a year or so, guess the deposits dried up, ran off with more than $300,000, never to be seen or heard of again.
Jon

Skeletor-delete

Pelle, yep, that will work. A lot of import engines with a belt driven overhead cam shaft use a offset center bearing for a belt tensioner. Look at the pic I posted above, of the G-62 belt reduction system. I dont think that toothed belts like that one stretch very much. V-belts will stretch. I think that even if the belt on the reduction system above did stretch a bit, the centrifugal force will keep the teeth of the belt in the groves of the pullies.

Nice CAD work!

hehehe

I have Turbo CAD and am just learning to use it.
Best of luck, James

Skeletor-delete

One more thing, the variable piched props I mentioned are a fixed pitch in use, but adjustable on the bench.

Pelle Gris

Skeletor, Where do you get those props? I´m a little unsure of how to determine what prop to use, when using a belt drive, and would rather not have to buy 20 different props of these sizes.
I don´t know if you noticed the screenshot at www.nuserne.dk/tinus ??? According to this program my Bully will be able to swing a 24x16 3-blader at about 4000rpm.... just don´t know if it´s that easy.
Also... would a 24x16 3-bl @ 4000rpm provide the same thrust and speed as a 24x8 3-bl @ 8000rpm?????
I have read somewhere that large slow revving props are more efficient than smaller props at high rpm...
Any thoghts???

aerografixs, Cool pics of the scale props.... do you know where one might get one of those???

BTW... I´m not using AutoCAD for this drawing, as I find that 3d is VERY much work with this program... Instead I use Rhino3D v1.0... Much easier to use...

Forgues Research

My Feedback: (7)

I don't have the coordinates for the propeller reprisentative, but I can tell about the Mustang prop in the picture, it is with a ZDZ 80 and the whole thing cost $1700.00 USD Not cheap

Damnathius

I'm with ya grampi...

As for swinging big wood, there is also the RCV line of 4 stroke engines. Where else can you get a 120 4 stroke that will swing a 24x8 woody at 4400 RPM and produce gobs of thrust? Perfect 1/4 scale WWI fighter power. I'm guessing it would work great for many WWII Scale fighters as well, spinning 3 and 4 blade props of the correct diameter.

I guess my outlook is that if I can't fly with a scale prop on a particular plane, I'll fly a different plane. Tiny props are just... Wrong!

JoeEagle

My Feedback: (26)

Pelle:

can you tell us where we can locate the program in your previous post that you have used to calculate prop thrust?

thanks

joe


ps, hi roger!

Forgues Research

My Feedback: (7)

Yo Joe, did you get my E-mail???

FalconWings10

My Feedback: (4)

Almost all warbirds have constant speed props that are variable pitch. Model props are fixed pitch .

This is it in a nutshell. Full size pilots are (were) able to vary the pitch of the prop which allowed them to optimize the torque and power of the engine. Model props are fixed pitch!

Pelle Gris

http://www.gylesaero.com Here you go... I dont see the "Extended Prop Selector", which is what I use for download, but I´m sure that the basic version will be enough for most people.

Captainbob

My Feedback: (4)

I see a lot of iinteresting comments here. some way off base others coming close, but none have touched on one important fact.
Actually the problem is the same in full scale aircraft as it is in models. Did you know that all full scale airplanes of the high horsepower variety, that is, have to use a gear reduction drive to swing a big prop! If these aircraft coupled the propeller directly to the crank, guess what, they would all be swinging tiny, silly looking, props.
If modelers could afford engines with reduction drives then more manufacturers would be building them and we would all be flying scale diameter props.
As a scale builder and flier for 40 yrs I empathise with you all but let's not make the problem more dificult than it is.