How do folding and non-folding props compare?

[R Shackleford]

I'm thinking in terms of efficiency and performance in general (excluding obvious gliding advantages). In particular, I'm interested in the larger (10" +) props. I'm not really interested in what software like Motocalc has to say. I think people's real world experiences are more useful.

I have a Graupner CAM 10x6 folding prop that I'm about to use for the first time. Yes, I could just do a comparison for my self, but my plane is a belly-lander and a folding prop is the only option unless I put the landing gear on.

I'm just wondering if there would be any noticable differences between folders and non-folders. For example, Graupner folding 10x6 vs. Aeronaut non-folding 10x6. Is there some general rule that the folder will not be as good?

[Ollie]

Originally posted by R Shackleford
Is there some general rule that the folder will not be as good?

The short answer is no.

The long answer involves considerations of differences in airfoil, blade shape, etc. The long answer recognizes that the nominal specifications of diameter and pitch are not enough to cover other factors affecting performance besides whether the prop is a folder or not.

Modification of the airfoil of a Graupner 9x6 folder used on the Alegro E-lite results in noticably improved performance. This fact establishes the need to make the props you are comparing the same except for folding to establish whether folding is important to performance or not.

You can make any folder into a nonfolder by simply locking the blades so that they don't fold. I think your experience will be that there is no noticable difference in performance between the folder and non folder versions of the same prop. Differences in performance are due to other things besides the question of whether the prop folds or not.

[DaveGherardini]

Graupner has some Cam slim props in the same size non and folders. I have tried a straight Cam slim 8x4 and then tried a folder cam 8x4. the plane i was using(high wing motor glider/old timer self design) the solid prop performed better. But when comparing the visualy they were still to different to make a good comparison. The folder has more benifits on this perticular plane as there is no landing gear and throttle off drag is less. The application and preferance makes the decision for me. But when im looking for speed i use a non folder. I have built some folders for gear drives in the 5:1 range from topflight power point 10x6 wood gas props. Excellent props for folder conversions but really cant give them a fair comparison because after the mod the folder version comes out 10.5x6. But amp draw was the same and no noticeable differance in performance. Here is a pic of the gas wood prop widdled into a folder. I dont recomend making one of these unless your very patient.

Dave G

[heli frapper]

For folders I personaly only use Aeronaut carbon 6 to 17 inch size

ridgity of foil not flatening out under loads which happens with cheapo plasic types means that I seem to get nearly the same preformance with folder as compared to fixxed


That wooden prop is interesting is it possible to have another photo with spinner off to see the holding system

I am trying to make a home brew 5*5 or 4.7* 4.7 for 30 to 40k rpm that is foling up for my pylons with kontronik 480 5500 and hacker bl40 wi s 3600

would be willing to use wood if its strong eneough

These cam fixxed break every two three flight on landing

Stephen

[DaveGherardini]

Stephen, Heres a better pic. I have not run this prop over 5k rpms. I used this one for a S300/ 5:1 GB. I was suprised that it out performed my APC TE props. This project was alot of fun to. The spinner is a Graupner soild plastic.. Not the best but was adequete for the low rpm's. Best of all, I buy these wood props for 2$. I spend about 20minuites converting it. Not that price matters but it is real cool. I had a couple guys tell me they thought about buying those Top flight wood folders but decided to go with Graupners as they were better...I got a chuckle out of it and agreed with them. heheheheeee... But anyways if I can help in any way just ask..

Dave G

[Ollie]

Centrifugal force puts a shear load on the short grain of the wood between the butt of the prop blade and the pivot screw. Maple has a shear strength with the grain of about 1800 PSI. It looks to me like the prop will fly off when the centrifugal force is around 80 pounds. Allowing for a safety factor of two, I wouldn't load the prop beyond 40 pounds of centrifugal force. I am sure that the prop will fail long before 40,000 RPM. The centrifugal force is mass times velocity squared divided by the radius of gyration. This will not be easy to determine because the radius of gyration depends on the mass distribution of the blade. Taking a SWAG at the radius of gyration as 3.5 inches, the circumference is about 22 inches and the velocity in feet per second is 22/24 times RPM divided by 60. The mass of the blade is the weight in pounds divided by 32. Assuming a blade weight of one ounce I don't think it would be prudent to run the prop beyond about 16,000RPM. If my estimates are off even 16,000 RPM may be too high.

[DaveGherardini]

Ollie. Each blade wieghs 6 grams. But should you include the weight of the sipnner and the bolts? Spinner assembly is 14 grams. Thanks for posting that equasion(man i suck at spelling).
I was shocked that the blade might be safe at 16k rpms. Thats about twice what i figured. I was also amazed that the prop in static would fold forward about 15 degrees. I didnt get the stops built correctly to keep the blades perfectly parrellel. But when its swing fully loaded the blades are parellel. I figured that it was because the centrifical force was way more than the thrust pull. And as you have shown me it was a correct asumption. Good stuff there Ollie, Thanks agin



R Shackleford, I apolligise for getting of the isssue but im learning something interesting here. Which agin proves that folding has nothing to do with efficiency when comparing identical props.

Dave G

[sayno2glo]

OT
heli frapper,

You should boil your cams for few hours instead going to folders. Those can be dangerous. Boiled cam props doesn't break easily they just bend and after little while they are okay.

[heli frapper]

Thanks for the info

Been traveling last few days just got back

Now lets see a little bit of salt a tad of pepper let simmer for 20 minutes and viola lunch is served BOILED CAMS

Just kidding but I will try this on my 10 pack of cams (cheaper by the dozen broken two all-ready this week)

However where I use my cams for fast level flight I need to use folders for the same planes for slope soaring saves me changing planes or engines if the slope mood grabs me

The planes slope ok with fixxed props as they are quite small and dont cause too much drag but it needles me so sooner or latter (unless some major manufactuer makes them to take 30k plus) I will have to start making them

I liked the idea of wood as it is still lighter than carbon or plastics

I think possibly a carbon molding insert made to fit wood into with epoxy to glue in root might just work as 5 inch prop blade might weigh a good bit less but will do some calculation with my trusty texas 99

Thanks Stephen in europe