speed – Radical RC Workbench

Customer asks a good prop question with implications…..

Hi Dave,

Quick question about the APC props. I note that for multi-rotor the sizes seem to be with 4.5 pitch. Is there a reason why I should not use say, 9×6 with 9x6R for multi rotor craft?

Thanks
David

Answer:
Hovering props or props that produce best thrust in static air tend to be pitched about 1/2 of diameter or less. As you add more pitch, they can fly faster, but have less bite in static air. They can actually be stalled and have less lifting force until the prop gets to moving forward. This is also why props which are the same otherwise make more noise with lots of pitch. Initially they are stalled or partially stalled. So, if you need more prop than a 9-4 to apply the power to the air you have available in your system, you go to 10-4, not a 9-6. Certainly a 9-7 would be such a bad choice as to be worthless.

All this is considering the model is essentially hovering all the time. Even forward flight isn’t quite as forward as an airplane. Other types of flying and machines can have other considerations that make higher pitch (relative to diameter) correct but this is unlikely in all multi-rotors except maybe a racer.

What we call these props is 1/2 square. Meaning pitch is about 1/2 the diameter. A pattern aircraft or war bird might use a 3/4 square (like a 10-7 or 11-8) or even a square prop (like 12-12) because hovering is not a required and speed is more desirable. These setups are poor on hole shot, but once they get moving they really go.

Dave
Hi Dave,

Quick question about the APC props. I note that for multi-rotor the sizes seem to be with 4.5 pitch. Is there a reason why I should not use say, 9×6 with 9x6R for multi rotor craft?

Thanks
David

Excellent Podcast: The Stratosphere Lounge – Speed and Angle

I’ve got some mixed reasons for liking this guy and his podcast. He is an avid aviation and space buff. He’s also a science fiction movie buff. Outside of this show, he’s a commentator on maters of liberty. His show “The Stratosphere Lounge” contains some of that but has a lot of personal interest content.

After a short housekeeping talk about his recent videos, he covers his experiences with full scale engine failures and emergency landings, full scale sailplane experiences and idiots promoting train service over cheaper faster existing air service. I’m not against trains, the conversation is an interesting tie in to aviation. This episode contains good aviation related stories and thoughts.

This show’s format is a live recorded UStream video/audio where he’s commenting on live chat and whatever else is on his mind. Clearly a more personal project for this professional.

The Stratosphere Lounge has bubbled up among my favorite online radio/tv shows to take in. Who needs cable?

Great Shock Wave Video With Narration

Video by AVweb.com.

“How much I love Radical RC… also Mini Stick fun…”

“Greetings…My name is Mitch, and I’ve been doing business with you folks for the better part of this year. I’m fortunate enough to be able to drive a short distance to the RRC shop. Ever since my first visit, you folks have treated me to fantastic prices, and best of all, priceless advice and knowledge. I live on a disability income, due to a severe back injury, and even despite my limited amount of money, I’m still able to have a fulfilling hobby due to the affordable prices you are able to pass onto your customers. It also helps to have Dick give me his opinion, maximizing my bang for my buck.

I’ve built a RRC intern trainer which was my 2nd RC aircraft, and I’ve just recently upgraded to one of your mini sticks.

First of all, your laser cutting is fabulous. It’s enough to spoil you if you have to go back and build a traditional die-cut or even scratch built plane. Its true, you can actually frame up nearly the whole plane without a drop of glue. The supplied balsa is light and strong as it should be for this ship. The magnet wing hold down is simply genius, and makes battery swap outs painless and quick. Instructions are clear and concise, but once you build one Radical RC kit, you probably won’t need them much honestly. =)

The mini stick is running a Radical RC CDROM brushless motor (1000KV) on a Castle Creations Thunderbird 9 amp speed control, plugged into a Berg 4L receiver. I’m running 3S 800-1025mAh lipos in that little plane, and the performance is fantastic. The 1025mAh pack just BARELY fits in the fuselage, but once it’s in the air, the added weight isn’t very perceptible amazingly enough. With 3 high capacity packs like that, you can fly until your thumbs wear out! I’m no expert pilot or anything, but it’s an absolute riot to flog this little thing around the sky, and with its diminutive size, its opens up a lot of opportunities for new places to fly. The little outrunner swings a 7×6 prop, and it’s not outrageously fast, but it’s got straight up vertical, and will anxiously climb out from just about any attitude. 3 GWS Pico BB’s servos are a nice match for the control surfaces.

My next project might be another Mini Stick on the opposite end of the spectrum. A 12mm inrunner turning tiny props at super high RPMs for ‘blink-and-you’ll-lose-it’ supersonic speed. =)

All in all, I just had to say thanks for all your hard work and dedication to this hobby. I am blessed to be able to know you guys and do business with you.

P.S. I call dibs on the double-size Intern Trainer if they ever make it to production!”

“Mitch”

September 2008

Bob Aberle writes:

“Dear Dave, Just a follow up to our meeting at the recent NEAT Fair. By the way the January 2002 RC Modeler will have the first published report of our NEAT Fair. Dates have already been set for next year; they are Sept. 13, 14 & 15, 2002. Hope to see you there again.

My reason for contacting you, at the Fair I purchased an 8 cell 720 MAH Sanyo NiMH battery pack from you. I just used this new pack the other day with excellent results. In my application I’m drawing 5.3 amps (at the start) on a Speed-300 motor geared 5/1. First flight was almost ten minutes with the motor running at full throttle the entire time. After landing the battery was only mildly warm. I have been fast recharging this pack at the field at 1.4 amps which takes an average of 30 minutes to reach a full charge. Do you feel the 5.3 amps is OK for these cells? I’m very impressed with the performance.

Bob Aberle
AMA 215
NEAT Fair
Event Director

Yes, they can take constant drains up to abut 6.5 amp range very well.”

October 2001