Oct 05, 2006, 02:02 PM Registered User Thanks Gene...Sounds easy enough, but I know that when I installed a 5/5 on this plane didn't fly near as fast as the 8/4. Any chance a 6/5 or 7/5 would be better than say an 8/4 or 8/6?
 Oct 05, 2006, 02:36 PM Registered User Ahhhhh ......... Guru speaks wise words for all grasshoppers .... where would we be without him ???????
Oct 05, 2006, 03:00 PM
Quote:
 Originally Posted by thetriguy Thanks Gene...Sounds easy enough, but I know that when I installed a 5/5 on this plane didn't fly near as fast as the 8/4. Any chance a 6/5 or 7/5 would be better than say an 8/4 or 8/6?
The reason the 5x5 didn't give you any more speed is easily explained. Every motor is designed to turn a certain rpm. In the case of your bp-21 it's probably 1750 rpm/V.

If connected to a 3S lipo, that would give around 10V under load, your motor would turn 10x1750 = 17500 rpm. Without a prop.

If you add a prop, rpm will drop. Sometimes it drops to 80%, sometimes 60%, it depends on motor design and prop choice.

Let's say a bp-21 drops to 60% of 17500rpm on a prop, it would turn 0,6 x 17500 = 10.500 rpm.

The key to maximum perfromance is to choose a prop that, while turning at 10.500 rpm, loads the motor to just it's allowed max amps.

With the 5x5 that didn't happen.

In the case of the bp-21, that can take 13A, common prop choices are tested in these links:

https://www.rcgroups.com/forums/atta...hmentid=672938
https://www.rcgroups.com/forums/atta...hmentid=724984
https://www.rcgroups.com/forums/atta...hmentid=725157
Oct 05, 2006, 08:13 PM
Registered User
had a full size with bp-21 ....... it flew well, but ate up my 25 acre field in nothing flat. managed to dork it in, but just nose kinda squished in. was very fixable. however, i decided to build it at 80% of plan (18'' wingspan) and use a gb/bl /8040 prop/ 830 2 cell lipo. had my maiden this evening
as a lighter version, as well as smaller, it still has all the great flight characteristics of it's larger brother. glide is great ... slow speed flight is very good .... and for my size field it's still a rocket auw / rtf is 6.3 oz. with the 830 pack. thanks for the great plans

jer

# Images

 Oct 05, 2006, 08:44 PM “There’s no place like Foam” Well I'm certainly glad Jer "broke the ice" and changed something ... so I too can confess now .... Mine is a Profile ... full size though and seemingly very light .... built it as a chuck glider , but decided to "go for it"!!! So we're using the Guru's recommended 15t26awg/8x4/2slipo ??? Looks FUN , but already ...how do you launch it ??? My Dumb!!! PS ... skewer wing struts keep everything aligned..
Oct 05, 2006, 10:08 PM
Registered User
Quote:
 Originally Posted by gpw Well I'm certainly glad Jer "broke the ice" and changed something ... so I too can confess now .... Mine is a Profile ... full size though and seemingly very light .... built it as a chuck glider , but decided to "go for it"!!! So we're using the Guru's recommended 15t26awg/8x4/2slipo ??? Looks FUN , but already ...how do you launch it ??? My Dumb!!! PS ... skewer wing struts keep everything aligned..
gpw
you are correct on cd/prop/batt. the new plans i used have a longer nose which not only helps with balancing for lighter motor ..... but actually allow launch via holding by nose behind prop area. skewers are great ... used because i i have no wing bracing.

jer
 Oct 05, 2006, 10:32 PM Crash Master OK, Must be confession time I've been thinking 150% Slow Flyer for the upcoming indoor season! W/ Landing gear, of course. Probably double the elevon chord, and add a rudder, as well. We'll see!
 Oct 05, 2006, 11:16 PM Registered User landing gear would be a very cool addition
 Oct 05, 2006, 11:51 PM Use whatcha got! indoor season...??? Whats that hehe Oh... You must mean when it gets real cold... Like 35 degrees outside... brrrr I know what ya mean. I generally spend those days inside w/ a cup of coffee, building and complaining about the chill in my bones... hehe... sorry... had to...
 Oct 06, 2006, 12:16 AM Grounded in Arlington Tail dragger or tricycle gear, what do you think? Allen
 Oct 06, 2006, 12:46 AM Crash Master I'm thinking tail dragger. Tricycle gear gets too tall for my tastes it seems.
 Oct 06, 2006, 03:41 AM Launchpad McQuack I can make some scaled plans if you wish. 150% FFF 6mm taildragger?
 Oct 06, 2006, 08:07 AM “There’s no place like Foam” Now that we've cleansed our souls by confessing to Padre Prop-er, we can continue with the FUN ... 150% sounds FUN ... I thought my printer was acting UP again when I printed this one ... seemed small , looks huge online ...Build was quick , thanks for the plans and info .... and why does this remind me of the end of a Mel Brooks movie???? V, we PROMISE not to complain to you if any of our changes don't work out... I always dislike complaints about "mutations" hahahahahahaaha
 Oct 06, 2006, 09:56 AM Launchpad McQuack I too wasn't prepared for how small it turned out. 30" sounds like a decent size to abuse this funflyer. And Gene can mount a CDR for his indoor flying. Everybody happy. I hope to maiden my Duplex Delta on Sunday. My Himodel 282616 Brushless Outrunner 1611KV did WOT @ 10,14A on the APC-E 6 x 5,5. It makes a very racy sound.
 Oct 06, 2006, 11:12 AM Registered User Gpw, can you link this TOG for welding instructions used with the hot glue gun? New to the craft and still doing my research. Thanks guy. Scott