First, thank you so much for the feedback and answer, it really helps!bjt4888 wrote:InfiniCuber,
You have indicated that you are using the Ikara propeller that comes with the Freedom Flight kit (but you are not using the Freedom Flight kit airplane) and your best time so far is 1:40 with .091" rubber and I believe that your last question is about what other propeller you should try.
I would like to try to help you, but would only be able to give general suggestions unless you can supply more information. Supply this information with your question and you will get very good, very specific ideas: airplane design specs, motor thickness, weight and length and indicate if black rubber o-rings or sliced plastic tube o-rings, for the particular best flight: maximum turns wound into the motor, backoff turns, maximum torque, launch torque, turns remaining when the airplane lands (measure by de-winding on your torque meter), propeller pitch at a particular radius (measure it at the 3" radius), flight description (here is an example of a flight description: climbed quickly about 6' in the first circle then five more circles to the ceiling (21 ft.) at about 1:00, cruise about four circles then descending for about 40 seconds, calm air, smooth flight no stalling and flat wings with little or no banking, approximate 25 ft. circle size).
Knowing data like this and more about your airplane and airplane flight characteristics would direct you to the propeller, motor, winding, trimming variable that you could work with to try to gain longer flight times.
Here is a general suggestion though. The students I am coaching are having pretty good success by increasing the pitch of the Ikara prop that comes with the Freedom Flight kit to about 12" (32.5 degrees at 3" radius) if it is not already 12". They have measured pitch on about eleven of these propellers and they have found most to be like this: 8.5" pitch at 1.5" radius, 10" pitch at 2" radius, 11" pitch at 2.5" radius, 12" pitch at 3" radius, 12.7" pitch at 3.5" radius and 13" pitch at 4" radius. This is not ideal pitch distribution, but they are getting flights of between 3 minutes and 3:15 in a 28' ceiling site pretty consistently. They are having greater success with a propeller that was modified from the "wide blade flaring" Ikara propeller. The modifications are similar to those shown on the Cezar Banks Leading Edge plan and the Chris Goins Double Trouble plans (attached). The Leading Edge plan shows a wide bladed Ikara "flaring" propeller with the trailing edge of the blade from the propeller spar rearward removed to reduce blade area and improve flaring. The Double Trouble pland shows a blade thickness diagram for sanding the Ikara "flaring" propeller to make it flare better. Obviously, I am not recommending using the exact Double Trouble or Leading Edge propellers as they are much smaller in diameter to fit the SO rules from that year. I am recommending the blade area reduction (reducing the wide bladed Ikara, not reducing the already small bladed Ikara that comes with the Freedom Flight kit) and the blade thinning (but maybe not quite as thin as shown on the Double Trouble). Generally, wider bladed propellers that are truly flaring will require thicker rubber motors to get the very best duration. The amount or trimming, thinning and initial pitch setting will require experimentation and testing. Another route to higher performance propellers, of course, is to build a balsa wood bladed "bucket prop".
Bye-the-way, based upon your current duration results (not knowing your ceiling height), it sounds like you are not winding your rubber motor hard enough. See previous posts in this forum about winding technique and winding close to maximum turns (and about finding the best launch torque, etc.).
Brian T.
Now onto the info specifics:
I am currently using a plane with a V dihedral. The span is about 44 cm, and 8 cm rib. Stabilizer is about 24 cm with a 6 cm rib. The length of the plane is 42 cm. Using the 24 cm Ikara prop from FF, using 0.091" thick rubber, 35 cm loop (i just had regionals and used that) , used black rubber o-rings. Whole motor weighed approx. 1.95 grams. Best flight used 65 turns, backed off to 60 on a 15:1 winder. I don't happen to know anything about the torque as my torque meter has not come in yet. I also do not know the pitch, I do not know how to measure it haha! and Flight Description: It climbed relatively slow to a max of 20' (about) which took a good 30 seconds. Then it began coming down smoothly, no stalls, for the remaining 1:10. Hope that is enough info!
I am currently building a new version of this plane with a 50 cm wingspan and 30 cm stabilizer span, and longer lenght, although i am unsure about how long to make it..
As Far as props go, i am ordering the ikara flaring prop! So I will have to check that. And what do you mean not winding "hard enough"? As in fast enough?
I test in a tall gym with a ceiling around probably 20-25, sometimes 30 or more because its a dome.Thanks!
Brian A.
