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Old 12-31-2012, 01:06 AM   #1
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I added a brushless combo to my harbor cub the prop is a 7x6 that came with the combo. Today I broke off the tip I have a 7x4 apc prop. What would be the difference in how the plane will fly with the 7x4. If i'm thinking right the 7x4 will not move as much air & the motor will turn a little higher rpm.
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Old 12-31-2012, 01:20 AM   #2
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Originally Posted by hangingon View Post
I added a brushless combo to my harbor cub the prop is a 7x6 that came with the combo. Today I broke off the tip I have a 7x4 apc prop. What would be the difference in how the plane will fly with the 7x4. If i'm thinking right the 7x4 will not move as much air & the motor will turn a little higher rpm.
If I am thinking right (I am NOT one of the power gurus) it will fly slower top speed but should give you more zip off the start. Think of it like downshifting for more torque. I might be corrected soon, so stay tuned!

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Old 12-31-2012, 01:53 AM   #3
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Originally Posted by xuzme720 View Post
If I am thinking right (I am NOT one of the power gurus) it will fly slower top speed but should give you more zip off the start. Think of it like downshifting for more torque. I might be corrected soon, so stay tuned!
Spot on.

Lower speed, less power consumed. It should work pretty well but won't fly as fast and it will use less power.

Mike
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Old 12-31-2012, 01:57 AM   #4
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I don't go full throttle any way so if I lose a little top speed that will be ok. What went wrong is I switched from my E-flite LP5DSM to DX6i elev & rudder were rev. so I went to go up and oops! I changed the settings and took off it still would fly I didn't see the tip of the prop till I landed.
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Old 12-31-2012, 01:59 AM   #5
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xuzme720 is quite right
But also remember the 7x4 will absorb slightly less power overall so although the static thrust may be the similar to the 7x6 the effective thrust will fall off more quickly as the speed rises.
The positive side is with the reduced power available you should get slightly more endurance!
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Old 12-31-2012, 02:01 AM   #6
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Thank you Mike less power used means more flight time sounds like a winner to me. This plane came with a 380 brushed motor so it has more power than it needs with the brushless.
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Old 12-31-2012, 02:16 AM   #7
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Thank you all ! you have been a big help. I had bought the APC prop when I couldn't find the stock prop which was a 7x2 which is thinner and less weight then the APC 7x4 the brushed motor didn't have enough power too spin the 7x4 so I have 2 of them setting around. I'm sure the APC's are better than what came with the combo. You can feel the difference in the 2.
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Old 12-31-2012, 09:39 PM   #8
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Originally Posted by hangingon View Post
I don't go full throttle any way so if I lose a little top speed that will be ok. What went wrong is I switched from my E-flite LP5DSM to DX6i elev & rudder were rev. so I went to go up and oops! I changed the settings and took off it still would fly I didn't see the tip of the prop till I landed.
That has happened to all of us, rev controls, here is how to avoid that from ever happening again, put the plane on the ground in front of you, pointing away from you, check all the control surfaces for proper operation before taking off, do this every time you go to fly, even if you know the controls are ok, get into this habit, and you will never take off with the controls reversed again, its a good habit to have Take care and have fun, Chellie

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Old 01-01-2013, 12:26 AM   #9
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Chellie thank you. I learn each time I go fly something new be it good or bad. The main thing I have learned is I enjoy the planes better than the heli's their easier to fly and cheaper too repair. If I had it to do over I would have used the money I spent on heli's for a better plane. I know no matter how long I fly and How well I improve I'm still going to crash & I can't afford to crash the mini titan Still in the hovering phase with the mini titan has cost me around 200.00 in 3 crashes plus the 450.00 for the heli. That money would have been enough for a few good quality planes.
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Old 01-01-2013, 08:35 PM   #10
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Originally Posted by hangingon View Post
Chellie thank you. I learn each time I go fly something new be it good or bad. The main thing I have learned is I enjoy the planes better than the heli's their easier to fly and cheaper too repair. If I had it to do over I would have used the money I spent on heli's for a better plane. I know no matter how long I fly and How well I improve I'm still going to crash & I can't afford to crash the mini titan Still in the hovering phase with the mini titan has cost me around 200.00 in 3 crashes plus the 450.00 for the heli. That money would have been enough for a few good quality planes.
Yea, helis are a money Pit I started off with a Piccilo heli, that was fun, then i bought a 400 size shogun ( Wakera 36 ) from hobby people, i should have got the Trex 400 its a better heli, but i was being cheap and did not know any better at the time I learned to fly simple circuts with the shogun, and stopped there with helis, but now I am back into helis, again I am being cheap I bought a 450 Trex clone from Hobby King for like $27.00, bought some used digital servos, bought a cheapy $13.00 motor, I am building this heli for under $100.00, so if i crash it, i am not out a lot of money its just to get some more training with a heli and not going broke doing it I can buy another heli kit for $27.00 for spare parts its a nice kit too, good enough for me to get some more Training in with, before i try to fly my 30 size Swift Heli Take care and have fun, Chellie




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Old 01-01-2013, 08:50 PM   #11
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Originally Posted by hangingon View Post
Thank you Mike less power used means more flight time sounds like a winner to me. This plane came with a 380 brushed motor so it has more power than it needs with the brushless.
Actually, it wont necessarily give you better flight time. The thing with finer pitch is that to move the model fast enough to fly then the prop needs to spin faster (like the engine of a car in low gear). To spin the motor faster requires more throttle, more throttle tends to flatten your battery quicker.
Think of the car again; would you get better mileage by driving in a low gear with the engine screaming

In reality what prop is most efficient is very complex and depends on many variables but as a rule of thumb for average models you want to look for a pitch/diameter ratio of roughly 0.75, give or take. So for your 7" prop a 7x5 or 7x6 should be a good option. 7x4 is a little on the fine pitched side and might be less efficient.

Steve
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