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Is anyone else having really unseasonably poor weather like in Western Canada?
We just had one of the coolest and wettest Junes that I can remember and the first week of July is not much better. In my last four trips to the field where I practice IMAC (an hour away) I have been rained out three times! Yesterday the rain held off and I did get a few flights in. I continue to test propellers. The Xoar 27A is not the right propeller for the Hacker A100-10 (on 12 cells) (at least for IMAC flying) as the overall speed of the plane is too slow. After one flight I installed a Xoar 27x10. This seems OK for power and I was putting back in around 3500 mAh in the 5800 mAh batteries after two sequences of the Sportsman routine. At the last contest I flew with the 27x12 but I found that I was using a bit more battery than I was comfortable with. I think that the 27x10 might be a bit more efficient. This week I will reinstall the A100-8 motor and test with the Xoar 27A propeller. |
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Last edited by Geoff Dryer; Jul 04, 2010 at 12:02 PM.
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I have the Hobby City 80-100-130Kv on my 33% Sukhoi running a 27x12 Xoar. I expect that their recommendation of a 24x12 is probably correct. |
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yeah, on their website they are not very specific about the stats of the motor, so thats why i called them. i had talked to them on the phone, and while they didnt give me exact stats on the motor, they did give me some data they got when they ran it. They are using a 24x12 on 12s and are only pulling about 90 amps WOT. he said they do most of their flying at only 30-40 amps. he sounded overly optomistic on the phone that it would handle those props very well and still not stress the motor very much.
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I have now done some tests with the Engel 28x14. Flew two rounds in an IMAC competition last week-end with this propeller, with the motor set up to 6200 rpm max. (Full power is about 6700 rpm on 15s, but I wanted to compare to my "normal" rpm with the Mejzlik. The load on the Engel 28x14 is very similar to the Mejzlik 26x15E, I get almost exactly the same current and static rpm.) The static pull was probably comparable to the Mejzlik, but the flying speed and performance was definitely not as good. It was also noticeably more noisy. Quite (actually very) windy condition. Switched back to the Mejzlik 26x15E, and found this to perform much better in flight. (It was commented on how well my model was able to penetrate in the wind, and keep the flying speed up.) I think electric motors give us the option to operate much higher pitched propellers than what is normal with gas engines, and I believe this is an advantage in IMAC. Look at the developments in electric pattern (F3A). 5-6 years ago a lot of people were flying big diameter propellers with relatively low pitch (e.g. 22x12) while now people are generally using higher pitched propellers (13-15" pitch is quite normal) Regards, Magne |
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The interesting thing about sound is that I was given a few 5s (10 is normally given to quiet planes) for sound at the last IMAC contest. I found this perplexing as the most noticeable component of the sound is the wind noise! I guess a few of the judges prefer the sound of a DA-100 on standard mufflers. Do you have any pictures from the IMAC contest? |
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Hi Geoff.
Sorry, I did not take any pictures during this competition. But we generally fly the same kind of models here as you do "over there", and they are generally produced in the same place. There are however some pictures (from various events) on the Norwegian IMAC internet site, (Norwegian language) look under "Galleri". This site is new and not yet 100% up and running. http://www.imacnorge.no/index.html Interesting about your sound score. Because we are not all that many IMAC pilots in Norway, we have decided to only run the Basic, Sportsman and Intermediate classes, although we may start running the Advanced class next year. I was flying in the Sportsman class and judging the Intermediate class. One Int. pilot was flying with a 3W 112cc 4-cylinder engine, nice and quiet engine. I gave him 10 pts. in the first couple of rounds. (But he has engine problems and decided to run at much higher power "on the flats" in the later rounds, and was put down to 5 together with the rest.) I flew the only electric model there, and got 10's in all rounds. There is a noticeable noise difference between the Engel 28x14 and the Mejzlik 26x15E propellers, not quite sure why. But as long as the Mejzlik also gives the best performance, I will continue to use that propeller. Due to the high pitch, I can run at fairly low rpm's on the flats, and only go to high/full power in the uplines. Even penetrating against a strong headwind is no problem at a moderate throttle setting. That helps in the overall noise impression. The Mej. 26x15E would definitely be too much load for your 100-8, not sure about the 100-10. I am operating at about 6100-6200 rpm for 8500W. (Full power is 6750 rpm and 11.6 kW, more than I need or want.) Has anybody tried the Biela carbon propellers? They have some coarse pitched propellers, such as 24x14, 26x14, 26x16, both 2 and 3-blades. (Not thin electric, though.) (I am a firm believer that high pitch is the way to go with electric IMAC models.) Magne |
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Last edited by Magne; Jul 06, 2010 at 03:13 AM.
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I had not even heard of the Biela brand. I notice that Chief Aircraft sells a few sizes. Thanks for the information.
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More Testing
I managed to sneak out yesterday afternoon to practice for this weekend's IMAC contest. I had reinstalled the Hacker A100-8 motor.
After 1 flight with the Xoar 27A I determined that this is not the correct choice. Motor and batteries were noticeably hot and I put back in an average of 4100 mAh in each of the 5800 mAh batteries. (2 sequences of IMAC Sportsman) For the rest of the day I ran the Xoar 24x12 propeller. Based on an average across 4 flights I put back in an average of 3200 mAh into each battery. My previous testing with the Hacker A100-10 and the Xoar 27x10 propeller used an average of 3500 mAh So.... My latest opinion is that the Hacker A100-8 and the Xoar 24x12 works best for me. I base this on battery efficiency and overall power. I also find that this combination flies smoother (easier throttle management) than the A100-10 and 27X10 combination. |
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Another IMAC contest last weekend. It was a well attended event with 14 pilots in Sportsman. No issues with the Extra (covering stayed on this time) and I managed a mid pack finish. I really need to practice more!
It was really warm this weekend mid 80s F (30C) and I noticed that the batteries did warm up more than I like. I am going to drill a few more cooling holes in the firewall this week to create more airflow over the battery area. |
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I'm very surprised that the 24x12/100-8 combination pulls this 35% plane around with such high efficiency.
Possibly there is a prop that would equal the efficiency on the 100-10, but it gets very expensive collecting so many props to test. In the end if it flies well and the numbers look good is all that matters. Kevin |
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New Modifications
I decided to try and improve the airflow over the batteries. My good friend Gerry was able to cut some plastic pipe into scoops. I epoxied them in place. I also added some new holes on the front of the firewall. Hopefully I will get some practice in this weekend.
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Yesterday I returned from flying at the Pacific Coast Freestyle Championships and American Aerobatics Grand Prix in Mollala Oregon. This is the biggest IMAC event in the NorthWest Division and the venue that draws the best Freestyle pilots. The event is also an excuse to camp out for the entire week. The contest is setup a little different as the Basic group fly on Thursday and the rest of the classes fly on Friday and Saturday. All day Sunday is the Freestyle contest.
I think there were around 60 pilots and at least 6 Hangar 9 260s. I was not the only electric plane as there was a 50cc class electric that flew in basic. My plane was flawless but unfortunately my piloting skills were not. The new cooling ducts seem to help to keep the batteries a little cooler. The biggest story of the weekend was Kyle Woyshnis destroying his famous plane "Patches" during the 3rd round of the Freestyle competition. RIP Patches |
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Last edited by Geoff Dryer; Aug 02, 2010 at 07:17 PM.
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Hi guys,
I just maidened my 35% H9 Extra (electric) this afternoon. I was taking a year off flying for travel and fitness, but was back on a mission this fall to get this plane in the air! Plettenberg Predator 30/8 on 14S/10Ah, Engel 28x14 prop (also have a Mejzlik 26x15 electric but I need shorter bolts to mount it), AUW 30lb 6oz. It pulls ~196A on the ground with full packs. I flew a short (5 min?) flight with the idea of seeing if the wings were going to fold on me or not (they didn't - I pulled +ive and -ive G but no snaps yet). Put 2800mAh back in on today's flight, which did include one long upline where I gratuitously used full throttle. Full throttle is never, ever necessary on this plane as currently set up. I need to prop down. I'm hoping the Mejzlik 26x15 might be more efficient, as power is well in excess of requirements and good flight duration is more of a concern. Over the winter I'll get a custom motor mount built from aluminum and that should shave off enough I hope to get it under 30lb AUW. Some guys were shooting video so hopefully will have a link sometime next week. In the meantime there is the ground test and motor runup from last week: http://www.bottomlinestudios.ca/Site...a_Testing.html |
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