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165cm frame with a 150cm prop


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Air Conception made a jump in the prop size. A Nitro XL. is exactly that. Same nitro engine but mounted to a 150cm propeller, using a 165cm frame. While it sounds huge its actually only 17.5cm wider each side, so not as drastic as it first sounds.

Thrust is up from 73kg to 80kg, economy is down to 2lph and less, noise is down, torque is unaffected due to special 600gram prop.


What do you think?

Will it catch on?

At first I was shocked but now I see it as a logical step, lots of benefits for what seems a little drawback of a larger frame.

Nitro Delta XL.png

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No, I haven't got one in yet. My synergy frame is 160cm and I didn't even notice it was bigger than 140cm AC frame till I measured it and put it side by side. 

As I said, my first thought was wow that's big, but I have come around to the idea. From shoulder straps down it would be about 92cm. 

The original test pilot is 1m65 tall and has no issues launching a 16m snake. His tests have managed below 2lph. I don't know what he weighs. 

I am 6'2" so well up for it. I'm pretty sure my next machine will have 150cm prop. Probably with electric start and a clutch.

Im told forward launches are fine and don't see why they wouldn't be. Eric has one on order and am waiting his views. 

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I would like to see a pic with a few machines though the ages lines up. From 90cm prop to 115cm to the 125cm then 150cm. That would be cool.

XL is not something I need at all but the idea of flying with low rpm just ticking along is appealing.

The large frame might be cumbersome or might be easy to live with, not in flight but for handling in and out of the shed etc. in flight it will all be behind me. The extra size actually makes it only 12cm longer behind my leg which should be fine as its a machine that sits high anyway plus im 6'2"

I have seen a pic with a guy wearing it who is the same size as the cage. See if I can find it.


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thats because the moster is running rich to keep it cool. The nitro runs well in the lower rpm, we have lighter and heavier pilots happily flying them. My on an XL is about the same as someone lighter on a 125cm prop. Still see if it catches on, it might, it might not. Credit to AC for leaping ahead with such a design which is a bit controversial / a little outside the box. Its interesting and helps move things forwards.

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Have some doubts about low fuel consumption looking at this table (not XL version), taken from the link below. Almost 9 litres per hour with 7900 rmp?!


4000 rpm = 2,25 l/h

5000 rpm = 2,66 l/h

5500 rpm = 3,27 l/h

6000 rpm = 4,80 l/h

7000 rpm = 6,74 l/h

7900 rpm = 8,57 l/h

Edited by Ivan
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Yes, they are from my website, genuine accurate and honest figures from a 130cm peszke prop. Fuel consumption recorded on an engine under thrust loads. Other engine manufacturers claims are not fully loaded or they just quote rpm and consumption at 30kg thrust, 30 kg thrust is not always level flight, that assumes a certain wing size. 30kg thrust is at about 4000rpm, which puts it at 2.25lph, I don't have that data to hand though.

I average 3.5-4lph on an average flight with 23m wing at 88kg pilot. I can get that down to 3lph just flying slow trims and keeping a constant height. My level flight is 5000rpm on 125cm prop

Jumping to a 150cm prop will get me down on that to nearer 2 lph.

Reports from other pilots range from 3 to 5.5lph depending on their weight and wing size. So although the high rpm shows high fuel consumption it is perfectly normal for a 190cc engine. If you think about the walbro carb, we are 1 turn out on low and 1 turn out on high, nicely balanced. Thats stock setting which I run, it can be tuned to 50min and 50min for economy. I then wonder what other engines are burning that run the carb 1+3/4 turns on high..

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