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Thrust testing


pete_b
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I have tried the thrust tester today and have to do some feta-ling to get a finished product.

Simo jet

Simonini mini 2plus

GSC 48 inch 2 blade ground adjustable set for max rpm of 6500

Run at 6000 rpm (as above this it started to lift the thrust meter off the ground)=

60 kilos of static thrust

4500 rpm level flight on my reaction 27 fast trim, 20 kilos over max weight=

30 kilos of thrust.

More to follow

Pete b

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Like to thrust test my Flat-Top Pete. Will try to make P&P next weekend.

Anyhow. Made a breakthrough today with the Simo 200 economy drive. Leaned off the slow jet and flew for 2 hours 10 mins on just proud of 6-5 litres. Chrome by the exhaust manifold JUST started to yellow so it's as lean as it's ever been. As you know, I'm over 100 kgs and the Sky Atis 2 is a large but only 26 metres sq (flat) (23. something projected) We landed out at a mates for coffee so there were 2 lots of TO's and climbs and we fleew on fast trims most of the time. It was thermic on the way home but I didn't go out of my way to use it for gain, apart from 5 mins in my favourite therm at home, trying to climb on tickover. Standard 51 " carbon 3 blade prop.

Feel pleased to know that a porker like me can achieve 3 hours on a tank of petrol and have rakes of power when it's needed >

Dave

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I will make sure to get a working tester by next weekend just for you Dave :D:D

I found that setting a coarser prop setting lowered the static thrust but also lowered the rpm in flight so used less fuel.

I am sure that you don't need all of your static thrust to get off so you could lose a bit to gain more dynamic and more economy??

Pete b

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hi my worth here goes the fuel consumption is affected by the wing you use? i have a walkerjet simonin engine 125 prop and was on a edel atlas i know ancient but i went up for an hour the other eve and i barely used half a litre, i have condifered getting a newer wing reflex but having read the figures it makes me think i would be filling up all the time so its a shame they dont do a reflex that wasnt so greedy on fuel, as for thrust i dont have a clue what it kicks out but its plenty enough, if i was to upgrade my wing what would the recomendations be i want somethin that aint greedy but obviously safe also id like to get places on it the wing i have is dosey and slow

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hi my worth here goes the fuel consumption is affected by the wing you use? i have a walkerjet simonin engine 125 prop and was on a edel atlas i know ancient but i went up for an hour the other eve and i barely used half a litre, i have condifered getting a newer wing reflex but having read the figures it makes me think i would be filling up all the time so its a shame they dont do a reflex that wasnt so greedy on fuel, as for thrust i dont have a clue what it kicks out but its plenty enough, if i was to upgrade my wing what would the recomendations be i want somethin that aint greedy but obviously safe also id like to get places on it the wing i have is dosey and slow

Its dosey and slow because you have loads of lift.

you have to sacrifice lift for speed, speed = more rpm = more fuel.

What rpm are you running at to only use half a litre best Ive got at the moment is 3-4 per hour (on fast trim)

Pete b

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well this atlas is a xl max weight is 125 kilo i aint sure of revs to keep level flight but it is virtually tickover i am 12 stone and all up weight aprox 115 kilo with motor il say this i been out four times with my mate and i got half a tank left and i done a fair amount of flying he thought there was a leak on his when he flew about and used about four and half litre in the hour but sayin that he has a very little machine i must say tho if any wind i dont really get anywere i virtually go backward lol so i try to take it up in nill wind

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yes it does and it worries me im at i think just above 45 degrees when i lift on take off in to the sky i soon release the throttle slowly id like more infpr on this as i did worry about the stall point on it if we got say a 5 mile wind reverse launch and one step i am up in the air so i avoid if i can putting full power on, i have a action which i think i am gonna start flying il be able to fly in slightly windier conditions and feel safer i am ok ground handling it pretty easy to play with on the floor so i think i will start using that then watch the fuel consumption go up lol

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I have tried the thrust tester today and have to do some feta-ling to get a finished product.

Run at 6000 rpm (as above this it started to lift the thrust meter off the ground)=

60 kilos of static thrust

4500 rpm level flight on my reaction 27 fast trim, 20 kilos over max weight=

30 kilos of thrust.

More to follow

Pete b

Been thinking........may have this wrtong but............

thrust is a measure of linear force in kg. It derives from the mass of the air that is taken from infront of the prop and placed behind (mass flowXvelocity = thrust)

So if we measure the velocity of the air just in front of the prop multiplied by the swept area we get mass flow?

If that is correct (can be calibrated or verified using a wind meter against the thrust tester), then dynamic thrust can be measured by holding a wind meter in the prop stream whilst in flight and again with engine off at same trim setting to get the difference in velocity of the air at that trim under power and power off.

Does that make any sense?

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  • 2 months later...

I don't know about anyone else, but I'd sooner have max rpm and thrust available then tune it out for economy. I guess it depends on flight goals. I find myself in serious sink from time to time and don't really want to be propped out because I tuned it out.

for example:

As flown that machine registered 120lbs static and that was it. Most it would ever make with that redrive (fine winter rejets notwithstanding). Replaced the redrive with 3.1:1 per WJ stock and it added more than 30lbs to the total (my scale broke after that).

For me, the safety factor is worth it. For an XC high flier, adjusting prop or even a different redrive may be in order. It's all a balance after all, the redrive in that video would have the engine last forever and carbon up faster too, but it's a waste of the engine's capabilities without having the entire engine range available. Better off with a cheaper hirth f-36 (solo).

If money is no object, get yourself an inflight adjustable prop and have both.

edit: http://www.ultralightnews.ca/Ivoprop/inflightultralightmodel.htm

Anyone with a mini2 may have noticed that the simonini HP curve stops at 26, while they're advertised as 28. If your rpm doesn't match the top of that hp/torque curve, you're limiting your engine by redrive or prop. Not saying that's bad, just a factor.

I prefer to fly then run as well. :twisted:

Edited by Guest
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