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question for ollie

Old 10-15-2002, 05:32 AM
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TexasAirBoss
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Default question for ollie

A friend built the diamond dust and put some screaming dubb jet 50 on it wi th a little prop. The manufacturer recommended the set up and advised him to expect speeds in the 240 range.
My freind also flys turbines and one Sunday morning we went to a nearby airport and my freind flew his tubine F16. Later that day we went to our model feild. My freind flew his diamond dust. I must say that the diamond dust was more impressive! I really beleive that the diamond dust was going 240mph.
How much faster do you think it can go?
Old 10-16-2002, 04:04 PM
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Cactus.
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Default question for ollie

1st i stoped believing these claims of 240+ from DD and such. too much shows a plane without some SERIOUS!!!! mods cant get close. however.... the turbine wouldnt have wizzed past your nose at 6' and is much bigger and smoother. this makes a big diffrence to how fast a plane looks. sit in the pits and watch a fast plane fly high, then stand on the flight line and have it go past eye level close in.
Old 10-17-2002, 01:07 AM
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Cajun
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Default question for ollie

My name is not Ollie, and I don't have his aeronautical intelligence, but what size prop was on the Jett, and what RPM was the Jett turning?

Just curious??

Cajun
Old 10-17-2002, 01:53 AM
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Default dubb jet prop

I'm not sure what prop it was on the dubb jet. I will say it was much smaller than the one we tried at first. I'll ask my freind and get back with the size of the prop. He called the diamond dust folks. We to didn't beleive 240 was a possibility and our original trial yeilded speeds that looked more like 150. We assumed that was that and the hipe wasn't for real. My freind called the DD folks and they advised him our est up was all wrong. In fact, they "overnite" delivered the correct props. Pow! Big difference. Since we had been flying turbines earlier that day I was used to seeing 200mph. This was every bit of 200mph and maybe more. If they say it was 240, I beleive it. I don't know if they used radar or if they timed it. We used thier set up and I would assume we would get the same results. And "NO", you do not fly a DD six feet away! They are pretty scary!
I would be suprised if any mods to the airframe could yeild any noticable gain in speed. Oh, the revs. Again, I will have to check, but I beleive he said in the mid to high twenties. However, he had to take off fairly rich with rpm's much lower than that. In the air it unloaded and really took off. In fact it leaned out several times before we realized just how rich we had to launch.
I would say that the limiting factor to the top end of the DD is the engine. Sorry I don't remember more. I'll find out.
Old 10-17-2002, 03:39 AM
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Default Re: dubb jet prop

moved
Old 10-17-2002, 04:22 AM
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Ollie
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Default question for ollie

I'm skeptical by nature. The only numbers I trust are those that are carefully measured with due consideration given to instrument calibration and error analysis. Eyeballed estimates can be way, way off. No measurement is complete without a probable error attached.

Back about 1980 some very talented Austrian machinists put together a plane called the Dassel, set up the required 150 meter course that the FAI required for a world record and proceeded to fly the glider through the course at about 250 KPH (~150 MPH) in both directions. At that speed it only took about two and a quarter seconds to fly the course. If one used human timers and stopwatches, how accurate would the measurements be if the reaction time of the human timers varied between 1/3 and 1/2 second? At any rate, the FAI at first recognized the world record but later had to withdraw their recognition when an error analysis was made. Very embarrasing to all concerned.

I've never seen a Diamond Dust fly. I believe they are very, very fast but I would not consider any claim of 240 MPH more than advertising hype until I knew all the details of how the measurements were made. What were the measuring instruments? How had they been calibrated? What was the wind speed and direction relative to the course? How was the course measured? Were passes through the course made in both directions? How free of parallax were the instruments' set up? Etc, etc, etc.

The pictures I have seen of the Diamond Dust show a plane that is loaded with parasitc drag. It's my intuition that the top speed of the Diamon Dust is limited by the RPM of the engine and the pitch of the prop in addition to the very, very high parasitic drag.
Old 10-17-2002, 03:32 PM
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Default question for ollie

i've seen a DD reach the top speed of the engine/ prop combo/ drag, it went as fast up as it did on the flat, yes its a nice thin section, but hell does it slow on the turns.
the Weston Magnum claims 200 mph, in real life terms even with the West 50, its touching that on dives if its all spoty dogs set up.
yes you do fly a DD 6' away, perferably 6" off the deck too. just have to avoid the darn electric fence battery the other side of the patch and those sheep. ever seen a 15 shrike jinx in and out of sheep? thats fun. anyway, what was the question again?
heres a speed graph to point the right direction.
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