Given that the original had a wingspan of 9.46m and a length of 12.13m (L-59: 12.20m), whereas the model has a wingspan of 120cm and a length of 132cm, the scale is approximately 9.46m/1.20m = 7.9 :1 .
Of great relevance of the overall fan efficiency, defined as
efficiency = (mechanical work done per unit time) / (input power) , in e.g. (N.m/sec)/Watts
A good substitute for the above quantity is, based on simple formulas relating work to fan thrust and fan efflux:
efficiency = (const.) x thrust^(3/2) / (input power)
You would imagine that if somebody is really serious about designing an efficient fan they would take the time to actually do relative measurements of different designs, in order to figure out which rotor/stator design in the end is best.
Indeed that is how serious fan designers (eg WeMoTec, Daniel Schuebeler etc.) indeed do it ...
But then often a new design comes up (nowadays every other week, in some cases a copy of somebody else's rotor, with one blade added or subtracted so it don't look like a copy ) - without any clear measurements of anything.
If it is a clear shameless copy of a DS-51 fan, then it has to be as good as the DS-51, right ?
Then the relentless overhype follows ("20% more efficient than anybody elses fan'" - to the point that now the overall efficieny adds up to 110% ), and more adverts such as "best fan I ever tried in my xx" etc.
Now, the Jetfan 90 data is interesting and accurate enough to pull out :
1) the relative efficiencies of different motors in the JF
2) the very slow rise of efficiency with power/voltage
3) the large errors inherent in all these measurements
4) the wide spread in motor efficiencies (up to 31%).
The museum is located within a large airport in the Bourget suburb of Paris, and is the site the Paris Airshow (which takes place usually in June).
It has an amazing collection of - what else - French (mostly Dassault) jet aircraft, including some weird looking experimental aircraft, but also Montgolfieres, some very early 20-th century planes (Bleriot), some very nice WWII warbirds (including a FW-190A and a Spitfire Mk. IX) and two Concorde.
The model's wingspan is around 55.9 inches, the length around 55.5 inches.
The original Sabre had a wingspan of around 37 feet, so that gives the model a 1:7.9 scale.
I entirely glassed the foam airframe using multiple layers of 3/4 oz glass cloth & laminating epoxy.
Now it flies on a 90mm fan on 9S lipos (4000mAh 40C's) at ca. 2900 W.
Weight rtf is around 8.3 lbs, so it's rather lightweight for its size - but nevertheless still reasonably fast and jet-like.
Posted by Herb |
Oct 21, 2007 @ 02:06 PM | 43,629 Views
Beautifully molded FG fuse MiG-15 bis with balsa sheeted wings, very fast (> 130 mph) and rock stable edf jet. Hacker B50 brushless motor in the WeMoTec HW-609 fan. At some point we were flying a whole squadron of them. More details here here and here.