SEN issue 1084 - 7 April 2007
- Category: Archive 2007
- Hits: 257
- Ancient History
- Thrust to weight ratio for power models
- 53 Wake
I see in the latest SEN (issue 1082) that model flying was
flourishing in the 13th century with models constructed from
interstellar material (Ed Mate 'Meteor Stick'). Is the history of the
USA being finally told ? Is it true that Chief One Wing won CLG with
a buffalo gut powered piece of chewed thorn bush ? I think SEN should
finally be told (over to you).
Reply to CHE / Ancient History:
Yes of course ! I immediately recognized the important date of 1449
(SEN 1082 contest report) as being a familiar one in modeling
folklore. The great Sir Lee of Hines, has often recalled to me in
great detail, the events of that year at the Wood Henge Spring Gala,
a Dark Ages Cup event. Regaling all with crystal clarity, he tells
the tale of flying what was probably the first known example of the
Battering Ramrod, in the 1/2 Hay event, at a time when modelers had
to crudely fashion airframes from bits of straw, reeds and twigs,
when balsa was still an unknown luxury, some 400 years before steam
engine reductor power models were flown by Stringfellow ! Retrieving
at these events though was slow and tough work, riding downwind on
oxen, through marauding hoards of Goths, Visigoths, Celts, Picts and
Druids, just to get your model back. And of course timekeeping was
fraught with unreliable timepieces, when the sand often got clogged
in the hour glass. But you can't keep the lads back from wanting to
fly at a good comp, and Sir Lee says that in those days the Catapult
event was at its height, and hugely popular back then, with both the
modeler and his aeromodel being launched skywards over the
battlements of the local hostelry from giant wooden contraptions they
called Ballistas. Great fun though, because the modeler already
found himself half-way downwind towards retrieving the model !
Although getting back over the castle wall late at night with your
model after the fling-offs, could take a while, once the drawbridge
had been closed. And of course, Knight-flying was virtually invented
back then, when armor-clad contestants stuck great burning lumps of
flaming pitch on their models before launch, so that you could see
where they landed in the dark. No snuffer tubes back then of course,
because they were not invented until the 16th century, after the
Great Fire. Ahh yes, 1449, those were the good old days when
contests were contests !
Thrust to weight ratio for power models
Can anyone tell me what the typical thrust to weight ratios are for the F1C/J/P/Q power classes, not forgetting AMA and other power models?
Current thinking is that a vertical climb, if it can be achieved, gives the highest altitude, and therefore the greatest potential duration. Starting with the simple equation of T = W+D (where T = thrust, W = model weight and D = total model drag), if the T/(W+D) ratio is 1.00 then the model will only hover in its vertical orientation. Perhaps interesting to see, but not much for duration. As the ratio increases, the excess thrust will accelerate the model until the point is reached at which the model's total drag plus its weight equals the vertical thrust. Of course, the model's design and trim should ensure that the wing is flying at, or close to, its zero lift coefficient angle, so as to minimise total drag, increase vertical speed and get as high as possible in the limited engine/motor run time available. Increasing the ratio even more should increase the acceleration, climb speed and altitude. However, is there a practical limit to this Thrust to Weight ratio?
For a car, to try to apply more power to the wheels than the tires have grip on the road just results in wheel spin. Noise, smoke and excitement, but no more use than our hovering model at getting anywhere.
Is there any phenomenon akin to wheel spin the might limit the useful power (i.e., thrust) that we apply in our models? Certainly wing flutter and airframe integrity can be limiting factors when considering climb speed, but these are, to a degree, controllable by design.
I don't know of any published data on actual model Thrust to Weight ratios, which is the reason I'm asking for your help. And, to be fair, Thrust here probably means only static thrust, which is fairly easy to measure. Dynamic in-flight thrust is another matter entirely, and I know of no way to measure that, and it undoubtedly changes as the model accelerates.
And, of course, there is the question of vertical climb being optimal for model duration. But if a 90 degree climb isn't the best option, what is? And how does the Thrust to Weight ratio then fit in?
It is of thoughts such as these that fill my time while I wait for sleep to overcome me at night, to dream, if I'm lucky, of that perfect climb into a cloudless sky.
From: John O'Donnell
From: John O'Donnell
Seen your comment to SEN re the 53 Wake Finals, and Ted Evans' oos fight in particular.
It is amazing how hero-worship and fan-mail can continue to perpetuate myth after 50 odd years. Evans' model did indeed get a sub-max score - but it is most unfair to criticise and blame the timekeeper(s).The man to blame is Evans himself, as he had a penchant for pale pastel coloured Jap tissue. The model in question was pale red and white and disappeared into haze/mist/murk only too easily.
Remember I was there. Moreover, some of my club members watched Evans with interest, and also lost sight of his model at about the same time as the Officials. The model was simply hard to see.
Hugh and I (and Copland for that matter) cared nothing about appearance and had black fuselages - and no visibility trouble.
I will say no more. Hopefully no-one else will.