|
||
|
Quote:
And the amount of full scale traffic you have to avoid! |
|
|
||
|
|
|
|
And remember, when you loose the stab from view and the wing is all you have, attitude becomes more difficult to assertain. Except unless you are Joe, and he always knows.
Full scale needs to be watched at all times anywhere, doing anything. Around here, you can get involved at about any TD contest much less flying from 2-4K AGL. Marc |
|
||
|
Quote:
I guess there will be no need to paint the tops. |
|
|
||
|
||
|
Quote:
It seems to me that this no-limit XC start height is a "bad rule", as defined by Blaine Rawdon. He once pointed out that "good" RC contest rules are ones which favor an airplane which is also good for sport flying, since this breeds participation and doesn't result in hangar-queen airplanes. RES and F3K rules meet this criterion very well. F3B rules somewhat less so. XC rules probably not, since it favors huge airplanes which are not very practical, at least for most people. One could enforce an XC start altitude with a Garmin-type GPS recorder onboard, although this adds a significant cost item which is not ideal. |
|
|
||
|
||
|
By the way, John Ellias recently posted on the XCsoaringpilot mailing list that Chris Bovis of the Naval Research Lab would be giving away free GPS data loggers to each team at the next XC contest at California Valley.
-John Elliott Below is the email from John Elias: ---------------------------------- We are planning a two day XC event May 23 and 24 at California Valley. The autonomous soaring team "ALOFT" is planning on attending. As part of their research Chris Bovis of the Naval Research Lab has very generously offered to provide a Skytrace GPS data logger to each team that attends. The only requirement is that each team provide the gps logs of each flight to the ALOFT team for their use in the autonomous soaring research project. After the event the Skytrace GPS is yours to keep! If you are not familiar with the logger take a look at: http://www.magtechinc.net/SkyTraceGPS.htm Quote:
|
|
|
||
|
||
|
Quote:
You mention RES. Great example of the planes evolving to the task. RES started life as a home for prior generation (generally built up) planes. That lasted for about 1-2 years until the current breed of HL on steroids came along, which were purpose designed to the task. The net result was the planes that RES was intended to promote were instantly obsolete for serious competition, and they were relegated to the Woody class was which was born for these relics. So how does RES qualify as a "good rule" when it made the planes it was designed for obsolete. Bad rule in my view. With the RES example of purposeful evolution in mind, why should XC be any different? The planes evolved to the task. Go higher, further, faster. That is what XC is about. If smaller or less visible planes were the technological answer to XC, thats the direction it would have gone. Limited span/weight XC has been tried on occasion. Never took because it wasn't as much fun as real XC planes. The task drives the technology, not the other way around. This shows up over and over in soaring, no? JT |
|
|
||
|
||
|
If a competitor launches early and then sinks out, is he allowed to relaunch without penalty?
(This might be a handy rule for me). -John Elliott Quote:
|
|
|
||
|
|
|
The course entry rule is relevant, BUT even if it were changed, the advantage goes to the plane that can fly higher. No matter what the entry altitude, you can climb while you're on the course, and generally speaking you'll want to follow the JW rule, "get high and stay high." A wide-chord wing will have a practical advantage over a high-AR wing no matter what course entry rule is used, way more than enough to offset the small increase in L/D that the high-AR wing will enjoy at a low CL. A plane with a 16 oz/sq ft wing loading has to fly at a CL of < 0.2 to go 60 mph, so a higher AR is of only modest benefit -- whereas an extra 1000 feet of altitude is of considerable benefit. Skip or some of the other guys who have flown high-AR scale ships in XC may have some good comments on this subject.
|
|
|
|
|
|
You can launch as many times as you want. We want people on course. Sometimes to get to the next thermal you need as much altitude as you can get at the start gate.
Fullsize contests at Montague will have a ceiling in the start cylinder, usually 10,000' msl. Regards Dean |
|
|
|
||
|
Mark,
The UAV autopilots I work with have no trouble with airspeed-hold and turn rate command, but you're right that this isn't COTS hobby stuff. My interest is more along the lines of an unlimited event but not necessarily autonomous soaring. I've seen the autonomous soaring work done by others and it is impressive at being able to work a thermal that happens to be on the course line. What it doesn't do well is gather visual cues of where the lift is (clouds, birds, other thermalling aircraft, etc.) which are vital for efficient long distance soaring. I'd be more interested in a design that can use pilot input for finding lift, but is able to work the lift to maximum altitude without visibility restriction limits. I can't imagine trying to control airspeed precisely on a model that is more than 1/2 mile above me and I don't think it would be much fun for me with my tired eyes to even attempt this. I wouldn't mind using a long range data link and live video feed so I could guide the model to areas of potential lift and then let the autopilot do the rest. This is my idea of what an unlimited class XC machine should be able to do. Another thought that this brings up is the issue of optimal wing loading. I'm guessing most XC models have low wing loading because they fly at relatively low altitudes (for visibility) and don't always work thermals to their maximum height. This results in many low saves and the need to be able to climb in weak lift and therefore, low wing loading. If maximum height weren't an issue it seems that XC models would be flown with much higher wing loadings to maximize average XC speed (i.e. MacCready speed to fly theory). I studied the XCBD 157's average XC speed using an estimated polar and found that the average XC speed is maximized at a wing loading of 6 lb/ft^2 for a soaring day with 400fpm thermals and 80 fpm sink. This produces an average XC speed of 29 mph at 78 mph inter-thermal glide speed. The same model with 1 lb/ft^2 wing loading is 25% slower (average XC speed) according to MacCready and cruises slower between thermals making it more susceptible to headwinds on course. Why are most XC gliders flown with such low wing loadings? Steve Morris Quote:
|
|
|
||
|
||
|
I believe that the present XC gliders are flown at the present wing loadings in order to stay under the 5 Kilogram limit. You could go with a higher aspect wing and have the advantage of a higher wing loading while staying under the 5 Kg limit but then you would have a small root cord and the visibility would limit your maximum altititude.
On the other hand, if you went for a very low aspect ratio wing (say 100" span with a 20" cord) you would have great high altitude visibility but your glide ratio and speed would be terrible. -John Elliott Quote:
|
|
|
||
|
|
|
mlb,
The primary drivers for XC design are the 5 kg limit, typical arid thermal size/strength/spacing, sink between thermals, and the classic mark 1 eyeball limits. Would be great to run a 5 lb/ft2 plane in an XC event, as long as the chase vehicle was a convertible Lamborghini! The open altitude start window also adds some spice to the mix. BTW, I developed a MacCready speed ring for my XC ship way back in the '80s (nerdish aero engr hopelessly enthralled with rc soaring...). Found out later that it had a description/name. Just wanted to define what I should be doing on the course. XC is one of the purest forms of soaring, no launch, no spot landing (unless you gotta land out), just thermal work/utilization. For the airspeed hold thing with primitive aircraft, the simple solution is lots of static margin, and a calibrated elevator trim. This is where an analog elevator trim capability is a wonderful thing. My old XC plane would be easily flyable if I removed 8 oz out of the nose, but that nose weight spreads the trim out such that you can define the airspeed via trim. One little caution is that one has to provide some lead gain/damping when changing the trim by more than a little bit. Actually enjoyed doing XC in the midwest the best. What a great concept, look down the course, and map out your flight path via the cu's! That is like cheating compared to the left coast XC events. BTW, the best I've done on short courses are about 30 min for 20 miles, and 57 min for a 42 mile closed course. The latter was done maybe in the late 80s, and the limiting factor for the day was the contest requirement to obey road speed limits on course. Good thing they didn't enforce stopping at stop signs (we went through a few at the road speed limit of 50 mph). The 57 min could have been about 3 min faster, we got held up by a bicycle race peleton crossing the course at just the wrong time... other than that, we drove the legal speed limit for virtually the entire course. The last six miles were done while looping, inverted flight, etc. due to the downwind final and low speed limit on the last section of the course. Not sure if we could get the conditions to do that again, was a great day for XC!!! MD, one concern with the datalogger method of limiting start altitude. How does one get feedback on the recorded start altitude to ensure compliance? If this rule is used, the optimal solution might be to climb to an extreme altitude, then trade potential for kinetic to get down to the limiting altitude when crossing the start, then reverse the trade until you get to the appropriate speed to fly. Another reason to build for ballistic performance! (Must be getting old, but have had some fun reminiscing.. time to get back to work) |
|
||
|
Quote:
JT |
|
|
Last edited by jtlsf5; Feb 02, 2009 at 05:00 PM.
|
|
|
|
|
I have flown probably as high an AR sailplane as anyone, an EMS Albatross (4m basically generic scaley). We had it over 3K, and it was hard in blue sky, with a cloud behind it, not quite as bad.
As far as speed, XC flights are limited by what goes on the ground, not in the air when things are hopping. I have never had a chance to fly out west, someday, but back east, crocked roads, more enforcement, etc are real limiters. my Albatros could out run us coming and going compared to our ground speed capabilities. Anker, I am surprise you are not placing warnings all over them already. I work with electric utilities, and no kidding, the belts they wear to climb and work on poles actually have warnings on them that climibing poles is hazardess. Shakespear and Don Henley were right, "Kill all the lawyers, kill them tonight!". Marc |
Thread Tools | |
Similar Threads | |||||
Category | Thread | Thread Starter | Forum | Replies | Last Post |
Aileron Bubble Dancer? | Yochim | Thermal Soaring | 1 | Feb 28, 2003 06:09 PM | |
Bubble Dancer, sort of, for 7-cell LMR | pocket rocket | Electric Sailplanes | 3 | Jan 22, 2003 06:37 PM | |
Rave | Any thoughts on Mark Drela's Allegro/Aegea/Bubble Dancer...? | Raymund Reyes | Thermal Soaring | 3 | Jan 05, 2003 03:38 AM |
Bubble Dancer reviews/info | cold boy | Thermal Soaring | 2 | Dec 11, 2002 09:04 AM |