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Old Mar 14, 2013, 08:58 PM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
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Originally Posted by OVSS Boss View Post
Don, question. Flying the Tragi last summer, with a fairly low (~300W) output power system. Much like JW spoke, I will flatten out at about 25s, and then at cut off, I go from reflex to native airfoil and just let it coast to where she ends up. Really clean sailplane, am I busting things via the rules? I am not going vertical and at especially 200M shut off, it seems plenty high no matter what.

Also, searched Altis 4 and could not find site, need new logger/cutoff since the one I got from BK is dead for what ever reason.

TIA, Marc
Marc,

Climbwise, your setup shouldn't really have a problem. I don't mean to get everybody's knickers in a wad over this. We are still early in the game and it getting everything nailed down to the nearest meter isn't really going to make a difference. I AM a little concerned with Joe's report. There is a big difference between what our 100 or so watt per pound planes can do and what a 400 watt per pound plane can do.

I think there are two different kinds of people who will end up with overpowered planes -- those who are not that familiar with competition and end up with overpowered planes on the advice of friends who were in LMR and those (especially TD fliers) who are very experienced with competition flying and are starting out gaming the rules to gain an edge without paying attention to the rules. It is probably worth doing our best to make sure these rules are understood before too many people get headed the wrong direction. And, it seems to me, that the experienced competition flyers will understand that there is no glory in winning by intentionally and explicitly breaking the rules. A little information might go a long way this year.

As to the Altis 4, they are supposed to be available this month. The American supplier is Esprit Models and they are out of stock on the Altis 3's -- I presume waiting for the new unit. It should be worth waiting for. In the mean time, I've got an Altis 3 I'd be glad to loan you if you want to check your plane out.

Happy Landings,

Don
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Old Mar 14, 2013, 09:15 PM
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Don, appreciate the info, my ship is nice, light and just as you pointed out is not overpowered I do not think. Being clean, and with the wattage it has can make it climb, but not be ballistic. I will take you up in the Altis 3, I will pm with address.

Really appreciate the help!
Marc
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Old Mar 14, 2013, 09:25 PM
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Miamisburg OH
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One thing that needs to be considered in talking about gaming the cutoff altitude with a zoom is how well you can judge your altitude. If you are on the low power end and have a plane capable of trading kinetic energy for about 20m of altitude, you have to be able to judge your altitude to within about 10m to take advantage of it, especially at 200m. So if you level off at 190m and get 20m more for a total of 210m, so what! nobody will notice.
If you have more power like enough for a 50m zoom, then you have more to work with. At the very high power you just climb straight up and get all you can, but it will be obvious to a CD. I have an Art Hobby Hi Aspect that I set up for unlimited LMR, about 1200w. When I put a CAM and Zlog in it, it was busting through the cutoff vertically at 90 ft/sec ---lots of zoom gain! No way to level off with that power without flying the wings off.
Marc - I've seen how you fly your plane and I don't think it is breaking the spirit of the rules. But put a Zlog in it and tell me how close to 200m you level off to do your dash-zoom manuver!
Another thing about gaming the system by trying to fool the CAM about the real altitude with pressurizing the fuselage. Having spent many of my waking hours concerned about how to get high quality flow from the inlet of an aircraft to the face of a jet engine, I can't see how any of the setups that I have seen can efficiently recover any of the meager dynamic pressure at speeds of around 100 ft/sec. If I saw a scoop and a duct to the Cam, I might believe it, but then it would also be obvious to the CD.

John Lueke
Somewhere in Virginia, but halfway to the East Coast ALES Festival!
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Old Mar 14, 2013, 10:14 PM
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John, it is all SWAG baby. I guess that I get close, but who knows, in my mind it works and that is all I have to make it work for.

Marc
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Old Mar 14, 2013, 10:52 PM
launch low, fly high
New Zealand, Hawke's Bay, Havelock North
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To get an idea of what sort of zoom capability your system has, launch to a low height. Then glide down to a couple of meters height, turn the motor on and keep it at that height for several seconds with the power on. Then, cut the motor and convert the airspeed into altitude. You can judge the delta altitude fairly easily when starting "on the deck".

There are a lot of variables involved (prop selection, gearing, the all important wattage, airframe drag, etc.) in the amount of energy one can build up via speed gain and then convert to altitude. This simple demonstration will show you visually what the delta is. You can use a logger, or just estimate the number of wingspans you gained in the climbout and do the requisite math (note: most people will be a bit low on this estimate!).

All it will take to change the competitors actions is for a few contest directors to make the hard call... this is sometimes difficult to do! I know I'd have difficulty in doing more than giving warnings on the first infringement. Without concrete measurements, or power limitations in the rules, preventing the "zoom" is difficult to objectively enforce.
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Old Mar 14, 2013, 10:53 PM
Red Merle ALES
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United States, Mt, Helena
Joined Apr 2002
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Interesting.

Two comments or thoughts.

If someone zooms to 220m in 15 seconds and I get to 200m in 30 seconds it's a close race as the extra 20m is less as he/she has already started down in the glide for the 15 seconds I was still climbing.

I would think it is not the intent of the rules but if Joe W with his different switched power settings were to launch with mid power then at sy 25 seconds increase the power to full to get extra zoom would then have an advantage. I believe the CAM unit only knows altitude and time and not power level.

Curtis
Montana
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Old Mar 14, 2013, 10:58 PM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
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Quote:
Originally Posted by John Lueke View Post
One thing that needs to be considered in talking about gaming the cutoff altitude with a zoom is how well you can judge your altitude. If you are on the low power end and have a plane capable of trading kinetic energy for about 20m of altitude, you have to be able to judge your altitude to within about 10m to take advantage of it, especially at 200m. So if you level off at 190m and get 20m more for a total of 210m, so what! nobody will notice.
If you have more power like enough for a 50m zoom, then you have more to work with. At the very high power you just climb straight up and get all you can, but it will be obvious to a CD. I have an Art Hobby Hi Aspect that I set up for unlimited LMR, about 1200w. When I put a CAM and Zlog in it, it was busting through the cutoff vertically at 90 ft/sec ---lots of zoom gain! No way to level off with that power without flying the wings off.
Marc - I've seen how you fly your plane and I don't think it is breaking the spirit of the rules. But put a Zlog in it and tell me how close to 200m you level off to do your dash-zoom manuver!
Another thing about gaming the system by trying to fool the CAM about the real altitude with pressurizing the fuselage. Having spent many of my waking hours concerned about how to get high quality flow from the inlet of an aircraft to the face of a jet engine, I can't see how any of the setups that I have seen can efficiently recover any of the meager dynamic pressure at speeds of around 100 ft/sec. If I saw a scoop and a duct to the Cam, I might believe it, but then it would also be obvious to the CD.

John Lueke
Somewhere in Virginia, but halfway to the East Coast ALES Festival!
John,

I understand your thoughts on "finding the right altitude" to start zooming. And that would be the case for a plane which required most of the allowed motor run time to get close to its cut-off altitude. But a 1200 watt plane can fly at a 30 degree angle to the ground and get to 200 meters altitude in about 16 seconds. In this case, its airspeed is going to be around 70 mph or 6160 fpm -- a ton of kinetic energy. And I have observed that getting the plane laid over to 25 or 30 degrees is plenty adequate to 1) accelerate the plane to near maximum speed and 2) to set yourself up for a near maximum altitude launch. It works on lightly powered planes with the caveat that you've got to have enough power to give you time to get to where you want to lay it over. My 700 watt Supra had way more than enough power to get to, say, 150 meters in less than 12 seconds, giving you plenty of time to lay it over and accelerate the plane. I have started launching this way because it helps me get a stall free transition from power to glide. (And I work to calibrate my altitude switch so my Starting Altitude does not exceed the allowable). If I did not, I could easily exceed the allowable by 20 to 25 meters. The idea that is important here is that when you lay your plane over to 30 degrees or less, it will accelerate to pretty near its horizontal maximum speed. Whether you go horizontal or not is not really that important. But a plane with 1200 watts and a prop correctly pitched for speed will exceed 70 mph. And a plane like that will perform pretty much as Joe described.

As to "fooling the CAM', the calculation for converting velocity to "altitude" pressure is pretty simple. Its what we do for pitot tubes. I have attached a table showing the distortion which can be induced by fully utilizing the dynamic pressure versus speed. And our 6000 fpm plane can theoretically distort the measured altitude by 50 meters. Like you I was curious and so I strapped an eAVA fuselage to the roof of my car and tested it. No special effort was made to seal the fuselage off -- its boom was fairly unobstructed clear to the opening on the tail. And even with the open tail I saw results which got to about 60 percent of the values shown below.

I have been testing planes since the first ZLOG came out to sort out the theoretical concerns from the real ones. I had an AVA that would fly vertically at 3750 fpm and 600 or so watts. Getting a plane to 6000 fpm AIRSPEED without adding more than 3 or 4 ounces is entirely realistic. And planes with that capability can exceed the launch altitude tolerance by substantially more than 50 meters if the pilot is so inclined.

I am not losing sleep over it. And I think that, at least for the time being, the credible threat of enforcing the rule should keep most of us down on the farm. But Joe's observations suggest that in the absence of a credible threat, things may get a little messy.

Happy Landings,

Don

BTW: If we start seeing much of this, perhaps it would be useful before dropping the hammer on guys to test some "hot" planes to see what they can do.
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Old Mar 15, 2013, 01:10 PM
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Quote:
Originally Posted by dharban View Post


BTW: If we start seeing much of this, perhaps it would be useful before dropping the hammer on guys to test some "hot" planes to see what they can do.
Good data is hard to come by but here are three results I have collected from pilots who were really trying to zoom.They are compared with my simple zoom model (very rough with no guarantees !)

Nan Shadow
Specific Power = 220 Watts/kg
Wing loading = 3.3 Kg/m2
Measured Zoom= 35m
Predicted Zoom = 37m

Pike Perfect ET
Specific Power = 350 Watts/kg
Wing loading = 3.4 Kg/m2
Measured Zoom= 50m
Predicted Zoom = 48m

F5B model (name unknown)
Specific Power = 3200 Watts/kg
Wing loading = 6.3 Kg/m2
Measured Zoom= 250m
Predicted Zoom = 223m

The first two are not really "hot" models but do help to validate the (mathematical) model which should give a reasonably good indication of the maximum zooms which can be acheived.A couple of outputs from the model at different power ranges and wing loadings are attached.Generally they just confirm everything that Don has reported on the matter in previous posts.
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Old Mar 15, 2013, 02:18 PM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
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Quote:
Originally Posted by Painter S View Post
Good data is hard to come by but here are three results I have collected from pilots who were really trying to zoom.They are compared with my simple zoom model (very rough with no guarantees !)

The first two are not really "hot" models but do help to validate the (mathematical) model which should give a reasonably good indication of the maximum zooms which can be acheived.A couple of outputs from the model at different power ranges and wing loadings are attached.Generally they just confirm everything that Don has reported on the matter in previous posts.
Good stuff. Very Interesting.

For those of us who live in the colonies and who understand meters to be devices to measure things with, let me explain these in simple terms that we colonials can understand.

My eSupra came out around 2.8 kg/m^2 and 375 or so watts/kg (I ran it at about 750 watts). Its performance pretty well matched Painter's data. Without adding any weight, I could have taken it to 1200 watts -- 604 watts/kg. This would suggest zoom potential in the range of 50 meters. Fifty meters, in ballpark numbers is about 150 seconds of flying time.

My experimentation asked how could I fly a powerful plane and consistently abide by the rules. And it was really very simple -- I adjusted my cut-off altitude to account for the zoom potential that I measured USING THE STYLE OF LAUNCH THAT I LIKED. Over hundreds of flights I have observed that if you use a reasonably consistent launch profile, you get very consistent ultimate launch heights. And it should be obvious, that it is very easy to fly far, far outside the intent of our rules.

I have come to enjoy flying more mildly powered planes, but in an environment where there is no intent to enforce our rule, it is hard to argue against letting the big dog hunt. I like to have power to give me the launch range that I want, but I do not want to use it to fly outside the intent of our rules.

Happy Landings,

Don
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Old Mar 16, 2013, 04:33 AM
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Originally Posted by dharban View Post
Good stuff. Very Interesting.

For those of us who live in the colonies and who understand meters to be devices to measure things with, let me explain these in simple terms that we colonials can understand.


Don
I understand that meters measure things too.In fact,the meeter and greeter at my local store could direct me to one which measures length ---- in metres!

Divided by a common langauge !

Spencer.

PS A zoom by any other name would be so far.
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Old Mar 16, 2013, 08:22 AM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
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Quote:
Originally Posted by Painter S View Post
I understand that meters measure things too.In fact,the meeter and greeter at my local store could direct me to one which measures length ---- in metres!

Divided by a common langauge !

Spencer.

PS A zoom by any other name would be so far.
Perhaps we should all simply revert to specifying weight in "stones", distance in furlongs and speed in furlongs per fortnight

Happy Landings,

Don
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Old Mar 17, 2013, 04:25 PM
Skye Malcolm
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Upper Arlington, OH
Joined Mar 2009
644 Posts
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Originally Posted by dharban View Post
Ouch!

Did the rest of your Saturday launches get to 200 meters inside 30 seconds? It looks like your ballasted flights did not come close.

Finally, how did you set up your transmitter to accomplish the multiple power choice? I've been fiddling with my SD10 and haven't figured it out.

Thanks for the graphs.

Happy Landings,

Don
Don I fly with the SD10G and one way to do 3 different power curves on an on-off switch is to have a different throttle curve for 3 different flight modes. I've done it and it works. Only down side is you're getting all the other separate control surface settings from each flight mode too and you're using up flight modes you might want for the rest of the flight. I did this on a 2 channel V tail (plus motor of course) so that wasn't a handicap.

Skye
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