Jason:
I could tell you were a Flanker fan by your Avatar. We're hoping the low-cost power systems work too.

Daren

All I can say, is Wow! Keep it up boys!!
Steve Neill

Originally posted by Daren


The WB-57 weighs about the same and flies pretty well on this set up. Granted it has more (lots!) wing area, but also a higher amount of parasite drag. The Flankers' estimated wing loading is approximately 24 oz./sq. ft.
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Yes - but the WB-57 have a high aspect ratio wing and is less draggy while turning. A delta is at the other end - very short ratioed and very draggy. The SU27 is more a delta than a glider.

<quote><b>
Our own concerns as to whether the power will be enough is why we have the testing planned that we do. If the static thrust and tailpipe velocity look okay, we'll move onto taxi tests. Fortunately, our runway is about 900 ft. of 150 ft. wide asphalt, so there's plenty of room to get slowed down (or land) in case it doesn't look like they'll fly. This is one of the advantages of ROG, you have a much wider go/no go window in which to decide.

Yes ROG gives you more leeway but I fear you guys will enter a stall once it rotates/climb out. The power might be enough to get it to rotate but once it does you'll bleed of energy and I fear it will loose momentum. This is of course my SWAG aka gut feeling but I truly hope you'll do great - but I'm doubtful.

Same applies inflight - with low energy available you'll constantly fly close to stall speed and you could risk loosing enough energy while climbing and turning for it to fall out of the sky.

Both of you seem to have given this some thought so I hope you have it all covered - prove me wrong will ya?

Happy flying!
Haldor

Originally posted by Haldor


Yes ROG gives you more leeway but I fear you guys will enter a stall once it rotates/climb out. The power might be enough to get it to rotate but once it does you'll bleed of energy and I fear it will loose momentum. This is of course my SWAG aka gut feeling but I truly hope you'll do great - but I'm doubtful.

Same applies inflight - with low energy available you'll constantly fly close to stall speed and you could risk loosing enough energy while climbing and turning for it to fall out of the sky.

Both of you seem to have given this some thought so I hope you have it all covered - prove me wrong will ya?

Happy flying!
Haldor

I appreciate the input, Haldor. I agree that the power is marginal, at best.

As Daren wrote, the test series will begin with static thrust and tailpipe velocity measurements. Luckily, we have access to a reasonably accurate scale from which to hang the models and measure thrust and an airspeed indicator from which to measure tailpipe velocity.

I intentionally kept the tailpipe a little on the large size (60mm-61mm) in order to keep from reducing the low-end thrust. Any readings below 28oz. total thrust or 65mph TPV, and the models won't be flown. This won't stop me from taxi tests to gauge ground-handling, but I won't attempt a take-off.

You're absolutely correct in your assessment about the dangers of flying in ground-effect and it's something that we'll keep in mind.

I've closely followed the various threads discussing power vs. performance. We went through this with the B-57 and have already resigned ourselves to the real possibility that there may not be enough power available with the brushed motors. If this is the case, then the next step will be to move up to rare-earth magnet motors and matched/zapped cells.

Mine's at the same stage of construction as what is seen in the pics of Daren's. I figure that I should have the base layer of covering and ready for testing next weekend, so we'll keep you posted.

Thanks again,

Dan

If the AUW comes in at or below 60 oz, and the thrust is at or above 60 oz, whats the problem??? Why is it the we feel power to weight in the 1 : 2 area is going to be barely flying ? Or do we just tend to throw money and watts at something for good measure ?

Hey, If it dose not fly well with the original set up maybe you guys could go with 2 Ralf D coxial fans and 4 speed 480s . Youll still come in cheaper than brushless and imagine the terrible sound 4 motors and 4 fans will make in that thing .

jason: i think the concern here is that they're looking at a thrust to weight of.31-1 and 55w per pound.
we've all flown jets that had a .5-1 and they fly nicely.
dan & daren are sharp cookies! they'll get it up and away........gregg

Originally posted by JasonJ
If the AUW comes in at or below 60 oz, and the thrust is at or above 60 oz, whats the problem??? Why is it the we feel power to weight in the 1 : 2 area is going to be barely flying ? Or do we just tend to throw money and watts at something for good measure ?

In Dan and Darens case they're looking at 80oz AUW and 24-28oz static thust (2x12-14oz) - thats 30-35% of the weight available as thrust (=> T/W ratio=.3-.35:1)

In comparison a stock T33 will have a similar T/W loading and we all know that it will handlauch okay but it wont readily loop whenever you want it.

-Haldor

Originally posted by Haldor
In Dan and Darens case they're looking at 80oz AUW and 24-28oz static thust (2x12-14oz) - thats 30-35% of the weight available as thrust (=> T/W ratio=.3-.35:1)

In comparison a stock T33 will have a similar T/W loading and we all know that it will handlauch okay but it wont readily loop whenever you want it.
-Haldor

Thanks for the clarification Haldor. Thinking back to flying my stock T-33, there wasn't very much it would do readily.

Let me pick your brain, if you don't mind. What would be the minimum motor/battery set up you would recommend if the present set up doesn't work? Parallel or series batteries?

Greg: Thanks for the vote of confidence. We hope to prove you right.

Steve: Thanks for the kind words.

Daren

A cheap option would be to find two AP29L's and run them in a lathe to shave off from the case so it would fit the MF motor housing. These motors seem to take ~30A reasonably well and you could probably use 8-10cells for each. At this ampdraw you'll need bigger batteries so weight goes up too.

This conversion have only been mentioned somewhere sometime so I cant comment on viability of this option.
Promax 400 series should offer a couple of options too but I dont know these. Efficiency is still low (60-70%) however in either case and power would be restricted to 300W (195W out each) for the AP and 200W (130W out) for the Promax.

To gain efficiency you need to go up in quality which means higher cost - not much way to go around that and you're talking $100 pr motor right away. HP200/2x/x comes to mind as a brushed alternative and then there are the BL options.

I'd aim for 500W total - 100W/pound:
<ul></b><li>HP200/20/6's in series fed by 20zapped CP1300's (=500W) <b>(g/W ratio 0,54)</b> or 10zapped 2400RC's for parallell rigging (=500W) <b>(0,61)</b>
<li>HP200/25/4 on 16-20zapped CP1700's in series (=500-800W)<b>(0.5-0,68)</b> or 8zapped 2400's for parallell (= 500W)<b>(0,67)</b>
<li>Kontronik FUN400-28 parallell on 10zapped 2400's (=550W)<b>(0,68)</b>
<li>Kontronik FUN400-36 parallell on 9zapped 2400's (=520W)<b>(0,73)</b> or dual 10zapped CP1700's (=800W)<b>(0,71)</b>
<b></ul></b>

The numbers in <b>bold</b> is a component (motors+batts.) weight vs system input power ratio. Dont know if they are useful but I tried to seperate the different options.

I believe 100W/pound is minimum for any satisfactory flight perfomance of such a cool jet. I have listed several options which would hopefully work but which one to actually choose is difficult as I dont know what yoor drive is
Its a compromise between need/price/power and duration....

I hope this offer you a little help and not too much confusion...
Happy flying!
Haldor

Guys can you help me? The ruskies had plans for a single engine su-27 trainer, never built. Do any of you know what it was called?

Originally posted by Haldor
Dont know if they are useful but I tried to seperate the different options.

I believe 100W/pound is minimum for any satisfactory flight perfomance of such a cool jet.

Its a compromise between need/price/power and duration....

Happy flying!
Haldor

Thanks Haldor! This is BIG help and very useful.

Judging by your numbers, this tends to confirm the way we were leaning (towards fewer more powerful matched, zapped cells, but run in parallel) to keep the weight nearly the same, but increase the performance.

Your description matches our compromise to a "T"!

Thanks again!
Daren

Originally posted by Magnaflux
Guys can you help me? The ruskies had plans for a single engine su-27 trainer, never built. Do any of you know what it was called?

You must be referring to the S-54/55. Sort of looks like a goofy version of the Flanker that you might see in a cartoon.

<img src="http://www.allaboutguppys.com/flanker/s541.jpg" height="297" width="400">

Or, click on the link below for more pics and info:
http://military.topcities.com/russia/s55.htm

Daren

Daren, your giving me idea's again. This looks like a natural for EDF.
Steve

Originally posted by Daren
(towards fewer more powerful matched, zapped cells, but run in parallel)

Regarding series or parallel motor connection, with sensorless brushless motors there's no option - it has to be parallel.

However, there was a fair amount of correspondence on the Eflight List a while back regarding problems with series-connected brushed motors. The ones in question were hot buggy-style motors, eg Magnetic Mayhems, etc. The problem being suffered was that after a few flights, one of the motors would overheat and be ruined.

The conclusion reached was that for series-connected brushed motors, their timing has to be as nearly as possible identical, otherwise one will present a higher impedance to the power source, draw a higher proportion of the available voltage, and hence power, and risk being overdriven. As a result of the discussion, the guy who raised the problem did get two new motors and synchronised the timing, and was able to report that the motors survived several flights more than the previous ones had, without smoking.

However, parallel connected brushed motors were considered a generally safer option for longevity.

The timing on the Pletti 200-series is not adjustable without using a needle file on the backplate screw-holes, and though one might think that for the price paid the timing should be identical, I had two 200/20/6s at one time which most certainly were not identical in rpm performance in the MF480 fan unit.

I must admith that after wearing down the brushes on a Pletti 200/20/6 with not too many flights on 10x1250SCR at about 20-24A, I decided that since EDF motors need to be driven to their limits to get a decent model performance, brushless was likely to be a better choice in the long run.

FWIW

Gordon

The power problem is an easy one, it only takes more money
So while the numbers don't look good once the airframe is complete you guys can step back and adjust what you need to get the job done

Magnaflux,
The trainer version was dropped and the last images I saw, I think, were from the 98 Paris Airshow. They had a revised pole model of a single seat fighter. The Western observers called it the Viperiski (F-16 wanabe). This is a subject that I wanted to model but I don't have enough views. It is an awesome looking model I will see if I can find the mag and post a pic.