E-Mirage with VLP and a few other changes - Page 7 - RC Groups
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Oct 14, 2011, 08:40 PM
Registered User
Almost forgot - logger data shows I was only getting 49 watts peak in flight and averaging closer to 40 watts. Thats about 20 watts per pound. Much less than static. Part of that is due to these ooold TP packs Im using. They are going on 4 years old now. New packs would hold voltage much better.

Climb rates were a little lower than I was expecting but not bad at all for this low a power level. It looks like I was averaging about 350 ft/min with my best sustained rate at 450 ft/min.

So the Mirage does climb more efficiently than the 2x6.

At least thats not a wildly unexpected result!

I still cant get over that CG position......

Tomorrow Im going to try a larger prop which should pull more power and give better climb rates.

This rate is ok and would be fine on calmer days but Id like a little more for when its this windy - mostly for better penetration into the wind.
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Oct 14, 2011, 09:23 PM
Registered User
Well, my ballancing jig shows I was actually 4 5/8" behind the leading edge with all 8 quarters in place. Just for fun I checked it with no quarters and I was at just a hair more than 3.25" back.

So my fingers were pretty close.

Still, thats is a very difficult number to believe..... even though I just finished flying it!
Oct 14, 2011, 09:28 PM
Registered User
To get the cg that far back without all the change hanging off the tail, the main pack needs to go well behind the cg point.

That means I can shorten up the nose and may even need to move the servos back.

For now I think I will just cut off some of my nose block and move the rx further back and mount the packs on the cg and see how close that gets me.

I need to fly this thing on a calm day to verify my tests results too. Tomorrow and Sunday are looking like better days. maybe i can even get out early enough to get some dead calm flying in.

I'll post some logging graphs in a while.
Last edited by MrE; Oct 15, 2011 at 08:46 PM.
Oct 14, 2011, 09:34 PM
Registered User
It occurs to me I may be approaching the trimming of this thing the wrong way.

This is my first large TD model in more than 30 years.

Im flying it and trimming it just like my DLG - with a fairly neutral but still positively stable CG.

The model seems to be responding like my DLG too. It turns on a dime, floats very well, is very responsive but not the least bit unstable. Pulls out of a shallow dive slowly but positively on a gentle curve. The stall is gentle and straight ahead. It handles turbulence well and lands easily pretty close to where I want it too.

Where am I off base?
Oct 15, 2011, 02:08 AM
Registered User
If anyone is interested in this sort of detail number crunching stuff, here are some logger graphs from the ICE controller and the Open Altimeter.

These show that Im getting about 420 ft/min early in the pack and it drops to about 335 ft/min at the end.

It also shows how tired these packs really are. I just ordered some new Hyperion G3 packs that should give me a good bit more power.

One other thing thats pretty obvious is that the further away the plane fly's, the harder it is to hold the "correct" climb angle to maximize the altitude gain.

On many of the other graphs you can see where Im adjusting the climb angle and how it effects the rate of climb. Too bad I dont have any way to get instant feed back while Im climbing out. That would be very useful!!

There are some guys working on a vario add on for the Open Altimeter. have to see where that goes.
Oct 15, 2011, 06:15 PM
Registered User
Just got back from flying with the next size up folder. I like this power level better. It was blustery again today - 7-12 mph so about all I did was hold the nose into the wind or fly ridge lift on the tree line.

Still, this is the EXACT glider Ive been wanting It handles just like my DLG (well, almost) - only bigger

It handles like a sports car, speeds up or slows down on command with a few clicks of trim, turns on a dime, can core the smallest thermal, is easy to land and most of all climbs on mouse farts. I love it!

I'll have new power level and climb rates later.

I dont understand how Im getting away with this but I've triple checked the CG and I'm now 4.5" back from the leading edge or exactly 50% of the center section cord.

This is after last nights work - cutting the motor mount back 1/2" and moving the rx and altimeter to the rear fuse behind the wing and putting the battery pack ON the CG.

There is no pitch instability and the model handles beautifully. Im very surprised but still jazzed
Oct 15, 2011, 07:48 PM
life long racing nut & modeler
granada don's Avatar
Hi E

Sounds like a great ship you have there, now you know why i wan't to build a 12 footer with that wing using a little larger cord.

I really like my Paragons but that flat bottom wing just stops in a breeze and i want what you have got there now a little more speed range then you have the best of both worlds.

Enjoy your new featherweight bird!!

G Don
Oct 15, 2011, 08:44 PM
Registered User
Thanks Don

You and Riserflyer sound like you have the same goals in mind. He is working on a 140" version of the Mirage over the winter.

I was even day dreaming today along similar but less ambitious lines

I think I will order a wing kit from Isthmus and build the center section with flaps.

I was trying to think of easy ways to add another 6" - 8" to each end of the center section. Im pretty sure I could get away with that much extra span without having to beef up anything. Im sure it would fly fine on this fuse I already got since the rudder and elevator are already over sized a bit.

Im surprised no one has commented on the CG Im flying at. This is the internet. You're not supposed to be nice, polite guys. I was expecting to be told it was flat impossible, Im an idiot and/or Im making it up.

Are all you Mirage guys flying with the CG this far back and you're just not telling???
Oct 15, 2011, 09:17 PM
Registered User
G Don: I was only going to 125% of stock size until I read your intent to go 144". Now, I'm going for 144". And FYI: although it looks close, the Mirage airfoil is not flat bottom.

MrE: My cg on stock Mirage is pretty far back although my distance from LE cannot be compared to yours with all the batteries and such. I am also contemplating a center section with flaps and will probably order adequate CF to make it happen. But first, the center section will be spoilers so I can get in the woody/RES competitions. I'll save the flaps to compete with Supras and such.

Oct 15, 2011, 10:59 PM
Registered User
If you get a chance without going to a lot of trouble, check where your Mirage is balanced. Im really curious about this.

I dont see how the batteries could have any effect on how a model flys with an aft CG - other than weight distribution.

Besides, I bet the lipo Im using doesnt weigh much more than the rx pack you're using now. The pack I have in there is 92 grams - 3.25 ounces. The packs Ive ordered will weigh about 74 grams or 2.6 ounces. Plus - my packs sit on the cg, so have no effect anyway.

Any other Mirage flyers out there know where their model is balanced?
Oct 15, 2011, 11:04 PM
Registered User
On the flaps - I was thinking to keep it simple and just use some 1/4x1/4 balsa just ahead of the trailing edge stock. Cut the ribs into that and bevel the trailing edge stock to use as the flap.

Do you think it will need any carbon to reinforce it?

Ah - I forget you have to worry about launch loads and I dont.
Oct 15, 2011, 11:08 PM
Registered User
I just did some fast number crunching with the larger prop. This is an 11x8 verses the 10x6 that was on there.

Im now pulling roughly 60-66 watts peak on average so about 31 watts per pound. My best sustained climb rate today was about 620 ft/min and my average was more like 500-550.

This is roughly the same numbers I was getting with the 2x6 which is a little disappointing. The Mirage is a lot larger though so that has to be some of the reason.
Oct 16, 2011, 12:47 AM
soaring guy

CG Mystery

The CG location you have ended with sounds more like some of the free flight power jobs from the 1970's era. They had large stabs, (30/40 % of wing area) and flat bottom lifting airfoils. It was not uncommon to have the CG as far back as 60%. Some I suspect were even further rearward.

Perhaps a note to Mark Miller at Isthmus Models with data re wing incidence and stab incidence and ETC could get a response to answer the question. I am going to build a Mirage shortly and can only hope mine handles as well as yours does.
Oct 16, 2011, 01:02 AM
life long racing nut & modeler
granada don's Avatar
Hi E

You have quite a bit more drag with more surface going throu the air.

Hi Riser

I know the Mirage wing is not a flat bottom as my E bird on post #25 has this wing, i was saying that is why i like it over the flat Paragon i should have word'ed it better sometimes at 70' what comes out on paper is not quite what is was thinking and since i'am an old Dude i will use that for my excuse like they say i had a ' Senior Moment ' well maybe more than one!!

Go Don
Oct 16, 2011, 08:49 AM
Registered User
pazi's Avatar
Hello Mr E,
do you have standard prop or folding prop? I think this thing can bias the dive test (I am assumign that you got the CG so far back from dive tests). But it is only theroetical thought.

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