Turbobearcat

Well with the new setup using the 6-blade 3500Kv motor - the Grey beast is now flying pretty quick now and after 4 minutes I landed with 15.2v on the battery.. I was surprised with that amount left on the battery but hey that's good! My white XB-70 can support 6 cell so I am wondering if I should give it a chance.. :-)

hadatom

Got to fly my XB yesterday late afternoon. I made a very dumb beginner mistake on my second low pass, flew right into the sun. Lucky for me, I saved it. You can see the harrowing moment on the Youtube video below.

https://www.youtube.com/watch?v=RlscA8jaqN0

Turbobearcat

Do you have the plans to build this you could share?

Quorneng

Turbobearcat
Sorry but like most of my scale Depron planes it was built from a 3 view, blown up to the size required.
I found this very detailed view (1 of 3 sheets) on the web.

Using this (and would you believe Microsoft Paint!) various detail views were cut/copy/pasted and printed out.
For example:
The complete duct.

Detail of the fan installation.

Of course none of it explains how to put it together but it did give me just enough information to size the major bits of Depron sheet.

The result is very much a 'one off' with quite a bit of its internal structure designed as it went along, indeed I would be hard put to make another exactly the same!

I do have quite a few construction pictures which sort of show how it was put together.

It flies really quite well (it is very light) but unless you are happy to spend a lot of construction hours it is not really a practical way of making an Valkyrie!

Turbobearcat

Either way you made a nice looking one- and it's totally honorable towards keeping the XB-70 Valkyrie memory alive and well.

Quorneng

Thanks Turbobearcat
But I must admit building the XB70 was not driven by any 'ideals' but simply the Depron project I was on at the time using 4 small EDFs was running into trouble and a single bigger EDF but with multiple exhausts seemed a better bet - which it proved to be!

The four EDF scale Concorde did eventually get sorted and was flown.

But 40mm EDFs with scale inlets and exhausts do tend to be a bit marginal.

Turbobearcat

I found out that FMS is selling 8 bladed fans now - two extra blades on my 3500KV would be interesting....

Turbobearcat

Everybody - one of my statements about flight times and C-ratings that I was pointed out to being wrong...and after much reading and now understanding...
I stand corrected and better educated. :-)

C- rating is how much power the battery is rated to belt out.
MAH is what gives you the amount of time you spend in the air..
C-rating can also be used in applications where the battery is getting hot due to demand- so try a battery with a higher C-Rating to keep your battery from puffing.
I was mistaken by thinking that the C-rating gave me more fly time.
reason behind my thoughts - I was flying with a 30c battery for 3:30 - battery started to puff up...went with 60c same size and battery is not even warm so with the lesser I fly at a reduced time.. see where I made a mistake.

Steve Westphal

I have an extra set of plans for a 7 or 8 foot XB70. Part of the printing is in German but have a translation. It was powered with a .90 pusher. I would put fans in it if I ever built it. Let me know if anyone is interested. Cost of copying plus postage would do.

Turbobearcat

Steve

have you flown your yet??

Turbobearcat

Ordered the 8 Blade fan for the Grey bird so I can't wait to see how this works out..

Turbobearcat

Ok new fan installed and testing will be done Thursday to see how much the amp draw went up..

stock it was at 45-48 amps so I am hoping it won't be much higher

Turbobearcat

OK did the testing with two different motors and here are the answers..

Detrem 3500 outrunner w/ 8 blade fan 62 amps and the motor was smelling bad..
Turnigy 2800 Kv Outrunner - 44 amps and 655 watts...and the sound I was getting was nice.. so I think I will fly with this setup for now...

Turbobearcat

Took this bird out with the new setup and I was happy with performance and sound of the bird..front landing gear is crappy loose so I ordered some new one for my LX F-22
which are the same size but the landing gear is beefier and I hope better plastic!.. if all goes well I hope to have her flying tonight.

Turbobearcat

Flew the bird with the new 8 blade and new landing gear - very happy with the setup I now have...now debating to upgrade the White XB-70 to the same setup.

Turbobearcat

OK new update
1. New landing gear from the LX F-22 is a perfect replacement - better plastic and more beefer to boot.
2. ordered the FMS 3000Kv motor for the 8 blade in the Xb-70- I hope this get the power up from the Turnigy 2800Kv motor..

should be ready to test when the weather decides to become normal again.

Turbobearcat

Wow it's been sometime since I updated this one.

The new motor works great but now the 60c battery gets hot and puffs... so I have to ask if I need to think 5 cell at this point.
The motor/fan comb is drawing about 65amps and I have a 2200 4s 60c battery..so if I go with say a 1800 5s 40c this would work better?
I need a formula to use for calculation when you go from battery size (cell count) and amp usage.

Quorneng

Turbobearcat
Drawing 65 amps from a 2200mAh battery means you are discharging at 30C. Never mind what the battery label says 30C is working a battery quite hard. At that rate it will discharge completely in 2 minutes. If you are getting near to full discharge that would certainly account for the puffing.

If your motor is drawing 65A on a 4s going up to 5s will simply make it draw even more!
To safely draw 65A you need a rather bigger battery. A 5000mAh 4s at 65A would be discharge at a 13C giving 4.5 minutes at full power.

To go to 5s you would need a motor with a lower kV (4/5 of the one you already have) it would draw approximately 4/5 the current (52A) which is still working a 2200mAh battery quite hard.

Of course you don't get something for nothing. Bigger capacity or higher cell count batteries will both weigh more than your current one. Can your XB70 handle the extra weight?

Turbobearcat

NO the size of the battery is pretty much it, I can use the 3500Kv motor and the battery is not taxed (2200 60c 4s) but I don't fly 100% balls to the wall, only at take off and then I cut back to 75% and then back to 50-60% for normal flight.. With the 2800Kv motor and a 8 blade fan it draws less amps but it takes longer to get up to speed..battery about the same as before, just warm but not hot!

Turbobearcat

It appears I can shove a 2260 30c-75c 4s battery in there, this is the same battery I use for the SR-71 I fly...

Turbobearcat

Has anybody thought about making the chamber behind the fan shorter and using thrust tubes up to the fan with the shorter chamber?

For some reason I am thinking this might work.

Turbobearcat

Long time no post - upgrading to the Freewing 12b fan so I hope this bump up the power/speed.