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Jun 11, 2012, 07:41 PM
Registered User
alexandermh's Avatar
Quote:
Originally Posted by falcon5
Back to work tomorrow Next weekend I will be out on the lake bed though..
Good deal man. Glad you found the gremlins. Now you have some time to prep for the weekend.
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Jun 11, 2012, 07:50 PM
Another one on the way...
ysolomon's Avatar
Quote:
Originally Posted by Endlesslag
Alright, can't wait! In the meantime I'll entertain myself trying to fix leaking retracts
You do that! Last weekend, I saw two giant P-51s belly landing. One couldn't lower the landing gear while the other dropped the wheels (I kid you not...) during flight... We thought those were simulated bombs, but it turned out to be the main wheels...
Jun 11, 2012, 07:59 PM
ShopCzar
Endlesslag's Avatar
Quote:
Originally Posted by ysolomon
You do that! Last weekend, I saw two giant P-51s belly landing. One couldn't lower the landing gear while the other dropped the wheels (I kid you not...) during flight... We thought those were simulated bombs, but it turned out to be the main wheels...
Wait, seriously?
I bet that's a feature for realism, the 1/4 scale mechanics lost their 1/4 scale wheel wrenches....

Retracts are a pain in the butt so far. Falcon made the right choice using electric ones. Pneumatics are a PITA...
Jun 11, 2012, 08:05 PM
Another one on the way...
ysolomon's Avatar
Well, sometimes electrics are not a walk in the park either... My F-18 uses pneumatic ones... But it also uses pneumatic breaks...
Jun 11, 2012, 09:04 PM
deltas are cool
AIR SALLY's Avatar
Quote:
Originally Posted by falcon5
Running the fans just to get the batts back down to around 3.8v per cell and WOW!!! what a differance from before from wall compared to no wall. Those fans must have been just starving for air from turbulance from the two fans fighting each other..I really have to hold it back now at full throttle, before it just didn't seem to push against my hand all that hard.

After a good long full throttle run the back of the motor reads 107 degrees with the laser temp gauge.
im glad you have picked up some preformance ...what are you using for wheel bering ? it seem to slow down really fast when you came off the power.???? just trying to help if your wheels are draging it could hold you back that few mph you need to get airborne.
Jun 11, 2012, 09:05 PM
jofro
Quote:
Originally Posted by ysolomon
jofro or anyone, how do you translate KW into lb of thrust? Is there a general rule of thumb? What other factors are you taking into consideration?

I was not aware that this model is 40lb... I'm a bit concerned too... At the same time, I will be flying an 18lb F-18 on a 4000W Dynamax fan, so my ratio is only slightly better.
To your first question, I don't think there is a rule you could translate. That's why you have efficient and lot of non-efficient EDF systems. I always upgrade my EDF models to give me aprx. 900-1100grams of thrust (2-2.5lb) per Kwatt. Your "F-18" figures don't look very good to me at 220w/lb. as most of my 90mm EDFs around 10lb AUW push over 4Kwatts. It's always good to have few spare bucks in your pocket, but then again there are some people who enjoy flying 'bricks' or cement blocks.
I only wish best of luck to "Falcon" with his model, that I find very in-efficient with the figures he showed so far. I would still like to know how much it actually pulls statically on the ground while being hooked to the digital scale. I'm aware it could fly nicely at 130m/h but you have to reach that speed first, Joe.
Last edited by jofro; Jun 11, 2012 at 09:22 PM. Reason: watts
Jun 11, 2012, 09:21 PM
Another one on the way...
ysolomon's Avatar
It's supposed to deliver 12lb of thrust on 4kw, which would be 1320g/kw. Why are you getting a different number?
Jun 11, 2012, 09:40 PM
Capt. Z
falcon5's Avatar
Quote:
Originally Posted by AIR SALLY
what are you using for wheel bering ? it seem to slow down really fast when you came off the power.???? .
Well I do not have berings yet, but do intend to get some.
Jun 11, 2012, 09:47 PM
Registered User
erh7771's Avatar
Quote:
Originally Posted by ysolomon
jofro or anyone, how do you translate KW into lb of thrust? Is there a general rule of thumb? What other factors are you taking into consideration?

I was not aware that this model is 40lb... I'm a bit concerned too... At the same time, I will be flying an 18lb F-18 on a 4000W Dynamax fan, so my ratio is only slightly better.
Saw the Planes episode on this bird

The full sized T-38 was a dog, they even did some variable AOA with it for take off like the A-4 and that's with more powerful engines.

SOMEHOW the thing did mach 1.5 but wasn't a good turner because of lower power to weight.

IIRC thrust was around .55 to 1 !
Jun 11, 2012, 11:11 PM
deltas are cool
AIR SALLY's Avatar
the f-5,f-20 had a adj nose gear. i dont believe the T-38 did ,but im not totally for sure.maybe the later models had it ???
andy grease them bad boys up or you might melt them .
Jun 11, 2012, 11:32 PM
Registered User
LOL, You should pin a star on A/S. I went back & found he was first to mention the wall. Nice troubleshooting.

Phil
Jun 12, 2012, 04:00 AM
jofro
Quote:
Originally Posted by ysolomon
It's supposed to deliver 12lb of thrust on 4kw, which would be 1320g/kw. Why are you getting a different number?
I was working out your 18 pounds AUW at 4000watts, which gives you some 220watts per pound. You didn't say anything about your "supposed" 12lb thrust, which is all subject to your inlets, outlets and other factors. Did you test your thrust? If you get 1320g/Kw you are laughing. I find the easiest way to check my real thrust, by holding the model in vertical position with exhaust 4-5 feet above the ground or higher and get someone to advance full power. If she hovers I'm happy chap. My 17kg "Triptych" pulled out of hover between 3/4 to full stick, meaning it must pull over 18kg. 10.5kg "Panther" almost but not quite hangs there on 9300watts at some 200 amp draw with 127mm fan. So both models produce some 400w/lb. With your 18pound Hornet it shouldn't be any problem to do vertical test to see what she really pulls. But then again, there is static and dynamic thrust and to get best of both takes some experimenting, Joe.
Jun 12, 2012, 06:45 AM
Another one on the way...
ysolomon's Avatar
Thanks jofro. You were talking about 220w/lb and not 220g/lb. that's where I lost you... None of my EDFs ever hovered, as I never had one with 1:1 thrust to weight... At the same time, the ratio I have is typically 0.66 to 0.8 and I'm happy with the scale flying. Haven't checked static thrust yet. Working on the inlet to fan tube now...
Jun 12, 2012, 07:53 AM
Registered User
JurassicJet's Avatar
Quote:
Originally Posted by Endlesslag
Wait, seriously?

Retracts are a pain in the butt so far. Falcon made the right choice using electric ones. Pneumatics are a PITA...
You got that right. I am sending my ELECTRIC nose gear back for the third time and now one main that failed. I bought some expensive (in my book) electric retracts and their reliability has been horrible. I'm bummed because I don't want to plumb and convert to pneumatic...
Jun 12, 2012, 08:15 AM
fly like an EAGLE ;)
corsair nut's Avatar
my 13.5Lbs F-86 had 3500W and went 160mph, and had huge vertical. were talking about scale models with airfoils jofro. its a whole differnt thing than a huge kite with fans on it lol.im not sure andy wants to hover his T-38 anyhow...

back to T-38's......


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