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Author Topic: Nitro boosts for weather conditions  (Read 1459 times)

Offline Steve Helmick

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Nitro boosts for weather conditions
« on: June 14, 2011, 05:36:30 PM »
This past weekend, it was not particularly hot...some were in short sleeve T shirts, but not everybody. The weather was more humid than normal. I suspect the barometric pressure was on the low side. I don't think Density Altitude was the problem, but lack of oxygen due to humidity and BP.

Mike Haverly and I both noticed that we had to crank in the needle quite a bit to get the rpm close to normal...and it didn't work very well. We realized that we needed more nitro, but were not prepared to do that. We usually use 10%, because the LHS doesn't want to carry 5-22 and 10-22 and it doesn't seem that 5-18 is likely popular with the R/C bods. Looks like I'll be mixing my own, and/or we'll be carrying some YS20/20 to spike the mix.

I understand that if I have the NV set for 5% and cool, high barometric pressure with low humidity, I can run 10% or 15% and see which runs better at the same NV setting. What I'm wondering about is the fuel load. With the same NV setting (and fuel viscosity), the same fuel load seems likely to be close.

What I want to ask, is how to determine the fuel load without putting in a test flight if you change nitro %. Would you run it on the ground and time the run (expecting it would burn more fuel in the air?)?  Mine (the SV-11/PA .51) not only had to turn the NV in (one turn plus on 10%!), but also didn't run as long as expected, which seems totally bizarre to me. I was expecting an over run problem, but it ended up starting to burp in the OH8 and aborted on both flights. No practise circle...<sigh>.  n~ Steve
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Offline Mark Scarborough

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Re: Nitro boosts for weather conditions
« Reply #1 on: June 14, 2011, 08:21:35 PM »
Steve,
the extra fuel you needed in the SV-22 sunday was in the twister when you fueled it for my flight on Saturday,, 7:55 , pretty close,, I sure am proud of those one flip starts you got, especially on my flight!!!!,,  ;D

That being said, Pat and Randy, if I recall correctly, always told me when I couldnt stuff enough fuel on board, to go to 5% fuel instead of 10%, it seems you do reduce the fuel burn with lower nitro, of course the potential reduction in power seems to be of no real issue on my planes,, say my old Oriental, with LA 46, or the Avenger with a Magnum 53,, even on 5% I dont seem to have a real power dilema,,The Oriental was limited by room for  tank, so lower nitro helped get that last few laps for me.
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Offline Martin Quartim

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Re: Nitro boosts for weather conditions
« Reply #2 on: June 15, 2011, 07:19:15 AM »

Hi Steve,

When it gets hot like that I change for a higher pitch prop, this has worked for me for 4S and 2S setups.

Martin
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Online Brett Buck

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Re: Nitro boosts for weather conditions
« Reply #3 on: June 15, 2011, 10:01:54 AM »
Quote from: Steve Helmick on June 14, 2011, 05:36:30 PM
What I want to ask, is how to determine the fuel load without putting in a test flight if you change nitro %. Would you run it on the ground and time the run (expecting it would burn more fuel in the air?)?  Mine (the SV-11/PA .51) not only had to turn the NV in (one turn plus on 10%!), but also didn't run as long as expected, which seems totally bizarre to me. I was expecting an over run problem, but it ended up starting to burp in the OH8 and aborted on both flights. No practise circle...<sigh>.  n~ Steve

   I don't know of any good way aside from testing it. It's not consistent between different setups. We have learned over the years how to change it at, say, Muncie, and usually 10 to 15 yields about the same run time and similar power. On a cooler day, it might need 12.5. If you get the needle in about the same spot, that should pretty much do it. So if you can get it to the same revs and the same "setting" on the ground with the needle in the same spot, you should be in the ballpark.

    Brett
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Offline Howard Rush

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Re: Nitro boosts for weather conditions
« Reply #4 on: June 15, 2011, 07:59:25 PM »
Density altitude at Thun Field at 12:15 Sunday was 1325 feet.  More useful is density / sea level standard day density, which was 96%.  Humidity doesn't affect oxygen content hardly any at that temperature, despite common toy-airplane wisdom. 
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Offline Steve Helmick

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Re: Nitro boosts for weather conditions
« Reply #5 on: June 15, 2011, 08:56:04 PM »
I just checked, and Thun Field altitude is 538' ASL. Most our sites are much lower. Eugene is about 375', TNA 284', Arlington 250', Scobee 63', Chehelis 176' and Salem 214'.  I'm used to flying in the Kent Valley, so about 63'.

Less prop load seems in order, but I don't see less pitch being good. I'm thinking 1/8" off each tip? And where can I get an affordable devise to measure Density Altitude?  ??? Steve


Edit: Did a search (which I should have done first) and found this thread...
http://stunthanger.com/smf/index.php?topic=13443.0
  It answered most of my questions...and then some. Thanks to all for their answers.

  
« Last Edit: June 15, 2011, 09:44:11 PM by Steve Helmick »
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Howard Rush

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Re: Nitro boosts for weather conditions
« Reply #6 on: June 15, 2011, 11:41:18 PM »
You can calculate it after you get home by looking at http://wahiduddin.net/calc/calc_da.htm and http://www.wrh.noaa.gov/mesowest/getobext.php?wfo=sew&sid=KAWO&num=72 (for your location).  An alternative is to use an OS .40 VF.  Put 10% in it, set the needle valve once, and you're in business.
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