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HelicopterMain Discussion › "Altitude"
01-23-2007 01:07 AM  10 years agoPost 1
Fernando Abascal

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Puebla, Mexico

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After a year and a half we finally found answers about our set up. Todd Bennet was right and nightmares finally end. We did really worked hard on set up, but any time seemed to be impossible, there was not enough power to keep heli flying as good as it used to be when we had lessons from Todd Bennet in LA. Phone calls and e-mails asking Todd about special set ups or missing something.

And all was about the "ALTITUDE", our place is located at 7220 feet over sea level. We had the chance to fly last weekend right at the coast, at sea level, and everything became so PERFECT, even rocks can be suspended in the air. I do really envy you guys flying at sea level. Motor power and heli performance become so perfect.

Driving five hours to get the coast on the weekend was worthy.

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01-23-2007 01:14 AM  10 years agoPost 2
Yug

rrMaster

UK. Herts

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I'm glad you've sorted this. The trouble with altitude is 2 fold; not only does the engine power suffer due to a smaller charge but the blades also have less air to work with. I suppose electrics solve half this problem.

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01-23-2007 01:19 AM  10 years agoPost 3
A. Bundy

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Aurora,IL. 30W/SW of Chicago

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So much for the saying "altitude is your friend".

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01-23-2007 01:26 AM  10 years agoPost 4
Fernando Abascal

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Puebla, Mexico

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I did try a T-Rex 450, and there is still lot of difference, night and day. Man is so easy to do many manouvers that I couldn't do at this altitude. I fell in love with it.

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01-23-2007 02:32 AM  10 years agoPost 5
HHawk

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Gardnerville Nv.

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I hear ya Fernando High altitude SUX!!!! Im at 6225ft.

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01-23-2007 02:43 AM  10 years agoPost 6
Fernando Abascal

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Puebla, Mexico

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You´re right high altitude sux! How do you handle it?

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01-23-2007 08:46 AM  10 years agoPost 7
Yug

rrMaster

UK. Herts

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Because the air is thinner, there is less air resistance, so you could try using longer blades. For the 90 size helis, there are some that use 710s in the summer and 690s during the winter due to the change in air density.

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01-23-2007 11:57 AM  10 years agoPost 8
Paul Woodcock

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Dubai - United Arab Emirates

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Hi guys

I have a theory.....

In aircraft, the wing behaves in relation to indicated airspeed and as altitde increases the true airspeed increases for the same indicated airspeed.

Now.....my theory....Our helis head speed is true airspeed and indicated airspeed would be lower. If you up the rpm by about 10 percent it is very roughly equal to what it should be.

I know nothing about heli theory but use my fixed wing basics. It seems to work. I have just moved to a sea level location and reduced the headspeed by 10 percent and the heli feels the same.....It has much more power but feels the same. I also run close to the same pitch range by using this rpm shift method.

Paul

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01-23-2007 01:58 PM  10 years agoPost 9
Fernando Abascal

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Puebla, Mexico

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It seems to be almost perfect, but if you are running 1850 RPM and increase head speed about 10%, you are over 2000 rpm, isn't it dangerous if you are using plastic blades holders?. I mean going to metal blade holders will help but since you are having problems with air density you would not like to add weight.

Actually I do fly a stratus 8.18 with plastic blade holders and 710 mm blades.

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01-23-2007 02:31 PM  10 years agoPost 10
Alejop

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Bogota - Colombia

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Altitude

Imagine....we are flying here in Bogota at around 8600 feet and definetly we feel the loss of engine power and heli performance.
High nitro % helps a bit with engine output but nothing we can do with the blades performance.
Everything is sort of critical here....doing autos is a real chalenge and a big adrenaline rush !!

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01-23-2007 04:45 PM  10 years agoPost 11
w.pasman

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Netherlands

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I'm not a fan of electrics but in your a case, an electric machine might have an advantage: no power loss due to lack of air. I guess also that the blades will just turn faster as air gets thinner (less resistance but same engine power) which might partially compensate the "less air to work with" problem.

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01-23-2007 06:21 PM  10 years agoPost 12
Alejop

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Bogota - Colombia

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Since there is a speed limit for the head before it fails, we have noticed that a better option at 8600 ft is to use larger blades to compensate for the loss of efficiency due to the low air density.
We also found much easier to cope with the engine factors using at least 15 % Nitro and a throttle governor.

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01-23-2007 07:19 PM  10 years agoPost 13
HHawk

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Gardnerville Nv.

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I installed the 8.73 gear ratio and run 1750 1950, 2150 head speed on my Raptor 50. Also 30% coolpower. You really learn collective management when flying at high altitude. Its still fun , just not as easy as low altitude. My next move is to get an electric to atleast solve half of the problem.

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01-23-2007 07:21 PM  10 years agoPost 14
Fernando Abascal

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Puebla, Mexico

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Alejop, you are right, autos are so critical and a challenge at high altitude. Can you work nice in autos at that altitude? Or it's still 50%/50%? We are running 30% nitro, governor and 710mm blades in 90's.
How is your personal opinion about 3d at that altitude? Lot more inputs to control lower performance in flight, right?

As I told you, last weekend, at the coast, manouvers seem to be really easy, specially autos, not that much inputs.

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01-23-2007 08:05 PM  10 years agoPost 15
Fernando Abascal

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Puebla, Mexico

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CrzHk, are you serius about flying at 2150? Metal or plastic blade holders? No problems at all?

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01-23-2007 08:11 PM  10 years agoPost 16
Alejop

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Bogota - Colombia

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Fernando,

Due to a fairly strong headwing at our flying field (10 to 15 MPH) we han manage to do nice autos most of the times .....
In respect to 3D (or any manouver in general) we notice that the response is SLOW both for cyclic and collective.
Some guys here use as much as +/- 12 degree in cyclic travel but still the response is sort of slow (besides also using high speed digital servos).
For example, it is almos imposible to do a nice looking Tic-Toc....it does'nt look crisp at all.

Alejandro P

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01-24-2007 09:14 PM  10 years agoPost 17
HHawk

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Gardnerville Nv.

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Ya 2150 headspeed for Hard 3D, the headspeed boggs into the sweetspot of 17000 rpm on the OS 50 Hyper. For mild flying I use the 1950 in idle up 1 gov mode with the multigov/9254. I run the TT SE metal head and plastic grips. Never had a problem. From what Ive seen in videos, the best thing one can do to a Reptor 50 is convert it to a Xero G rush with a Kasama head and Electric 10S setup. Then you have the power to weight ratio of a 90!

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01-25-2007 06:42 AM  10 years agoPost 18
Fernando Abascal

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Puebla, Mexico

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I know what you mean, when you are flying with a 90, I guess you should keep something about 15000 RPM, in the specific case of the stratus with a 8.18 ratio and OS 91 SZ-H PS, you are talking about 1833 RPM in headspeed to get the maximum of power out of your motor. If you increase headspeed over 1833 RPM, you might start loosing PS, in that case it might be better to change to a lower ratio, but then again, if you increase RPM, you decrease power, and power is what you need for hardcore 3D.

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01-25-2007 07:11 AM  10 years agoPost 19
Spacey

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Pretoria, South Africa

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I am all too familier with this problem. I also fly at close to 4500feet and it is a real problem. The helis don't have anywhere near the power it has closer to sea level. Up here we have to use full fuselages on our F3C helis to be able to make some of the manuvers in the schedules and even then still you only get one chance and no room for errors. At sea level I can fly the manuvers with power and speed to spare with a normal pod and boom Sylphide. The 3D stuff also pose quite a challenge as the power is just not nowhere near the same. My parents live in a rather distant town which is much closer to sea level and it sure is a change going for a fly there.

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01-28-2007 03:55 AM  10 years agoPost 20
gigi

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Port-au-Prince, Haiti

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One positive thing...

I normally fly at sea level, but sometimes go up our mountains for a couple of flights as well. At about 5,000 feet, it's true the response is a lot slower (watch the loops!) but the heli also feels a LOT smoother. Whether it's due to the blades slicing thinner air or the motor turning more freely, the difference is noticeable.

I have decided to not do aerobatics up in the mountains. It's too different, and not worth the risk.

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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