What is T-Rex 800 top speed?

[utrinque]

I did not find any measurements of T-Rex 800 top speed with GPS.

I am not going to start competition. I am just curious.

I know 700 can go 105-115 mph before retracting blade stalls.

I wonder why Banshee can fly much faster without stalling. Seems it is only a measure of RPM.

Higher RPM should protect from stalling.

Anyway... Please put your old Garmin GPS on 800 and try to measure top speed.

I will tomorrow fly with GPS and record some tracks to determine top speed.

I have 4,2kW motor only so I want to accelerate with a little help of gravity.

Anyway GPS measures horizontal speed. Actually mine has "Jumpmaster", but I have not idea what it does.

[nmdesertracer]

I clocked mine at 72mph thats with 11 degree pitch. Fast enough for me..

[utrinque]

...

[utrinque]

My first measurement 164 km/h equals around 102 mph. Nothing fancy. Good news is cheap $48 Gartt motor designed for 700 did not get hot. I use YEP 180A HV regulator.

I am not going to push its limits. I assume with strong lipos 800 can easily reach 200 km/h.



Banshee can achieve 286km/h:
http://markkovalcson.wordpress.com/2...-of-a-banshee/

[907Heli]

It's not just rpm. It's the amount of pitch that the retreating blade has to have to match the demand. A lighter Heli needs less pitch just to.maintain altitude so more can go to forward speed therefore getting more speed before reaching the stall point. A more aerodynamic Heli does the same thing. Higher head speed helps but only to the point that the tips exceed the sound barrier then the blades will stall.

[utrinque]

Originally Posted by Aksport

Higher head speed helps but only to the point that the tips exceed the sound barrier then the blades will stall.

When you do the math it is clear tips are never close to sound barrier.

Anyway in the past I had the same theory. ; ) Really, I am not kidding.

[slickporsche]

Utrinque

No offense meant, but maybe your math is off. When you hear a whip crack, that is because it (the tip) has gone supersonic. Is that no what I hear when I fly a fullsize heli, when it goes wop wop? Of course the blades are much longer, and the forward speed is greater. It seems we hear that on our models. If you consider the length and speed of around 2000 rpm on an 800 traveling at over 100 mph one must be getting close to supersonic. In addition, it is not theory, but fact. Of course 2000 ,may be a bit high for a 800.

[utrinque]

Math is simple:

Circumference equals 2*PI*radius.
PI=3.141593

Lets assume 1 meter radius and 2000 RPM:
Circumference is 6.283185 meters
2000 times per minute 12566 meters
12.566 kilometers per minute

753.9822 kilometers per hour - this is the speed of blade tip.
Speed of sound at sea level = 1225.044 kilometers per hour

We lack 471.0618 km/h

Even Banshee can not fly 300 km/h. Speed record was around 280 km/h.

We are still FAR from speed of sound.

Speed of blade stall is much lower. I assume this is the problem. Stall speed depends on angle of attack of the blade.

[mikeylama]

A pretty easy approach of explaining why is it impossible for the blades to spin faster then sound

The Helicopter Speed Limit - Helicopter Physics Series - #7 - Smarter Every Day 51 (5 min 40 sec)