200mph, 30A ESCs and Nano Tech Lipo???
Yes, not spectacular and not good for marketing the latest hyper-amped ESCs and 100C+ lipos. There still is a need for those, but not when it comes to top speed builds.
The gift that keeps on giving
That gift actually starts by taking away something: drag. Once this is done, we are given the gift of speed, and speed starts a seamless circle that keeps on giving:
- Less drag = more speed (less force needed to push through air)
- More speed = props less loaded (blog on prop unloading is here)
- Less loaded prop = less torque needed to spin props
- Less torque = more RPM
- More RPM = more speed
- Steps 2-5 repeat seamlessly up to the “terminal drag” point
This is where either:
- The residual thrust equals the drag force. Remember the faster we go, the less thrust we have which, as long as the drag is low, isn’t a big deal.
- The propeller tips start going transonic (about Mach 0.75-0.80). This is where torque requirements skyrocket and things go bad from there.
For brushless motors, volts = RPM and amps = torque. Now we see (and tested) why 80A ESCs and 10s batteries will do absolutely nothing but create heat and flames (didn’t I say that about 6s at one point? Hmmmm…..) The faster we go, the less amps we need to keep moving. However, we need the volts (RPM) to get there – up to a certain point: the prop tip transonic speed limit. This is where amp draw will jump and things go into a downward spiral – sometimes literally.
Just a quick note: the above is also the reason there is still a need for higher amp ESCs and batteries. Race quads and freestyle quads do a lot of direction change and throttle hammering. This means the props are undergoing a lot of stress and loaded a relatively high amount of time. Think of a bicycle with a fixed gear ratio. When you are travelling at high speed, pedaling effort (like amps) is easy. Now if you were to start doing some frequent stop, accelerate, repeat over and over… pedaling effort has increased tremendously.
World Record Attempts
More things went wrong than I am willing to admit, but the biggest lingering issue was the video reception. It was a huge “duh” moment. The whole event was pretty chaotic, but this is a general overview.
Witnesses involved in the runs (we had a lot more than required) were people from various engineering backgrounds including several from the aerospace industry and even a former ground control person that took part in 24 shuttle launches.
April 4th: Practice day. I brought 5 frames with me, 2 5s frames and 3 6s but I only got to practice with 5s since video range was bad and I was afraid that 6s would quickly leave video range. 5s practice went OK, but the frame was very unstable at high speed. Max for practice with 5s was 171.5mph/276kph.
April 5th: Speed runs. Still had video issues which only allowed for a good run in one direction (100m average in one direction). To add more to the mess, the GPS lost connection on the last battery (due to a broken wire) and then had a minor crash. Max speed was 181.44mph/292kph. However, since the 5s frame was so unstable, it couldn’t keep up a consistent speed. The best I had was an opposite 100m average of only 163.61mph/263.3kph. It was a good time for a break and to do repairs. While doing repairs and since we had the means to record and measure it, Josh Cook gave a try at the ascent record – this way, if things went really bad and I never got the chance to give the ascent a try, at least one record would have been broken. Josh ended up with a 100m ascent in 2.80 seconds which was roughly a full second quicker than the previous record.
Being very careful not to go out of video range, I got in a quick practice run on my 6s “mutt” frame at the end of the day. If any frame was going to crash, this was going to be it since it was pieced together with some beat up motors and ESC’s. First pass hit 167mph and was very smooth. Second pass ended in a crash. As I was going throttle up, an ESC failed (not exactly sure why, nothing was burned up). This single run gave me confidence in the 6s, but the video issues lingered.
April 6th: Speed runs continued and ascent attempt. This was scheduled as the backup date since we were leaving the next morning. Starting with 5s, video issues continued and seemed to be even worse. It got to the point where I had to stop things and figure it out. Thinking my goggles were bad, I sent an SOS to Jayson Smith (MetropolisFPV) and he let me use his goggles. Once I had those, I did some on ground comparisons of video reception of all the vtx’s I had and between my goggles and Jayson’s. Truthfully, reception was only marginally better with Jayson’s – not enough for me to feel comfortable.
As time was running out, Jayson asked what the tail cone was made out of. I told him it was 3D printed and that all I know is that the material is carbon reinforced. Jayson pointed out what should have been obvious to me about 4 months ago. The carbon is messing with the rf signal. Duh. So I then realized the antennas had to be moved to the outside.
Before I did that, I made an attempt at the ascent record. Since I had Wraith32 ESCs on this quad, I thought I would be able to see the quad easily, especially since it was very late and nearly completely dark out… Well, that didn’t work out that well. The thing took off, I didn’t get the stop signal, so I was on the throttle a bit too long and lost it. Good thing is that the video of the ball and string (100m string attached to a whiffle ball) was recorded. Time started at quad launch and ended when the ball moved. The string was taped on the drone so the string wouldn’t follow along and get wrapped in the motor (this happened to Josh). The whiffle ball was attached securely to the ground so the whiffle ball would win the tug-o-war. After review, the time was 1.70 seconds. I then got to work on putting the antenna outside the tail cone for a last attempt.
The ascent video: As expected, the take off does look SLOW. This is due to the high pitch 5260 props – calculations showed that they would take off a little “slower” than a 5″ pitch prop, but the 6″ pitch would over take a 5″ prop in a 100m race.
April 7th: Last chance. Everything went great. Video test of the new antenna placement looked good so I decided to use my own FPV goggles while my son wore Jason’s as a backup. It flew like a dream, did 4 passes and then decided to bring it in early since I easily could have done 2 more passes but I wonated to play it safe. I knew it went fast, but when I saw the 325K max speed on the OSD, I could hardly believe it. I then took a look at the log and double checked to make sure all looked good; the quad was slightly climbing for both of the fastest opposite passes and the headings were only 4.16° off from 180°.
Opposite direction average over 100m: 195.99mph/315.42kph
- Direction 1 average over 100m: 196.70mph/316.55kph
- Direction 2 average over 100m: 195.28mph/314.28kph
- Max Recorded Speed: 202.11mph/325.26kph
- Blackbox data is here
- Spreadsheet with decoded GPS data is analysis is here
- How the data is analyzed is here
Special thanks to Forrest Frantz for making this happen, Jayson Smith for saving this speed attempt, and to Jon Blackburn for printing/designing the nose and tail cones.
Why Not Official?
A very long story short (about 2 years), Guinness eventually found technicalities with the witnesses. Although the evidence and speed were verified, there was a slight technicality that cannot be resolved easily. So, although I am confident that I can repeat this speed (I regularly fly over 200mph and have now achieved 257mph), the process is very time consuming and exhausting. Well, the time has come to give it another try.
Links to witness statements and flight data:
- Witness statement 1 (jpg since I couldnt redact pdf)
- Witness statement 2 (jpg since I couldnt redact pdf)
- Speed data analysis
- Blackbox file
3 thoughts on “XLR-1”
Great write-up of this project! I’m particularly impressed by the carbon in the later version and the rocket-like streamlining!
Hey Ryan, I am a bit of a noob at drone electronics and it seems to me that they more the cells and amps, the faster your drone can travel at (until it reaches terminal velocity?)
I am building a drag drone and I was wondering what would happen if I put bigger motors on larger props. Could we be expecting a 7 inch speed drone!?
Within the relmes of reality, what do you think would be the perfect setup for a guy on a budget that wishes to have a 200+ mph drone?
Thank you for your time!
Late last year I did some rough educated calculations on the best diameter for speed and that turned out to be between 4.75 and 5.25 inches. The reasoning behind it involves a lot of aerodynamics and a balance of many different factors. A quick explanation: all props have a speed limit. Not the speed of the quad, but the speed of the tip of the propeller – it cannot go past (roughly) Mach 1 (it would help to read this: https://quadstardrones.com/2017/07/11/quadcopters-have-hit-the-sound-barrier/ ). In other words, the larger the prop, the less RPMs it can go. What makes it a deal breaker is that the larger the prop, the lower the pitch (due to aerodynamic reasons). So even though we can create a lot of thrust, thrust means nothing if the air it is pushing isn’t going very fast. Why not use a 4″ prop and spin it at super high RPM? The 4″ prop won’t produce enough thrust to overcome drag (resulting in low terminal velocity). As you can see, it’s a balancing act and the 4.75 to 5.25 inch optimum prop size for speed won’t apply to all propeller driven aircraft since it will be dependent on weight, surface area, drag coefficient, etc. Larger aircraft have the luxury of having variable pitch props which takes care of the prop diameter vs. pitch issue.