By STAN 
KASPRZYK
FlightLog Archive
∟Aircraft Flown
Flying the Tetra-15/HP-24 - Jan 2012
Flight test notes from N599GK, 28 Jan 2012, Arlington, WA
You have a great sailplane, Brad! I found your Tetra-15/HP-24 to be a joy to fly, with no major issues evident in flight. Even with my 6' 1" height, I had another detent of rudder authority available if needed, and while the top of my head was close to the canopy, I was wearing a sweatshirt, winter jacket and the chute. The cockpit size for you will be perfect, especially for those long cross-country adventures.
Stick feel and throw are well balanced in pitch and roll. I held the stick slightly forward of a neutral position for the initial part of the takeoff roll, which lifted the tail wheel in the early part of the takeoff. Even with only a small 4-5 knot headwind on takeoff behind the SuperCub tow plane, the Tetra-15 had no tendency to drop a wing on takeoff roll, and the ailerons felt responsive a few seconds after the takeoff roll began. As the tow continued, I held neutral stick and allowed the bird to fly herself off at around 50 knots. Once away from the bumps of the grass runway, climb out behind the towplane was smooth and effortless, with the trim in the third detent back, which provided very light stick forces at my weight of 205 pounds. Visibility forward was very good, with no issues keeping the tow plane in sight. Above 1500 feet, the air became quite turbulent, but I had no problem maintaining a very stable tow position.
I tried raising the gear as I passed 3000 feet AGL, since I was so stable behind the towplane. I made two attempts, but just couldn't get good leverage, and decided to wait until I released from tow to try in earnest. I had very good roll response once I separated from the tow, and successfully raised the gear with a concerted lift of the handle. Some tweaking will be needed to reduce the force needed to get the gear up, but the gear doors appeared to seal tight, with no wind noise from the lower fuselage area.
Since we had pre-briefed formation flying with the tow plane for some in-flight photos, I joined back up on the towplane's right wing, and the Tetra-15 was very controllable while formation flying with the towplane for the photos, with speed ranging from 60 to 105 knots at 0 and -1 flap settings while maneuvering in the formation flight and repositioning for decent photos. At the 3rd detent trim position, I did notice a tendency for the Tetra-15 to really want to smoke along, so I stabilized at around 55-60, and set the pitch trim back to about 5 or 6 detents. I just need to figure out the best trim setting for me to keep her slowed down a bit - she wants to haul! Flap use is intuitive, and we need to explore best cruise flap settings and use of +1 and +2 options for landing. I did notice that the flap handle moved from +1 to 0 with very little force, and might needed to be tightened up a bit to avoid inadvertent flap setting changes.
The Tetra-15 is easy to keep coordinated in shallow- and medium-banked turns, with normal coordinated rudder input needed rolling into and out of turns. I tried slow flight to 42 knots, approaching a stall, and noticed a very slight tendency to drop the left wing, but the air was quite turbulent and it was not a good environment for a very quantitative assessment of slow flight capabilities.
I did notice the howling noise that you had experienced during different portions of the flight, but especially in the 55-65 knot regime with the flaps at the +1 position. I was able to increase/reduce the noise using different flap settings, but it was hard to isolate the true source, but it did seem to originate aft of the cockpit, but I couldn't isolate it to the cockpit air exhaust area. We'll have to try taping the exhaust port to see if it provides immediate relief, or if it's related to the tape on the rudder that could be vibrating.
Regarding instrumentation, we discussed the obvious need for a replacement altimeter, while the GPS backup readout matched the tow plane altimeter within 100 feet. Airspeed comparison with a calibrated baseline will be needed later, but generally also matched the towplane during today's flight. Your radio was quite clear, and the speaker arrangement near my right shoulder worked well.
I lowered the gear before practicing a few approaches at altitude, and unlike the raising heroics, lowering the gear was comparatively easy, with a reassuring locking sound when the handle was down. I configured for landing at +1 flaps, and flew a full practice approach at altitude, noting that spoiler activation produced little to no pitch change.
Once I descended for the actual pattern and landing, I had very good visibility in the pattern, with the spoilers easy to deploy and very effective in accurately controlling my aimpoint. With a little practice, you'll have no problem in short fields. I flared and touched down at around 47-48 knots, touching the tail wheel and the main wheel nearly simultaneously. I just tapped the brake slightly, but it seemed to work well.
Overall, I really enjoyed flying your Tetra-15! It's a very comfortable ship, with only a few issues to work through beyond expanding the speed envelope, exercising more stalls, slips and potentially spins:
- Gear retraction force needs to be reduced
- Investigate the howling noise aft of the cockpit, especially at +1 flap setting
- Assess if the flap handle moves too easily from +1 to zero
Overall, Brad, you've built yourself a keeper! She's a blast to fly, and looks great also!
Here's a link to a compilation of cockpit video from the first flight tests: Tetra-15 Flight Video.
Epilog
After years of successful soaring, Brad and the Tetra-15 made the cover of Soaring magazine in March 2018. Way to go, Brad!
Epilog 2
After repairs were completed from a hard landing and main gear collapse, Brad Hill sold his Tetra-15/HP-24 to Florin Botezatu in 2021. Florin requested a test flight, since the aircraft had not flown since the repairs. After a condition check was completed, I flew the Tetra-15/HP-24 on 27 July 2021, with most systems working correctly in-flight, other than an inoperative airspeed indicator. Handling felt great, and after a smooth tow, thermaling turns, slow flight and speed calibration with pitch and an iPhone app displaying groundspeed, I flew a normal approach and landing for a smooth touchdown and no main landing gear issues. After an easy fix to the airspeed issues, Florin completed his own first flight on 31 July 2021. The Tetra-15 soars again, enjoy your new bird, Florin!