Referring back to the older posts discussing engine options, does anyone make a high-bypass turbofan engine for models?
There was a UK company displaying a TF engine they were developing at Oshkosh in 2004. The centrifugal engine without the geared fan was probably in the 40lb thrust range. They were talking 2-400 lb thrust with the fan. I tried to contact them without success a few month later for a follow up. I'm sure the gear box was the deal breaker or we'd see them all over the place. Reducing that kind of rpm to a 20" fans useable level with reliability would be a project worth doing but certainly not easy.
I'm afraid that nobody here can answer that for you. This is a "numbers" question. You're going to have to run the stability and control numbers (all three axes) for the increased wing area and span, and then decide if the existing tail is adequate. Since you're already reporting "weak" yaw control, the answer may clearly be, "no", but only running the numbers will tell. You're redesigning the airplane at this point.... My question for the group is, would a 18 meter wing work with the current HP-18 fuselage geometry (current tail boom length and stabilizer/ruddervator area) and might anyone else have experience with such an idea....
I have a much easier solution to suggest: Ditch the fancy retractable outriggers and go for simple plug-in units. My thinking is that in situations where you need maximum soaring performance, you're almost certainly going to have a wing-runner available at any regular soaring operation. For the situations where you're doing a powered cross country or air-show performance, you can plug in the outriggers and take the slight drag penalty. In the rare situation where you want good soaring capability and there's no wing-runner, make sure you've got small (fixed) tip wheels (or skids) and do a wing-down takeoff. Should be a piece of cake from a paved runway. My soaring club had a usual deficit of wing-runners, so I've done more wing-down takeoffs in a pure sailplane than I have takeoffs with runners. It's really not a big deal, and certainly worth saving the weight and complexity of retractable outriggers, IMHO.... 3: Install electric linear actuators into each wing for extension/retraction of wing stabilizer wheels for self-launch procedures. This would be similar to the Europa motor glider but faired into the wings for drag reduction. The reason for this addition is to keep the wings level and away from the runway and taxi lights. The self-launch operations will be conducted off of the hard surface to reduce the rolling resistance and takeoff roll length.
Ditch the 2-part wing. Really.I am considering the construction of a new wing with a 18 meter span. This would be a one off project made out of foam and carbon with construction similar to the Rutan composites (hot wired cores, carbon shear webs,carbon spar caps and carbon wing skins. My thought is to build it with a 15 meter length and add removable polyhedral wing extensions for a 18 meter length with double duty winglets (15 and 18 meter wing).
It depends. Do the math and calculate Sv and Sh and share those with us. It's likely that we can then give a good answer.My question for the group is, would a 18 meter wing work with the current HP-18 fuselage geometry (current tail boom length and stabilizer/ruddervator area) and might anyone else have experience with such an idea.
Torsional loads on the tailboom increase with the square of such an extension. Unless you do the math; don't extend them!Change ideas from existing design:
1: Increase the area on the stabilizers/ruddervators by some amount (possibly 4-6” in height with an extended ruddervator trailing edge). Goal is to improve yaw and elevator authority without extending the tail boom length. New surfaces could be manufactured like the new wings with foam cores and carbon spars, shear webs and skins. Currently my ship is nose heavy and I have weight in the tail cone for mid CG flight testing. Some added weight at the tail would actually be beneficial.
Don't. Your typical Nimbus 3 wing tips and self-launching in medium-sized grass works fine.3: Install electric linear actuators into each wing for extension/retraction of wing stabilizer wheels for self-launch procedures. This would be similar to the Europa motor glider but faired into the wings for drag reduction. The reason for this addition is to keep the wings level and away from the runway and taxi lights. The self-launch operations will be conducted off of the hard surface to reduce the rolling resistance and takeoff roll length.
The weather and wind was favorable for the one remaining flight test last Friday. After assembly and one turbine test run the HP-18J was pulled out to the runway for the last remaining flight test - the self-launch exercise.
Wind speed and direction was 5 to 10 mph almost right down the runway. I strapped in and powered up the aircraft, extended the turbines and proceeded with the start sequence. Once both turbines were started and stabilized at idle (33,000 RPM) the thumbs up was conveyed to the wing runner. Full power was applied (105,000 RPM) and the takeoff roll was started.
Once the aircraft speed exceeded the wing runners pace the left wing dropped and the roller blade wheel at the end of the wing did its job. Within a short time the ailerons took effect and I was once again level and accelerating towards takeoff speed. The airspeed was climbing rapidly and the tail was next to lift followed shortly by the sailplane takeoff. I stayed in ground effect for a couple of seconds then started my climb.
By the time I crossed the end of the runway I had gained 400'. I continued the climb at 60 to 70 KTS until reaching my goal altitude of 3000' AGL. Upon reaching altitude the engines were shut down, cooled and retracted. I soared for 30 minutes, did some more spin exercises to spend my excess altitude and did one re-lite to verify the restart success for the previous weeks testing. Both turbines started successfully and were shut down after a couple of minutes. I returned to the airport for landing and was greeted by my support crew once I rolled onto the taxiway.
My Oudie flight computer provided all of the finite statistics from the flight. The runway takeoff run was between 850 to 900'. The time to climb to 3000' from a standing start was 4 minutes and 45 seconds. The climb rate from the standing start averaged 631' / minute. Total fuel burn for the takeoff, climb and one restart was 3.5 gallons. Remaining fuel in the header fuel cell was 3.5 gallons.
Anticipated flight sequence. Self-launch and climb to 3k, shut down the turbines and retract. Utilize one engine for sustained flight if needed at reduced throttle. This should provide a 25 to 30 minute duration run with the remaining 3.5 gallons of fuel.
Note: The flight test performance results came within 10% of what my preliminary calculations provided. This was quite satisfying and shows that the math can really work for predicting performance results.
Lots of fun but I am glad it is over,
Hoping for video and photos from the flight crew later this week,