About 6 hours invested into reading and understanding the prints.
$536 for the design prints and operating manual.
$140, in 6061T6 2x2’s, 0.125 plate stock (4sqft), and AN hardware. This material will construct the inner core of the aircraft comprising the main keel, rotor mast, center cabin diagonal keel, and the gusset plates required for these members.
Now I can say I’m about 90% complete; however, that last 10% seems like it takes forever!
Anyway, as designed this machine is HTL… I know, I know, I know. I do want to say this design does have a good amount of both vertical and horizontal stabilizer immersion in the prop’s wash, so that is a significant positive attribute to offset the HTL tendency of this particular HLT design.
I think it’s logical to say that in an HLT design when you are in straight and level flight, and add power the nose would otherwise tend to lower (not desirable or an unstable trait). However in this HLT design because the horizontal stabilizer is right behind the prop the increased air velocity from the additional power would generate greater additional negative lift to counter balance the tendency of the nose to drop.
Has anyone ever built a Gyro that has a progressive trim tab on the immersed horizontal stabilizer that is coupled to the throttle in an HLT design? So, that when you apply power the elevator rotates slightly to increase negative pitch to the H stab which keeps the nose level or even raises it slightly? Also as power is reduced in an HLT design the nose tends to raise (undesirable) in the above described throttle linked to the horizontal trim tab, more positive lift would be generated when power is retarded to cause the nose to drop slightly. Is this a common way to reduce the natural instability of an HLT design? I think it probably is, but I’m not an aircraft designer.
In regard to PIO and PPO of this design, it is aerodynamically “neutral” based on the dimensions of the design as built to plan specifications during computer modeling. PIO in this design does not amplify if a disturbance of one of the other forces of flight on the airframe changes (thrust, drag, lift or weight) There is no amplification of the disturbance that increases the pendulum swing effect when left in a “hands off the controls satiation.” In other words if oscillation is induced in this design either by the pilot or natural factors, it remains constant, but does not amplify/increase or diminish/reduce. This is neither good or bad, it’s indifferent.
As to my understanding of stability, you desire an aircraft that will raise the nose on acceleration and lower the nose on deceleration. The great question/debate is how do you make that occur…
Hi Dan, I was planning to keep it as much as possible to the original design, but I may not use fiberglass in the areas it calls for fiberglass. I’m not yet sure how I want to approach that yet, I’m leaning to carbon fiber or I could use aluminum. I could even use fabric and dope in a few places. I can say that I’d like to bump the fuel tank size from 12 to 15 gallons, and thinking I’ll go with the EJ Subaru 2.2 EFI which drinks 6.0GPH at 75% power. That should get me a full 1.6 hour flight time at 80MPH, and the aircraft can handle the extra 3 gallons for the weight, and it falls within the CG range as well. This also would give me my 30 minutes reserve fuel level. I don’t like the design of the current fuel tank; it holds 1.5 gallons unusable, which is a lot for only a 12 gallon tank.
Thanks Vance, I got the 6.0GPH from a supplier of aircraft prepped 2.2 subies and they advertise that at 75% power, they consume 6.0GPH with the EFI, Also the rotax 912 (carbed) (80HP) that i fly burns 4.0 GPH at 75% power, as an observation, at full slant she drinks about 5.2GPH.. ON the subie I bet I'll be about 7.0GPH, so you can see why I want 15 Gallons gas on board... cause I actually want to fly places more then 25NM miles away from home...
In the design of the Hollmann HA-2M (Hamster) because the cabin enclosure makes it look like a hamster with food packed into its cheeks… Anyway, the fuel tank centroid is essentially an aluminum box that is located 23 inches forward of the center of the operational range of the aircraft’s center of gravity. The tank is 12 gallons with only 10.5 usable. I intend on making a few tweaks of the tank bottom to increase the usable fuel level, and to increase the fuel level to 15 gallons. I have the room in around the tank to do so.
23 inches centroid to centroid seems pretty far forward of Aircraft CG for a fuel tank? What say you…
Because the tank is so far forward of aircraft CG I was not able to simply make a larger tank at the same location, because it puts my max weight takeoff CG forward of the operational CG limit by about 1 inch. Bummer!
I did my calculations last night on the original design and discovered that I can leave the tank exactly where it is in its same foot print, but instead of it being simply rectangle with a constant centroid at 23 inches fwd of CG, I can transform it into the shape of a parallelogram sloping in the direction of the rotor mast. By doing that, the tank now has a moving center of gravity. Full fuel moves the tank’s CG back toward the rotor mast by approximately 6 inches, ½ tank by 3 inches aft, and at ZF I’m right back to where I started. I verified that under all fuel and passenger loading configurations where the aircraft meets minimum and maximum operational weights, my aircraft CG falls with in design limits. And I am not over gross weight by increasing full fuel load from 12 to 15 gallons.
Actually it’s not a parallelogram, as the back side slopes more then the front does, so the sides are not parallel; therefore, it is not a parallelogram! That is how I got the increase from 12 to 15 gallons, the fact that it is not a parallelogram. I added this paragraph in as an after thought, because I figured someone here would catch this fact and taunt me
So how far forward or aft of aircraft CG range is your fuel tank?
Also with the additional fuel, I’m at 1070 pounds max gross flight weight assuming that my engine comes in at under 233 pounds.
IMHO, I'd stick with using the Lycoming O-320. The simplicity is in the installation. With the Subaru, lots of modification, set up, tinkering, and the like which add complexity. There are numerous used O-320s out there at reasonable prices, ready install and operate.
Still, I'm enjoying reading about your ideas and progression.
I think your right, I think I’ll go with a O-320, simple… and I can have it fuel injected for a price.
I made my first cuts tonight. The 81deg rake of the double 2x2 rotor mast, the center cabin keel, and the main cabin lower keel, these three members comprise the main inner core of the whole aircraft and everything else will be added to these three tubes. The diagonal 2x2 runs through the center of the cabin and separates the pilot and passenger.
Very interesting build thread. I have one of Martins Bumblebee's and was looking at the sporter but did not like the cabin. It will be interesting to see how it flys and handles with the changes you do. I bet it would make a great side by side trainer without a cabin on it at all.
Sorry to hear about your loss, it’s most unfortunate, and you can bet I read the post on the forum about this with much interest. I intend to stick with the plans as produced in regard to all critical airframe parts and dimensions. My plans say that the rotor mast is required to be redundant 2x2, which is a fancy way of saying that you sandwich two separate 2 x 2 beams into a single 2” x 4” mast.
It might make a good side by side trainer without the cabin, but it certainly would take quite a bit of recalculation and verification, as this would definitely change the type of drag and its ratio to each other (Dynamic/Parasitic) in addition the change in weight would have tremendous affect on it as well. The “as built” cabin enclosure weights about 70ish pounds, and is well forward of the aircraft’s operational range of CG. Coupling both the weight and drag changes would produce a different aircraft, that’s for sure.
Cool! Another build thread. You sure have picked an interesting one Good luck with it Cort, it takes a lot of effort and talent to build something from scratch. I am always interested seeing solutions to problems and during a build you'll run into some stuff for sure I'll be following your build for sure.
Well for crying out loud! Why didn’t I think of this sooner! SEAT TANKS! That solves by small gas tank problem! Each seat tank is 7.4 gallons, and that gives me 14.8 gallons on board, most of which is usable fuel, (unlike the factory design.) It will move my CG aft nicely, enough so that I can have a radio and transponder in the instrument panel… and, and… it will slightly raise my vertical CG by varying amounts, putting me closer to CLT. Now I don’t have to heli-arc this monstrosity that weights 15 pounds empty, only holds 12 gallons and has 1.5 unusable level… and I now can scrap the stock tube and nylon webbing seats for molded plastic comfort! My girlfriend has already begun to quilt seat covers! Yessssss.