The HP-13-H Returns to Service
Doug Hoffman - August 18, 2003


N2YB, an HP-13-H, (the only HP-13-H?) has been returned to service. This was after storage in a hangar for the last 11 years. Originally built by William Holbrook in Maryland and completed in 1968, the glider had accumulated 480 hours of flying through 1992.

See Photo 1. This is how I found the glider in April of 2003. It was located in Gregory, Michigan at the Sandhill Soaring Club. Note that the wings are unpainted. That is because they were assembled in 1974 but were never installed on a glider. Also note the missing flaps/ailerons. Why the "new" wings? It appears that the last owner of N2YB believed that water had accumulated inside its original wings, causing irreparable corrosion damage. So he threw away the wings and located the wings you see in New York state, built from an HP-14 kit. He also picked up a set of impeccably built V-tails, also unpainted and from the same builder and kit. Why someone would be willing to sell these parts without a fuse is a mystery to me. An A&P mechanic mated the wings to the fuselage. The flaps and ailerons still needed to be built and installed. All of the original kit parts for the flaps/ails were supplied, including sheet metal, rivets, magnesium ribs, root and aileron fittings, a complete set of drawings, and so forth. The previous owner was not mechanically inclined and was having to pay someone else to do any work. I believe that it was getting too expensive for him and that is why work had halted and he opted to sell.

I already own a nice RS-15, so why did I buy the HP-13-H you may wonder? Well, the wings of my RS are still in my basement, in the process of having Udo's airfoil installed. See Photo 2. My plan was to have that project complete by May 2003. I live in Michigan where the flying season is roughly from May though September/October. But it was not to be. I seriously underestimated the time I could devote to the RS project and it had become obvious that the RS would not fly in 2003. So I needed something to fly until the RS is completed. The price on the HP-13-H was right and it didn't look like much work to get it flying. I decided to purchase it, make it flyable, fly it, and then sell it when the RS was completed. I plan to simply get my money out of it, no profit and no charge for the labor. It even came with a surprisingly nice open trailer (large wheels/tires) that tows quite well. I had to install all new floorboards, new tires, and new taillights. Delightfully, I found that the v-tail could remain unfolded on the trailer during transport and during storage in the hangar. The tail uses no taper pins, just straight bolts. There is "zero" play in the tail.

A quick aside. Irn Jousma, our local 1-26 expert, warned me about attaching a glider to an open trailer. There is inherently a lot of flex in an open trailer, which is not a problem in and of itself. A big time problem can occur if you very rigidly affix your glider parts to the trailer. Your glider parts then become part of the trailer structure and will be subject to a lot of unwanted and large loads while being hauled down the road. You may even render your glider unflyable. So allow the glider to move a bit, using bungee and so forth to tie it down.

Building and installing the flaps and ailerons was interesting and of course took more work/time than I had estimated. (See the article I wrote about this.) website.

I also read about John DeJong's wingtip fences on the website. Since I had to fabricate the tip plates anyway, I decided to go ahead and make the Dejong tip fences at the get go. See Photo 3.

My original goal was to have something safe and fun to fly for 2003 that didn't cost too much and could be easily sold later. Although I knew I was going to sell it I had vowed not to screw up anything for the next guy. Alumiprep and zinc chromate were applied to the wings prior to painting, etc. The flaps and ailerons are straight and properly assembled. All new instrument tubing. And so on. But here it was August 1 and I was still working on the HP-13-H! I determined that I was being too much of a perfectionist and in so doing was defeating my original purpose. So I stepped things up and let a few things be: such as the landing gear doors are not installed, the new (much better) v-tail is not installed, the landing gear is frozen in the fully extended position, and the finish/paint job is definitely not up to par. But the glider is safe, fully functional, and easily passed its annual inspection. See Photo 4. The other stuff could be done later or by the next owner. Note the total energy probe mounted vertically on the fuse behind the wing. The 2 static ports are on the sides of the fuse at roughly the same station as the TE probe. The pitot for the airspeed indicator is mounted inside the integral nose vent. See Photo 5. The tailwheel is the stock 3" job and is fixed (not steerable).

But the "proof" was to be found during its first flight. A bathroom scales weight and yielded a 503 pound empty weight and a 32% MAC with my 205 pound 6' 0" frame in the cockpit. Plenty of room. Someone taller and heavier would have no trouble. See Photo 6, where the 13-H is getting ready to enter the launching grid at Ionia, Michigan. This is where the glider is now based. The blue canopy cover is installed. In front of me were a 1-26, SZD-55, ASW-19, and an LS-3a, as you can see.

With a slight knot in my stomach (remember, this glider hadn't flown since 1992 and it also had a new never-been-flown wing installed) I hooked up, went through the checklist, and gave the thumb-up signal to the wing runner. No wing drop! The tow was very stable and uneventful. No parts fell off. Looking good. I released at 1600' AGL because that was the current cloudbase and was quite pleased to find the 13-H had very good , even docile, flying characteristics. Compared to my RS, it seemed to need a bit more rudder input to initiate a turn, and the aileron control was a bit heavier. But it was a pleasure to fly. Very stable. It will nicely groove a thermalling circle. Thermals were weak that day, only 1 knot at best. But it seemed to thermal well and was quite willing to go slow while turning without dropping a wing. Perhaps the DeJong wingtip fences are performing well. Stalls and incipient spin behavior would have to wait for another day when more altitude was available.

Landing was also uneventful. I think the HP-14 constant-chord flaps are noticeably more powerful than those on my RS (my RS has the stock full-length but tapered flaps). Also this ship was easier to land well than my RS. I have no idea why. It was easy to bring the 13-H in slow with about 45 degrees of flap, rotate, hold it off, and let it settle very gently to the ground. Repairing the oleo struts suddenly didn't seem like much of a priority... I believe my RS is more nimble than the 13-H and can probably out-thermal it. But the 13-H is a fine ship and flies quite well. Maybe I won't want to sell it (my wife warned me that would happen). We'll see.

As another aside, I tried the Micro-Mesh canopy repair/cleaning system on the center canopy. I'd never used Micro-Mesh before. The canopy had no cracks or significant scratches, but did look a bit hazy. Starting with the 1500 grit sandpaper I was a bit alarmed at the sizeable scratches being put into the Plexiglas. But I stuck with it per the instructions, slowly working up to the 6000 grit and then the polishing paste. I'd estimate at least 5 hours of hard labor wet sanding (!). But the results were worth it. Except for the frame, it looked like a new canopy! I would recommend Micro-Mesh. Also, I probably started at too coarse a grit.

There are some "unique" features on this particular ship, I believe. Looking at the cockpit the first thing you notice is that all of the instruments except the electric vario are located in the nose in front of the rudder pedals! See Photo 7. My initial reaction was "this has got to be changed". But, as I indicated, summer was running out and I wanted to fly, not build. So I decided to just leave it as is, test fly it, and change it only if I couldn't tolerate the location. I was quite surprised to find that not only could I read the instruments just fine, I didn't need my bifocals to do so. The cockpit is definitely roomier with the instruments up there out of the way. So they are staying put. The next guy can change them if he so chooses. Also note the paper element fuel filter in-line in the pitot hose to the airspeed indicator. To keep bugs and dirt out I suppose.

Photo 8 gives another perspective of the cockpit. Note the 2 capacity flasks, one for the electric Cambridge vario and one for the backup mechanical vario, also in front of the pedals. The Cambridge audio vario is installed close to the pilot so that it can be adjusted in-flight (averager on/off, response rate, volume, etc.). The battery mounts directly beneath the vario. There is no radio installed. The eyeball vent is very effective and also has adjustable on/off and direction. And no, the vent piping does not interfere with use of the right rudder pedal. I was afraid that it might. Schweitzer seat/shoulder belts are installed. Standard-issue flap crank on the left and sliding rod for gear retraction on the right. It all works fine. The rudder pedals rotate about a vertical post (maybe this is borrowed from the -11?) and in-flight pedal adjustment is accomplished by flipping the top half of the pedals 90 degrees back so they are about 2" closer. Only 2 positions available.

The canopy system is certainly not unique. But it was my first experience with the transparent turtledeck, Rearward visibility is fantastic! Maybe all gliders should be made this way...

I can easily solo rig the ship using one of Udo's dollies (the same one I use for my RS). The ship is kept disassembled and on its trailer in a hangar when not in use. I remove the wings from and install them to the trailer simply by rolling the dolly right onto the tilted trailer using a small ramp.

So what "is" an HP-13-H? I'm not 100% sure. The Soaring Index says it is an HP-14 wing fitted to an HP-11 fuselage. Not true in this case. I know that the wing and tail are directly from the HP-14. The fuselage is definitely "not" from an HP-11. To my eye, the 13-H fuse looks a whole lot like (identical to?) a -14's. Maybe a -14 has different landing gear and rudder pedals or something. I am guessing that the 13-H may have been a prototype for the 14. Just a guess. There are no other 13-H's registered or in existence, to my knowledge.

Anyway, I come away from this experience very impressed with the 13-H and look forward to many more hours of soaring in it this summer. I hope you enjoyed reading about it and viewing the pictures. It is certainly gratifying to see this stately-looking bird back in action, where it belongs.

Now, back to work on the RS wings.