I've finally gotten around to compiling a list of frequently asked questions about the HP-24 project.
How long will it take to build?
The HP-24 is kit supplied in a relatively quick-build form: The wing skins and spars will be already bonded together, and the right and left fuselage shells will also be bonded together. Since you don't have a bunch of big floppy shells to work with, and you don't need large alignment cradles to get them straight, the basic construction should go pretty quick. I figure to supply a kit with comparable completion level and build time as the Apis or the Russia gliders. So your best bet is to ask someone who's built one of those what their build time was.
What are the performance criteria for the HP-24?
The basic performance criteria is to duplicate the best glide and high-speed performance of European racing ships of the mid-1980s, but with improved ergonomics and economics.
When will kits be available?
After we're satisifed that we've developed a safe, pleasant-flying aircraft. We expect to be done by mid- or late 2005.
How much will it cost?
Base kits should cost around $17500 in Year 2000 US Dollars. The base kit gets you a flyable aircraft, but excludes optional equipment such as the following:
Because it is basically an extended development of the HP/RS-series kit sailplanes developed by Richard E. Schreder from the 1960s through the 1980s. The last entry in Dick's design notebooks was something called the HP-23, for which there was only a table of bending moment values for the wing main spar. I decided that since I've learned so much of what I know about sailplane design by reverse-engineering the HPs, that it would be a fitting tribute to extend the original numbering series. Besides, Dick and Angie said that it was OK with them.
Why is the cockpit so large?
Because its big enough. A more appropriate question would be, why are the cockpits of European ships so small?
Why is development going so slowly?
Because I am pretty much funding it out of my own pocket. Development is proceeding as fast as I can afford.
Why are the fuselage molds divided into forward and aft sections?
It was my original intent to have a composite forward fuselage and an aluminum semi-monocoque aft fuselage like the HP-18. However, for a variety of reasons I decided to change to a composite aft fuselage. Some time in the future, we're going to convert the fuselage molds so that each mold section embodies an entire right or left fuselage and vertical stabiliser half.
Why did you change from a straight cockpit rail to a curved cockpit rail?
Because everybody else is doing it. The latest designs from both Schleicher and Rolladen Schneider have curved cockpit rails. It is a bit more difficult to develop the canopy seating surface that way, but the results looks pretty slick and has no other substantial costs associated with it.
Will there be a self-launching version?
Probably. But I won't be developing it until much later. Self-launch capacity more than doubles the kit price. You can buy a lot of tows and retrieves for that kind of money. There is a disticnt possibility of a motorglider version, but we'll have to see how that pans out.
Will it be available with BRS?
Probably. I've reserved internal volume for BRS components, and have arraged for the wing center section cover to be non-structural so it can serve as a frangible membrane over the BRS deployment parts. However, I won't be installing a BRS system until we get to the Block III aircraft.
What will be the maximum pilot size and weight?
About 300 lbs, 6'6" will be a realistic maximum in 15-meter trim. With the 18-meter tips, the maximum pilot weight goes down to about 250 lbs.
What are the wing spans available?
The basic wings are 15-meter, but I'm designing the wing spar structure with the bending loads of 18-meter wings in mind. So 18 meter tip extensions will be a kit option.
Why are you designing the HP-24 as a kit, and not as a finished aircraft?
On this topic, I once wrote:
Because I have to. This approach represents an adaptation to a somewhat onerous regulatory paradox. As a domestic US manufacturer, I can design and manufacture kit aircraft that builders can register and operate as amateur-built experimental aircraft. However, in order to manufacture finished aircraft, I would need to obtain FAR part 23 or JAR-22 certification for the aircraft. The certification process typically costs on the order of a million dollars for a glider of the size and complexity of the HP-24.
On the other hand, it is OK for foreign manufacturers to sell uncertified finished aircraft into the US market. The aircraft get registered and operated under the rules for either experimental, racing or experimental, exhibition aircraft. So far as gliders go, there is no real problem operating under those rules, since every flight can be considered as a proficiency run for some future race or exhibition. By definition, the people who fly those aircraft but do not ever race them are exhibitionists. Go figure.
It turns out that I was wrong when I wrote that. A subsequent conversation with George Applebay revealed that George manufactured Zuni sailplanes without certification, and that operators had no particular trouble registering them as Experimental, Racing or Experimental, Exhibition. And, if George could do it, I don't see why I couldn't, if I wanted to. So, now that that option is potentially available, I'll need to think on it more.
Are you using much carbon fiber?
I'm using about 15 lbs of pultruded carbon strip in the wing main spar, and a few other pounds of carbon reinforcement in some other spots. Other than that, the structure is almost all conventional glass fibers and resins.
Why isn't the HP-24 an all-out racing ship?
So that it can be affordable. By trailing the real racing ships by about 5% in performance, I can cut corners that let me reduce the kit price to about 25% of the cost of a factory racing ship. It also gives me margin to make the ship more comfortable and provide more room for systems and amenities.
Will winglets be available?
Absolutely. My aero engineer friend Steve Smith, who has designed winglets for transport aircraft, has agreed to design winglets for the HP-24. I just happen to think that winglets are generally sort of ugly, so I never put them in my 3-views. However, I won't let my personal prejudice get in the way of either good design or good performance.
Why are you using conventional molded composite technolgies?
Because they are proven and cost-effective for low- and medium-volume production enterprises.
Why aren't you using [insert name of latest miracle fiber or resin]?
Either because cost/benefit doesn't justify it, because it won't make any difference in safety or effectiveness, or because I don't know that it exists yet. Feel free to suggest any new miracle materials that you may have heard about.
What are your qualifications to design a sailplane?
First off, I am not an engineer. I am not qualified to do any of my own engineering, although I do some aspects of engineering under close supervision. However, I have been around sailplanes since about 1974, and have been studying their structures and technologies since about 1980. I have been designing sailplane control systems since about 1995, when I started developing the mechanism that later became the HP Aircraft HP-18 center stick retrofit kit.
My greatest qualification is recognizing that I am not qualfied. That simple fact informs me that everything I do needs to be thoroughly tested, veriried, and validated. However, I take comfort in knowing that most engineering failures are not failures of calculation, but rather failures of imagination. They are situations where engineers failed to imagine a failure mode or load path. The are situations where engineers failed to anticipate the lengths to which Murphys Law will go to smite them.
What is a "sport/racing" sailplane?
A sport/racing sailplane looks fast, and has enough performance so that it is only a few percent behind real racing ships. However, it has a comfortable and roomy cockpit to allow for more comfort and better ergonomics.
Why a molded canopy instead of free-blown?
I've chosen to design the HP-24 forward fuselage around a stretch molded canopy so that I can achieve the same level of fit and finish as the european racers. I have seen many free-blown canopies, both for original installations and for retrofits. None of them has ever met the level of profile continuity that you get consistently and repeatably from a molded canopy.
Why a completely new sailplane, and not just a new fuselage or new wing for the HP-18?
I believe that the social and economic landscape of soaring and of homebuilt aviation have changed drastically since the HP-18 heyday in the 1970s. Pilots demand more performance and amenities, and builders expect lower build time, better kit quality, and greater return on investment. The only way to satisfy that demand in a manner consistent with the current social and economic aspects is with an entirely new design.
What are the "amenities" you keep talking about?
Amenities are those nice little things that have become standard equipment on factory ships, but which have been absent on most homebuilt gliders. Things like:
Throughout most of the history of homebuilt aviation, used homebuilt sailplanes have typically sold for prices that, balanced for inflation, are lower than what the kit or materials would cost. The most common exception to this principle is the RV series of homebuilt airplane. I want the HP-24 to be the first major exception in kit sailplanes, with resale prices of 125% to 150% of the kit price, and perhaps greater.
Why are auto-connecting controls so important?
My friend Steve Smith has calculated that there is one instance of mis-connected or unconnected controls for every thousand assemblies. On the US contest soaring scene, there are about 2000 assemblies per year. About 50% of all mis-assembly incidents are fatal. Auto-connecting controls does not eliminate the problem, and is not an absolute solution. However, it does go a long way towards reducing the severity of the problem.
How much of the HP-18 design are you retaining?
Originally, it was my intent to retain about 40% of the HP-18 structure, including the semi-monocoque aft fuselage and the V-tail surfaces. However, popular demand for a T-tail version dictated that there be at least an option for a composite aft fuselage and tail. It soon became evident that I could not afford to develop both V-tail and T-tail versions in parallel. Due to popular demand, I decided to drop the V-tail version and develop only the T-tail version with composite aft fuselage.
Why are you going to a T-tail instead of the standard HP V-tail?
Because people have asked for it in numbers that are impossible to ignore. I do not have the resources or time to pursue an ideological or aesthetic fight on behalf of V-tailed gliders.
Why are you going to a center stick instead of the HP-18 side stick?
Because I think that most pilots will like the center stick better than the side stick, and that such a control system will enhance the value of the aircraft.
Why are you not using aluminum construction?
Two reasons: Holes and fasteners. With conventional aluminum construction, there are literally thousands of holes. Each hole must be located, drilled, deburred, dimpled or countersunk. And then the hole must be filled with a rivet. Every single operation on every single hole takes some amount of time, and all of that time adds up. With composite technologies, we can make the kit parts and assembly process much simpler and more time-effective.
What finished parts will the kit include?
I'm not sure yet. However, I'm pretty sure that the kits will include:
The major tasks will probably be:
Your workshop should be at least 26 feet long. You probably should have at least 8 feet of width.
What are the differences between the Block I, Block II, and Block III aircraft?
The Blocks are described below:
Right now we are developing the following HP-24 variations:
There is. But it will not get off the drawing board until HP-24 development is pretty much wrapped up.
How can I get the latest information?
I have a YahooGroups forum that I use to email periodic updates, and that members can use to freely discuss the project with each other. The forum is not listed in the YahooGroups directory to protect it from spammers. Drop me a note and I'll add you, or tell you how you can add yourself.
page updated 10 April 2003 all text and graphics copyright (c) 2003 HP Aircraft, LLC