DH 88

Discussion in 'Classics' started by Atomic_Sheep, Nov 7, 2008.

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  1. Nov 8, 2008 #21

    orion

    orion

    orion

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    Well, a lot to go over here but in order to put things in perspective there's probably two basic statements that have to be made up front. First, although you're starting with a given airframe, the moment you changed from wood to metal you might as well pretty much figure you're starting from scratch. Certainly from the structural end of things but from the overall design also. The new material will change the weight and balance of the airplane, as will the new engines, all of which may require you to shift a thing or two in order to make sure the airplane remains flyable.

    Given the reportedly unfriendly flying qualities of the airplane, it may certainly be of benefit to tweak certain aspects of the design in order to improve the handling, preferably without sacrificing the performance. This will require a good background in aerodynamics and flight mechanics, something that you're unlikely to get regardless of how many books you read. You'll most likely need someone experienced in this field to keep looking over your shoulder in order to make sure you don't miss anything. And that goes for structures also.

    The second thing to point out is simply that as you get into this in more detail, you'll probably recognize that the more you'll learn, the more you'll come to understand how much your really don't know. Those of us that have been doing this for some time always run across something new or something that we've maybe not had as much exposure to in years past. This may end up being a bit discouraging at times because sometimes you might feel like you're chasing your own tail. This is where getting experienced help will aid you in keeping on track.

    Regarding costs, as was pointed out above, if the cost of a kit scares you, you haven't seen nothing yet. One of the most important things to come to grips with as you get into this is that your cost vocabulary is about to shift a few decimal points. Even if you do everything yourself, just the tools you'll end up needing will set you back bunches. And of course there are things that you wont be able to do so those you'll have to buy. The old joke for boat owners is that the word "boat" stands for "bring on another thousand". If that's so, then for airplanes it'll be "another ten thousand". And that's just the basics.

    Anyway, to your text:

    If you haven't done this before and you don't have the background for this type of work you really have only two choices: One, go get a couple of degrees (aeronautics and structures) and then get industry experience for a few years or two, get ready for lots and lots of reading before you even put pencil to paper or plug in the computer. No, you don't generally need that sheepskin, after all, there are a few who have gone this road before (albeit on simpler projects), learning as they go. But that really can be a long process.

    As you start to learn, one of the first steps you can do along the way is to gather as much information and data on the airplane as you can. This includes pictures, drawings, flight reports or specific publications - anything that will allow you to familiarize yourself with the airplane to the point where you'll know it inside and out. that will give you a good starting point for the new evolution of the design.

    Regarding computers, one thing that's critical is knowing and understanding that all the software in the world will not make you a functional engineer. As they say, garbage in, garbage out, and nowhere is this more the case than in the the discipline of aerodynamics and structural design. It is very important to know and intimately understand what it is you're analyzing, what the changes your making will do to the airplane and what affect little details may have on the overall assembly. this cannot be overstated if your goal is a safe end product.

    Yes, that's how we'd all like things to work. Unfortunately they don't - computers have no way of accounting for builder quality, material variability, and at times even basic things like tolerance stack-up. Computers, CAD modeling, CNC manufacturing are all great tools but none take the place of practical experience and know-how.

    Well, figure a kit like an RV may take anywhere from about ten months (full time) to five years to assemble. Some may take longer, depending on the builder's situation. Going from scratch and not counting your design time, you can probably figure ten years. Granted that's a guess since we don't know how much time you'd be devoting to this but regardless, figure on a long process. Just your learning curve and design effort may take many years, especially if you have to work for a living at the same time.

    Well, as I said, unfortunately it doesn't work that way, especially if you haven't done anything like this before. Part of your learning will be associated just simply with fabrication issues and technologies. After all, you can't design it on the computer if you don't know how it should be made.

    And of course that brings up another subject - in order to make something you need the tools to do so. Ribs for instance just don't fall out of the sky. You'll need to develop the proper tools (balancing cost and utility), accounting for all the considerations of material behavior and assembly requirements. As such, you'll be designing not only the parts but also the additional hardware that is needed to make all this and then to assemble it. Simply said, this'll take time.

    Use the search function here - this has been discussed quite a number of times and several of us have listed numerous books that will begin to shed a light on all this.
     
  2. Nov 8, 2008 #22

    Atomic_Sheep

    Atomic_Sheep

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    The cost of the kit was a massive pleasant surprise not a nasty one. As for BOAT... I know all about it. My RC airplane cost $140 dollars, the engine $240, radio $340 or there abouts. So that would sum up to $740 dollars. As the plane came as an almost ready to fly, it had the tank, and all the the other stuff already included. So just from these 3 components you could build the plane in its entirety. But the fact is, I spent around the same amount on top of that (not including tools) to get it to fly as a result of the other accessories. And thankfully we have boxes of tools that proved sufficient to do the job otherwise it would have cost thre or maybe 4 times that because I believe in good quality tools.

    As for rest... all I can say is you definately have a great way of explaining things! Very concise and to the point and what you say immediately paints a fantastic picture.

    I knew that this was not going to be an overnight job but just wanted a ballpark.

    Degree wise... I've been considering it for the past 24 hours and have been leaning towards continuing with my studies more and more. Especially since an engineering degree I think would complement my current degree perfectly. The question now is, can I get into aerospace engineering on financial terms that I want.

    Books... search function... gocha

    As for becomming inately familiar with the airplane, well that process has already begun. I've gone through every search result that google has thrown at me in relation to the 88. Mainly because there isn't much there.

    Edit: Going to start a new thread under Design called Black Fury and it will serve as a design/builders blog/log/whatever you want to call it.
     
    Last edited: Nov 8, 2008
  3. Nov 17, 2008 #23

    smenkhare

    smenkhare

    smenkhare

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    Here's something that might interest you

    DH-88 Comet
     
  4. Dec 17, 2009 #24

    Woodenwings

    Woodenwings

    Woodenwings

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    There is a chap in the US making a full scale replica Spitfire and replacing a lot of metal with wood to reduce weight. He has redesigned the whole plane at great expense and time to get it right. He has outsourced his engineering to a firm in Colorado who specialises in wooden construction. If the Dh88 or even the 98 were to be replicated it should be done by creating a whole new airplane that looks like the original. This would be a labour of love but I imagine a lot of people would want one. Fournier make a Superber little motor glider out of wood. It has a VW engine and one has flown from Canada to Spain non-stop! The Dh88 looks very similar in proportion. Perhaps a fun place to start a replica! The twin engines with fixed props might be a sticking point. Could a single engine run both?
     
  5. Dec 2, 2014 #25

    Atomic_Sheep

    Atomic_Sheep

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    Question regarding the handling qualities of the DH88. This thing was prone to tip stalls, what about gliders, they have short chords but aren't prone to tip stalls or are they?
     
  6. Dec 5, 2014 #26

    Mapleflt

    Mapleflt

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    Your observation re: sailplane/glider is a little off, narrow chord yes but a very long span therefore a low wing loading. Your beloved DH88 is a combination of narrow chord, short span and high wing loading, no comparison can be made with a sailplane, sorry.

    Mapleflt
     
  7. Dec 5, 2014 #27

    WonderousMountain

    WonderousMountain

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    Gliders have tailored airfoils near the tip, and the winglets help a lot also. Winglet stall???

    It's only a matter of matching flight conditions so that the root stalls before the tip. Roll can cause tip stall with excess AoA, gusts can too. Elasticity?

    I agree, forget about the glider comparison.

    LuPi
     
  8. Dec 6, 2014 #28

    Tiger Tim

    Tiger Tim

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    It's worth remembering that the Comets were designed with a single mission in mind and that was to go very fast. The cost of that is often tricky handling. If tip stalls are your concern, maybe you should be asking yourself why you're planning to spend so much time in such a vulnerable flight regime. All airplanes stall, some nastier than others, but all airplanes will eventually bite the pilot who doesn't respect them. Stalls don't just happen out of the blue. If you inadvertently stall an airplane you have made a series of terrible mistakes to get to that situation and while I'm not saying the pilot who stalls deserves it, I am saying these things need to be recognized and trained for along before you're in a complex aircraft.

    Having said that, I would think you could make a Comet more docile but you have to accept it as a compromise. I suspect that of easy handling, scale fidelity, and original performance you can have only two of the three. Get some wash in or a little friendlier airfoil near the tips and it's going to slow down. Keep the high speed profile but adjust the planform and you lose accuracy in the overall shape of your plane, it becomes less of a Comet.

    If I were building one, it would be all moldless composite for ease of construction and that beautiful glassy smooth finish. The outlines of all major components would be true to the originals but the details would be smoothed over; balance weights moved inside their controls, clamshell doors to cover the retracted landing gear, maybe a retractable tailwheel. In the air it would look more like a sculpture of a DH-88. A pair of supercharged 210hp LOM sixes, electric landing gear with a manual backup. And it would be green, the green one never gets any love. At least, that's how I would do it.
     
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