Some Planemaker Help

[simbabeat]

Hi all,

I have recently started developing a couple planes for x-plane.  After just fooling around in planemaker with some makeshift designs for a while I have started on my first serious plane. An Evektor Sportstar Max.  I have acquired a POH and have contacted some pilot's.

but anyway I have some questions about planemaker.  I have set the horsepower at 100HP in the engine specs window.  yet somehow in the sim, it always has 134 horsepower as shown in the pic below.

Also, I have set the engine redline at 5800, that is the max engine RPM, however the POH states that it can only do 5800 RPM for a minute and the max continuos RPM is 5400.  How would I set that in planemaker.

So those are my two little problems but here is my big one.  I have modeled the whole planes body and everything perfectly in planemaker.  Everything matches up to the 3 view exactly just like the Danklaue tutorials have shown how to do it.  I have inputed as much info from the POH into planemaker as possible. Yet when I get in the sim, the plane will not take off at the Sportstar's V_LOF of 40ish.  It will not take off until 80kts.  And even then the stick must be pulled all the way back to keep it airborn.  Even once I get up to 120kts, I have to keep the stick all the way back to keep it in the air.  Naturally, the first thing I checked in planemaker was the COG.  It was right on as per the POH.  I even moved the COG as far back as it could go without the plane tipping over and the same thing would still happen when flying.  What could I possibly be doing wrong here folks?  I'm really lost.

Thanks for helping me!

[tkyler]

Well perhaps now you know why Plane-maker's nickname is "Pain-maker"!   

It's a very deep topic dealing with all that goes into modeling an aicraft and probably too deep to answer your questions in depth with all the "caveats" and "exceptions" however, we can address a few. 

For the horsepower, there's some checkboxes in the upper right corner labeled "FADEC".  There's one there that says roughly, "don't exceed max power".  Now WHY that's in there is a much more complex discussion regarding engine modeling, but in the absence of a really fine tuned engine model in x-plane, Austin gives us a few ways for us to get around it.

Regarding engine RPM, the real limitation on the aircraft engine is due to stress levels which could cause the engine to fail.  X-Plane doesn't model stress so the concept of a running 5800 for only a minute doesn't really mean anything.  The fact that the engine CAN rev to 5800 is the best you can simulate with default functionality.  If you were to use a plugin, you could monitor engine RPM and if the user left it over 5800 for more than a minute, you could fail the engine, but only with plugin programming, not through plane-maker.

As far as the flying qualities,  there are lots of things that can affect that and unless you were willing to let someone else look at your aircraft, no one could really say what the issue is as the "final result" is a balance of a lot of things to be checked.

[simbabeat]

Thanks for your reply.  It sure is pain-maker.

As for fadec, I'm one step ahead of you.  I already had that box checked and yet the engine is still going 30HP over it's limit in-sim.  Why would it do that?

As far as the flying qualities,  there are lots of things that can affect that and unless you were willing to let someone else look at your aircraft, no one could really say what the issue is as the "final result" is a balance of a lot of things to be checked.

Alright.  Well I don't wanna release anything because right now it is a serious embarrassment.  I have full plans for an .obj body and right now I have just pieced together a rudimentary panel just as means for test flying.  If anybody would like to take a look at it please PM me.  I would really appreciate it.

[Lukasz]

Power depends on air pressure and temperature. Always do your test flights with calm weather set to +15^OC and 29.92 inHg - it's called "standard day" and most, if not all, POH's are calibrated to that. You could play with mixture also. Usually X-Plane calculates power in an accurate way (at least so far for me), so there must be something missing or not set properly elsewhere, like f.e. max throttle > 1.0 or some critical altitude, where shouldn't be any. See, if this 100hp are produced at redline or at some other rpm in real engine. Hard to tell without examining the whole a/c, because usually one thing is affected by three other, each of them being affected by three other things and so on.

My main suspect with incorrect t/o speed are airfoils not generating enough lift. Change (or finetune) the airfoil to other with higher coefficient of lift and see if that helps. Other causes could be too high gross weight, high airfield elevation or lack of flaps deployed to takeoff position. Or...

... or you can't get proper angle of attack needed to generate enough lift for t/o, because of troubles with elevator authority. Afterall it's also a wing and has low efficiency at low (40kts) speed, where even it's full deflection is not enough to raise the nose to proper t/o attitude. Try adding some degrees to max "nose up" deflection and see what happens. Check out if elevator area is correct. Check/change airfoil. Check trim settings, in Plane Maker as well as in sim, just in case of some unknown/involuntary/accidental setting/engagement is messing with the plane. Many things to look for, hard to tell.

Check out, if your a/c point of reference is the same as in real plane. In PM it's usually the first station of fuselage (the nose), but in real planes there are offsets, like point of reference being 24in aft of nose tip, for example. If that is the case, then recalculate everything accordingly. Check out, where are your fuel tanks. Also real airfoils put lift vectors in various places along the chord, while in the sim it's always 25% of chord. Check out the flight model graphical output while flying (/ key) and see for yourself what really goes on behind scenes.

It's cool, that you're building this plane From your post I see lots of good work put into it already, with attention to details. Keep it up!

One more tip, if I may. Read as much as you can, on how real planes are being designed, how aerodynamics works and apply as much of it as possible into PM, but keep in mind, that it's only a mathematical simulation of really complex and fluid processes and sometimes you have to input false data to get true results.

[simbabeat]

Thanks for the tips Lukasz.  I'll try some of them later when I have time and then I'll post the results.

Thanks

[simbabeat]

Well I changed the airfoil to the Sportstar's sister plane's airfoil and it worked very well.  Liftoff was at correct speed and all.  I never had the sportstar's airfoil in the first place. 

But anyway, I am still getting 130 hp in-sim even when I set it to 100 hp in planemaker and I have checked the FADEC box.  Should i set it to 70 hp in planemaker to get 100 hp in sim?

[Lukasz]

Something is definitely wrong there. A moment ago I've checked four projects I've been working with previously and with "wrong" use of throttle and mixture, I've been able to raise the power over the Plane Maker basic data, but only by 4-6hp, along with a little increase in rpm (remember, that power is tied to rpm). When I used the controls in a "right" way, both the power and rpm stayed within their normal ranges, on all four planes.

In my previous post I've outlined, what you can look into - add to that the propeller itself. Check, if it has the right shape, dimensions, airfoils, twist etc. Other than that, not much more can be said without taking the plane for a flight and looking into the model.

[simbabeat]

In my previous post I've outlined, what you can look into - add to that the propeller itself. Check, if it has the right shape, dimensions, airfoils, twist etc. Other than that, not much more can be said without taking the plane for a flight and looking into the model.

Which brings me to another question of mine.  Could someone please explain to me how to shape and twist the propeller in planemaker.  All the chord stuff just doesn't make sense to me.  Also, how does the shape and twist of the propeller effect the hp of the engine?

[Lukasz]

Most of the functions have pop-up descriptions, when you hover mouse pointer over them for a second or two. Read them and experiment. Learning how real propellers are being designed would also help, there is plenty of solid and reader-friendly information over the Internet. http://www.google.pl/search?q=propeller%20design&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:pl:official&client=firefox-a&source=hp&channel=np

Propellers are made in Plane Maker in a similar way as wings - you define tip, root and span (radius) lengths, which will give you simple rectangular shape. Chords are used to make more advanced shapes, like "real" propellers or elliptical wings, by making selected chords smaller/bigger (default 1.000) or translated forward/aft (default 0.000). Take note, that tip and root are in fact special cases of chords. Play with that concept.

Propeller is one of the suspects on my list, because:

- obviously it has a rather significant impact on a propeller-driven aircraft behaviour

- I have an aircraft with a non-standard propeller (to say the least) and it can go 15hp above redline specified in Plane Maker

- it's only a mathematical model and there is always a possibility, that some specific combination of data will produce amusing effects - like my another propeller plane project, going over 500KIAS (M.76) with only 460hp

That would be all, that can be said just "out of the thin air". Read, experiment and double review all elements of the plane. The learning curve is steep, but it will be higly rewarding in the end.

[simbabeat]

Thank you so much for helping kind sir.  I am really starting to dive deep into it.

My next question that I can't seem to find:  If it is a fixed pitch prop where do I set the pitch that it always is in planemaker?

[Lukasz]

Watch out, few more questions and you'll have to include me in the credits

Plane Maker twists the propeller for you, based on design prop rpm and design aircraft speed (it "optimizes" the prop for these conditions, as set in PM). There is also a possibility to twist it any way you like, by manually setting angles of inicidence for propeller chords. Look for them inside "standard -> engine specs -> location & -> propeller" menus.

[simbabeat]

Watch out, few more questions and you'll have to include me in the credits

Ha, I will!

Thanks for your help guys.  I feel like I have kind of gotten over the hump.  If I have any more questions I won't hesitate to ask.  But I think I'm all clear now.

Thanks!