New big prop, facing the A320 & 737: TurboLiner.

[keesje]

Refinements & adjustments based on input : Turboliner mark III

Hello folks,

I promised to do an updated mark III based on all your input last week-end. Kids & home improvement caused a small delay. I went through the comments and implemented some suggestions .

Result is the Turboliner Mark III


1. lemurian
Why the leading edge flaps ? The #1 behind the props seem to be both an overkill in terms of aerodynamics, weight and dimensions ( they are also subject to the prop wash). I would have thought that the wing behind the engines will already be in a good lift-generating position.

True I took the Embraer 190 wing as a startingpoint. I removed the leading edge flaps on mark III. Ice protection plates are now situated behind the prop.


2. lemurian
The shoulder wing choice: as a pilot, I've loathed the crosswind susceptibility of airplanes like the Nord 262 or the ATR, because of their narrow landing gear. See the balance of weight savings on a comparison between A/- structural gains in getting away from the project as it is now and B/-the advantages of a low wing, wide landing gear, wing bending moments...etc...

3. low n' slow
Also I feel a little sceptic to the gear/wing configuration. It would feel more sturdy having the gear in the nacelles (Fokker and Dash) instead of the ATR-type placement. A high wing I argue will make the plane more sensitive to strong crosswinds.

I took a long & hard look at gear in the nacelles. To keep the size of the main landing gear within a reasonable envelope it becomes necessary to make the fuselage as flat as possible like on An32, Q400 and F50. This aircraft is meant to replace 737 and A320 on shorter legs. Also leisure / low cost flights where people take a lot of luggage. Doing a Google on Q400 and luggage I found a lot of complaints. It is a major restriction on this aircraft caused by the aircraft cross section. The Turboliner doesn’t have to have cargo container / pallet capability like the A320 and I did flatten the lower fuselage. However it has to have enough space to stow 160 serious bags. This would result in a very long and heavy main landing gear. Also including electric drives on it could create issues. So I decided to stick with the ATR / military style landing gear. I included the Q400 cross section for reference in the drawing.




4. lemurian
Another advantage of the low wing is the easier integration of the airplane with existing airport gates - that will allow you to do away with at least one integrated airstairs, hence a further weight saving.

Having the very large prop would create some ground clearance issues requiring very high main landing gear legs. I did a lot of different studies and in the end concluded a high wing isn't so bad for a prop.


5. lemurian
Lastly, the fuel system would be simpler, with the added possibility of a centre tank.

True for narrowbody aircraft, but they can do flights up to 3000nm. The Turboliner is an uncompromised short haul aircraft, mostly up to 1000nm. I think the long un-interrupted wings would provide enough space for its limited payload range requirements.



6. low n' slow

Make the nose looke a little more like the Saab and less like the Dornier and you're home free!

:-) I see you have a national preference. I drew the nose low to maximize the viewing angle for the pilots. This aircraft is driving over airports a lot during the day.


7. low n' slow
It's all very nice with the electrical tug system, but I feel it will function just as all the other "nice to have capabilities" I have so far seen, and that is occasionally/sporadically. Having complex electronics in an area that will take up a lot of force in everyday operations just doesn't feel sound to me. Reliability and ease of maintenance is very important and any factors compromising this must be taken into consideration.

The assumption is the silent aircraft will be allowed to operate where noise restriction are important. Fuel will be saved by running the APU instead of two engines and not requiring push back tugs.. (less lost slots too I guess..)


8. low n' slow
I also notice you have given the plane speedbrakes similar to the Bae. You would save more just getting rid of them. Remember, it's a turboprop. Not only are they inherrently slow, but they also have a fantastic stopping capability by means of the props... Having liftdumpers/flight spoilers though (Dash) makes a little sense considering manouverability and landing the wing upon touchdown.

9. kiwilad
I agree with a earlier comment about crosswinds, the problem with the ATR is the wing continues to fly to around 40-50kts, spoilers that dump lift on landing would start to solve some of the issues surrounding the interesting crosswind handling techniques.

I removed the speed brakes. I installed a patented (Lockheed) system called DLC (direct lift control). In combination with other control surfaces & black boxes it allows to decent without changing pitch or engine settings. Gliders have something similar and Lockheed used it on the L1011 Tristar. For an high winged aircraft doing steep approaches up to 8 times a day, its seems very useful interms of comfort and limiting noise (no engine thrust variations). During landing they act as additional spoilers.



10. kiwilad
If you do go with the apu, something that you can leave running unattended would be great. As I understand most props with apu's require someone on the flightdeck or at the least in the cabin as they don't have automatic fire extinguisher capabilities. I stand to be corrected.

If it is allowed it should be possible. It is a relative small and high placed APU.

11. kiwilad
Have you dug around for info on the ATR 92 concept that is on the drawing boards at ATR at the moment. The Q400X is another one in concept at the moment. I personally think the ATR concept is better as it will be a clean sheet design, with a gear design similiar to yours.

I could not find sketches, do you have any links?


12. Bushfiva
Regarding the overhead storage, we're always being told what the maximum size is. And with loco's we're being educated that you're a burden for bringing checked baggage. On the third hand, one of the problems with this type of aircraft is that one can board with a carryon-sized item for which there is no longer any space. So my suggestion is, a check-in - side check that one's roller case is the correct size, which gives one a chit for an overhead slot on the aircraft. It doesn't matter when you board, that slot will be there. Those with the random-sized packages get to stuff them below the seat in front. One would receive a boarding pass with a seat number and baggage slot number.

I have experienced this issue with regional jets often. I think the Turboliner offers handluggage space comparable to narrowbody jets (cross section is narrower but rectangular).


13. James (Fleetbuzz)
Some details which become apparent include that the wing box will conflict with the overhead bins. The fuselage cross-section is similar to a typical low wing aircraft and would be slightly different in a high wing aircraft. In a low wing aircraft the cargo bay is the natural location for the wing box to intersect the fuselage. In this high wing aircraft the thin side-walls will not be enough between the wing box and the landing gear and also have a cut-out for an emergency exit at the same time. There is a lot of load in the frames especially in the area between the rear spar and the landing gear.

The wing box may limit headroom unless the wing is located higher on top of the fuselage. High enough to allow headroom, overhead bins, and for a cargo version an unlimited cargo volume. Also the fairing around the landing gear and the wing to fuselage would be much bigger to smoothly cover the box and gear. One benefit of the larger fairing is it allows for structural supports and some system components to be located outside of the fusealge skin under the fairing. External structural features under a fairing are more efficient so the designer will use them whenever possible as soon as the fairing is deep enough to allow them.

I took a look and you seem to be right. I heightened the wing a bit, it comes into the cabin / bins. The fuselage height in the lowest point of the aisle should still be better then 2.1 meters (it's a big cabin for a prop.) Height is about similar to the BAE146 only Turboliner cross section is more rectangular shaped.


14. James
Early design decisions include arranging the structure to allow for a side cargo door and sizing the cabin for standard containers. A swing nose or tail would allow full access to load cargo but may be too complicated. Swing nose/tail has only been used on very specialized aircraft.

I think a conventional side door would be sufficient for typical short haul parcel loads, like the BAE 146 Quiet Trader..


15. James
A high wing may end up with the slight dihedral shown in the illustrations and the vertical stabilizer looks almost big enough to react a one-engine-out yaw. The top of the vertical stabilizer would also need a fairing big enough for the screw to adjust the horizontal stabilizer pitch trim. Also the aft fuselage may be longer/forward fuselage shorter to react the weight of the engines forward of the wing.

The mark II had your concerns covered. I think the place of engines, wing, tail and the fuselage length is pretty accurate. I measured many top views of twin props for reference.Of cause I could have made a spreadsheet estimating all weights & load arms and determine the Lift locations but decided someone else might want to pick up that challenge..


16. James
The wing box may need to be thicker to take the engine loads. Try to avoid the limited life problems seen on the C-130 and P-3; easier said than done. A thicker wing immediately impacts the cruise speed....and many, many other design parameters all of which influence each other.

A thicker wing box has consequences for the aerodynamics high speed performance of the wing. I think it should be a CRFP wingbox. There would be indeed serious loads from the big engines and long fuselage.


17. James
If the overhead windows are to allow light in the cabin to save exectricity for cabin lights, then the windows should be minimal in size and make use of a reflector/diffuser and not make a hole in the fuselage any larger than necessary. Side windows are subjected to pressurization and shear loads, the top of the fuselage also has bending loads in either tension or compression and a large window may have a weight penalty.

I made the drawing a bit clearer, small windows indeed and brackets to take the loads. The 4 overhead windows came in place of 20% / 12 windows deleted in comparison to the A320/737. It is mainly a weight reduction combined with a better space experience / admosphere for people sitting in middle / aisle seats.

18. James
It remains to be seen if the TP400 lives up to it's potential in-service. An excellent engine design that delivers the fuel burn and thrust can still fail if it costs too much to maintain.

The Turboliner should become available years after the A400M enters service. Child deceases could be engineered out of the TP400.

19. James
Composite fuselage?

Personally I have my doubts on CRFP for short haul, airport intense operations. Damage, ramp rash is a fact of live for an aircraft that does 6-8 flights a day.. Also not sure if layered composites and prop resonance go together well..

BTW I adjusted cabin for 6 more seats reducing pitch from 32 to 31 inch. (some low cost airlines I flew do 28 inch ..)



20. James
TP400 implies bleed air.

The TP400 use a microjet as a starter. I hope this could limit the size of the APU and save a lot of piping.

21. James
Props can shed ice of there is usually a reinforced skin next to the props.

Indeed. I included protection plates behind the props like most turbo prop aircraft have.

22. enicalyth
All my research and that of my colleagues is published in the leading journals. But you have to buy it. It is not free. But reasonable. It is a shame you are not using it.

I have no reference, may you could lift a tip of the curtain / provide some keywords?


23. James
A clever design will address the issues with solutions which solve multiple needs at the same time and do it with elegant simplicity. The 777 would not exceed performance specs unless it included very clever design solutions.

I would be interested in hearing any other comments on the design details implied by this configuration. The details help clarify the accuracy of the overall performance analysis so as to avoid overestimating.


Agreed, any comments / ideas are welcome!