Aerobatic Tandem Two-Seater

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Radicaldude1234, Nov 26, 2017.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Nov 26, 2017 #1

    Radicaldude1234

    Radicaldude1234

    Radicaldude1234

    Well-Known Member

    Joined:
    May 30, 2009
    Messages:
    386
    Likes Received:
    153
    Location:
    Front Range, Colorado
    So personally, I think the CAD exercise at my other thread https://www.homebuiltairplanes.com/forums/showthread.php?t=28640 has run its course. I can finish the model, but as I have no desire to build a P-51 replica given there is no viable engine and there are a bazillion of them around anyways, I've decided to go back to a design that I've been working on awhile back.

    This is my second draft of the design using the techniques I've learned in the aforementioned thread.

    Intended Equipment:
    -Engine: (I)O-470 in prototype. IO-520/IO-540/IO-550/IO-720 in later versions. Maybe O-360 in fixed gear version
    -Avionics: IFR Capable
    -Other: Retractable Landing Gear; electric or electrically powered hydraulics

    Goals:
    -Performance: 7.5G Load limit; However fast a 230-300hp engine will take it; <55kt stall
    -Crew Accommodations: "Functionally Comfortable" cockpit (28" wide at shoulders); Harmonized control system; Sliding Canopy
    -Ease of Construction: ~1000hr build time; Composite cowl; Sheet metal construction for majority of airframe

    First Pass Design:

    2016_0616_1.jpg

    2016_0414_3.jpg

    Personal Critiques:

    -Too blocky
    -Canopy could have caused aerodynamic issues
    -Slab sided fuselage looks awkward

    Second Pass (Current) Design:
    2017_1125_Shape.jpg

    2017_1124_FrontRetake2.jpg

    2017_1125_SizingStudy.jpg

    More to come....
     
    cluttonfred likes this.
  2. Nov 26, 2017 #2

    Tiger Tim

    Tiger Tim

    Tiger Tim

    Well-Known Member

    Joined:
    Apr 26, 2013
    Messages:
    2,902
    Likes Received:
    1,629
    Location:
    Thunder Bay
    First draft needs a M-14, the rest of it sure looks like a little T-28.
     
  3. Nov 26, 2017 #3

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    3,015
    Likes Received:
    2,012
    Location:
    BDU, BJC
    Looks good. What is the approx. gross weight & wing span?
     
  4. Nov 26, 2017 #4

    Toobuilder

    Toobuilder

    Toobuilder

    Well-Known Member

    Joined:
    Jan 20, 2010
    Messages:
    4,471
    Likes Received:
    3,277
    Location:
    Mojave, Ca
    The big bore Continentals are fantastically heavy, as is the Lyc 720. Thats fine if you are planning for it, but as a side benefit, that puts you solidly in V-8, redrive category. Might include the P-85 FWF recepie as well.
     
    Last edited: Nov 27, 2017
  5. Nov 26, 2017 #5

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,721
    Likes Received:
    3,320
    Location:
    Memphis, TN
    Is this going to be a primary aerobatics machine like an Extra, or an all arounder like an RV?
     
  6. Nov 26, 2017 #6

    DeepStall

    DeepStall

    DeepStall

    Well-Known Member

    Joined:
    Dec 26, 2010
    Messages:
    136
    Likes Received:
    44
    Location:
    Colorado
    How does your geometry compare against a T-34?
     
  7. Nov 27, 2017 #7

    Radicaldude1234

    Radicaldude1234

    Radicaldude1234

    Well-Known Member

    Joined:
    May 30, 2009
    Messages:
    386
    Likes Received:
    153
    Location:
    Front Range, Colorado
    An all rounder like an RV. Aiming for stable but aerobatic capable...a bit like a Citabria: it can perform aerobatics but your arms will be sour afterwards and you'll be covered in sweat.


    Given its weight and size, there's no way it can compete with something like an Extra. However, the goal is to open up the other end of the flight envelope via higher Vne.

    It's funny that you guys mentioned those two airplanes as this design is highly influenced by both. I used to be in a flying club that had 2 T-34s, and I've sat in one, though never flown it. If it was close to brand new, I'd buy one in a heartbeat. The ones at the aeroclub were old and tired; aerobatics were prohibited because of the spar AD and they were slow because their engines were also old and tired.

    Given the spar AD (wing folded with fatalities on one), an asking price of ~$200k, and an empty weight of 2250lbs; I thought I could do better.

    The T-28A, on the other hand, has about the same asking price as a Mentor. It has no structural ADs given it was built like a brick craphouse.

    As for downsides, I'm in awe everytime I see a T-28 in person....it's ENORMOUS! Coupled with the need to feed and maintain that huge radial FWF (25gph for A model; ~50gph for B-D models!), makes the plane a bit of an overkill to, let's be honest, just to bore holes in the sky. Plus the Trojan doesn't any interchangability with a more popular airplane, like the T-34 does with the Bonanza.

    I did like the canopy layout, which is on this draft.

    Aiming for ~30ft wingspan and 28ft fuselage, an empty weight of ~1800-2000lb, a useful weight of 800lbs (2 heavier than FAA adults; 40gal fuel; not a plane to carry luggage in), so a gross of 2600 to 2800lbs. Lighter if I can get away with it, but structural robustness is a higher priority.


    Yup, was aiming for the middle-of-the-road of high perfomance motors. The firewall profile is a bit too narrow for a radial engine, which would also ruin the downward visibility. For those with wallets big enough to feed their need for speed, the cowl is spacious enough to fit a PT6 turboprop...

    Next up, going to crunch some numbers for aero analysis. Luckily for me, I have some spreadsheets that I made for the Draft 1.
     
    mcrae0104 likes this.
  8. Nov 27, 2017 #8

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    3,015
    Likes Received:
    2,012
    Location:
    BDU, BJC
    This is ambitious. I like it.

    I think you will find as you iterate that the quickest way to lighter is smaller (if that is what you want--and it is of course your airplane).

    Please keep us all updated as it comes along!
     
  9. Nov 27, 2017 #9

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,840
    Likes Received:
    5,467
    Location:
    Orange County, California
    I certainly like the looks, and the intended mission.

    I'll second this. It looks a skosh large to me, more like a Navion than any acro ship I've seen. It's totally up to you, but making it smaller will help in a variety of ways, all performance-related.
     
  10. Nov 28, 2017 #10

    Toobuilder

    Toobuilder

    Toobuilder

    Well-Known Member

    Joined:
    Jan 20, 2010
    Messages:
    4,471
    Likes Received:
    3,277
    Location:
    Mojave, Ca
    Given the size and the modest power, I question the need for retracts. Dont think they will buy you any speed, but will add a lot of weight and headache.
     
  11. Nov 28, 2017 #11

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,721
    Likes Received:
    3,320
    Location:
    Memphis, TN
    I can sell you an RV 4 with retracts and a 10 hr angle valve 360 right now.
     
  12. Nov 28, 2017 #12

    Radicaldude1234

    Radicaldude1234

    Radicaldude1234

    Well-Known Member

    Joined:
    May 30, 2009
    Messages:
    386
    Likes Received:
    153
    Location:
    Front Range, Colorado

    Well, wingspan and fuselage length can always change with the aero analysis. The tail length was the perceived need for directional stability during aerobatics and spin manuevers. I realized this was made redundant by the large tail area, so I pulled the length in to 26ft. Wingspan might be reduced to enhance roll rate.



    Aircraft has a secondary (or primary) purpose of being an complex high performance trainer. That and it's easier to design a plane with retractable gear and then have a fixed gear conversion than the other way around.



    Are you trying to make a sale or are you just trying to be sarcastic?
     
  13. Nov 28, 2017 #13

    TFF

    TFF

    TFF

    Well-Known Member

    Joined:
    Apr 28, 2010
    Messages:
    11,721
    Likes Received:
    3,320
    Location:
    Memphis, TN
    No, I can set you up. Not the same as designing your own plane, so not expecting you to bite or anyone else, really. I do have a friend who's time has come flying and he is getting rid of it.
     
  14. Dec 8, 2017 #14

    Radicaldude1234

    Radicaldude1234

    Radicaldude1234

    Well-Known Member

    Joined:
    May 30, 2009
    Messages:
    386
    Likes Received:
    153
    Location:
    Front Range, Colorado
    Did some preliminary aerodynamics work. I've been too lazy lately to actually input the parameters into my excel sheet (which I created while working on the 85% FW-190 replica, another story, and which doubles as hand calculations) so I built up the aerodynamic model in XFLR5 and rigged up the model in Solidworks for CFD.

    I will be using four methods to validate the aerodynamic model: through hand calculations (through equations in excel), the program XFLR5, use of CFD in on the CAD model itself, and a controllable model in X-Plane.

    The former three will be used first to generalized performance, then hand calcs will be used to calculate stability derivatives, which can then be checked with the CFD and XFLR5. X-Plane will be used as a "big picture" testing tool.

    So far I've set up the preliminary models for XFLR5 and CFD, of which the results are below. I have not yet adjusted the performance with tail trim and the stability analysis depends greatly on component placement through balance and MoI for static and dynamic stability, respectively.

    Please note that the XFLR5 plot is with the flying surfaces (wings/H-tail/V-tail) only and that the CFD study is with half the model to save on computation time (old wind-tunnel trick), so multiply the values in that picture by 2.

    XFLR5 Results:
    2017_1207_XFLR5.jpg


    CFD Results:
    2017_1207_Goals.jpg


    So far the drag differs greatly, understandable since one has a fuselage and the other doesn't, but the lift values is within ~10% of each other. Will investigate and tweak accordingly.
     
    mcrae0104 likes this.
  15. Dec 8, 2017 #15

    mcrae0104

    mcrae0104

    mcrae0104

    Armchair Mafia Conspirator HBA Supporter

    Joined:
    Oct 27, 2009
    Messages:
    3,015
    Likes Received:
    2,012
    Location:
    BDU, BJC
    What's your aim for cruise alpha? Do you expect adding the fuselage into the picture will get Cm vs. alpha where you want it?

    This looks like fun. I need to learn XFLR5.
     
  16. Dec 8, 2017 #16

    jac

    jac

    jac

    Well-Known Member

    Joined:
    May 18, 2013
    Messages:
    74
    Likes Received:
    9
    Location:
    Gore, Southland New Zealand
    Sounds like you want a F1 EVO with retracts.
     
  17. Dec 8, 2017 #17

    Radicaldude1234

    Radicaldude1234

    Radicaldude1234

    Well-Known Member

    Joined:
    May 30, 2009
    Messages:
    386
    Likes Received:
    153
    Location:
    Front Range, Colorado
    Alpha is actually hard to define. The ideal cruise alpha (@180-200 knots) with regards to fuselage thrust line would be 0°. The wing actually has a 3° washout in order to avoid tip stall at higher alphas associated with maneuvering. The CAD model actually lags behind the XFLR model in development as the root has 3° in the former while the latter is 0° at the root. The effect of camber with the Riblett airfoil I've selected is so that it has considerable lift at 0°. I hesitate to give the wing root negative incidence, so the aircraft could very well fly at a negative AoA (with regards to thrust line) at higher speeds...

    XFLR5 is a good program to approximate aerodynamics. It's geared more towards R/C aircraft, but I think its well suited at speeds GA aircraft fly at. You input airfoils using DAT files, which allows you to design with the vast airfoil online library hosted by UIUC http://m-selig.ae.illinois.edu/ads.html. It's also a convenient CAD tool, as I can manipulate the same coordinates in those files directly into the drafting program. That way, the airfoil in the CAD drawing is the exactly the same as the one analyzed in XFLR5.

    More like a modernized Beech Mentor. The EVO has great performance, but it doesn't have much growth potential and dual control capability. The goal of this design isn't as clear cut as chasing after performance or cost-effectiveness. Those things are nice and are certainly accounted for, but the focus is the link between the pilot and the airplane; an airplane that feels like an extension of your own body and can do things where you'll break before it does. That's currently reflected in the cockpit layout and will be in designing the control system.
     
    Last edited: Dec 8, 2017
  18. Dec 8, 2017 #18

    flyboy2160

    flyboy2160

    flyboy2160

    Well-Known Member

    Joined:
    May 25, 2014
    Messages:
    326
    Likes Received:
    165
    Location:
    california, USA
    It's great that you are using hand calcs to check things! Which SOLIDWORKS CFD are you using? The simple built-in Flow Express or the very capable (and more expensive) Flow Sim?
     
  19. Dec 9, 2017 #19

    Radicaldude1234

    Radicaldude1234

    Radicaldude1234

    Well-Known Member

    Joined:
    May 30, 2009
    Messages:
    386
    Likes Received:
    153
    Location:
    Front Range, Colorado
    Using Flow Sim. Yeah, when it comes to manned aircraft, it never hurts to have multiple sanity checks. That and to prevent "parameter tweaking" to convince yourself that a design is higher performing than it really is.

    Anyhow, did a quick performance analysis using equations from Raymer's "Simplified Aircraft Design for Homebuilders". I have other texts to verify estimate performance, but his has the simplest equations and is more suited for what is more or less a "back of the envelope calculation".

    I did verify two datapoints with a CFD analysis, and Raymer's equations came surprisingly close.

    The analysis below is for at sea level in the current configuration:

    2017_1208_RoughPerformance3.jpg

    Observations:
    -The numbers are pretty much in the range expected with the current configuration. Performance speed-wise is primarily a battle to reduce total wetted area, of which the wing usually has the most percentage of.
    -The wing is currently designed to be able for the aircraft to pull 7.5Gs at 150kts. By coincidence it also stalls flaps up at ~61kts. As flaps are planned, this means the stall speeds are in line with average GA aircraft; expected to be ~55 knots.
    -It bears reminding that, unless planning to go to Reno or flying over international waters, a max sea level speed of over 240KTAS is pointless. A 650HP PT-6 will give you that performance. The 1650hp PT-6 is the largest that can be mounted.
    -Higher power on piston engines can be attained through turbocharging. However, turbocharging is not recommended for aerobatics because of reliability issues.
    -It's worth mentioning that the radial engined T-6 with 600hp had around the same top speed as the IO-470 engined configuration here. The T-28A with 800hp wasn't much better.
    -Given the increased drag of radials, I would not expect the performance with a M14P (which can be modified to produce up to 460hp) to be significantly better than the IO-550 or IO-720 versions.

    Optimizations:
    -If the maneuvering and/or stall requirements are tweaked, top speed can be increased. Remaining roughly within design goals will, however, yield an improvement of no more than 10 knots.
     
  20. Dec 9, 2017 #20

    flyboy2160

    flyboy2160

    flyboy2160

    Well-Known Member

    Joined:
    May 25, 2014
    Messages:
    326
    Likes Received:
    165
    Location:
    california, USA
    As do I. It has a bug that I discovered and which was verified by SW: an external centerline-symmetrical flow analysis has significant errors along a significant strip of cells near the centerline. Cells away from the centerline are ok. (I've run a 767 half model at work with most excellent results for airflow along a sensor window away from the centerline.)

    Even though a full model has more cells, it will solve faster (~2.5X to 4x fewer iterations!!!) than the half model. (Some of my half models had goals that never converged; I had to terminate the runs.)

    When I told SW I'd update my seat if they fixed it, they said weren't going to. Notice the caveat in the instructions: don't use symmetry unless you know it won't cause errors.

    This error will affect your analysis: you will probably get nose down pitching from your canopy and nose up pitching from the canopy downwash onto the aft fuselage. These numbers need to be correct to get a correct pitching moment. You can SWAG the canopy effect by hand calcing it as a little fat wing. Multhopp's method probably won't catch this.

    If you doubt what I'm saying, run a test for yourself: run a hershey bar wing all by itself with centerline symmetry and full span. Notice the flow anomaly near the centerline. Compare the lift, drag, cp, and pitching moments, both to each other and to the hand calc numbers.
     
    Last edited: Dec 9, 2017

Share This Page



arrow_white