Moni Motorglider

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Urquiola

Well-Known Member
Joined
Aug 23, 2013
Messages
192
Location
Madrid, Spain
Can it do - 10 G negative G-push over ?
View attachment 93628
Any comment about how the tail unit would do if put upside down? Meaning no longer a 'V' tail, but an 'A' tail. I was told by an engineer in Romania this has structural difficulties, don't know about the influence of propeller wind, but for sure, induced rolling is in the right sense when banking with an 'A' tail unit. Or not? Salut +
 

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
Comparing the Eppler 580 with the Fx61-147 from Airfoiltools, they seem to pretty close to the same airfoil with the E580 being 16.1% and the Fx being 14.9. Would they fly the same? Any aero guys want to chime in?
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Any comment about how the tail unit would do if put upside down? Meaning no longer a 'V' tail, but an 'A' tail. I was told by an engineer in Romania this has structural difficulties, don't know about the influence of propeller wind, but for sure, induced rolling is in the right sense when banking with an 'A' tail unit. Or not? Salut +
As long as you never have to land!
 

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
Comparing the Eppler 580 with the Fx61-147 from Airfoiltools, they seem to pretty close to the same airfoil with the E580 being 16.1% and the Fx being 14.9. Would they fly the same? Any aero guys want to chime in?
I guess my question is: Is the FX 61-147 subject to bugs, rain, or dust as VB said about living in MN? I have the spar, ribs, skin to just build it as is. It would save me time to not have to make 32-ish ribs of a different airfoil for little to no gain. Or would a different airfoil be the better solution? I'm sort of in lock down so I have time on my hands. I'll entertain any suggestions...

Thanks to all of you in advance, I truly appreciate it.
 

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
I measured the flange on the Moni ribs and they are only 3/8” wide. The riveting would have to be perfect to maintain the correct edge distances. Maybe making new ribs is the way to go. Any suggestions on an airfoil? Thus far we have thrown around the Eppler 580, Wortmann FX 81, FX 61-147. The Xenos uses the same airfoil as the Sonex, NACA 64-415. Any help would be greatly appreciated.
 
Last edited:

Jay Kempf

Curmudgeon in Training (CIT)
Lifetime Supporter
Joined
Apr 13, 2009
Messages
4,288
Location
Warren, VT USA
Can't remember which came first but this shares the same lineage:

There was a lot of press about wing skins delaminating back in the day. I think the fix was to strip the wing and use metal ribs.

The KFM engine on a stick (not retractable) version had the same engine issues. Cute little design.

The HP 18 was a very grown up version along the same sort of modular mixed construction lines with bonded skins, molded pod, rolled sheet metal tail boom, v tail, yadda.... but very high performance.

Boku, the above sentence is not a slight or anything just a sort of design continuum statement.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,777
Location
Port Townsend WA
A 5/8"x5/8" X.025" angle could be riveted around the existing ribs. Use a crimper to curve the vertical flange..
 

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
i hadn’t thought of that. The angle would go under or over the existing rib flange? Just trying to visualize the fix.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,777
Location
Port Townsend WA
Doesn't matter much. Outside would look better, but the size would increase slightly larger. My tolerance for rib size is relaxed. They tend to conform to spar size if close.
 

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
8,785
Location
KWHP, Los Angeles CA, USA
I measured the flange on the Moni ribs and they are only 3/8” wide.
3/8 inch is really going to make these ribs un-usable for a realistic E-AB project in my opinion. Boeing or Lockheed could certainly electron-beam weld them to the skins. But you and me... probably not. 3/8" is not enough to glue or rivet. Toss the ribs IMHO.

Get with one of our HBA genius caliber guys who fully understands the airfoil selection process and whatever computer program is current. Have that person select an airfoil that is appropriate for a flush riveted, but not perfect, riveted skin. Make a new set of ribs using Zenith style fluted flanges. or the John Thorp backing plate method, or the rubber block forming method.

Constant-chord wings are fine, but definitely use Dan Moser's triangular tips on the last 10-12% of span. Leave the trailing edge straight and put all the taper into the leading edge. No control surfaces on the tips, end the ailerons at the end of the constant chord section.

Design the new ribs in such a way as to put the fuel in traditional RV or Sonex style tanks at least 24 inches outboard of the pilot. Get RID of the Moni center doghouse tank. Plumbing is a little more complex, but your wife and kids will thank me.

If you like the Moni V-tail, then leave it. If you are undecided, consider making a cruciform tail (Onex, Sonex style). The Moni had a few instances where a sideslip on landing caused part of the tail to stall and the airplane got wonky.

If you are feeling adventurous, build an aluminum version of the Colomban Luciole tail. Less drag, lower parts count, easier to build than any of the Monnett series tails I believe. Not going to make the airplane 20 knots faster, but it will be less drag and you do get a couple of extra points for style.

If you get rid of the stock fuel tank, that gives you room to install a sailplane style (monowheel) retractable main wheel using the same space. Definitely a little extra work, but that will give you 8 or 12 MPH and a measurably higher amount of fuel efficiency. And 100 "cool points".

As I mentioned before, consider a 22-23 foot span. That is a total wild-ass guess on my part, but I'll bet you a steak dinner it will make a really neat little powerplane on 30-35HP.
 

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
8,785
Location
KWHP, Los Angeles CA, USA
NO. The T-tail costs more in weight than it gives you in drag, when you are solving th equation for weight. On the Luciole, Colomban figured out a way to have the same number of aerodynamic intersections as a T-tail, but without any of the extra structure built into the fin and rear fuselage. THEN he eliminated an entire hinge line and all of the parts associated with that. The Luciole staggered tail is definitely a winner IMHO.
 

Jay Kempf

Curmudgeon in Training (CIT)
Lifetime Supporter
Joined
Apr 13, 2009
Messages
4,288
Location
Warren, VT USA
The Luciole style tail has been around for a long time. CAP is sorta the same, with this configuration allowing bolting the stab to the top of the boom longerons and the fin hingeline at the end of the boom. Much more about structural efficiency than aerodynamic. Also leaves the bottom of the fin out in the clear for stall/spin recovery. But to say that it eliminates intersection drag is a bit misleading. That horizontal tail makes a large turbulent wake that impinges on and tries to reattach to the vertical. This is a pretty big source of drag that a properly designed T tail doesn't have. There is a really good paper by Junkers of South Africa about the drag of wing wake walking down the tail boom of modern sailplanes and effecting the bottom of the T tail/boom junction. Something they spent a lot of time, effort, engineering and CFD time with real world testing to verify the CFD. Big turbulent boundary layers are tricky.
 

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
VB said: “The Moni had a few instances where a sideslip on landing caused part of the tail to stall and the airplane got wonky.”

IIRC, the Moni flipped onto it’s back. Luckily, the pilot had plenty of altitude to recover. I’m pretty sure spins are prohibited in the Moni. Maybe the solution is to make the ruddervators longer? I think that’s what Dan did.

The Luciole tail looks a tad complicated to put on the Moni fuselage vs the stock V tail. Plus, I think it would make the Moni MORE pitch sensitive. I don’t see where there would be much weight savings simply trading the ruddervators for the Luciole set up. The Moni fuselage has a lot more structure in the tail compared to the Cri Cri. All the ribs in the Cri Cri are foam with the skins bonded to them. The edges are riveted and I don’t think the Cri Cri had a problem with delamination.

I’d like to get away from the V tail but to what? The Cri Cri tail would be the easiest to incorporate into the Moni fuselage. I think the Onex tail is doable, I’d just need to think it through and rework drawings. I’d also need to calculate the proper areas for adequate tail volume coefficients. Not exactly a stroll in the park.

Is weight the only thing wrong with the T-tail? Or am I missing something?
 

Topaz

Super Moderator
Staff member
Log Member
Joined
Jul 29, 2005
Messages
14,308
Location
Orange County, California
The Luciole style tail has been around for a long time. CAP is sorta the same, with this configuration allowing bolting the stab to the top of the boom longerons and the fin hingeline at the end of the boom. Much more about structural efficiency than aerodynamic. Also leaves the bottom of the fin out in the clear for stall/spin recovery. But to say that it eliminates intersection drag is a bit misleading. That horizontal tail makes a large turbulent wake that impinges on and tries to reattach to the vertical. This is a pretty big source of drag that a properly designed T tail doesn't have. There is a really good paper by Junkers of South Africa about the drag of wing wake walking down the tail boom of modern sailplanes and effecting the bottom of the T tail/boom junction. Something they spent a lot of time, effort, engineering and CFD time with real world testing to verify the CFD. Big turbulent boundary layers are tricky.
+1

Another plus for a T-tail is that it's so easy to make the horizontal tail removable. Many sailplanes have an arrangement where you pull one pin and off the tail comes, self-connecting controls are part of the attachment. Yes, you pay a price in a little more weight. There will always be a price. You can't have everything.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,072
Location
US
The Luciole style tail has been around for a long time. CAP is sorta the same, with this configuration allowing bolting the stab to the top of the boom.... That horizontal tail makes a large turbulent wake that impinges on and tries to reattach to the vertical. This is a pretty big source of drag that a properly designed T tail doesn't have..
So, while we are mulling over the options, what are the "cons" to a reverse Luciolle setup with the h-stab and elevator at the very end of the boom and the v-stab and rudder mounted forward of that? In a spin the v-stab and rudder remain clear of "shadowing" from the horizontal surfaces, theoretically the intersection drag is reduced compared to a "regular" cruciform tail, and any drag caused by wake/vortices from the fin/rudder impinging on the horizontal surfaces would presumably be much smaller than the Luciolle arrangement because the lift produced by the vertical surfaces is much smaller (in max magnitude but especially as a % of normal flight time). Yes, the vertical surfaces have to be slightly larger than in a standard cruciform tail because they are closer to the CG.
I think I've seen this type of tail more frequently than the Luciolle style.
 

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
8,785
Location
KWHP, Los Angeles CA, USA
If you shorten the span of the Moni, the tail becomes proportionately larger.

The Moni V-tails work OK, and as I said... if you like the V-tail than keep it. My issue is that adding a T-tail to a stock Moni fuselage is going to put some additional loads on it that it may not have been designed for.

I also have no problems with T-tails, most of my flight time is under a T-tail :)

Jay is probably correct, the raw number of 90 degree intersections is not the whole story.
 

henryk

Well-Known Member
Joined
Mar 8, 2010
Messages
5,904
Location
krakow,poland
+

+

+
 
Last edited:

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
Greetings!

I haven't had much time to look at the Moni. I've been busy getting outdoor things done before winter hits. In, fact according to the WX Chan, there is a 100% chance for snow TOMORROW!🤣 So, soon I'll be forced to be indoors and that's when I plan to start the Moni. I'm planning on a 22 foot span, constant chord.

I have two problem areas that I would greatly appreciate some guidance on:

1: Airfoil selection
I have the wing ribs for the FX61-147 that have the 3/8" flange. Should I use them and add a formed 5/8" x 5/8" angle riveted on as BBerson mentioned in Post #87? If I did, then the kit wingtips could be used. VB mentioned looking at older wooden sailplane designs since the wings wouldn't have been perfectly smooth. The Breigleb BK-12 used a NACA 44XX airfoil. The 4415 would fit the Moni wing spars configuration. The Riblett GA 30-415 is similar and would fit also. The Xenos uses the NACA 64-415 and is a pop-riveted wing. The Monerai used an FX61-190, according to UIUC database. The Hummel UltraCruiser and H5 us the Riblett GA 30-618. Since my Moni will be more of a sport plane than a motorglider, would a conventional airfoil (NACA, Riblett, etc) be a better selection vs. a glider airfoil as lr27 mentioned in Post #69? BoKu, you mentioned something similar about the HP-18B in Post #70. What airfoil was that? For reference, the spar configuration on the Moni puts the main spar under the bent knees of the pilot and the rear spar carry-through at the bottom of the seatback with 18" between them. The stock ribs put the main spar at 30% chord.

2: Tail configuration
I'm not a fan a V-tails as has been discussed here on HBA in various threads. I do like the Cri Cri T-tail and it would be very easy to adapt it to the Moni fuselage. The Cri Cri aft fuselage where the VStab spar attached was only about 6"x8" with no real longerons. The Moni fuselage would be approx. 7"x7" .025 2024-T3 with 1/16" 2024-T3 aluminum angles for the the lower longerons and .040 2024-T3 formed angle for the upper. I have the plans for the Cri Cri, so I would have a starting point. I also came across a box with the Klegecell ribs and the aluminum parts for the tail group. I believe the skins were epoxied on using Hysol epoxy, vacuum bagged and then riveted along the trailing edges. Or, I could do a version of the Sonex conventional tail as VB mentioned earlier.

I don't have an engineering degree so I don't know if structural calculations would be needed. I don't even know the right way to ask for that support if it is needed. Any help would be very much appreciated! If need be, it could be discussed off-line on PM.

Thank you all for your insights and suggestions to this point. I'm looking for to more suggestions and the chance to start my 50+ year dream to build my own airplane!

Cheers!
 

wwz7777

Well-Known Member
HBA Supporter
Joined
Aug 8, 2012
Messages
81
Location
Northfield, MN
Hello and Happy Valentine’s Day!

As I’ve been going through my Moni stuff in preparation to begin building, I came across the spar design for the Aerosviluppi AS-10 motor glider. The AS-10 was the Italian version of the Moni and since they couldn’t get Monnett’s I-beam extrusion, they designed a standard built-up aluminum spar with sheet aluminum web and .125” angle for the caps. All aluminum is 2024-T3. The dimensions are the same for the Moni spar for spar depth and length/span so it could be a drop-in replacement (all fuselage attachments are the same).

One thing they did for the web was to use two different thicknesses of material and joined them with a riveted joggle. The inboard section was .063 mating to a .040 outer web. This is where my question comes in: It would be easier (maybe??) to construct the web if the web were .040 from the inboard end of the spar to the tip and then put a doubler to reinforce the portion of the inboard section that was originally thicker. If one were to put a .040 or .032 (or thicker) doubler on top of the .040 web it would have a total thickness greater than the original .063 inboard web. Is this:

1) Doable as described above
2) Not doable due to stresses and would need a total re-engineering of the spar
3) Or, a joggle is no big deal to create and just stick to the original design.

FWIW, I haven’t been able to find the original designer to ask him this question. The spar as designed was rated at +6/-3 G’s at 255kgs.

The reason I rehash this question is because I’m having reservations (again!) about cutting the original Monnett spar that can’t be replaced if I mess something up.

Any thoughts would be greatly appreciated. Thanks for putting up with my questions!

Cheers!
 
Top