Miles M5 Sparrowhawk by Walt Mooney

[Stunthenk]

Ever since I received the March '76 Aeromodeller I've been intrigued by the Mooney Sparrohawk. Now, in a later era I am contiplating building it. But there are some points that aren't clear. For instance, on the plan the wing ribs are semi-symmetrical, but with a dotted line indicating a flat bottomed section. Is the wing built  flat on the plan with flat bottommed ribs or semi symmetrical with supported LE and TE? The second point is the enlarged dihedral. Are the ribs meant to be vertical while a wingpanel is being built flat on the plan, or are they angled to be vertical in the head on view? And finally, the wing has two spars on the top but none on the bottom. Is this a stable construction? I would be greatfulf to anyone who has built the model who could shed some light on these issues.

[Jmk89]

Having a fresh look at Walt's plan, my approach would be:

• Make the wing on the building board with flat bottomed ribs, and then when it's all set, and after doing the dihedral, because you want the centre section pinned flat for that operation,  stick very light pieces on the bottom of all the ribs and sand to get the semi-symmetrical profile
• put all ribs in upright and make the dihedral by cracking the spars ,LE and TE and gluing at the right angle to get the dihedral. This will leave the ribs at the dihedral break upright.  I think I would put gussets in around the crack sites to support the spars etc at the right angle. It seems that the wing fillet is not just purely decorative - as I read the plan, they are an essential part of joining the wing and fuselage, since none of the wing ribs are located to glue to the fuselage. Walt may have taken the view that the fillets will operate like gussets in relation to the spars, LE and TE, so he didn't put in gussets.

[AndyB]

Ever since I received the March '76 Aeromodeller I've been intrigued by the Mooney Sparrohawk....

You and me both!   The attached photos show my second attempt (first attempt was in the late 1970's it didn't go well...)

The pictures should explain how I made the wing; I just flattened off the bottom of the ribs because it was easier. I didn't bother with gussets at the wing root but probably should have, although I was careful with the covering and pre-shrunk the tissue, so it doesn't seem to have pulled-in at the edges. Also, I didn't bother with the wing fillets because they were a pain, and I'm quite lazy.

I have a moveable rudder on mine but you might not need one if you're flying outdoors. All Sparrowhawks I've seen (about three or four, I think) seem to like rolling left and flying (briefly) knife-edge (I suspect that the spiral airflow coming off the propeller is interacting with the spats), so what I did was to put washin on the port wing and washout on the starboard wing and then balance off the right bank with left rudder. It needs very little right thrust, but about 4-5 degrees of downthrust.

I didn't like the paper spats so made some from balsa, covered with 1/64" sheet.

And finally... if this is your first peanut, I salute your courage and fortitude. If it was my first peanut, I'd build something simpler and easier to trim first (not preaching, just saying)*

A.

*Thanks, Crabby... at least, I think it was Crabby who coined the phrase :-)

[malc]

This was the first peanut I ever built, it must have been the early 80s. I built a jig for the wings including the dihedral and washout and built the wing in one piece on the jig. The LE and TE were supported off the jig to allow the full depth ribs to be used without having to add bits underneath afterwards. I moulded the turtle deck on a former before attaching it to the fuz.  Made the spats from paper just as the plan. Flys really well.
This is it with my Mooney MLG.
Malc.

[MKelly]

All Sparrowhawks I've seen (about three or four, I think) seem to like rolling left and flying (briefly) knife-edge (I suspect that the spiral airflow coming off the propeller is interacting with the spats)

My dime scale Sparrowhawk exhibits this exact behavior.  At some point as the torque burns off it flips around into a tight, flat right-hand circle for the remainder of powered flight.  I'll have to try your trimming tips...

Cheers,

Mike

[malc]

Thats interesting, if I overwound mine it would climb in to a stall turn, do 2 or 3 flat spins, then recover as if nothing had happened!
M.

[Stunthenk]

I would really prefer to do the full wing section as shown on the plan, using strips under the LE and TE during construction and while the dope is drying. I also intend to trim the model - if I build it- to fly in left-hand circles. I also believe strongly in adding the wing fillets, both for structual as for aerodynamic reasons. I plan to fly the model indoors. I do hope that the reports on flat spins were about outdoor flying! It is not my first Peanut, but it will be my first low wing peanut. I will be sure to use wash-in on the right wing and wash-out on the right wing. A I will modify the plan to have adjustable rudder and elevators. Good insurance!

[AndyB]

FWIW, my experience with moveable elevators on indoor models has not been positive - they are, however, excellent for losing the trim when you either a) drop the model or b) knock the elevators whilst getting it out of or putting it into the transport box... 

A.

[steve-de24]

Some inspiration for you.
Sparrowhawk

It's about 60% bigger than your Peanut and a real beauty.
Steve

[AndyB]

You're right - it's very inspirational! 

[Stunthenk]

FWIW, my experience with moveable elevators on indoor models has not been positive - they are, however, excellent for losing the trim when you either a) drop the model or b) knock the elevators whilst getting it out of or putting it into the transport box... 

A.

Checking with a little piece of balsa cut to the current trim angle of the elevators (or other movable surfaces as applicable) will ensure the correct angle before the next flight.

However, the question remains on the best trim pattern. In his article Walt Mooney says about trim: The model climbs in a wide right hand circle and glides in tighter right circles. Under the first 'power burst' the Sparrowhawk banks to the left and flies almost straight - allowing the model to turn left under power usually results in a spiral dive. ' On the other hand, Butch Hadland in his 'Indoor Trim article ' https://www.flyingacesclub.com/PFFT/IndoorTrimming.pdf
states: 'My low-wing models always fly left. Flying right against the torgue is suicial and should be avoided at all cost'.
This conundrum leaves me in a quandary: what to do about the trim of the Sparowhamk?

[AndyB]

...
Checking with a little piece of balsa cut to the current trim angle of the elevators (or other movable surfaces as applicable) will ensure the correct angle before the next flight.... snip

Yes, but I'm too lazy to have to go through all that kerfuffle before every flight! 

If you're flying outdoors I think you could probably get away with the Walt Mooney trim as long as the wings are pretty much level, particularly if there's some washout. If the inside (right) wing gets too low scale models normally start spiralling in, which is only going to end one way.

I can only report that my Sparrowhawk has a Hadland-esque set of warps and rudder deflection and flies indoors quite happily to the left. I always fly my low-wing models to the left, mainly because I don't like having to do repairs, and flying left works Ok for me.