Hoehnia

[Mowerman]

Only just read this blog and the end result looks great.

Looking forward to flying shots.

A bit late but in the past when I didnt have the right size balsa to carve wing tips I have carved them from foam ( I used eps) covered with water based varnish & tissue then glued on.

[IanN]

Posted by Mowerman on 19/03/2010 09:03:01:

 in the past when I didnt have the right size balsa to carve wing tips I have carved them from foam ( I used eps) covered with water based varnish & tissue then glued on.

 

That's an idea. I'll make a point of trying that in future.

 

Maiden was on Wednesday (2 hours total air time), another session today (55 mins total logged before rain stopped play) and it flies great. Brilliant design by Mike Parry, which has achieved all the objectives I set out at the start. I'll update in more detail later but I was gobsmacked by how such a relatively low powered and lightly loaded model carved through a stiff and bumpy wind with ease.

 

No flying shots though, I didn't think of that. However the one at the start of the original build article is spot on - it gives a very accurate impression of how the plane "sits" in the air

 

 

Edited By IanN on 19/03/2010 17:52:18

[IanN]

The verdict is that Hoehnia has got to be a contender for all time best cheap fun hack

 

Hoehnia tracks dead straight and handles wind with ease. No tendancy at all to dig the nose in even during tight banks. Very responsive but also goes exactly where you point it and will happily fly from one end of the field to the other with no input. Landings are a doddle - just float it in to your feet.

 

This would make a perfect follow on model from that first trainer. Indeed, if set up with the appropriate rates and expo I reckon that any decent instructor could train a novice pilot to solo standard on this. Its so vice free, and can be flown so slowly, that the lack of dihedral wouldn't be an issue IMO. (Or, just build a second wing with a bit of dihedral added)

 

Easy to solo hand launch. On my first outing I forgot the tranny strap so had to throw the model left handed, whilst I held in a little up with my right. Even with those less than hefty (actually, quite feeble ) throws the plane gets away no problem. And on the occasion when it didn't (motor cut) it simply glides down onto the grass without drama.

 

Perfectly adequately powered by the OS15. However, the wing is easily big enough to take a larger motor. I'll be trying a .25 at some future date just out of curiosity, and I doubt whether the extra couple of ounces will even make a dent in the handling charcteristics

 

Easy and cheap to build. Like all plan builders I made the odd tweak but the only mod I'd regard as essential is a better tail mount than the method shown on the plan.

 

Step forwards and take a bow Mike Parry - a cracking design

 

 

 

 

[IanN]

Postscript. Having originally used one centrally mounted aileron servo, driving bellcranks, I'm now changing that for two reasons

 

Firstly, I didn't plan my original central servo installation very well at all; I should have factored it in far earlier in the wing build. So, not having left myself much space to play with I ended up packing it in with wood, and holding it with a retaining strap. That worked perfectly well, but with a few hours airtime under its belt there are definite signs of the wood having compressed, allowing the servo to move. Not good.

 

Secondly, I want more aileron differential than I had installed mechanically.

 

Sure, I could redo the central servo mount and rejig the bellcrank angles but if I'm going to that much trouble why not go the whole hog? So, its out with the pushrods, cranks, and mounts in favour of a servo in each wing.

 

My intention was to use two standard futaba servos. However, the position of the rear lower spar (highlighted with red arrow below) pretty much rules that out. There simply isn't enough room

 

 

So, I've installed HS81s in between the lower rear spar and the T.E. - but even those were tight.

 

If anyone is building this and installing wing mounted aileron servos I'd seriously consider moving that rear spar from the underside to the top. The wing is very strong, and I doubt that change would have any real structural implications, unless anyone thinks differently

 

 

[IanN]

Time for some minor surgery on my Hoehnia

 

Had a fly on my way home from work in conditions that were way more blustery than was sensible and (surprise) got blown around quite a bit. Ever the sucker for punishment, I then had a second flight just to check that I was really being blown around as much as I thought I was.

 

The thing will take a bit more weight with ease, so I'm going to replace the OS 15LA with a 25LA, the intention being to fly this "hack" through the winter. Will let you know how it goes

 

[IanN]

Finally found a couple of hours shed time and the motor swap was achieved with ease. So, an OS25LA now sat up front, but how best to balance that extra 2oz?

 

One problem that had started to materialise towards the end of summer was that the model's trim seemed to be becoming increasingly erratic from session to session. On investigation, the built up tail that I had used in deference to the original OS15 was found to be warped.

 

Either I didn't build it sturdily enough in the first place, or maybe I'd inadvertently stressed it by uneven shrinking of the film covering. Or it could be that my habit of leaving it in the car all day on the offchance of grabbing a flight on the way home from work had allowed it to twist on hot days. Who knows? Whatever the cause, various attempts at reshrinking the covering to get it straight again all only effected temporary cures.

 

As a fix was essential, and I needed weight at the back, it seemed the obvious thing to do was fit a sheet tail. Less than an hour's work sees a med 3/16 tail cut, covered, and glued to the fus with the original elevators stitched on. I retained the original built up fin (which hadn't warped - so maybe it really was that I hadn't built the first tail sufficiently rigidly)

 

Back in the balancing cradle, moving the rx battery from lying flat under the tank, to standing vertically behind the tank, achieves exactly the same balance point as the .15 powered version.

 

Not much point posting a photo because it looks exactly the same as it did before . Plumbing checked for leaks, motor runs fine in the model, so the only thing left to do is to fly it

Edited By IanN on 17/10/2010 00:06:53

[IanN]

Dry weight is now a smidgen over 3lb. At 14oz per sq foot its still far from lardy, even with the bigger engine

[Barry W]

Thanks Ian for your reply to my issues with My Hobby Store in a recent post.

Concerning the Hoehina I have followed your postings with interest.  I am at present making progess  with the wings. As I am not a Top Gun model airplane pilot I was planning on sticking with the OS 15 engine. From what you mention this may require some added weight to the nose. Do you think it would be better to lengthen the front of the fuselage by an inch or so to obtain the correct Cof G without adding weight? Also what throws did you use on the elevator and ailerons as nothing is mention on the plan?

[IanN]

Barry, very many apologies - not sure how but I missed your post

 

You've probably long solved your issues already by now, but if using an OS15LA it certainly wouldn't hurt to lengthen the nose a little, then move the radio gear and battery around to get the balance.

 

Flew the Hoehnia with the OS25 for the first time this evening. You certainly don't need to be a top gun for that. Main benefit I noticed was that the the added grunt helps a little if solo hand launching, but it certainly isn't ballistic. Needs more downthrust, as climbs much faster under WOT than the 15. Other than that, no discernible change in handling.

 

In summary, its fine with a bigger engine but remains perfectly ok with a .15, as designed - a good model