BH Blitz mini Mig

[19000rpm]

The BH mini (50mm fan) Mig showed up last week. It's a kit with the foam, hardware, motor and fan. It came undamaged with no issues.

In anticipation, I had a Target Hobbies "blue" 2.4 Rx, 3ea. 8grm servos (Not really sure of the origin of those) and ordered a Sky Lipo 1000 mAh 20C 3S and a 25A Detrum ESC from HobbyPartz. Actually I ordered 3 of the Lipos and 3 ESC's because I anticipated I would be ordering more of the pocket EDF's from BH...And I did. But that's another story.

So, this is where I admit I went partially brain dead and forgot to photo the kit or the build. In all too much fairness to me I have been working on so many builds the past few months I just dove into this one with out thinking about documenting it. But the work is going to pay off since I've got 7-8 planes to maiden IF spring ever comes.

The build was really simple. The foam was perfect, with nice paint application and decals and went together quickly with hot glue. The most time was spent on getting the wiring for the motor, ESC and battery shortened to the correct length to fit in the compact airframe. Things are really tight. I've never had an ESC or battery with such short leads leads before.

[Gabe]

Wow I'm shocked! Glad it worked out so well!

[akent]

Is that a 50mm fan in that one?
EPS or EPO?

I look forward to hearing how it flies!

[19000rpm]

It's a 5 blade 50mm in EPO. I wouldn't buy an EPS belly lander.

There's no CF in the wing. It feels plenty strong for its weight which is around 13 oz's.

One thing that should help the mass vs. landing speed damage scenario is the light weight. The major contributer in that area is the small 1000mAh 25C 3S.

The unknowns, as yet; is the flight time such a small battery will yield. I'm thinking maybe 4 mins. ;D And, will there be adequate thrust? The bench test thrust feels pretty good, so I'm encouraged.

[Gabe]

There's a decent amount of thrust in those puppies. Not a whole lot, as my AMX mini will stall on the vertical fairly quick. Its enough to get her going though.

I have my timer set for 3 minutes, although I've squeezed out 4 min at 3/4 to full throttle.

[19000rpm]

Thanks for the info gabe. That enough time to have a little fun.

[19000rpm]

Finally a decent day to fly yesterday. Winds about 10 and the ground has started to dry out some.

The mini Mig was the second plane I flew. Well I shouldn't say flew, because it didn't. I gave it a nice toss at just a little angle up. It went about 20 ft. and did a loop on its own and belly flopped when I cut the power. WTH?

First thing I thought of was the CG. That checked out according to the manual. All of the control surfaces are set neutral and operating as they should. Could the CG be wrong? Is it just under powered? Although, that wouldn't account for the loop. It's got to be the CG.

Then I tossed it again and it stalled and spiralled in. Looking more like a CG issue. Broke a wing tank off.

This kind of reminds me of the Wings Makers X35. I had the CG spot on, according to the manual, and the thing was so nose heavy I had my hands full landing it in one piece. The guys at Wings Makers insisted that the published CG is correct. ;D

I guess it's up to us to find out where the CG is on some of these planes. Although, it's a little frustrating trying to fly and having to save the plane from crashing just because the published CG isn't correct. Unfortunately, there's no way to find this out without flying the plane.

[akent]

Wow! That sure does sound like a CG issue.

Where did they spec it? Usually if it is not known, you set it for 1/3 cord back from the wing front to start with.
The F86 is a little more towards the front than that...Similar wings...

It will be interesting to hear what you find out!
Kent

[19000rpm]

The CG's said to be 95mm (3.74") back from where the wing meets the fuse in the manual. I'm thinking it's about 1/4" off; which is quite a bit on a model this small. I've moved the battery all the way forward, that's about 3/16", and added a little weight to the nose. Possibly I'll get a chance to test it again on Saturday.

I'm really hoping this works out since I've also bought a Blitz F18 and F35 and would order the F16 as well. The bad news is that I may have blown $90. The good news is that they'll all look nice hanging from the ceiling if they don't fly.

[Gabe]

Ya know, I just jammed that battery as far toward in the bay as it would go. I put my fingers on the c of g mark and make sure it's nose heavy - not just balanced. I know it's not the "correct" way to set up a plane, but it works great for me. I just added a little up trim to the elevator. At these speeds, the tiny amount of drag won't make a noticeable difference.

[19000rpm]

Apr 8, 2011 8:37:17 GMT -6 Gabe said:

Ya know, I just jammed that battery as far toward in the bay as it would go. I put my fingers on the c of g mark and make sure it's nose heavy - not just balanced. I know it's not the "correct" way to set up a plane, but it works great for me. I just added a little up trim to the elevator. At these speeds, the tiny amount of drag won't make a noticeable difference.

Yeah, I hear that, but the thing was already a little nose heavy according to the published CG. So, it's not so much making it a little nose heavy it's knowing where the CG is to make it that way. When you know that then it's easy to make it balanced the way you like it.

[19000rpm]

Holy moly it flies! This has been the first nice day I've had to try it out since the last, less than glorious, attempts at maidens. Bright and sunny even if a bit windy, 12-15, to test fly a mini jet with an unknown CG. But, what the heck! No guts no glory.

I had the DX7 set on low rates. I had mechanically trimmed a tiny bit of down elevator, at least I think it was down elevator since it's a little hard to see the horizontal stabs acutal angle of incidence where they're located, so high on the vertical stab. From how it flew that trim must have made it neutral.

A nice toss, WOT, at about a 15 degree angle and it went straight as an arrow with no added elevator. It gained speed quickly so I lowered the throttle to 75% and cautiously began a left bank as it turned downwind.The gusts rocked it a little but it was still tracking well. I was quite high now and thought I'd turn it back into the wind without increasing throtlle. If it stalled I'd have enough altitude to recover. It handled it well. WOT and into a nice roll and then kind of a lazy loop still pointed into the wind.

A couple more go rounds and I brought it into the wind and cut the throttle to about half and let it sink in with no elevator input until I cut the throttle to 20% and then off for the last 30 ft or so, using the headwind maunly for lift, and the flair. Nice glide angle and gentle landing.

Flight time was around 3 mins. limited by my inexperience with the plane. I think there was another good minute in there based on the battery coming in at 12 volts.

The headwind definitely was a plus on the launch and landing. It was easy to keep it from stalling. It may be a slightly different story on a calm day. I'll probably need more throttle on landing and turns. I was impressed that it had no tendency to stall under today's conditions.

It was hard to accurately estimate speed, but it was accelerating well into the wind at WOT and the downwind legs were pretty fast even at 50-75%. I'm guessing in the 60 mph range.

I'm going to go full rates on the elevator next time and leave the ailerons on low rate. The loops will probably improve with a bit more elevator throw. The rolls are OK for now.

I almost hate to say it, but this little light weight 50mm EDF from BH may be better than the HL 64mm series weighing in at another 3-4 Oz's.

Here's some tentative conclusions comparing the HL F86 and BH mini Mig. I'll see if they bear out as I fly the BH Mig and the new HL Jolley Roger F86 more through the spring and summer:

1) The HL and BH jets are both about the same size, but the differences in weight vs. power seems to have come out on the BH Migs side.

2) The added weight of the HL F-86 makes you fly it into the ground on landings or it might stall. More speed at landing translates into potential damage. This doesn't seem to be the case with the BH Mig.

3) Additional power is required in most conditons to keep the HL F86 from stalling in turns. It's a nice Jet, but strict attention to throttle management seems to be the order of the day when flying the HL jet. The BH Mig seems to be more stable in all areas of the flight envelope. Part of this could be because of the air dams on the Mig's wings. The air dams certainly played a part on the full sized Mig's stability, so this may also be the case with the BH mini Mig.

4) My only disappointment in the BH mini Mig has been the difficulty in establishing the true CG. Now that the CG is no longer an issue I couldn't be more pleased.

5) The BH mini Mig is a jet you can fly almost anywhere. Hardly any venue would be too small. Baseball fields, soccer fields and a neighborhood park are all good spots to fly this plane and that translates into more convenience and more flights. And, that is a big advantage in my world and kind of the whole idea behind these mini EDF's. They're not exactly ultra micros like the PKZ planes, but they're darn close.

I'm sure we'll be seeing even smaller EDF's coming out soon. The more the better IMO.

[thegnman]

Could you please put up a link where I could check Your plane out I might be looking to buy something like that. Thxs

[akent]

That's great, 19k!!

Now the ultimate question:
Where is the CG now??

I like the idea of that little jet!

And you are right about the HL F-86. It WILL snap on you if you let it slow down too much.
Kent

[19000rpm]

Apr 12, 2011 17:06:35 GMT -6 thegnman said:

Could you please put up a link where I could check Your plane out I might be looking to buy something like that. Thxs

Here ya go thegnman. www.bananahobby.com/2083.html This is the PNP version. All you need is the Rx and battery.

Or, if you look further on the site you can buy the airframe with the fan & motor and hardware and add your servos; (3) 7-8 gram, 20-25A ESC, 4ch Rx and 900-1000mAh 20C 3S volt battery.

Kent, Oh yes. All that blah, blah, above and and not the CG. ;D The CG's about 3/16" forward of the published 3.74".

In order to make that work I needed to add some weight up front, I used 3 1" aluminum screws, and pushed the battery all the way forward. Pushing the battery forward required cutting some of the foam from the front "hook" on the canopy to get the canopy on.

The only reason I needed to add so much weight forward is that I used hot glue for the assembly, kind of heavy compared to Epoxy, and used 3 9gram servos. I believe the servos in the PNP version are only about 7grams each. Most of the glue was behind the CG as well as the extra weight of the servos. Although, when I used the published CG, a little too far back, the balance appeared perfect.

Had I used the same weight in glue and components as the PNP uses all I would have needed to do was move the battery forward; just like Gabe said he did on his AMX. The published CG would still have been incorrect, but the plane would have flown ignoring the CG all together.

One other thing: What appeared to be a level stab and elevator really weren't. Actually, the position was such that it created what amounted to an up elevator position. This with the tail heavy plane made the looping situation worse. Just by adding a couple of degrees of down elevator the plane flies neutral with the right CG.